User:Binclima811/Common raven physiology

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The common raven (Corvus corax), also known as the northern raven, is a large, all-black passerine bird. Found primarily in the Northern Hemisphere, it is the most widely distributed of all corvids. Their Northern range encompasses Arctic and temperate regions of Eurasia and North America, and they reach as far South as Northern Africa and Central America. The common raven is an incredibly versatile passerine to account for this distribution, and their physiology varies with this versatility. This article discusses this bird's physiology, including its homeostasis, respiration, circulatory system, osmoregulation, and thermoregulation.

Respiration
The respiratory tract of birds possesses unique air movement properties. Air moves in a unidirectional flow and blood travels in a concurrent direction to air flow. An advantage of this type of system is it minimizes dead space and enables the bird to maintain a highly oxidative, active output. The respiratory system of the common raven is no different.

Fick's laws of diffusion can be applied to oxygen cascade events in avian species. There is a proportional relationship between the volume of the pulmonary capillaries and respiratory surface area. Avian respiration follows a system of countercurrent flow in which inspiratory and expiratory processes are dependent on an efficient rate of diffusion to oxygenate blood through the air capillaries. The optimization of the volume of tissue within the capillaries in conjunction with the large respiratory surface area allow for an effective diffusion rate. Finally, in the avian respiratory system, the partial pressure of oxygen between the gas, lung, and the vascular capillaries depends upon the ventilation rate and air that is already inhaled.

A unique feature of avian respiration involves the usage of turbinates within the nasal cavity during routine breathing. The nasal cavities in avian taxa are the first organ to moderate the inhalation of air humidity during periods of rest. The epithelial-lined turbinates within these cavities act as countercurrent heat exchangers. During this exchange, air inhaled becomes saturated as it brought further down into the respiratory tract. The air being exhaled stays saturated, allowing for a recovery of heat and moisture.

Environmental challenges on osmoregulation
The Corvus corax lives in a wide variety of habitats, and as such it is well suited to many different environments. Because Corvus corax is an osmoregulator, living in a terrestrial habitat presents some challenges for Corvus corax as it must consistently ingest water and salts to balance the content of its blood. To regulate solute concentration, common ravens use their kidneys to regulate blood composition and filter out toxins. This filtering results in the formation of a dilute excrement which is then released from the cloaca. The ability of the kidney to retain water and concentrate dilute urine is modulated by the osmolarity gradient induced by a countercurrent exchange system in the renal medulla. Corvus corax is an omnivore, and as such consumes whatever is available to it depending on its environment. This can include but is not limited to invertebrates such as insects, fruit when available, potentially other birds and their eggs. Corvus corax is an opportunistic hunter, relying on social cues and sense of sight to find food. When not hunting, Corvus corax is typically scavenger, and much of its intake comes in the form of carrion and garbage left behind by humans and large vertebrates. In instances where carrion and garbage are available, ravens will eat in groups alongside other scavengers such as bald eagles and other species in the family Corvidae. The difference in diet between the populations of Corvus corax in marine environments in comparison to terrestrial environments is immense; ravens near the more marine based terrestrial habitat prey primarily on gulls eggs and hatchlings as well as supplementing their diet with seaweed.

These populations have a much higher intake of salt compared to the populations in the more inland regions and therefore excrete a more hypotonic urine. A diet with sufficient salt concentrations pushes ravens in marine environments to focus on water intake. This is primarily through the food it eats, but if this is not sufficient it will drink water or consume snow in the winter. Corvus corax is adapted to survive across its large range, and as such exhibits a number of variations in osmoregulation to suit its environmental needs. Because these birds are omnivores, their basal rates reflect the diet they follow along with other factors such as environmental conditions.

The interactions between this species and humans present various challenges for these birds. Trash and carrion scraps, whether anthropogenic in origin or not, present opportunities for feeding consistent with ravens' scavenging behavior. These food placements attract breeding and non-breeding birds, which present competitive challenges for breeding adults collecting food for their broods. Corvus corax also present several problems in their normal ranges for humans, and as such efforts to reduce their numbers through osmoregulatory means factor into the viability of this species in certain regions. Specifically, the use of the toxicant 3-chloro-4-methylanine hydrochloride (DRC-1339) is used to induce renal failure and death in ravens impacting the conservation status of other species of bird and livestock numbers.

Evaporative Water Loss
Through the respiratory pathway of evaporative water loss, the common raven is able to effectively maintain body temperature within their variable range. The mechanism by which Passeriformes such as the common raven regulate evaporative water loss comes in the form of respiration through panting. Unlike mammalian endotherms, birds do not have sweat glands and instead must rely on respiratory and cutaneous gas exchange to regulate body water. Passeriformees like Corvus corax are also reliant on panting, as they depend much less on supplementary processes such as cutaneous evaporative heat exchange and gular fluttering. This involves a gradual increase in in the exchange of gases and breathing rate. This increased breathing rate is induced by an increased tidal volume along with a greater ventilation of the mucosal surfaces. As well, a higher breathing rate leads to an increase in the resting metabolic rate of the individual.