Opportunity makes a predator: Great Spotted Woodpecker predation on Tit broods depends on nest box design

摘要

Secondary cavity nesters are species that breed in cavities made by other species. A variable but marked proportion of their nests undergo predation, especially in areas where specialized and/or opportunistic predatory animals are abundant. Indeed, predation is the most common cause of nest loss in primeval forests (Walankiewicz 2002a, 2002b, Wesolowski 2002, Thompson & Burhans 2004, Weatherhead & Blouin-Demers 2004, Yamaguchi et al. 2005). Because of their special construction, nest boxes may be less accessible to predators than are natural cavities, especially if they are equipped with protective devices, such as metal plates surrounding the entrance hole ( Walankiewicz 1991). On the other hand, nest boxes can be more easily spotted by predators and humans. In addition, ornithologists often distribute them at regular distances apart, which may make them still easier to find (Mand et al. 2005). Under these circumstances, wooden nest boxes without protective devices may greatly suffer from predation. Interestingly, while building their nests, secondary cavity breeders seem to maintain the distance between the cavity entrance and the nest cup by modifying the nest size (Alabrudzinska et al. 2003, Kosinski & Ksit 2007, Mazgaj ski & Rykowska 2008). The reason may be that the greater this distance is, the more difficult it will be for larger predators to reach eggs or nestlings in the nest.