Habitat-dependent effect of a rare predator on apparent survival of male Black-headed Bunting

Abstract

Both habitat changes and predation can cause population declines in farmland birds. Habitat changes may allow novel or invasive alien predators to establish populations in new environments, which can have major ecological consequences for native prey species. We studied effects of a novel avian predator, the Montagu’s Harrier (Circus pygargus), on the survival of male Black-headed Buntings (Emberiza melanocephala). Between 2011 and 2015, survival of 35 territorial Black-headed Bunting males was monitored and their apparent survival in years with and without predators was computed. The apparent monthly survival (reported ± SE) was very high during the breeding seasons when Montagu’s Harrier was not present (0.957 ± 0.035) as well as in nonbreeding periods (0.981 ± 0.011). It was significantly lower during the breeding season of 2013 when Montagu’s Harrier was present in the area (0.600 ± 0.136). Changes in habitat structure due to alteration in agricultural practice and temporal changes in weather conditions have presumably enabled Montagu’s Harriers to breed in the study area and led to increases in the importance of birds in Montagu’s Harrier’s diet. The appearance of Montagu’s Harriers in the study area strongly coincided with the steep decrease in the apparent survival of the male Black-headed Buntings. The lack of appropriate response in male Black-headed Buntings made them extremely vulnerable to attacks of this aerial predator.