Editing Common ostrich (section)

===Thermoregulation===

Common ostriches are [[Homeothermy|homeothermic]] [[endotherm]]s; they regulate a constant body temperature via regulating their metabolic heat rate.<ref name=zool241 /> They closely regulate their core body temperature, but their [[appendage]]s may be cooler in comparison as found with regulating species.<ref name=zool241 /> The temperature of their beak, neck surfaces, lower legs, feet, and toes are regulated through heat exchange with the environment.<ref name=polly /> Up to 40% of their produced [[Warm-blooded|metabolic heat]] is [[Dissipation|dissipated]] across these structures, which account for about 12% of their total surface area.<ref name=polly>{{cite journal|author1=Polly K.|author2=Phillips |author3=Sanborn Allen F. |name-list-style=amp |doi=10.1016/0306-4565(94)90042-6|title=An infrared, thermographic study of surface temperature in three ratites: Ostrich, emu and double-wattled cassowary|year=1994|journal=Journal of Thermal Biology|volume=19|issue=6|pages=423–430 |bibcode=1994JTBio..19..423P }}</ref> Total evaporative water loss (TEWL) is statistically lower in the common ostrich than in membering ratites.<ref name=Mitchell />

As ambient temperature increases, dry heat loss decreases, but evaporative heat loss increases because of increased [[Respiration (physiology)|respiration]].<ref name=polly /> As ostriches experience high ambient temperatures, circa {{cvt|50|C}}, they become slightly hyperthermic; however, they can maintain a stable body temperature, around {{cvt|40|C}}, for up to 8 hours in these conditions.<ref name=Schmidt-Nielsen/> When dehydrated, the common ostrich minimizes water loss, causing the body temperature to increase further.<ref name=Schmidt-Nielsen/> When the body heat is allowed to increase the [[temperature gradient]] between the common ostrich and ambient heat is [[Thermodynamic equilibrium|equilibrated]].<ref name=zool241 />

====Physical adaptations====

Common ostriches have developed a comprehensive set of behavioral adaptations for [[thermoregulation]], such as altering their feathers.<ref name=Deeming /> Common ostriches display a feather fluffing behavior that aids them in thermoregulation by regulating [[Convection (heat transfer)|convective heat loss]] at high ambient temperatures.<ref name=polly /> They may also physically seek out shade in times of high ambient temperatures. When feather fluffing, they contract their muscles to raise their feathers to increase the air space next to their skin.<ref name=zool241 /> This air space provides an insulating thickness of {{cvt|7|cm}}.<ref>Mitchell</ref> The ostrich will also expose the thermal windows of their unfeathered skin to enhance convective and radiative loss in times of heat stress.<ref name=Mitchell>{{cite journal|last=Mitchell|first=Malcolm|title=Ostrich Welfare and Transport|journal=Ostrich Welfare|series=Ratite Science Newsletter|pages=1–4|url=http://www.worldpoultry.net/PageFiles/28775/001_boerderij-download-WP6727D01.pdf|access-date=28 December 2013|archive-date=28 December 2013|archive-url=https://web.archive.org/web/20131228103741/http://www.worldpoultry.net/PageFiles/28775/001_boerderij-download-WP6727D01.pdf|url-status=dead}}</ref> At higher ambient temperatures lower appendage temperature increases to {{cvt|5|C-change}} difference from ambient temperature.<ref name=polly /> Neck surfaces are around {{cvt|6|-|7|C-change}} difference at most ambient temperatures, except when temperatures are around {{cvt|25|C}} it was only {{cvt|4|C-change}} above ambient.<ref name=polly />

At low ambient temperatures the common ostrich utilizes feather flattening, which conserves body heat through insulation. The low [[Thermal conduction|conductance coefficient]] of air allows less heat to be lost to the environment.<ref name=zool241 /> This flattening behavior compensate for common ostrich's rather poor cutaneous evaporative water loss (CEWL).<ref name=Louw>{{cite journal|last=Louw|first=Gideon|author2=Belonje, Coetzee|title=Renal Function, Respiration, Heart Rate and Thermoregulation in the Ostrich (''Struthio Camelus'')|journal=Scient. Pap. Namib Desert Res. STN|year=1969|volume=42|pages=43–54|url=http://www.the-eis.com/data/literature/Louw_1969_sci_pap_NDRS_ostrich.pdf|access-date=29 November 2013}}</ref> These feather-heavy areas such as the body, thighs, and wings do not usually vary much from ambient temperatures due to this behavioural controls.<ref name=polly /> This ostrich will also cover its legs to reduce heat loss to the environment, along with undergoing [[piloerection]] and [[shiver]]ing when faced with low ambient temperatures.

====Internal adaptations====
The use of [[Countercurrent exchange|countercurrent]] heat exchange with blood flow allows for regulated conservation/ elimination of heat of appendages.<ref name=zool241/> When ambient temperatures are low, [[Heterothermy|heterotherms]] will constrict their arterioles to reduce heat loss along skin surfaces.<ref name=zool241/> The reverse occurs at high ambient temperatures, arterioles [[Vasodilation|dilate]] to increase heat loss.<ref name=zool241/>
 
At [[Room temperature|ambient temperatures]] below their body temperatures ([[thermal neutral zone]] (TNZ)), common ostriches decrease body surface temperatures so that heat loss occurs only across about 10% of total surface area.<ref name=polly/> This 10% include critical areas that require blood flow to remain high to prevent freezing, such as their eyes.<ref name=polly/> Their eyes and ears tend to be the warmest regions.<ref name=polly/> It has been found that temperatures of lower appendages were no more than {{cvt|2.5|C-change}} above ambient temperature, which minimizes heat exchange between feet, toes, wings, and legs.<ref name=polly/>

Both the Gular and air sacs, being close to body temperature, are the main contributors to heat and water loss.<ref name=Schmidt-Nielsen/> Surface temperature can be affected by the rate of blood flow to a certain area and also by the surface area of the surrounding tissue.<ref name=zool241/> The ostrich reduces blood flow to the trachea to cool itself and [[Vasodilation|vasodilates]] to its blood vessels around the gular region to raise the temperature of the tissue.<ref name=Schmidt-Nielsen/> The air sacs are poorly vascularized but show an increased temperature, which aids in heat loss.<ref name=Schmidt-Nielsen/>

Common ostriches have evolved a 'selective brain cooling' mechanism as a means of thermoregulation. This modality allows the common ostrich to manage the temperature of the blood going to the brain in response to the extreme [[ambient temperature]] of the surroundings. The morphology for heat exchange occurs via [[cerebral arteries]] and the [[Ophthalmic artery|ophthalmic]] [[Blood vessel|rete]], a network of arteries originating from the [[ophthalmic artery]]. The [[Ophthalmic artery|ophthalmic]] [[Blood vessel|rete]] is [[analogous]] to the [[carotid rete]] found in mammals, as it also facilitates transfer of heat from arterial blood coming from the core to venous blood returning from the evaporative surfaces at the head.<ref name=Maloney/>

Researchers suggest that common ostriches also employ a 'selective brain warming' mechanism in response to cooler surrounding temperatures in the evenings. The brain was found to maintain a warmer temperature when compared to [[carotid]] [[arterial]] blood supply. Researchers hypothesize three mechanisms that could explain this finding:<ref name=Maloney/>
# They first suggest a possible increase in [[metabolic]] heat production within the brain tissue itself to compensate for the colder [[arterial]] blood arriving from the core.
# They also speculate that there is an overall decrease in cerebral blood flow to the brain.
# Finally, they suggest that warm venous blood [[perfusion]] at the [[Ophthalmic artery|ophthalmic]] [[Blood vessel|rete]] helps to warm the cerebral blood that supplies the [[hypothalamus]].
Further research will need to be done to find how this occurs.<ref name=Maloney/>

====Breathing adaptations====

The common ostrich has no [[sweat glands]], and under heat stress they rely on panting to reduce their body temperature.<ref name=Schmidt-Nielsen/> [[endotherm|Panting]] increases [[heat transfer|evaporative heat]] (and water) loss from its respiratory surfaces, therefore forcing air and heat removal without the loss of metabolic salts.<ref name=Mitchell /> Panting allows the common ostrich to have a very effective respiratory evaporative water loss (REWL). Heat dissipated by respiratory evaporation increases linearly with ambient temperature, matching the rate of heat production.<ref name=Deeming /> As a result of panting the common ostrich should eventually experience alkalosis.<ref name=zool241 /> However, The CO<sub>2</sub> concentration in the blood does not change when hot ambient temperatures are experienced.<ref name=Schmidt-Nielsen/> This effect is caused by a [[Shunt (medical)|lung surface shunt]].<ref name=Schmidt-Nielsen/> The lung is not completely shunted, allowing enough oxygen to fulfill the bird's [[Metabolism|metabolic]] needs.<ref name=Schmidt-Nielsen/> The common ostrich utilizes [[Gular fluttering#Endothermy|gular fluttering]], rapid rhythmic contraction and relaxation of throat muscles, in a similar way to panting.<ref name=zool241 /> Both these behaviors allow the ostrich to actively increase the rate of evaporative cooling.<ref name=zool241 />
 
In hot temperatures water is lost via respiration.<ref name=zool241 /> Moreover, varying surface temperatures within the respiratory tract contribute differently to overall heat and water loss through panting.<ref name=Schmidt-Nielsen/> The surface temperature of the [[Gular skin|gular area]] is {{cvt|38|C}}, that of the [[Vertebrate trachea|tracheal area]] is between {{cvt|34|and|36|C}}, and that of both anterior and posterior air sacs is {{cvt|38|C}}.<ref name=Schmidt-Nielsen/> The long trachea, being cooler than body temperature, is a site of water evaporation.<ref name=Schmidt-Nielsen/>
 
As ambient air becomes hotter, additional evaporation can take place lower in the trachea making its way to the posterior sacs, shunting the lung surface.<ref name=Schmidt-Nielsen/> The trachea acts as a buffer for evaporation because of the length and the controlled vascularization.<ref name=Schmidt-Nielsen /> The Gular is also heavily vascularized; its purpose is for cooling blood, but also evaporation, as previously stated. Air flowing through the trachea can be either [[Laminar flow|laminar]] or [[Turbulence|turbulent]] depending on the state of the bird.<ref name=zool241 /> When the common ostrich is breathing normally, under no heat stress, air flow is laminar.<ref name=Schmidt-Nielsen/> When the common ostrich is experiencing heat stress from the environment the air flow is considered turbulent.<ref name=Schmidt-Nielsen/> This suggests that laminar air flow causes little to no heat transfer, while under heat stress turbulent airflow can cause maximum heat transfer within the trachea.<ref name=Schmidt-Nielsen/>

====Metabolism====
Common ostriches are able to attain their necessary energetic requirements via the [[redox|oxidation]] of absorbed nutrients. Much of the metabolic rate in animals is dependent upon their [[allometry]], the relationship between body size to shape, anatomy, physiology, and behavior of an animal. Hence, it is plausible to state that metabolic rate in animals with larger masses is greater than animals with a smaller mass.

When a bird is inactive and unfed, and the [[Room temperature|ambient temperature]] (i.e. in the [[thermal neutral zone|thermo-neutral zone]]) is high, the energy expended is at its minimum. This level of expenditure is better known as the [[Basal metabolic rate|basal metabolic rate (BMR)]], and can be calculated by measuring the amount of oxygen consumed during various activities.<ref name=Deeming/> Therefore, in common ostriches we see use of more energy when compared to smaller birds in absolute terms, but less per unit mass.

A key point when looking at the common ostrich metabolism is to note that it is a [[passerine|non-passerine]] bird. Thus, BMR in ostriches is particularly low with a value of only 0.113 mL O<sub>2</sub> g<sup>−1</sup> h<sup>−1</sup>. This value can further be described using [[Kleiber's law]], which relates the BMR to the body mass of an animal.<ref name="Willmer_2009">{{cite book|last=Willmer|first=Pat|title=Environmental Physiology of Animals|year=2009|publisher=Wiley-Blackwell|isbn=978-1405107242|url=https://archive.org/details/environmentalphy00will}}</ref>

:Metabolic rate = 70''M''<sup>0.75</sup>

where ''M'' is body mass, and metabolic rate is measured in [[Calorie|kcal]] per day.

In common ostriches, a BMR (mL O<sub>2</sub> g<sup>−1</sup> h<sup>−1</sup>) = 389&nbsp;kg<sup>0.73</sup>, describing a line parallel to the intercept with only about 60% in relation to other non-passerine birds.<ref name= Deeming/>

Along with BMR, energy is also needed for a range of other activities. If the [[Room temperature|ambient temperature]] is lower than the [[thermal neutral zone|thermo-neutral zone]], heat is produced to maintain [[Thermoregulation|body temperature]].<ref name=Deeming/> So, the metabolic rate in a resting, unfed bird, that is producing heat is known as the [[Basal metabolic rate|standard metabolic rate (SMR)]] or [[Basal metabolic rate|resting metabolic rate (RMR)]]. The common ostrich SMR has been seen to be approximately 0.26 mL O<sub>2</sub> g<sup>−1</sup> h<sup>−1</sup>, almost 2.3 times the BMR.<ref name=Deeming/> On another note, animals that engage in extensive physical activity employ substantial amounts of energy for power. This is known as the maximum [[Allometry|metabolic scope]]. In an ostrich, it is seen to be at least 28 times greater than the BMR. Likewise, the daily energy [[Enzyme kinetics|turnover rate]] for an ostrich with access to free water is 12,700&nbsp;kJ&nbsp;d<sup>−1</sup>, equivalent to 0.26&nbsp;mL&nbsp;O<sub>2</sub>&nbsp;g<sup>−1</sup>&nbsp;h<sup>−1</sup>.<ref name=Deeming/>