According to the taxon cycle concept, relictualization occurs after a time of geographical expansion and diversity, meaning that lineages that are currently species-poor and phylogenetically isolated were formerly far more diverse. Although more species-rich corvoid families may show evidence for a variety of taxon cycle stages, another possibility is that corvoid lineages that are currently species-poor and phylogenetically isolated have had low rates of net diversification and have maintained low species diversity throughout their histories.

          Pectoral muscle and heart mass were significantly higher in winter compared to summer, but summit metabolism was lower during winter, in contrast to previous studies associating higher pectoral muscle and heart mass with increased thermogenic capacity in higher-latitude birds. To the best of the researchers' knowledge, it's the first study to describe increased pectoral muscle mass without a corresponding rise in summit metabolism, and it's conceivable that cellular changes that are required for improved thermogenic capability did not occur in sparrow-weavers. This is also the first study to look at seasonal variation in pectoral muscle mass in the context of summit metabolism adjustments in a subtropical bird, and more research is needed to understand the mechanisms and factors that drive metabolic flexibility in birds living at lower latitudes with milder winters.

              There was no seasonal variation in the dry masses of the gizzard, intestines or liver of sparrow-weavers, and during the same period, basal metabolic rate did not vary seasonally. Researchers found significantly higher heart (~ 18% higher) and pectoral muscle (~ 9% higher) dry mass during winter, although ultrasound measurements did not detect seasonal changes in pectoral muscle size.

        The observed differences between the two feeding guilds (insectivores and omnivores) are most likely the result of differences in digestive needs.

INSECTIVORES

OMNIVORES

           Some DTMs of the omnivorous M. nigra were more similar to those of insectivores, which is consistent with findings by Sam et al. (2017) that insects are a major component of the diet in some individuals of this species. Variable diets between individuals thus likely induce variation in DTMs. This is supported by the finding that the DTMs of some individuals of M. nigra are similar to insectivores, while others resemble omnivorous species.

 

 

Feather's separating from each other in the same wing - this feature maximizes the silencing of air that hits the wings of the owl during flight, making them more silent which can help the owl.

Tail Feathers - the tail feather helps the owl in order for redirection during flight.

Feathered Ear Tufts - while it is not very certain as to what is the use of this, there are some theories for its purpose: Acts as a camouflage in order for the owl to hide

in a tree; Feature that distinguishes owls from other owls; A sign of aggressiveness; For communication: Alert and watchful (ear tufts up), scared or angry (ear tufts down)

Serrations of an owl feather - at the edge of an owl feather, it can be found tiny-comb like structures that help in reducing noise, which helps the owl during hunting.

Upper surface of the owl's feathers - this has a velvet-like covering, stabilizes the airflow allowing slower flight, and is 

known for suppressing the sound of feathers that move over each others

Trailing edge of the owl's feather - it is fringed, which prevent the separation of the airflow between adjacent feathers, where it reduces turbulence and reduces noise.

Feathered Ear Tufts: 

Facial Disk: 

Ear

Eyes

Beak

Talons

An owl can turn its head up to 270 degrees left or right from the forward facing position. An owl cannot turn it's head full circle from a forward facing position as is the common belief. There are several adaptations that allow this:

1) An owl's neck has 14 vertebrae, which is twice as many as humans.

2) Owls have only one occipital articulation with the cervical vertebrae. (There is only one bone situated on top of the backbone.) Humans have two articulations. This allows the owl to pivot on the vertebrae column much like your body can pivot on one foot. Their muscle structure is arranged in a manner that allows this movement as well.

3) Owls have a special arrangement of the jugular veins with associated bypass connector blood vessels, to ensure that blood supply (and return) are not impeded as the neck is rotated.

 

The large flat breastbone, or Sternum, supports the large and powerful flight muscles. It also protects the heart, lungs and other internal organs. In the Tytonidae family of owls, the Carina, or Sternum Keel is broad, becoming narrower towards the abdomen, and the lower edge of the sternum has only small notches on each side. In the family Strigidae, the carina is narrow at its upper part, and becomes broader towards the belly, while the lower edge of the sternum has two deep notches on each side.

The wing bones are relatively long in owls, and the associated wing surface area is broad, producing a low wing loading. This allows for easy take-offs, and effortless flight, even when carrying prey.

The foot bones, or tarso-metatarsi, are relatively short and stout in owls, most likely to aid in the efficient killing and carrying of prey.

Depending on the size of the owl, some dine on insects; many dine on small rodents like mice and voles; the largest owls eat rabbits, other birds or even fox. Owls eat smaller prey whole. The food goes to the proventriculus where digestive enzymes break down the meal. Owl stomach acid is weak (pH 2.2 to 2.5) so they only digest soft tissue of prey, not bones or fur. The food moves to the gizzard where usable substances get used by the body and indigestible parts remain in the gizzard.

 

Gizzard remains include bits of undigested prey. Owl gizzards work like trash compactors. The muscles in the gizzard compress the leftovers into an oval pellet. That pellet remains in the owl's gizzard until the bird is ready to eat again, a time period of 10 to 12 hours. Pellets inhibit eating, so prior to the next meal, owls regurgitate pellets from the gizzard. The pellet is forced out by spasms in the esophagus, a process lasting a few seconds to several minutes.

The blood then flows back to the heart into the first chamber, or the right atrium, through blood vessels called veins, which bring all blood to the heart. From the right atrium, the deoxygenated blood goes to the right ventricle. The right ventricle is a larger chamber that pumps the blood to the lungs.

At the lungs, the blood picks up oxygen and is moved to the left atrium of the heart. The left atrium pumps blood to the left ventricle, the strongest chamber of the heart. The left ventricle's job is to pump blood through the arteries to the entire body, so it needs to have a thick wall of muscle to do such a big job. From there, the process repeats again with each heartbeat.

Only birds and mammals have four chambers to their heart. The purpose of this is to divide the oxygenated and deoxygenated blood efficiently. Other animals have two chambers, or no chambers in their heart, so all the blood mixes together. To be the most efficient at delivering oxygen, we want to keep the oxygenated blood moving towards the body and the deoxygenated blood coming back to the heart to get more oxygen.

        In the brain, the optic lobes are large and the olfactory lobes small, correlating with their senses.

        The cerebral hemispheres in birds are large and well-developed, as in mammals, but the center of complex behavior in the cerebrum is different in the two groups. The brain of a mammal is dominated by the top layer of the cerebral hemispheres (cerebral cortex) which have a high capacity for learning. The bird brain is dominated by the middle of the cerebral hemisphere which lacks learning capacity. So mammals, in general, learn behavior and bird behavior tends to be instinctive and stereotyped. Birds’ brains are also particularly sensitive to control by hormones; implanting a pellet of testosterone in a dove elicits courtship, copulation, and aggressive behavior. Experimentally, large sections of the cerebral cortex have been removed with little effect on the birds’ behavior.

        The cerebellum, the center for motor control, is well-developed in birds as is logical with their ability to fly and the related need for agility.