Physiology of Cold Adaptation in Birds

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How Wild Animals Cope With Icy Winter Temperatures

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Mah Jong Quest. Subscribe Top Menu Current Issue. Book Shop. Like this article? The Karez is a modern-day engineering marvel and a prime example of people working with, not against, the forces of nature to deliver their needs—in this case, water. Comment on this Story. Last Name. First Name. Address 1. This cyclical process aids in homeostasis. Homeothermy and poikilothermy refer to how stable an organism's deep-body temperature is. Most endothermic organisms are homeothermic, like mammals.

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However, animals with facultative endothermy are often poikilothermic, meaning their temperature can vary considerably. Most fish are ectotherms, as most of their heat comes from the surrounding water. However, almost all fish are poikilothermic. By numerous observations upon humans and other animals, John Hunter showed that the essential difference between the so-called warm-blooded and cold-blooded animals lies in observed constancy of the temperature of the former, and the observed variability of the temperature of the latter.

Almost all birds and mammals have a high temperature almost constant and independent of that of the surrounding air homeothermy. Almost all other animals display a variation of body temperature, dependent on their surroundings poikilothermy. Thermoregulation in both ectotherms and endotherms is controlled mainly by the preoptic area of the anterior hypothalamus.


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In cold environments, birds and mammals employ the following adaptations and strategies to minimize heat loss:. In warm environments, birds and mammals employ the following adaptations and strategies to maximize heat loss:. As in other mammals, thermoregulation is an important aspect of human homeostasis. Most body heat is generated in the deep organs, especially the liver, brain, and heart, and in contraction of skeletal muscles. High temperatures pose serious stresses for the human body, placing it in great danger of injury or even death.

For example, one of the most common reactions to hot temperatures is heat exhaustion, which is an illness that could happen if one is exposed to high temperatures, resulting in some symptoms such as dizziness, fainting, or a rapid heartbeat. Scattered throughout the body in both peripheral and central nervous systems, these nerve cells are sensitive to changes in temperature and are able to provide useful information to the hypothalamus through the process of negative feedback, thus maintaining a constant core temperature.

There are three avenues of heat loss: convection, conduction, and radiation. If skin temperature is greater than that of the surroundings, the body can lose heat by radiation and conduction. But, if the temperature of the surroundings is greater than that of the skin, the body actually gains heat by radiation and conduction. In such conditions, the only means by which the body can rid itself of heat is by evaporation.

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So, when the surrounding temperature is higher than the skin temperature, anything that prevents adequate evaporation will cause the internal body temperature to rise. Thermogenesis occurs in the flowers of many plants in the family Araceae as well as in cycad cones. Heat is produced by breaking down the starch that was stored in their roots, [27] which requires the consumption of oxygen at a rate approaching that of a flying hummingbird.

One possible explanation for plant thermoregulation is to provide protection against cold temperature. For example, the skunk cabbage is not frost-resistant, yet it begins to grow and flower when there is still snow on the ground. Animals other than humans regulate and maintain their body temperature with physiological adjustments and behavior.

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Desert lizards are ectotherms and so unable to metabolically control their temperature but can do this by altering their location. They may do this, in the morning only by raising their head from its burrow and then exposing their entire body. By basking in the sun, the lizard absorbs solar heat. It may also absorb heat by conduction from heated rocks that have stored radiant solar energy. To lower their temperature, lizards exhibit varied behaviors.

Sand seas, or ergs , produce up to They also go to their burrows to avoid cooling when the sun goes down or the temperature falls. Aquatic animals can also regulate their temperature behaviorally by changing their position in the thermal gradient. Animals also engage in kleptothermy in which they share or even steal each other's body warmth. In endotherms such as bats [31] and birds such as the mousebird [32] and emperor penguin [33] it allows the sharing of body heat particularly amongst juveniles.

This allows the individuals to increase their thermal inertia as with gigantothermy and so reduce heat loss. Other animals exploit termite mounds. Some animals living in cold environments maintain their body temperature by preventing heat loss. Their fur grows more densely to increase the amount of insulation. This minimizes heat loss through less insulated body parts, like the legs, feet or hooves , and nose.

To cope with limited food resources and low temperatures, some mammals hibernate during cold periods. To remain in "stasis" for long periods, these animals build up brown fat reserves and slow all body functions.


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  6. True hibernators e. Some bats are true hibernators and rely upon a rapid, non-shivering thermogenesis of their brown fat deposit to bring them out of hibernation. Estivation is similar to hibernation, however, it usually occurs in hot periods to allow animals to avoid high temperatures and desiccation. Both terrestrial and aquatic invertebrate and vertebrates enter into estivation. Examples include lady beetles Coccinellidae , [37] North American desert tortoises , crocodiles , salamanders , cane toads , [38] and the water-holding frog. Daily torpor occurs in small endotherms like bats and hummingbirds , which temporarily reduces their high metabolic rates to conserve energy.

    Previously, average oral temperature for healthy adults had been considered In Poland and Russia, the temperature had been measured axillary. Recent studies suggest that the average temperature for healthy adults is Variations one standard deviation from three other studies are:. Measured temperature varies according to thermometer placement, with rectal temperature being 0. In humans, a diurnal variation has been observed dependent on the periods of rest and activity, lowest at 11 p. Monkeys also have a well-marked and regular diurnal variation of body temperature that follows periods of rest and activity, and is not dependent on the incidence of day and night; nocturnal monkeys reach their highest body temperature at night and lowest during the day.

    Sutherland Simpson and J. Galbraith observed that all nocturnal animals and birds — whose periods of rest and activity are naturally reversed through habit and not from outside interference — experience their highest temperature during the natural period of activity night and lowest during the period of rest day. In essence, the temperature curve of diurnal birds is similar to that of man and other homoeothermal animals, except that the maximum occurs earlier in the afternoon and the minimum earlier in the morning.

    Also, the curves obtained from rabbits, guinea pigs , and dogs were quite similar to those from man. During the follicular phase which lasts from the first day of menstruation until the day of ovulation , the average basal body temperature in women ranges from Within 24 hours of ovulation, women experience an elevation of 0. The basal body temperature ranges between Fever is a regulated elevation of the set point of core temperature in the hypothalamus , caused by circulating pyrogens produced by the immune system. To the subject, a rise in core temperature due to fever may result in feeling cold in an environment where people without fever do not.

    Some monks are known to practice Tummo , biofeedback meditation techniques, that allow them to raise their body temperatures substantially. It has been theorised that low body temperature may increase lifespan. In , it was reported that transgenic mice with a body temperature 0. This mechanism is due to overexpressing the uncoupling protein 2 in hypocretin neurons Hcrt-UCP2 , which elevated hypothalamic temperature, thus forcing the hypothalamus to lower body temperature. The mice were fed ad libitum. There are limits both of heat and cold that an endothermic animal can bear and other far wider limits that an ectothermic animal may endure and yet live.

    The effect of too extreme a cold is to decrease metabolism , and hence to lessen the production of heat. Both catabolic and anabolic pathways share in this metabolic depression, and, though less energy is used up, still less energy is generated.

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    The effects of this diminished metabolism become telling on the central nervous system first, especially the brain and those parts concerning consciousness; [52] both heart rate and respiration rate decrease; judgment becomes impaired as drowsiness supervenes, becoming steadily deeper until the individual loses consciousness; without medical intervention, death by hypothermia quickly follows. Occasionally, however, convulsions may set in towards the end, and death is caused by asphyxia. In experiments on cats performed by Sutherland Simpson and Percy T. Death appeared to be mainly due to asphyxia , and the only certain sign that it had taken place was the loss of knee-jerks.

    That said, for endotherms, having control over their body temperature can be a real advantage, as they are far less vulnerable to fluctuations in environmental conditions. Whatever the weather, they can carry on grazing, hunting or mating. However, in nature there are always some exceptions. Not all mammals need to keep their body temperatures within the same narrow range as humans do. The opah fish or moonfish is one of the only species of fish that can stay warm, independent of the temperature of the surrounding water.

    It achieves this thanks to a system of heat exchanging blood vessels in its gills. This species is the ultimate cold-weather specialist. They accomplish this thanks to their incredibly thick fur, which is made up of two layers: outer hairs, called guard hairs, and an undercoat for additional insulation. As musk oxen are herd animals, living in groups of individuals, they also huddle together to reduce heat loss. This is an example of a behavioural adaptation. When temperatures rise, their heart starts beating again and their body replaces any damaged cells. Weighing up to 1.

    Physiological adaptations include a small surface area to volume ratio, to minimise heat loss, and an extremely thick layer of blubber for insulation. As an endotherm, the walrus relies on metabolic heat to survive. An adult must consume around 25 kg of food per day, usually in the form of clams, snails, crabs, shrimps, as well as the occasional seal carcass! While insulation is key to survival in cold conditions, the opposite is true for desert dwellers. As with walruses, camels also have large reserves of fat, which is broken down to produce water and energy. Instead of storing the fat all around their body like walruses do, camels keep it all in one place: their hump.

    This way, they limit any unwanted insulation. This species of invertebrate, endemic to Australia, builds elaborate mounds that reach 4m in height and can house a million individual termites. Their mounds are always oriented in a north-south direction, which is how they got their name. This detail ensures that their nest receives heat from the sun on their eastern and western sides at dawn and at dusk, while exposing less surface to the sun in the middle of the day, when there is a much greater risk of overheating.

    It has evolved massive ears that can grow to be half the size of its body. As well as helping them to detect prey, they contain an extensive network of blood vessels that allows rapid heat loss through a process called vasodilation. As for behavioural adaptations, they display nocturnal habits. They hunt at night and retreat to their underground dens during the heat of the day.

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