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Inside Nature's Giants : Free Download, Borrow, and Streaming : Internet Archive

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A team of scientists reveal the mysteries of the evolutionary process by exploring the inside of giant animals, uncovering the anatomical secrets of some of...

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Gliding, Parachuting & Flying

Aerial locomotion can be classified into three types - gliding, parachuting and flying. Only group of mammals, the bats (Order Chiroptera) are capable of true flight sustained by flapping of the wings, but representatives of a number of other arboreal groups (squirrels, possums, colugos) are able to glide or parachute considerable distances through the air. The ability is useful as a means of escaping from predators, travelling from one location to another location, or as part of predatory behavior. The wings or flight membranes of flying and gliding mammals comprise a web of skin, the pataguim, which is supported by skeletal elements of the limbs and sometimes also the tail.
The purpose of a wing is to create lift, while a parachute increases and slows the rate of descent by increasing air resistance or drag. Both lift and resistance are related to wing area and angle, and flying or gliding mammals are able to make postural adjustments in order to control speed and trajectory and to maximize the duration of a glide.

Japanese giant Flying squirrel (Petaurista leucogenys)
Forest glider

Fig. 29 Note the long limbs and needle-like cartilage to increase the wing area.

Greater horseshoe bat (R.ferrumequinum)
True flight

Fig. 30-1 Continuous picture of flapping bat flight

Fig. 30-2 A:The skeleton of forelimb of human and wing of bird and bat. B:Skeleton of the greater horseshoe bat.

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Aerial locomotion can be classified into three types - gliding, parachuting and flying. Only group of mammals, the bats (Order Chiroptera) are capable of true flight sustained by flapping of the wings, but representatives of a number of other arboreal groups (squirrels, possums, colugos) are able to glide or parachute considerable distances through the air.

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4.1 Discuss osmoregulatory function challenges of animals living in terrestrial versus aquatic environments;

4.2. Explain how ion and water balance function in sample animal saltwater systems; and,

4.3. Explain how ion and water balance function in sample animal freshwater systems.

Osmoregulation is the process of maintaining salt and water balance (osmotic balance) across membranes within the body. The fluids inside and surrounding cells are composed of water, electrolytes, and nonelectrolytes. An electrolyte is a compound that dissociates into ions when dissolved in water. A nonelectrolyte, in contrast, does not dissociate into ions in water. The body's fluids include blood plasma, the fluid that exists within cells, and the interstitial fluid that exists in the spaces between cells and tissues of the body. The membranes of the body (both the membranes around cells and the "membranes" made of cells lining body cavities) are semipermeable membranes. Semipermeable membranes are permeable to certain types of solutes and to water, but typically cell membranes are impermeable to solutes.

The body does not exist in isolation. There is a constant input of water and electrolytes into the system. Excess water, electrolytes, and wastes are transported to the kidneys and excreted, helping to maintain osmotic balance. Insufficient fluid intake results in fluid conservation by the kidneys. Biological systems constantly interact and exchange water and nutrients with the environment by way of consumption of food and water and through excretion in the form of sweat, urine, and feces. Without a mechanism to regulate osmotic pressure, or when a disease damages this mechanism, there is a tendency to accumulate toxic waste and water, which can have dire consequences.

Mammalian systems have evolved to regulate not only the overall osmotic pressure across membranes, but also specific concentrations of important electrolytes in the three major fluid compartments: blood plasma, interstitial fluid, and intracellular fluid. Since osmotic pressure is regulated by the movement of water across membranes, the volume of the fluid compartments can also change temporarily. Since blood plasma is one of the fluid components, osmotic pressures have a direct bearing on blood pressure.

Excretory system

The human excretory system functions to remove waste from the body through the skin as sweat, the lungs in the form of exhaled carbon dioxide, and through the urinary system in the form of urine. All three of these systems participate in osmoregulation and waste removal. Here we focus on the urinary system, which is comprised of the paired kidneys, the ureter, urinary bladder and urethra ( Figure 4.1). The kidneys are a pair of bean-shaped structures that are located just below the liver in the body cavity. Each of the kidneys contains more than a million tiny units called nephrons that filter blood containing the metabolic wastes from cells. All the blood in the human body is filtered about 60 times a day by the kidneys. The nephrons remove wastes, concentrate them, and form urine that is collected in the bladder.

Internally, the kidney has three regions-an outer cortex, a medulla in the middle, and the renal pelvis, which is the expanded end of the ureter. The renal cortex contains the nephrons-the functional unit of the kidney. The renal pelvis collects the urine and leads to the ureter on the outside of the kidney. The ureters are urine-bearing tubes that exit the kidney and empty into the urinary bladder.

Blood enters each kidney from the aorta, the main artery supplying the body below the heart, through a renal artery. It is distributed in smaller vessels until it reaches each nephron in capillaries. Within the nephron, the blood comes in intimate contact with the waste-collecting tubules in a structure called the glomerulus. Water and many solutes present in the blood, including ions of sodium, calcium, magnesium, and others; as well as wastes and valuable substances such as amino acids, glucose, and vitamins, leave the blood and enter the tubule system of the nephron. As materials pass through the tubule much of the water, required ions, and useful compounds are reabsorbed back into the capillaries that surround the tubules leaving the wastes behind. Some of this reabsorption requires active transport and consumes ATP. Some wastes, including ions and some drugs remaining in the blood, diffuse out of the capillaries into the interstitial fluid and are taken up by the tubule cells. These wastes are then actively secreted into the tubules. The blood then collects in larger and larger vessels and leaves the kidney in the renal vein. The renal vein joins the inferior vena cava, the main vein that returns blood to the heart from the lower body. The amounts of water and ions reabsorbed into the circulatory system are carefully regulated and this is an important way the body regulates its water content and ion levels. The waste is collected in larger tubules and then leaves the kidney in the ureter, which leads to the bladder where urine, the combination of waste materials and water, is stored.

The bladder contains sensory nerves, stretch receptors that signal when it needs to be emptied. These signals create the urge to urinate, which can be voluntarily suppressed up to a limit. The conscious decision to urinate sets in play signals that open the sphincters, rings of smooth muscle that close off the opening, to the urethra that allows urine to flow out of the bladder and the body.

Osmosis is the diffusion of water across a membrane in response to osmotic pressure caused by an imbalance of molecules on either side of the membrane. Osmoregulation is the process of maintenance of salt and water balance ( osmotic balance) across membranes within the body's fluids, which are composed of water, plus electrolytes and non-electrolytes. An electrolyte is a solute that dissociates into ions when dissolved in water. A non-electrolyte, in contrast, doesn't dissociate into ions during water dissolution. Both electrolytes and non-electrolytes contribute to the osmotic balance. The body's fluids include blood plasma, the cytosol within cells, and interstitial fluid, the fluid that exists in the spaces between cells and tissues of the body. The membranes of the body (such as the pleural, serous, and cell membranes) are semi-permeable membranes. Semi-permeable membranes are permeable (or permissive) to certain types of solutes and water. Solutions on two sides of a semi-permeable membrane tend to equalize in solute concentration by movement of solutes and/or water across the membrane. As seen in Figure 4.2, a cell placed in water tends to swell due to gain of water from the hypotonic or "low salt" environment. A cell placed in a solution with higher salt concentration, on the other hand, tends to make the membrane shrivel up due to loss of water into the hypertonic or "high salt" environment. Isotonic cells have an equal concentration of solutes inside and outside the cell; this equalizes the osmotic pressure on either side of the cell membrane which is a semi-permeable membrane.

Different osmoregulatory challenges and solutions in aquatic and terrestrial environments

Fish living in freshwater requirements have very different challenges in terms of ion and water balance in their body than the fish living in saltwater environments. Although structurally some solutions to these challenges are similar (chloride cells in gills and nephrons), the functional aspect of each solution is different. The next two figures ( Figure 4.4 and Figure 4.5) offer a summary of these solutions and introduce challenges in solutions on land as well, which are discussed in further details in Chapter section 4.2.

Question 4.1

What is the difference between osmoregulator and osmoconformer?

Question 4.2

What are the biggest osmoregulatory challenges for fish in saltwater?

Question 4.3

Summarize how salmon survive in both salt and freshwater. Use this journal article to learn about salmon migration in more details.

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4.1 - Osmoregulation in Animals Living in Aquatic Environment

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Osmoregulation is the process of maintaining salt and water balance (osmotic balance) across membranes within the body. The fluids inside and surrounding cells are composed of water, electrolytes, and nonelectrolytes. An electrolyte is a compound that dissociates into ions when dissolved in water. A nonelectrolyte, in contrast, does not dissociate into ions in water.

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This combines with water to produce toxic ammonia.

Animals must safely excrete these toxins. This is the function of the excretory system.

x

x

x

x

x

x

contains one nitrogen per molecule

is highly toxic

requires large amounts of water for dilution and flushing from the body.

Animals with constant access to fresh water
excrete much of their nitrogenous waste as ammonia.

Examples: freshwater fish, amphibian larvae

x

Terrestrial animals have less access to water, and have been selected to

repackage ammonia as less toxic compounds

flush those compounds with less water

Urea...

requires metabolic energy to build (unlike ammonia)

is manufactured in the liver, excreted by kidneys

contains two nitrogens per molecule

is less toxic than ammonia

requires less water to dilute and flush from the body

is excreted by a wide variety of animals

Examples: adult amphibians, mammals, marine fish

x

Animals that evolved in very dry environments have been
naturally selected to excrete nitrogen using even less water.

Uric acid...

requires more metabolic energy to build than either ammonia or urea

contains four nitrogens per molecule

has very low toxicity, so does not need to be diluted

is not readily water soluble

requires little water for flushing from the body

is the primary nitrogenous waste product of reptiles (including birds)

The white, crystalline substance you see in a typical bird or lizard poop is actually urine.

white is uric acid crystals

brown/green is fecal matter

Animals have evolved to produce the nitrogenous waste
products most adaptive in their particular environment.

Consider what type of environmental pressures would
drive natural selection for each of these excretory products.

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This combines with water to produce toxic ammonia. Animals must safely excrete these toxins. This is the function of the excretory system. x x x x x x contains one nitrogen per molecule is highly toxic requires large amounts of water for dilution and flushing from the body.

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Inside Nature’s Giants Giraffe - Season 1 Episode 4

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Since the 20th century, scientific ornithology has been closely linked to the conservation of birds. The study of feathers is one such factor that is often overlooked. In museums, the majority of their bird skin collections are archived, stored away in drawers under lock and key and only ever seen by a very selective audience and not the general public.

The German behavioural scientist Konrad Lorenz once said: "You only love what you know, and you only protect what you love." Being able to touch, feel and study a feather in the hand engages people, especially children, with nature; what child hasn't stopped to pick up a feather in a park or their backyard and marvel at it, and wonder what bird it came from. From a long, slender Arctic Tern primary, which has undertaken an incredible migratory journey of around 44,000 miles from pole to pole, to the soft, downy feather of a Barn Owl, helping the bird to fly on silent wings as it hunts at night; every feather has a fascinating story to tell, each so unique in its makeup, shape, form, texture, colour and function they serve to the bird. Feathers can teach us so much about birds and how they live. They bring people closer to the natural world - and therefore play an important role in its preservation.

Featherbase is a working group of German feather scientists who came together with their personal collections and created the biggest and most comprehensive online feather library in the world. Using our website, it is possible to identify feathers from hundreds of different species, compare similarities between species, work out gender or age-specific characteristics and look at the statistics of countless feather measurements. In contrast to the conventional work of museums, Featherbase is much more oriented towards the general public, allowing not just enrolled scientists the opportunity to gain access to the collection, but anyone with an interest in studying birds and their feathers. Featherbase also frequently collaborates with scientific or educational organizations by offering images, data or teamwork in general.

Featherbase works completely independently, without administrative affiliation, and first and foremost without commercial interests. We are a non-profit making entity and funded entirely by our own contributors. The collecting of feathers and skins for our database is approved by the relevant authorities, and for any protected/CITES listed species held, we are fastidious about maintaining records of their origin.

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Alexander Haase, Jörg Schlusen, Kristin Schwenk

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Since the 20th century, scientific ornithology has been closely linked to the conservation of birds. The study of feathers is one such factor that is often overlooked. In museums, the majority of their bird skin collections are archived, stored away in drawers under lock and key and only ever seen by a very selective audience and not the general public.

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Humans are unique among primates in that they alone practice obligatory bipedalism and their skeletons show distinctive adaptations for this form of locomotion. Humans’ ability to regulate their body heat over long periods of heavy activity is also unique, as are their large brains that are highly d…

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The Digital Morphology library is a dynamic archive of information on digital morphology and high-resolution X-ray computed tomography of biological specimens. Browse through the site and see spectacular imagery and animations and details on the morphology of many representatives of the Earth's biota. Recent additions or updates to the site include:

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Digital Morphology at the University of Texas

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Digital Library focuses on the skull and skeleton, which it surveys from fossils to embryos and adults of living species. The Library serves slice-by-slice animations, animated volumetric and 3D surface renderings, an introduction, references, links, and archival museum data for each specimen

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Davies, N. B. Cuckoos, Cowbirds and other Cheats. London, UK: T. & A. D. Poyser, 2000.

Davis, S. K. & Sealy, S. G. Cowbird parasitism and nest predation in fragmented grasslands of southwestern Manitoba. In Ecology and Management of Cowbirds and Their Hosts. eds. Smith, J. N. M., Cook, T. L., Rothstein, S. I., Robinson, S. K., & Sealy, S. G. (Austin: University of Texas Press, 2000): 220-228.

Grim, T. The evolution of nestling discrimination by hosts of parasitic birds: why is rejection so rare? Evolutionary Ecology Research 8, 785-802 (2008).

Hauber, M. E. Researching wildlife in New Zealand: conservation applications are both constraints and opportunities. In Blue sky to deep water: the reality and the promise. Proceedings of the ANZCCART Conference 2008. eds. Cragg, P., Keenan, J. & Sutherland G. (Wellington: Australian and New Zealand Council for the Care of Animals in Research and Teaching, 2009): 83-88.

Hauber, M. E. & Kilner, R. M. Coevolution, communication, and host-chick mimicry in parasitic finches: who mimics whom? Behavioral Ecology and Sociobiology 61, 497-503 (2007).

Honza, M., Polacikova, L., et al. Ultraviolet and green parts of the colour spectrum affect egg rejection in the song thrush ( Turdus philomelos). Biological Journal of the Linnean Society 92, 269-276 (2007).

Kilner, R. The evolution of virulence in brood parasites. Ornithological Science 4, 55-64 (2005).

Klippenstine, D. R. & Sealy, S. G. Differential ejection of cowbird eggs and non-mimetic eggs by grassland passerines. Wilson Journal of Ornithology 120, 667-673 (2008).

Noble, D. G., Davies, N. B., et al. The red gape of the nestling cuckoo ( Cuculus canorus) is not a supernormal stimulus for three common hosts. Behaviour 136, 759-777 (1999).

Peer, B. D. & Sealy, S. G. Correlates of egg rejection in hosts of the brown-headed cowbird. Condor 106, 580-599 (2004).

Rothstein, S. I. & Robinson, S. K. Parasitic Birds and Their Hosts. Studies in Coevolution. New York, NY: Oxford University Press, 1998.

Schuetz, J. G. Reduced growth but not survival of chicks with altered gape patterns: implications for the evolution of nestling similarity in a parasitic finch. Animal Behaviour 70, 839-848 (2005).

Servedio, M. R. & Hauber, M. E. To eject or to abandon? Life history traits of hosts and parasites interact to influence the fitness payoffs of alternative anti-parasite strategies. Journal of Evolutionary Biology 19, 1585-1594 (2006).

Sorenson, M. D., Hauber, M. E. et al. Sexual imprinting misguides species recognition in a facultative interspecific brood parasite. Proceedings of the Royal Society of London B 277, 3079-3085 (2010).

Smith, J. N. M., Cook, T. L., Rothstein, S. I., Robinson, S. K., & Sealy, S. G. eds. Ecology and Management of Cowbirds and Their Hosts. Austin: University of Texas Press, 2000.

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Davies, N. B. Cuckoos, Cowbirds and other Cheats. London, UK: T. & A. D. Poyser, 2000. Davis, S. K. & Sealy, S. G. Cowbird parasitism and nest predation in fragmented grasslands of southwestern Manitoba. In Ecology and Management of Cowbirds and Their Hosts. eds. Smith, J. N. M., Cook, T.

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In 47 episodes, Hank Green will teach you anatomy and physiology! This course is based on an introductory college level curriculum, with Human Anatomy and Ph...

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Information for students and teachers of our BTEC Nationals in Animal Management (2016), including key documents and the latest news.

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What a phylogenetic tree is. How to read phylogenetic trees and determine which species are most related.

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Explore the Tree of Life

News

Darwin 200: the celebration continues... read more

The Tree of Life Web Project (ToL) is a collaborative effort of biologists and nature enthusiasts from around the world. On more than 10,000 World Wide Web pages, the project provides information about biodiversity, the characteristics of different groups of organisms, and their evolutionary history ( phylogeny).

Each page contains information about a particular group, e.g., salamanders, segmented worms, phlox flowers, tyrannosaurs, euglenids, Heliconius butterflies, club fungi, or the vampire squid. ToL pages are linked one to another hierarchically, in the form of the evolutionary tree of life. Starting with the root of all Life on Earth and moving out along diverging branches to individual species, the structure of the ToL project thus illustrates the genetic connections between all living things.

read more about the Tree of Life Web Project...

"The affinities of all the beings of the same class have sometimes been represented by a great tree... As buds give rise by growth to fresh buds, and these if vigorous, branch out and overtop on all sides many a feebler branch, so by generation I believe it has been with the great Tree of Life, which fills with its dead and broken branches the crust of the earth, and covers the surface with its ever branching and beautiful ramifications."

Charles Darwin, 1859

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Darwin 200: the celebration continues... read more The Tree of Life Web Project (ToL) is a collaborative effort of biologists and nature enthusiasts from around the world. On more than 10,000 World Wide Web pages, the project provides information about biodiversity, the characteristics of different groups of organisms, and their evolutionary history ( phylogeny).

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The difference between endotherms and ectotherms. How to read graphs related to endotherms and ectotherms.

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From the Summer 2017 issue of Living Bird magazine. Subscribe now.
Fish do it. Frogs do it. Even insects lay eggs with color. But birds do it best.

Only birds produce eggs in such a wide range of eye-pleasing shades and intricate patterns on the hard surface of their eggs.

Like gems in a jeweler's window, they vary in base color, how shiny they are, and whether they are covered in Sanskrit-like scrawls or patterns of spots.

But, how does the color get there? What is it made of? Does it benefit the embryo? And, why are some eggs plain white?

Egg pigmentation is surprisingly complex.

Building the Egg

An egg's story begins in a female bird's single ovary. When an ovum is released into the oviduct and fertilized, it is just a protein-packed yolk. The albumen-the gelatinous egg white-is added next. The blobby mass then gets plumped up with water and encased in soft, stretchy membrane layers. The first globs of the calcium carbonate shell are then deposited on the exterior, with the mineral squirting from special cells lining the shell gland (uterus). Pigmentation, if any, comes next, with an overall protein coating added before the egg is laid. It takes about 24 hours to build a single egg.

In his book, The Most Perfect Thing: Inside (and Outside) a Bird's Egg, University of Sheffield zoologist Tim Birkhead compares the pigmentation process to an array of "paint guns." Each gun is genetically programmed to fire at a certain time so that the signature background color and spotting of a species' eggs is produced.

"Examination of birds' oviducts at the time the color is placed on the egg suggests that the color is produced and released over a very short time frame," Birkhead says, "usually in the last few hours before the egg is laid, and that makes it very hard to study."

Coatings of Many Colors

Despite the variety of egg colors and patterns, the palette is surprisingly small. Egg pigments are versatile substances made of complex molecules synthesized in a bird's shell gland. Only two pigments are at work. Protoporphyrin produces reddish-brown colors. Biliverdin produces shades of blue and green. More of one pigment, less of the other, and the egg gets a different background color, spots of a different color, or a combination of both.

For example, the intense brick-red of Cetti's Warbler eggs comes from protoporphyrin alone. All birds are likely to have the basic genetic machinery to produce the two pigments, even if they use only one of them, or use none at all and produce plain white eggs.

A female bird needs to take in extra calcium in order to produce the eggshell, and her diet can also be a factor in the production of the type and quantity of pigments. Paler-than-normal colors may be the by-product of a bird's poor diet or an immune system challenged by disease. Even in the same clutch, each egg will be pigmented somewhat differently.

"Birds that lay multiple eggs, such as thrushes and flycatchers, seem to change the color of their eggs throughout the laying cycle as if they were running out of the pigments," says Cornell PhD Mark Hauber, who wrote The Book of Eggs and studies them at Hunter College of the City University of New York.

And over time, eggshell colors and patterns within a species can also change. Mark Hauber feels bird-egg pigmentation may have evolved and disappeared multiple times and says it seems to be a rather "pliable" trait.

"With just two mutations, a Japanese Quail, which lays beige eggs with brown speckles, can start laying plain blue eggs," Hauber says. "So, it's really easy to genetically regulate metabolic pathways to start laying different colored eggs."

The deep history of egg color remains unknown. Some scientists think the dinosaur ancestors of birds produced only white eggs, as reptiles still do today, and that pigmentation came later. Others suggest dinosaur eggs could have been blue.
Left: The eggs of the Black Tinamou (top) and the Red-winged Tinamou (bottom) get their high-gloss shine from a protein-based coating. Right: The background color of a Guira Cuckoo egg can range from gray to the lovely turquoise shade shown here. Note along the broken edge, the turquoise color is not just deposited on the surface but permeates the entire shell. Photos of tinamou eggs by John Weinstein © 2014 The Field Museum. Cuckoo egg by Paula and Michael Webster.
Finishing Touches

Though all bird eggs are made of calcium carbonate, the underlying shell structure differs among species. The outer coating of the shell-the cuticle-can also make a difference in the finish of the egg. For example, the glossy eggs of the tinamou family-from the reddish-purple egg of the Red-winged Tinamou to the emerald green of the Elegant Crested-Tinamou-give off a high-wattage shine.

The Guira Cuckoo's egg is a wonder. Before the egg is laid, the base color is covered with a chalky layer of flaky calcium carbonate called vaterite that is structurally different from the eggshell itself. During incubation, the outer layer flakes off in patches, revealing a smoky gray or turquoise underneath in intricate patterns, rather like an artist's scratchboard. It's one of Hauber's favorite eggs.

"It's like having a little jewel in your hand," he says. "The eggs of some species of anis are like this, too. Among communal nesters that chalky layer might act as a bumper to prevent damage when the eggs knock against each other. We're trying to figure out if that flaky white material has any pigments in it."

Pigmentation as a Parental Cue

Some egg pigment functions are well established by science. Camouflage is one. Many species that nest on the ground produce speckled or streaked eggs that blend in well with their surroundings and befuddle predators. Look at the eggs of any shorebird and you'll find nearly all of them are speckled to blend in among rocks, pebbles, and sand to foil egg-stealing snakes, lizards, squirrels, and raptors.

As a general rule, birds that lay all-white eggs tend to be cavity-nesting species, such as owls and woodpeckers. Their eggs are already hidden from view so there's no reason to produce pigmented eggs. There's also a theory that white eggs show up better in a dark cavity.

But, there are exceptions. Even though camouflage makes sense for most species that lay their eggs in nests on the ground, some ground-nesting species-such as tinamous and nightjars-produce bright-colored, conspicuous eggs, which means other forces are at work. It helps to understand a species' life history.

Several Great Tinamou females may lay their shiny, unspeckled turquoise eggs on contrasting brown leaf litter in the same depression or scrape on the ground without building an actual nest of sticks or mud. Cornell PhD Patricia Brennan, now at the University of Massachusetts, Amherst, studied these birds in Costa Rica, noting that the eggs are not camouflaged or well concealed despite the threat of predation. Brennan suggests that egg color is a signal to other females, drawing their attention to the nest and promoting synchronous laying. The benefit to the birds is that, even if a predator does strike, it cannot eat all the eggs and those of any one individual stand a better chance of surviving.

Scientists say some species get away with laying conspicuous eggs because the parents sit tightly on the nest, with both male and female sharing round-the-clock incubation duty so the eggs are almost never exposed to view. In fact, another novel, though disputed, explanation for brightly colored, conspicuous eggs is called the "blackmail theory." Bucknell University's Daniel Hanley has theorized that, because conspicuous eggs are at greater risk of predation, females may lay them to blackmail their mate into more active participation at the nest. If the male wants the showy eggs to stay covered up and protected, he must take turns incubating on the nest himself or bring food to the female so she can stay on the nest.

Pigmentation as Identifier

Some eggs are pigmented and patterned in defense against brood parasitism, which is when one species lays its eggs in the nest of another species as a ploy to get host parents to raise its young. Brown-headed Cowbirds are among the most famous nest parasites in North America, inducing Red-winged Blackbirds and other species into caring for cowbird nestlings.

Evolutionary biologist Claire Spottiswoode from the University of Cambridge says egg speckling can be a strategy to help parents differentiate their own eggs from those laid by an intruder. But it doesn't always work.

"It seems likely that natural selection seized on egg speckling and elaborated upon it to generate the complex egg signatures of identity that we see in host birds," explains Spottiswoode. "But those patterns can also be mimicked to some degree by their parasites."

Spottiswoode's studies of a species called the Parasitic Weaver in Zambia attempt to measure the competing pressures on both host and parasite in what she terms a "coevolutionary arms race." The battle between host and parasite often plays out in alternating egg pigmentation changes. Over time, the host species alters the look of its eggs, which the parasite then tries to mimic closely enough so that its eggs are not rejected. These changes happen surprisingly quickly-even within a few decades.

"What we've seen in Zambia is primarily a shift in the frequency of existing colors, given that the range of egg pigments is actually quite limited," Spottiswoode says. "We know from other systems that natural selection can sometimes be startlingly effective in generating evolutionary change and that eons aren't always needed!"

But again, nature throws in a few wrinkles that are hard to explain. For example, the Tawny-flanked Prinia produces fine squiggles on its eggs that are impossible for Parasitic Weavers to replicate, yet the weaver often successfully parasitizes prinia nests.

"This is a real mystery to me because having apparently evolved a perfect signature, the prinias seem not to use it," Spottiswoode says. "Unsquiggled eggs are clearly accepted at least sometimes, otherwise this strain of parasites would be defeated and have died out."

Pigmentation as Sun Block

Pigment may also have a specific function related to sunlight. David Lahti, at Queens College of the City University of New York, and Cornell PhD Dan Ardia at Franklin and Marshall College, studied specimens of Village Weaver eggs from Africa, which naturally vary from white to blue-green. Their theory is that egg color can represent a balancing act between two impacts of light-one good, one bad.

"There must be a trade-off between embryo protection from damaging UV rays, what we call the parasol effect, and the cost of additional pigmentation causing overheating, the dark-car effect," Ardia explains. "We found good evidence that DNA-damaging UV light transmits more easily through the eggshell when there isn't much pigmentation. But heavily pigmented eggs do heat up faster, which is also very dangerous for the embryo."

Lahti plans further studies to explore whether light levels have an influence on egg colors in other species.

Multiple studies have examined egg color in relation to the embryo's growth. Some theories suggest that variable amounts of pigment at each end of an egg allow differing levels of light to filter through, which may help the embryo develop a sense of direction and also cue the development of specific structures in its body. Another idea is that darker or lighter colors among eggs in the same clutch might play a role in whether the eggs hatch all at once or in sequence.

Some researchers think the intensity of an egg's color may say something about the health of the female bird, important information for males who may be deciding how much time to invest in incubating eggs and bringing food to the nest.

"There are many competing hypotheses to explain egg coloration and they're not all mutually exclusive," Ardia points out. "Pigment function is almost surely a complicated combination of factors depending on the idiosyncrasies of each species."

More Questions

Despite the research already done on the colors and patterns of bird eggs, plenty of questions remain.

For example, what do the birds see when they look at the eggs? Mark Hauber's lab is investigating how some birds see more of the light spectrum than humans do.

"Some birds, such as most galliforms or ducks, don't see ultraviolet light," Hauber explains. "But some gulls, hummingbirds, most songbirds, and even ostriches do see UV light and might be picking up more information from egg colors and patterns than we can see."

Lahti is fascinated by instances in which some birds lay only blue eggs, but other individuals of the same species lay only white eggs, as is the case with Eastern Bluebirds.

"I don't know what's going on there," he says. "Bluebirds are in the Turdidae family in which nearly all species have blue eggs. But bluebirds may be making an evolutionary transition to white eggs, which would be expected since they nest in cavities or nest boxes."

"One persistent mystery is why many open-nesters like the American Robin lay blue eggs. Is this camouflage? Does it signal, as one study strongly suggests, female quality? We don't know," muses Birkhead. "Among other species, we also don't know how those exquisite pencil-like scribbles are produced on some eggs."

Whether scientists are trying to unlock their secrets, or simply enjoy their beauty, bird eggs are one of nature's little miracles-a fragile, self-contained, breathable package evolved to protect the tender bud of life unfolding within.

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From the Summer 2017 issue of Living Bird magazine. Subscribe now. Fish do it. Frogs do it. Even insects lay eggs with color. But birds do it best. Only birds produce eggs in such a wide range of eye-pleasing shades and intricate patterns on the hard surface of their eggs.

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Vertebrate Circulatorium | This interactive module explores the circulatory systems of major vertebrate groups to gain insights into their evolution.

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Introduction

If you prick your finger or scrape your knee, you'll see some droplets of blood form. Just by eye, these droplets may seem to be made of uniform red liquid, similar to food coloring or paint. However, if you were to look under a microscope, you would see that your blood is actually a mixture of liquid and cells. And if you could zoom in even further, you would see that there are also many macromolecules (such as proteins) and ions (such as sodium) floating in the liquid. All of these components are important to the roles blood plays in the body.

What is blood?

Blood, by definition, is a fluid that moves through the vessels of a circulatory system. In humans, it includes plasma (the liquid portion), blood cells (which come in both red and white varieties), and cell fragments called platelets.

Plasma is the main component of blood and consists mostly of water, with proteins, ions, nutrients, and wastes mixed in.

Red blood cells are responsible for carrying oxygen and carbon dioxide.

Platelets are responsible for blood clotting.

White blood cells are part of the immune system and function in immune response.

Cells and platelets make up about percent of human blood, while plasma makes up the other percent. The diagram below shows red blood cells, white blood cells of different types (large, purple cells), and platelets.

Plasma, the liquid component of blood, can be isolated by spinning a tube of whole blood at high speeds in a centrifuge. The denser cells and platelets move to the bottom of the tube, forming red and white layers, while the plasma remains at the top, forming a yellow layer.

The plasma is about water, with the remaining made up of ions, proteins, nutrients, wastes, and dissolved gases. The ions, proteins, and other molecules found in plasma are important for maintaining blood pH and osmotic balance, with albumin (the main protein in human plasma) playing a particularly important role.

Some of the molecules found in the plasma have more specialized functions. For example, hormones act as long-distance signals, antibodies recognize and neutralize pathogens, and clotting factors promote blood clot formation at the site of wounds. (Plasma that's been stripped of its clotting factors is called serum.) Lipids, such as cholesterol, are also carried in plasma, but must travel with escort proteins because they don't dissolve in water.

Red blood cells

Red blood cells, or erythrocytes, are specialized cells that circulate through the body and deliver oxygen to tissues. In humans, red blood cells are small and biconcave (thinnest in the center, just in size), and do not contain mitochondria or a nucleus when mature.

These characteristics allow red blood cells to effectively perform their task of oxygen transport. Small size and biconcave shape increase the surface area-to-volume ratio, improving gas exchange, while lack of a nucleus makes additional space for hemoglobin, a key protein used in oxygen transport. Lack of mitochondria keeps red blood cells from using any of the oxygen they're carrying, maximizing the amount delivered to tissues of the body.

In the lungs, red blood cells take up oxygen, and as they circulate through the rest the body, they release the oxygen to the surrounding tissues. Red blood cells also play an important role in transport of carbon dioxide, a waste product, from the tissues back to the lungs. Some of the carbon dioxide binds directly to hemoglobin, and red blood cells also carry an enzyme that converts carbon dioxide into bicarbonate. The bicarbonate dissolves in plasma and is transported to the lungs, where it's converted back into carbon dioxide and released.

Red blood cells have an average life span of days. Old or damaged red blood cells are broken down in the liver and spleen, and new ones are produced in the bone marrow. Red blood cell production is controlled by the hormone erythropoietin, which is released by the kidneys in response to low oxygen levels. This negative feedback loop ensures that the number of red blood cells in the body remains relatively constant over time.

Platelets and clotting

Platelets, also called thrombocytes, are cell fragments involved in blood clotting. They are produced when large cells called megakaryocytes break into pieces, each one making platelets as it comes apart. Platelets are roughly disc-shaped and small, about in diameter.

When the lining of a blood vessel is damaged (for instance, if you cut your finger deeply enough for it to bleed), platelets are attracted to the wound site, where they form a sticky plug. The platelets release signals, which not only attract other platelets and make them become sticky, but also activate a signaling cascade that ultimately converts fibrinogen, a water-soluble protein present in blood plasma, into fibrin (a non-water soluble protein). The fibrin forms threads that reinforce the platelet plug, making a clot that prevents further loss of blood.

White blood cells

White blood cells, also called leukocytes, are much less common than red blood cells and make up less than of the cells in blood. Their role is also very different from that of red blood cells: they are primarily involved in immune responses, recognizing and neutralizing invaders such as bacteria and viruses.

White blood cells are larger than red blood cells, and unlike red blood cells, they have a normal nucleus and mitochondria. White blood cells come in five major types, and these are divided into two different groups, named for their appearance under a microscope.

One group, the granulocytes, includes neutrophils, eosinophils, and basophils, all of which have granules in their cytoplasm when stained and viewed on a microscope.

The other group, the agranulocytes, includes monocytes and lymphocytes, which do not have granules in the cytoplasm.

Each type of white blood cell plays a specific role in defense. For example, some white blood cells are involved in engulfing and breaking down pathogens, while others recognize specific microorganisms and launch immune responses against them. Different types of white blood cells have different lifetimes, ranging from hours to years, and new cells are produced primarily in the bone marrow (although some are made or mature in the thymus, lymph nodes, and spleen).

Stem cells and blood cell production

Red blood cells, white blood cells, and platelet-producing cells are all descended from a common precursor: a hematopoietic stem cell.

A hallmark of stem cells is that they divide asymmetrically. That is, one daughter cell remains a stem cell of the same type, while the other daughter cell acquires a new identity. For hematopoietic stem cells, which are found in the bone marrow, one daughter cell remains a hematopoietic stem cell, while the other goes on to become a different type of stem cell: either a myeloid stem cell or a lymphoid stem cell.

The myeloid stem cells and lymphoid stem cells also divide asymmetrically, with their non-stem cell daughters generating the mature cell types of the blood. Myeloid stem cells give rise to red blood cells, platelets, and some types of white blood cells, while lymphoid stem cells give rise to the types of white blood cells classified as lymphocytes.

Hematopoietic, myeloid, and lymphoid stem cells divide throughout a person's lifetime, generating new blood cells to replace old and worn-out ones.

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Components of blood (article) | Khan Academy

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All About Feathers

Unique to birds and their dinosaur ancestors, feathers have evolved into impressive biological structures that come in a surprising diversity of colors and forms. Here, we cover the breadth of feather biology by looking at feathers from a variety of scientific viewpoints including their anatomy, function, development, and evolution.

From the fluffy down on a swan chick to the brilliant spiral on a King Bird-of-Paradise tail, feathers are remarkable not just in the way they look to the naked eye, but also for their intricate microstructure. Understanding feather anatomy at the microscopic level provides insight into how feathers function. For example, the interlocking Velcro-like structure on many bird feathers creates the smooth, flexible, and resilient surface that supports flight and sheds water.

As feathers grow, they mature into highly branched structures. Careful study of this process inspired new hypotheseshypothesisan explanation that is testable through study and experimentation about the evolution of feathers through stages of increasing complexity. Newly unearthed dinosaur fossils from China and Canada have supported these hypotheses by providing specimens from each stage in the proposed evolutionary history-a clear example of how investigating biological structures across contexts can create scientific breakthroughs.

Feather Science From Many Angles

Thorough understanding of biological structures like feathers requires examination from many angles. We now recognize that how feathers function is intricately connected to how they're structured, and how they grow is closely linked to how they evolved.

Niko Tinbergen, a 1973 Nobel Prize winner for his work to understand animal behavior, developed what he called the four levels of analysis that biologists have been using ever since to structure their research. For us to fully understand anything in nature, he said, we need to think about these four questions:

How does it work? (mechanism)

How does it function? (adaptation)

How does it develop? (development)

How did it evolve? (evolution)

Here we have taken Tinbergen's advice and explored each of these questions to give you a comprehensive understanding of feather biology.

Feather Anatomy: How Do Feathers Work?

Feather structure

Although feathers come in an incredible diversity of forms, they are all composed of the protein beta-keratin and made up of the same basic parts, arranged in a branching structure. In the most complex feathers, the calamuscalamus<span class="phonetic">CAL-a-muss</span>the hollow barbless base of a feather's stiff central shaft extends into a central rachisrachis<span class="phonetic">RAY-kiss</span>the stiff central shaft of a feather from which barbs branch which branches into barbsbarbone of the main branches off the central shaft of a feather , and then into barbulesbarbule<span class="phonetic">barb-YOOL</span>one of the secondary branches off a feather barb with small hooks that interlock with nearby barbules. The diversity in feathers comes from the evolution of small modifications in this basic branching structure to serve different functions.

Downy feathers look fluffy because they have a loosely arranged plumulaceousplumulaceous<span class="phonetic">ploom-yoo-LAY-shuss</span>having a loose, non-interlocking feather structure microstructure with flexible barbs and relatively long barbules that trap air close to the bird's warm body. Pennaceouspennaceous<span class="phonetic">pen-AY-shuss</span>having an interlocking feather structure that creates a smooth surface, or vane feathers are stiff and mostly flat, a big difference that comes from a small alteration in structure; microscopic hooks on the barbules that interlock to form a wind and waterproof barrier that allows birds to fly and stay dry. Many feathers have both fluffy plumulaceous regions and more structured pennaceous regions.

Feather types

Feathers fall into one of seven broad categories based on their structure and location on the bird's body.

Wing feathers

The wing feathers specialized for flight are characterized by uniform windproof surfaces, or vanes, on either side of the central shaft that are created by an interlocking microstructure. Also called , these feathers are asymmetric with a shorter, less flexible leading edge that prevents midair twisting.

Tail feathers

Most tail feathers, or , feature an interlocking microstructure similar to wing feathers. Arranged in a fan shape, these feathers support precision steering in flight. Typically, birds have six pairs of feathers on the tail, which display increasing levels of asymmetry toward the outer pairs. In some birds, tail feathers have evolved into showy ornaments that are useless in flight.

Contour feathers

Contour feathers are what you see covering the bird's body and streamlining its shape. Arranged in an overlapping pattern like shingles, the waterproof tips are exposed to the elements and the fluffy bases are tucked close to the body. Sometimes brilliantly colored or uniformly drab, contour feathers can also help the bird show off or stay camouflaged. Contour feathers on the wing, called , shape it into an efficient airfoilairfoilwinglike structure that produces lift and drag as it moves through the air by smoothing over the region where the flight feathers attach to the bone.

Semiplume

Mostly hidden beneath other feathers on the body, semiplumes have a developed central rachis but no hooks on the barbules, creating a fluffy insulating structure.

Down

Similar to semiplumes with an even looser branching structure but little or no central rachis, down feathers are relatively short and positioned closest to the body where they trap body heat.

Filoplume

Short simple feathers with few barbs, filoplumes function like mammal whiskers to sense the position of the contour feathers.

Bristle

Bristles are the simplest feathers, with a stiff rachis that usually lacks barb branches. Most commonly found on the head, bristles may protect the bird's eyes and face.

Further Learning

Feather Function: What do feathers do?

Each feather on a bird's body is a finely tuned structure that serves an important role in the bird's activities. Feathers allow birds to fly, but they also help them show off, blend in, stay warm, and keep dry. Some feathers evolved as specialized airfoilairfoilwinglike structure that produces lift and drag as it moves through the air for efficient flight. Others have been shaped into extreme ornamental forms that create impressive displays but may even hinder mobility. Often we can readily tell how a feather functions, but sometimes the role of a feather is mysterious and we need a scientific study to fill in the picture.

Flight

The primary and secondary wing feathers, or , permit birds to take to the skies. Unlike other feathers, remiges are anchored to bone with strong ligamentsligamentband of tissue that connects a bone to another bone, piece of cartilage, or feather so they can withstand the demands of flight and be precisely positioned. The primariesprimaryone of the feathers occupying the outer half of the wing that can be controlled to generate forward thrust during flight are longest of the flight feathers. They occupy the outer half of the wing, can be controlled and rotated like rigid fingers, and provide most of the bird's forward thrust. While secondariessecondaryone of the feathers occupying the inner half of the wing that overlap with other secondaries to form an airfoil that provides lift during flight cannot be controlled as extensively, they provide most of the lift by overlapping to form an efficient airfoilairfoilwinglike structure that produces lift and drag as it moves through the air . Tail feathers, or , are also classified as flight feathers. They are essential for steering, but only the two most central feathers attach to bone.

Display

Some feathers are so highly modified for display that they almost don't look like feathers at all. For example, the iridescent spiral from a King Bird-of-Paradise ( Cicinnurus regius) tail functions as an ornament in the male's courtship display. Structurally, the feather is bizarre, with a bare that ends in a tight spiral of barbsbarbone of the main branches off the central shaft of a feather and arranged only on one side of the rachis to form an eye-catching brilliant medallion.

Modified contour feathers on the head are also commonly used in courtship displays. For example, the male Wood Duck's ( Aix sponsa) crest forms a colorful fan that completely changes its head shape. During this transformation, the bird elevates thousands of tiny feathers in unison by manipulating muscles just under the skin.

Not all fancy feathers are used to woo a partner; some are used in displays of aggression. For example, Blue Jays ( Cyanocitta cristata) keep their crests lowered when they are at rest or with family and flock members, but raise them during aggressive interactions.

The drab contour feathers covering the body of some birds may seem lackluster, but subtle brown patterns can create an impressive degree of camouflage in forested environments. Famous for hiding in plain sight, the Common Potoo ( Nyctibius griseus) is covered with feathers that mimic the colors of the tree branches it perches on. Adding to the disguise, the potoo will adjust its posture and close its eyes into tiny slits, making itself appear to be an extension of the tree.

Not all camouflage has to be drab. For example, the vibrant green contour feathers of male Eclectus Parrots ( Eclectus roratus) serve a camouflage function during foraging trips in the rainforest canopy. Back at the nest cavity where the green stands out against the brown tree bark, the male coloration aids in the intense competition with other males to win female mates. Male Eclectus Parrots likely evolved their green coloration as a tradeoff between effective camouflage and display. This is a rare example of feathers that allow birds to both hide and show off.

Insulation

Have you ever wondered why some birds hatch naked while others are covered in a coat of fuzzy feathers? Many young water birds must be able to swim and forage alongside their parents almost immediately after hatching. These chicks hatch with a full coat of natal down to keep them warm in cold water. Young Mute Swans ( Cygnus olor) for example, hatch with a fuzzy coat of natal down and after a few weeks, replace the natal down with an inner layer of adult down and an outer coat of contour feathers. In contrast, the young of many songbirds are born completely naked.

These species stay warm by absorbing heat from attending parents and huddling together in an insulated nest. Utterly dependent at hatch, altricial species, like Purple Martins ( Progne subis), require lots of parental care.

Weatherproofing

Arranged in an overlapping pattern on a bird's body to expose the waterproof tips, contour feathers allow water to roll right off a bird's back. Birds constantly maintain their waterproof coat through extensive grooming, or preeningpreenusing the beak to maintain the health and structure of feathers to ensure that every feather is in good shape. The interlocking structure is so important that any disruption to it-such as if spilled oil coats the feathers-leaves the bird waterlogged and helpless. For ducks and birds like the Common Loon ( Gavia immer) that spend most of their time in the water, maintaining a waterproof coat is critical for survival.

Still a mystery

Some feather functions remain a mystery. The feather tufts on the heads of Great Horned Owls ( Bubo virginianus) are often mistaken for ears. These modified contour feathers are completely separate from the ear and do not help owls hear, yet there is no scientific consensus on the function of these tufts. Some have proposed that the horns are for display. Others have suggested that owls use them for more complete camouflage while roosting in daylight, but other functions are also possible and no one has yet done a detailed study to find out.

Further Learning

Feather Growth: How do feathers develop?

Feathers are dead structures that cannot repair themselves when damaged. Because a healthy and functional coat is critical to survival, each year birds shed their old feathers and then grow a whole new set. This moltingmoltin birds, the process of losing and regrowing feathers on a regular cycle process is a carefully timed affair in which feathers are shed and regenerate in turn over a period of weeks so the bird can maintain its protective outer layer and ability to fly. Once the new set of feathers has matured, molt is complete and new growth only occurs before the next molt cycle when feathers are accidentally lost.

The growth process

A close look at feather growth reveals how these intricate structures form.

1. Each new feather grows from a small outgrowth of skin called the papilla.

2. As feathers mature, their tips get pushed away from the papilla, where the newest parts of the feather form. Like human hair, feathers are youngest at their base.

3. The feather's structure develops as proteins are laid down around the surface of this bump of skin. It's here that the branching patterns form by smaller branches fusing at the base to make thicker ones-barbulesbarbule barb-YOOLone of the secondary branches off a feather barb fuse into barbsbarbone of the main branches off the central shaft of a feather and barbs fuse into a rachisrachis RAY-kissthe stiff central shaft of a feather from which barbs branch .

4. As the feather grows, it stays curled in a tubular shape around the papilla until it is pushed away from the growth area.

5. A protective sheath maintains the feather's cylindrical shape until it starts to disintegrate near the tip, allowing the mature part of the feather to unfurl.

6. The sheath falls off and the growth process is complete.

Once the feather unfurls, its interlocking structure is fully formed. Throughout the year, the bird maintains its mature feathers through regular care, or preeningpreenusing the beak to maintain the health and structure of feathers . Whenever the become disturbed, the bird uses its beak to carefully guide them back into place. By the following molt season, many of the bird's feathers have experienced enough wear and tear that preening can no longer maintain their structure. Fortunately, during molt the bird grows a completely new set.

Further Learning

Feather Evolution: How did feathers evolve?

Flight feathers, with their intricate microstructure, are impressive examples of natural engineering. But how did they evolve? From the fossil record, we know that birds evolved from dinosaurs, some of which had feathers. But those first feathers had nothing to do with flight-they probably helped dinosaurs show off.

Scientists recently worked out a hypothesishypothesisan explanation that is testable through study and experimentation to explain how flight feathers could have evolved. They probably began as simple tufts, and then gradually developed through stages of increasing complexity into interlocking structures capable of supporting flight.

Evolutionary stages

1. The earliest feather was a simple hollow tube.

2. The simple tube evolved into a cluster of barbsbarbone of the main branches off the central shaft of a feather .

3. (a) The base of the barbs fused together to form a central and (b) branched from the barbs, as we see in modern-day down feathers.

4. The barbules evolved hooks that interlock to make flat vanes as in current contour feathers.

5. The feather structure evolved asymmetry with the aerodynamic properties of modern-day flight feathers.

Fossil evidence recently unearthed in China and Canada has confirmed that bird ancestors did indeed possess feathers from each of the steps in this proposed evolutionary pathway. Surprisingly, many dinosaurs had simple stage 1 feathers covering their bodies. This "dino fuzz" even covered close relatives of the great Tyrannosaurus rex. These early feathers may have been insulating, or when colorful, may have helped dinosaurs show off or stay camouflaged. There is also intriguing evidence of more complex Stage 3 and 4 feathers from finds like Ornithomimus edmontonicus. As adults, these large, bulky creatures sported feathers arranged along wing-like structures, but no wing feather traces have been found among the juvenile specimens. This suggests that even as dinosaurs started to evolve wings, the wing feathers were likely used for courtship or territorial display, not flight.

Though it may take time for people to get used to the idea of fuzzy or elaborately plumed meat-eating dinosaurs, this scientific breakthrough reminds us that asking questions from multiple perspectives helps generate new testable hypotheseshypothesisan explanation that is testable through study and experimentation and scientific knowledge. For this reason, it is becoming more and more common for scientists to work across disciplines. In fact, the active field of evolutionary-developmental biologyevolutionary-developmental biology (evo-devo)a field of biology that investigates the relationship between an organism's development and its evolutionary origins ("evo-devo") focuses on discovering a structure's evolutionary past by observing its process of growth and development.

Further Learning

Studying Feathers: How do scientists use Tinbergen's four questions?

We've just used Tinbergen's approach to look at feathers from several different perspectives-but it's not just a learning exercise. Scientists like those in the evo-devo crowd, are making discoveries in just the same way, by linking findings from across the biological disciplines.

One such scientist is Kim Bostwick, who used this integrated approach to untangle the mysteries of a bird whose feathers work like a musical instrument. This may sound like an outrageous idea, but male Club-winged Manakins of Central and South America use a highly modified feather structure to play a powerful one-note tune. Strong evolutionary pressure on these males to attract females has made them unique in the bird world, but it took years of scientific investigation by Bostwick and colleagues to work out the full story of how and why these birds sing with their wings.

Singing wings

So how do they do it? Club-winged Manakins sing with their wings by rubbing specialized feathers together. One of these feathers is club-shaped with ridges along its edge. The adjacent feather is slender, and bent at a 45-degree angle. This bent feather acts as a pick, while its ridged counterpart acts as a comb to produce a one-note song. This method of producing sound is called stridulationstridulation<span class="phonetic">stri-du-LAY-<br>shun</span>the act of rubbing together body parts to make a sound and also occurs in insects, such as crickets.

Kim's story

Kim Bostwick began her study of Club-winged Manakins by asking questions about how they sing with their wings. She spent years piecing together how the birds accomplish this feat mechanically, but she did not stop there. Because Kim had always been interested in evolution, she also asked questions about how their specialized feathers and associated behaviors evolved. This led her to study other birds closely related to Club-winged Manakins to see what behavioral innovations occurred in their evolutionary history that contributed to the display we see today. It turns out that the behavior evolved through a series of small steps, including short wing clicks and backwards hopping, into one of the most unusual displays in the animal world. Like Niko Tinbergen, Kim is one of the many scientists who prefer to ask scientific questions from many angles, going beyond the mechanics to make discoveries about function, development, and evolution.

To learn more about Kim's story at the Singing Wings website.

Further Learning

References

1. Heinsohn, R., Legge, S., & Endler, J. A. (2005). Extreme reversed sexual dichromatism in a bird without sex role reversal. Science. 309(5734), 617-9.
2. Perrone, M. (1981). Adaptive significance of ear tufts in owls. The Condor, 83(4), 383.
3. Prum, R. O., & Brush, A. H. (2002). The evolutionary origin and diversification of feathers. The Quarterly Review of Biology, 77(3), 261-295.
4. Zelenitsky, D. K., Therrien, F., Erickson, G. M., DeBuhr, C. L., Kobayashi, Y., Eberth, D. A., & Hadfield, F. (2012). Feathered non-avian dinosaurs from North America provide insight into wing origins. Science. 338(6106), 510-4.
Suggested citation: Cornell Lab of Ornithology. 2013. All About Feathers. All About Bird Biology <birdbiology.org>. Cornell Lab of Ornithology, Ithaca, New York. < add date accessed here: e.g. 02 Oct. 2013 >.

Acknowledgements:
Author: Mya Thompson
Web Designer: Jeff Szuc
Web programmer: Tahir Poduska
Illustrator: Andrew Leach
Content assistants: Marie Russell, Feven Asefaha

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Everything You Need To Know About Feathers | Bird Academy * The Cornell Lab

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All About Feathers Unique to birds and their dinosaur ancestors, feathers have evolved into impressive biological structures that come in a surprising diversity of colors and forms. Here, we cover the breadth of feather biology by looking at feathers from a variety of scientific viewpoints inclu ...