Body Temperature, Torpor, and Growth in Chicks of Fork-Tailed Storm-Petrels (Oceanodroma furcata)

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Abstract
Chicks of fork-tailed storm-petrels (Oceanodroma furcata) are left unattended for several days following hatching. They achieve thermoregulatory ability at about 5 days of age and generally maintain body temperatures ( ) of between 37.2 and 37.4 C until fledging. However, if adults do not return regularly with enough food, of chicks may decrease to as low as 10.6 C, and chicks become torpid. If feeding is resumed, chicks recover normal and growth with no apparent ill effects. Younger smaller chicks experience lower than older larger chicks, probably because their surface-to-volume ratios, food storage capacities, and feather insulation are less favorable. The correlation between food load (mean weight gain) and body temperature is highly significant, but neither variable was strongly correlated with tarsal growth rates. However, the variability of food loads did significantly affect growth, with the slowest-growing chicks having the least variable food loads. These findings suggest that the metabolism of chicks of fork-tailed storm-petrels is adjusted to a gorge-and-fast feeding pattern resulting from this species' exploitation of scarce or unpredictable food resources.