Title
Neck-drooping posture in oriental white-backed vultures (Gyps bengalensis): An unsuccessful predictor of mortality and its probable role in thermoregulation
Author(s)
Gilbert, M.; Watson, R.T.; Virani, M.Z.; Oaks, J.L.; Ahmed, S.; Chaudhry, M.J.I.; Arshad, M.; Mahmood, S.; Ali, A.; Khan, A.A.
Published
2007
Publisher
Journal of Raptor Research
Abstract
Populations of three Gyps vulture species in the Indian subcontinent have undergone recent rapid declines due to elevated mortality rates caused by diclofenac poisoning. Researchers have proposed that vultures adopt a previously-undescribed neck-drooping posture prior to death. Our study investigated two hypotheses: (1) neck drooping is temperature-dependent, (2) neck-drooping is indicative of poor health in Oriental White-backed Vultures (Gyps bengalensis) and is a prelude to death. Observations of neck-drooping were highly seasonal, with the majority of vultures observed neck-drooping in the hot season from April to October and no vultures observed neck-drooping during the cold months of December and January. Above a calculated threshold ambient temperature of 15.4°C (95% CI 9.9-22.5°C), there was a significant positive correlation between temperature and the proportion (expressed as an angular transformation) of vultures observed neck-drooping. Neck-drooping vultures were observed significantly more frequently with their back toward the sun with their head in their own shade than birds that were not neck-drooping, and vultures that were not neck-drooping were observed more frequently facing the sun than those neck-drooping. Together, these observations strongly suggest that neck-drooping posture has a role in thermoregulation. In contrast to the highly seasonal pattern of neck-drooping, mortality of vultures occurred in all months of the year. This finding indicates that neck-droping has low specificity and sensitivity as an indicator of poor health and impending death in vultures. © 2007 The Raptor Research Foundation, Inc.
Keywords
mortality; posture; raptor; thermoregulation; Aves; Gyps; Gyps africanus; Gyps bengalensis; Neck-drooping; Oriental White-backed Vulture; Head-drooping; Diclofenac; TEMPERATURE REGULATION; POPULATION DECLINES; INDIAN SUBCONTINENT; TURKEY VULTURES; PAKISTAN
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PUB12143