The response of the Eagle Owl (Bubo bubo) to an outbreak of the rabbit haemorrhagic disease

Abstract

The Eagle Owl (Bubo bubo) is a generalist predator that in Mediterranean areas feeds mainly on Rabbits (Oryctolagus cuniculus) At the end of 1997, a local outbreak of the rabbit haemorrhagic disease (RHD) decimated Rabbit populations in the area of Alicante (eastern Spain) so that Rabbit numbers in 1998 crashed to almost nil. Prior to the outbreak we had found 19 occupied Eagle Owl territories, and the owls had been feeding mainly on Rabbits. After the RHD epidemic, we found only six occupied territories and the owls were still feeding mainly on Rabbits. Diet composition was very similar between the periods, indicating that the owls did not diversify their diet in response to main prey scarcity. No significant differences in the proportion of Rabbit in the diet were found between the periods, suggesting that the impact of predation on Rabbits may be independent of the density of Rabbit populations (type I functional response). This response is not typically associated with generalist predators. In the territories that were still occupied after the outbreaks, the owls took substantial numbers of Hedgehogs (Erinaceus europaeus) and Red-legged Partridges (Alectoris rufa). Rats (Rattus spp), a common alternative prey, were not taken in the study area. Six breeding attempts were recorded before the RHD, and none after the RHD. This leads a to believe that only the combination of Hedgehog and Red-legged Partridge availability with the readier availability of sick Rabbits allowed a small population of owls to survive in the area, but did not allowed breeding. The predator-prey system formed by Eagle Owls and Rabbits in Mediterranean regions is more fragile than previously thought.