The feeding ecology of cape vultures Gyps coprotheres in a stock-farming area
ABSTRACT Cape vultures Gyps coprotheres in the southwestern Cape Province feed exclusively on sheep carcasses, within a limited foraging area. The size and shape of the foraging range was determined by means of a postal survey and confirmed by a radio-tracking study. The quantity of food available within the range, while seasonally variable, was estimated to exceed the colony's requirements. Data pertaining to daily feeding forays of individuals, monthly foraging patterns of the colony and the growth of nestlings indicated no seasonal shortages in the amount of food obtained. The colony remains susceptible to the effects of poisons used in the area; levels of contaminants recorded in most eggs are considered low.
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ABSTRACT: Survival rates are crucial demographic parameters for modelling the population dynamics of the Cape Griffon vulture. Previous survival estimates based on ring recoveries are seriously flawed and have been heavily criticized. To provide better estimates, 97 nestlings were individually colour-ringed in the winterrainfall region of South Africa from 1979 to 1987 and an intensive resighting campaign was mounted for 17.5 years (1980 to mid-1997). Although survival rate is known to vary with age, particularly in the first few years of life, this study indicates that it is also a function of calendar year. Supplementary food was provided for the study population from 1984 onwards and there was a concomitant increase in the survival rate of first-year birds. Eighty generalized linear models were built to estimate survival rate as a function of age, calendar year, cohort and supplementary feeding. First-year survival rate was estimated as 42.3% per annum (95% limits: 29–56%), increasing to 68.9% (54–81%) after the introduction of supplementary feeding. Age-specific survival rates were 88.8% per annum (77–95%) in the second year, 78.7% (64–88%) in the third year and 67.6% (58–76%) for birds aged four years or more. Our survival estimates are higher than previous values and have greater reliability because they are based on direct observations of known-age birds. The loss of colourrings is a serious impediment to estimating survival among older birds and the technique described here was not used to estimate adult survival.Bird Study 01/1999; 46. · 1.02 Impact Factor
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ABSTRACT: Outdoor feeding trials were used to determine gross energy intake, energy assimilation efficiency and metabolizable energy intake of captive adult Cape Vultures (Gyps coprotheres). The mean ash-free dry energy density of daily pooled samples of feces and urine was 14.0 + 0.2 kJ/g. A consistently high mean energy assimilation effidency of 86.2 + 2.7% caused daily energy content of excreta to fluctuate according to the quantity of energy assimilated. Mean gross energy intake was 2926.8 + 349.1 kJ/day and mean metab- olizable energy intake was 2552.9 + 300.9 k J/day for birds with changes in body mass of 2% or less between start and end of feeding trials. The daily energy expenditure of a free-living adult, weighing 8.3 kg, was estimated to be 3006 kJ/day (DEE = 826.7 kJ/day x kg06').
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ABSTRACT: Capsule Young Griffon Vultures Gyps fulvus suffer intense competition from elders at feeding sites and this reduces their intake rate.Aims To explore the costs and benefits of feeding in groups in Griffon VulturesMethods In a French population of individually marked vultures, we studied by video the dynamics of feeding events and the difference in competitive ability to access carrion between ages and sexes.Results When several carcasses were available, the distribution of the birds at the beginning of feeding event was generally different from an ideal free distribution. Depending on food availability, the potential group size was always higher than the maximum group size observed. However, the number of birds landed increased with food mass and was always higher than the potential group size, in accordance with the stable group size hypothesis. The timing of arrivals and departures of individuals differed with respect to their age, with old adults arriving and leaving before the arrival of other age-classes. Some birds, mostly old adults with a lower interaction rate, aggressiveness and dominance, regularly started the feeding events first.Conclusions At high-intensity feeding sites close to the colonies younger vultures probably access a lower quantity and quality of resources than old adults.Bird Study 01/2012; 59:182-192. · 1.02 Impact Factor