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Green woodhoopoes phoeniculus purpureus and obligate cavity roosting provide a test of the thermoregulatory insufficiency hypothesis

, : Green woodhoopoes phoeniculus purpureus and obligate cavity roosting provide a test of the thermoregulatory insufficiency hypothesis. Auk 108(2): 285-293

In Kenya, Green Woodhoopoes (Phoeniculus purpureus) seem constrained to sleep in aboreal cavities in spite of a high risk of capture within these chambers by nocturnal predators. Ligon et al. (1988) proposed that because woodhoopoes are incapable of adequate shivering thermogenesis at low nocturnal ambient temperatures, they are forced to roost in insulated tree cavities to maintain their body temperatures. We tested the thermoregulatory insufficiency hypothesis on 10 wild-caught woodhoopoes. From measurements of oxgyen consumption (.ovrhdot.VO2) at ambient temperatures from C to + C, we find no support for the hypothesis. Below thermoneutrality, .ovrhdot.VO2 increased linearly as ambient temperature (Ta) decreased. The equation, .ovrhdot.VO2 (ml O2 .cntdot. h-1) = 525.5 - 5.53 (Ta), described the relationship for males, and .ovrhdot.VO2 (ml O2 .cntdot. h-1) = 252.8 - 5.65 (Ta) for females. Body temperature (Tb) for the sexes did not differ (mean = C). Birds that were in good body condition maintained their Tb even at C for several hours. Within the thermal neutral zone, .ovrhdot.VO2 averaged 124.6 ml O2 .cntdot. h-1 for males and 115.9 ml O2 .cntdot. h-1 for females. Body mass averaged 79.70 g for males and 72.19 g for females. Total evaporative water loss of Green Woodhoopoea showed no relationship to Ta below C. Evaporative water loss averaged 179.6 mg H2O .cntdot. h-1 in males and 170.9 mg H2O .cntdot. h-1 in females. Above C, water loss increased exponentially with temperature. At C, woodhoopoes dissipated 55.8% of their metabolic heat production through water evaporation from respiratory passage and skin. Dry thermal conductance (.ovrhdot.Hd) between 0 and C averaged 31.7 mW .cntdot. .degree. C-1 for males and 32.5 mW C for females. Above C, .ovrhdot.Hd rapidly escalated, reaching nearly 80 mW C-1 at the highest temperatures.


DOI: 10.2307/4087953

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