Heat energy exchange between the Killdeer, its eggs, and the environment Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/x920g118t

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  • The vegetation surrounding a nest shades and insulates the incubating bird in addition to concealing it. The vegetative material that makes up a nest insulates the eggs from its warmer or cooler surroundings. Since a Killdeer builds a stone-lined nest on barren ground, both egg and adult are subject to more climatological variation than most other bird species and their eggs. In May and June, 1973, six nesting pairs studied at the Malheur National Wildlife Refuge were directly exposed to air temperatures (T[subscript a]s) as low as 0°C and to intense solar radiation. At T[subscript a]s helm, 12°C, the maximum "dummy" egg temperature (T[subscript e]) recorded from five nests was 34°C as opposed to a maximum T[subscript e] of 37°C from nest #3 at 25°C T[subscript a]. This information suggests that at low T[subscript a]s, the Killdeers' heat output did not keep pace with the increased rate of heat loss from the eggs to the ground. Three of four pair of Killdeers showed the lowest incidence of preening at T[subscript a]s below 12°C. The movements involved in this interruptive behavior would tend to, decrease the thickness of the birds' feather insulation. Thus the Killdeers may have foregone preening at low T[subscript a]s in the interest of conserving body heat. Data from five nesting pairs showed that the Killdeers began to open their mouths (increased evaporative cooling) and stand over their nests (increased convective cooling) at T[subscript a]s betw 25-29°C. The incidence of these thermoregulatory behaviors increased with increasing T[subscript a] (up to 40°C). Between Tas of 28-38°C, two of four pairs spent less time standing when there was wind at ground level than they did when it was still sitting in response to air flow, the Killdeers were probably attenuating convective heat loss. "Dummy" T[subscript e]s from five nests ranged between 35-40°C when the Killdeers were standing. The fact that the eggs were always in the birds' shadow explains why lethal T[subscript e]s (43-45°C) were never reached. The rate of radiant and conductive heat input from the ground and air must have been sufficient to prevent T[subscript e]s from dropping below 35°C.
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