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Batbayar, Nyambayar – Nesting ecology and breeding success of Cinereous Vultures (Aegypius monachus) in central Mongolia. 2004.

cinereous vultureUsing data from nest surveys and habitat measurements made at three sites in central Mongolia, I described nest habitat characteristics, nest habitat use, and nesting density of this little studied vulture in Mongolia.  I compared an area with abundant livestock with two protected areas in which livestock herding was restricted.  Nesting density and habitat variance between used and unused vulture nests was considerably different when comparison was made at site level due to terrain morphology and land use.  But within the site, habitat variance at used and unused nest sites was smaller. Use of trees and a variety of forms of rocks and cliffs for nest substrate by cinereous vultures indicated that the species is a nest site generalist.  Also, the number of nests I found at two study sites reveals that the nest site is not limiting the nesting abundance of this species in central Mongolia.

Higher nesting density of breeding pairs in the intensive livestock herding area, compared to the protected area where there were less livestock and few wild ungulates, suggests that food abundance might be an important factor limiting nesting density by cinereous vultures.  Nests in the livestock area were bigger than nests in protected area.  I modeled the nest site occupancy using logistic regression.  Distance to water and water type were important predictor variables among other variables that were entered in the full model.  The model showed consistent proportions of use across distance to water, but with the use for nests close to wells higher than the use for nests close to springs.  Nest site occupation decreased with the odds of occupation, dropping about 2 percent with each 100-m increase in distance to water.

I studied nesting success of this species. The nesting of cinereous vultures in central Mongolia started in early March and finished in the middle of August.  The overall nesting success was 59% (n=166).  The proportion of young fledged per breeding pair per year was 0.6 in Erdenesant and 0.4 in Khustai.  Totally, 70% of brood loss occurred during incubation and 30% occurred during the nestling period (n=54).  The successful nests in Khustai NP were significantly bigger in size than failed nests.  The nesting density and productivity were higher in the livestock abundant area of Erdenesant than the Khustai National Park protected area.  Comparisons of nest site use and breeding performance between the intensive livestock herding area and the protected area suggests that cinereous vultures choose their nesting site in association with food availability.  The livestock herding associated with human activity is likely to benefit the vultures.

Evidence of greater nesting density, and better nesting success and productivity, suggest that the livestock areas are a higher quality-nesting habitat for cinereous vultures in Mongolia.  In Khustai, it is likely that the removal of livestock from the area after establishing the park might have caused a long-term change in food abundance for cinereous vultures in this area.  The logistic regression for all nests revealed no variable that is important for identifying probable successful cinereous vulture nests among occupied nests.  However, the reduced model showed that nest width is the best predictor for probable successful nests, correctly classifying 77% of all successful nests in Khustai NP.

The future of cinereous vultures in central Mongolia is likely connected with food availability.  Therefore, for maintaining the cinereous vulture population size, I recommend management to increase the large wild ungulate numbers, to continue current livestock herding practices for food, and continue ongoing monitoring of cinereous vultures and detect population change due to change in livestock husbandry or introduction of toxins such as diclofenac that has decimated vulture population in south Asia.

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