Adaptive Thermoregulation in Different Species of Birds

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Adaptive Thermoregulation in Different Species of Birds
Birds are classified as homeotherms meaning they have ability to
regulate their body temperature in relation to their immediate
environment. This is in contrast to poikilotherms whose body
temperatures are affected the temperature of the neighboring surrounding
(Hoffman et al, 2007). Birds across the world experience regional
variation in body temperature which means that, they have to develop
adaptive strategies in order to cope with these variations. Birds
inhabiting different regions, whether polar or equatorial, exhibits
exceptional capability for regulating their body temperature.
Birds dwelling in polar region have physical, physiological and
behavioral adoptions that enable them to survive in extremely low
temperatures throughout the year. Bird’s feathers are among the most
important physical possession that enables them to maintain body
temperature within the range that is required to carry out all internal
metabolic processes. In many bird species dwelling in polar and
temperate regions where temperature is low, feathers offer outstanding
insulation against cold. Those species like the polar penguins living in
icy habitats have extra feathers to offer them with a thick protection
against the cold (Wojciechowski et al, 2011). Some species have large
fat deposit on their skins that insulate them further against the low
temperatures. Their feet are also covered with specialized scales that
shield them from losing too much heat to the cold surrounding. Other
species especially those that do not possess specialized scales, have
special ability of controlling their feet temperatures free from the
rest of their body. They do this through constriction of blood vessels
passing through the feet, thus reducing the level of blood flow to the
feet and thus preventing heat loses through evaporation (Hoffman et al,
Huddling is another important behavioral adaptation of bird living in
habitats where temperatures fall below their body temperatures. This is
a behavioral feature where birds live and move in large social group as
a way of conserving energy. Huddling conserves energy through increasing
the operative temperature of all members of the group by raising
radiative heat gain and reducing heat loss through convention
(Wojciechowski et al, 2011). The emperor penguins exhibit one of the
most noticeable examples of huddling in a single huddle, temperature
can rise above 35 degrees. To maintain a constant internal environment
amid the cold surroundings, birds dwelling in the arctic and Antarctic
have a comparatively higher metabolic rate than their counterparts do in
tropical and temperate regions. A lot of heat is generated through the
chemical process of oxidizing food, which ensures the body temperature
of these birds does not fall too low. They also feed more and increase
their physical activity all in a bid to generate extra heat.
Other behavioral characteristic of birds living in habitats with low
temperatures include, fluffing, sunning, tucking, roosting, torpor and
shivering. Fluffing of feathers creates a cushion of air that insulates
the bird from losing heat to the cold surrounding. Birds also make use
of solar energy to raise their body temperatures by turning their back
in the direction of the sunlight, what is referred to as sunning
(Wojciechowski et al, 2011). In this behavioral characteristic, bird
expose a larger surface area so that solar energy can heat their
feathers and skin all in a bid to create a film of warm air around their
bodies so that less heat is lost to the environment. Birds in these
regions also tuck their beak and legs in their feathers to prevent heat
loss. Shivering, which is the involuntary movement of skin muscles, also
generates heat as a temporal solution to cold.
Some species dwelling in cold habitats will go into a period of
inactivity to save energy during winter. During this state, the
metabolic rate of the bird is greatly reduced and as such low energy
content is required to maintain suitable body heat. Even though torpor
reduce the overall body temperature it significantly decreases the rate
of metabolic reaction in the body and the amount of calories required to
maintain basal metabolic rate. Swifts and hummingbirds are some of the
species that use this behavioral adaptation to regulate body
temperatures and thus endure cold temperatures (Wojciechowski et al,
The ability to regulate temperature makes it possible for birds to
exploit many habitats. Birds have a range of behavioral and physical
features that enable them to regulate the heat loss and gain depending
on the nature of the environment. In essence, constriction of vessels
supplying blood to the legs reduces the level of blood flow and thus
preventing heat loss through the uncovered feet. In some species, there
is a counter current blood flow in the legs. As cool blood from the legs
in the veins passes through the body trunk, heat moves from the warm
arteries through conduction and warms up the cool blood (Hoffman et al,
Behavioral temperature regulation can be achieved through many ways.
Changes in the birds’ inclination and posture towards the sun can
significantly adjust the amount of heat lost or gained. Birds living in
hot habitat constantly face the danger of overheating, Gulls for
instance, swivel 180 degrees to prevent overheating by ensuring their
reflective parts (white breast and neck) face the sun and by reducing
the total surface area that is exposed to the sun to prevent excessive
heat gain through radiation. They also stand on water to prevent heat
gain through their legs that are not covered by feathers (Hoffman et al,
Species dwelling in warm and hot habitat have special physical features
that ensure that they do not overheat. Birds in such habitats have
higher respiration rate that permits greater loss of heat gained from
the hot environment and from the physical and metabolic activities. Even
though the air in the surrounding environment is warmer, it is still
degrees cooler than that being respired. Rapid breathing ensures warmer
air is ejected faster allowing for more heat dissipation. Also cooler
air passing through the breathing system carries with it heat from the
body, in some of these species their breathing system is modified such
that air moves only in one direction ensuring hot air from within does
not mix with cool air coming inside. Most of the species in hot habitat
like those in tropical regions have bare skin on the legs that permit
loss of heat through conduction. Some like the toucans have excessively
large bills which have dense network of blood vessels and that help to
release heat (Scott et al, 2008).
During the hot seasons, birds significantly reduce their activity to
reduce the amount of heat generated. They reduce their movement and
search for food to prevent heat gain through radiation. The metabolic
rate at this time is also significantly reduced and less heat is
generated (Scott et al, 2008). Other species migrate to higher latitude
areas were the temperatures are lower Some like the songbird bathe in
water during the hot season while others such as the waterfowl get
completely submerged in the water to cool their bodies. Some species in
hot tropical habitat seek for shade during the hottest days of the
season to avoid direct radiation from the sun or vibrate the lower part
of their buccal cavity to generate enough water that will evaporate
together with the heat from the body (Wojciechowski et al, 2011)..
Thermoregulation is a crucial process in birds since it dictates the
extent to which a bird can exploit a given habitat. As previously,
mentioned birds have evolved several physiological and behavioral
adaptations to enable then survive in their habitat. Just like mammals,
birds are homeotherms and their body temperatures must be maintained
within a narrow range. Their feathers, unique respiration system and
other behavioral traits have enabled them to survive in almost all parts
of the globe.
Hoffman, T. C., G. E. Walsber G.E and Denardo, D.(2007). Cloacal
Evaporation: an Important and previously undescribed mechanism for Avian
Thermoregulation. Journal of Experimental Biology 210: 741-749
Scott, G., Cadena V, Tattersall G, and Milsom W. (2008). Body
temperature depression and peripheral heat loss accompany the metabolic
and ventilatory responses to hypoxia in low and high altitude birds. The
Journal of Experimental Biology 211, 1326-1335 HYPERLINK
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Wojciechowski, M. S., Jefimow,M and Pinshow, B. (2011). Heterothermy and
the Energetic Consequences of Huddling in Small Migrating Passerine
Birds. Integrative & Comparative Biology 51:409-418. HYPERLINK
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