Vultures are obligate scavengers, as they depend totally on carrion. Facultative scavengers, like foxes, on the other hand exploit carrion opportunistically and are generally ubiquitous.
A new paper investigates the hypothesis that vultures can indirectly regulate the abundance of facultative scavengers through modulating their access to carrion resources. The authors studied scavenging efficiency and red fox abundance in two areas of South-eastern Spain where griffon vultures are present (Cazorla) and absent (Espuña).
As part of their study they monitored ungulate carcasses consumption during winter and summer, and counted red fox scats along walking transects as a proxy of fox density. Their results confirmed that scavenging efficiency was higher in the mountain with griffon vultures (to be expected) and in carcasses visited by vultures. This mean that scavenging opportunities for foxes were higher in Espuña, and indeed the mean red fox abundance was higher there!
This result suggests that when vultures disappear there may be an increase in these facultative scavenger numbers.
The study has also demonstrated that facultative scavengers exploit carrion on a slower time scale and so are not able to functionally replace vultures. You can download the paper below.
Photo: Bruno Berthémy/VCF