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	Other hypotheses for the decline Other hypotheses put forward for the vulture declines include reduced food availability, increased numbers of dogs, habitat destruction, use of pesticides and disease. No evidence can be found that supports these hypotheses across the geographic range that the declines have occurred, although some of these factors may have been important at a local scale. These studies indicate that at a national scale depletion of food resources, competition with dogs or loss of nesting habitat, are not responsible for the decline in vulture numbers. Lack of food? Survey teams in India in 2000 recorded over 260 livestock carcasses along road-transects and carcass dumps across India still handle hundreds and thousands of dead animals. Despite the presence of such a large food supply, vultures are absent or rare (of the 260 livestock carcasses surveyed by Prakash et al. (2003) vultures in small numbers were only in attendance at <5% of carcasses. These results indicate that there is no shortage of food supply linked to the declines. Competition from dogs? A common finding at carcass dumps is the presence of other scavengers, particularly feral dogs, as well as black kites, steppe eagles, crows and egrets and it has been proposed that the decline in vultures is due to the increase in feral dogs (Chhangani and Mohnot, 2004). However, vultures and dogs have always coexisted at carcass dumps in India and in over eight years of observations no instances of predation by dogs on vultures has been recorded. Most importantly, the increase in dog numbers only occurred after the collapse in vulture numbers. Hence, the data indicate that the increase in feral dog numbers occurred after the decline in vulture numbers, and this increase in dogs is a consequence, not a cause, of the loss of vultures.


	Loss of habitat? Observations of vulture breeding colonies indicated that in some areas there had been losses of nesting sites, with felling of nesting trees and quarrying of some cliffs. However, vultures exploit a large range of tree species for nesting (from coconut palms to pine trees!) and across South Asia the availability of large suitable trees far exceeds the number of nesting vultures. Similarly, observations of long-billed colonies on cliffs indicate the presence of many suitable nesting sites but very low numbers of vultures (e.g. cliffs at Bayana, Rajasthan that formerly supported thousands of breeding long-billed vultures had 10 breeding pairs in 2007/08). Thus while loss of trees or cliffs may be significant locally, it is not feasible that loss of nesting habitat could be affecting vulture populations at a national or international scale.


	Use of pesticides? The use of pesticides, herbicide and other persistent organic chemicals was put forward as a potential cause for the loss of vultures across Asia, as the use of pesticides (e.g. DDT) is a known problem for birds of prey. While trace levels of pesticides were detected in some carcasses, these were only found in a very few birds and not at levels likely to be damaging. Additionally, the known problems caused by DDT and other pesticides (the thinning of egg shells and low reproductive output), could not explain the 50% a year declines observed in Asian vulture populations, which can only be accounted for by high rates of adult mortality. Disease? The potential role of disease in the decline of Asia's vultures was raised as a hypothesis in 2000 to explain the loss of vultures at such a rapid rate and across such a wide geographic scale. Scientists studied both live and dead vultures to see if new and novel diseases were present. Two pathogens were identified, however the prevalence of these diseases in dead and dying vultures was very low (indicating that they are not a major factor in the declines) and the presence of these pathogens was not linked to visceral gout, the clinical sign seen in >80% of carcasses. More recently avian malaria has been cited as a contributing factor to the population declines (see XXXXX). While vultures may carry malaria parasites it is again unlikely that this is a major additional cause of mortality (see XXXXXXX) These studies indicate that at a national scale depletion of food resources, competition with dogs or loss of nesting habitat, use of pesticides and disease were not responsible for the decline in vulture numbers.