Action: Provide supplementary food for vultures to increase adult survival
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- A before-and-after study from Spain found a large increase in griffon vulture Gyps fulvus population in the study area following multiple interventions including supplementary feeding.
- Two studies from the USA and Israel found that Californian condors Gymnogyps californianus and Egyptian vultures Neophron percnopterus fed on many of the carcasses provided for them. The Egyptian vultures were sometimes dominated by larger species at a feeding station supplied twice a month, but not at one supplied every day.
Well-fed animals are likely to be in better physical condition than those with too little food: having greater muscle mass and larger fat supplies to help them survive lean periods. However, it is worth noting that species that forage in groups can have dominance hierarchies, which alter the relationship between weight and fitness. For example Gentle and Gosler (2001) found that, amongst great tits Parus major in Oxfordshire, England, more dominant birds had a lower mass than subdominants, particularly when perceived predation risk was high. Birds with lower masses are better able to take off and therefore escape predators than heavier birds (Krams 2002). However, because of their dominance, they were able to usurp other birds from food resources when hungry. Care should therefore be taken when interpreting results which do not directly examine survival.
Krams, I. (2002) Mass-dependent take-off ability in wintering great tits (Parus major): comparison of top-ranked adult males and subordinate juvenile females. Behavioral Ecology and Sociobiology, 51, 345–349.
Gentle, L.K. & Gosler, A.G. (2001) Fat reserves and perceived predation risk in the great tit, Parus major. Proceedings of the Royal Society of London. Series B: Biological Sciences, 268, 487.
Supporting evidence from individual studies
A study in California, USA, between February 1971 and May 1973 (Wilbur et al. 1974) found that Californian condors Gymnogyps californianus fed on at least 47 of 83 carcasses provided over the study period. Another 27 carcasses may well have been fed on and the remaining nine were taken by black bears Ursus americanus before condors could feed. Carcasses were mainly mule deer Odocoileus hemionus. This study is also discussed in ‘Provide supplementary food to increase reproductive success’.
A before-and-after between 1969 and 1989 in the western Pyrenees, Spain (Donazar & Fernandez 1990), found that the population of griffon vultures Gyps fulvus increased from 282 pairs (in 23 colonies) in 1969-75 to 1,097 pairs (46 colonies) in 1989 following the initiation of multiple conservation interventions including the installation of feeding stations between 1969 and 1979. However, the authors note that only two of six feeding stations were used by vultures and food was never apparently a limiting factor for the population in the study area. This study is also discussed in ‘Habitat protection’, ‘Restrict certain pesticides or other agricultural chemicals’ and ‘Use legislative regulation to protect wild populations’.
A study in the Negev Desert, Israel, in April-August of 1989 and 1990 (Meretsky & Mannan 1999) found that adult Egyptian vultures Neophron percnopterus were able to dominate a feeding station supplied daily with 5-10 kg of chicken, but not a station supplied approximately twice a month with large amounts (20-350 kg) of meat. Peak numbers of vultures were higher at the irregularly-stocked station (30-40 vultures present at once vs. 20-30) but they were sometimes excluded by mammals (e.g. striped hyaena Hyaena hyaena) or Eurasian griffon vultures Gypus fulvus, which did not occur at the regularly-stocked station.
- Wilbur S.R., Carrier W.D. & Borneman J.C. (1974) Supplemental feeding program for California condors. The Journal of Wildlife Management, 38, 343-346
- Donázar J.A. & Fernández C. (1990) Population trends of the griffon vulture Gyps fulvus in Northern Spain between 1969 and 1989 in relation to conservation measures. Biological Conservation, 53, 83-91
- Meretsky V.J. & Mannan R.W. (1999) Supplemental feeding regimes for Egyptian vultures in the Negev Desert, Israel. Journal of Wildlife Management, 63, 107-115