Monitoring of facultative avian scavengers on large mammal carcasses in Dinaric forest of Slovenia

Facultative vertebrate scavengers have an important role in forest ecosystems, however, not much is known as to their use of carrion in temperate forests. Three carcasses of Red Deer Cervus elaphus and European Roe Deer Capreolus capreolus found dead or killed by Grey Wolf Canis lupus were monitored in March and April 2010 and 2011 on Menišija Plateau in northern Dinaric Mountains (central Slovenia) using photo-trapping and video surveillance. Carcasses were monitored for 26 days, during which 708 photos and 43 video recordings of scavengers were taken. In the 91% of all visits recorded, birds were the most frequent scavengers, with Common Buzzard Buteo buteo as the most frequent species present at 76% of all visits. On average, Buzzards returned to carcasses twice per day, with an average visit lasting 29 min. Common Buzzards used carcasses to a significantly higher degree on days with snow cover, which was due to the more frequent visits per day and not to longer visits. Recorded antagonistic interspecific interactions suggested that Common Buzzards were the dominant species in the observed avian scavenger guild, as they displaced Ravens Corvus corax and Goshawk Accipiter gentilis from the carcass. However, Ravens frequently mobbed Common Buzzards while scavenging. Once an Ural Owl Strix uralensis also visited prey remains of Grey Wolf, but feeding could not be confirmed. Observations suggested that carcasses of large mammals could be locally and temporarily an important food source for some facultative avian scavengers in Dinaric forests, especially in times when other food is scarce. Data from the two wolf kills also confirm the importance of predation by large carnivores in providing food for scavengers. Given the small amount of meat consumed, kleptoparasitism by solitary raptors did not bring significant losses to large carnivores, whereas gregarious avian scavengers like corvids can importantly affect the consumption process and consume large amount of biomass in a relatively short time.