Short communication Landscape and season effects on the diet of the

• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: corvids; grouse; predation; prey avail- ability; vulnerability; Helle; Petty; Northern Goshawk
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.617.7461; http://users.jyu.fi/~vemonkko/Tornberg et al. 2009_ibis_910.pdf

There are two general effects of habitat loss and frag-mentation of mature boreal forests (Schmiegelow & Mönkkönen 2002). First, fragmentation by farmland creates stable structures such as permanent edge zones with enrichment of species diversity and density (Andrén 1992, Berg & Pärt 1994). Secondly, modern forestry with clear-cuts creates sharp, unstable bound-aries between forest and open areas, usually with less pronounced edge effects (Helle 1983, Schmiegelow & Mönkkönen 2002). Considering the vast array of stud-ies on the effects of habitat loss and fragmentation on bird populations, relatively little attention has been paid to the role of predators, other than nest preda-tors, across different landscapes (Lampila et al. 2005). Predators ’ searching efficiency may improve due to a diminished area where prey live (Storaas et al. 1999). By killing smaller predators and nest predators, top predators may contribute positively to prey species populations (Petty et al. 2003, Mönkkönen et al. 2007). Increased availability of alternative prey as a result of landscape change may deflect predation from the main prey species (Angelstam et al. 1984). The final outcome of these landscape-related predator–prey interactions is likely to depend on direct functional and numerical responses of predators to the variation in the abundance and vulnerability of the main and alternative prey, as well as on the indirect controlling effect of top predators on smaller predators and nest predators. In northern latitudes the Northern Goshawk Accipi-ter gentilis relies mainly on grouse as a staple food dur-ing most of the year (Tornberg 1997, 2001, Tornberg & Colpaert 2001). Breeding season diet, however, con-tains a large spectrum of alternative prey species, mainly birds (Tornberg 1997). The proportion of grouse in the diet is at the lowest during late nestling phase when fledglings of alternative prey such as larger passerines and waterfowl are readily available (Lindén