Comparing predation on forest grouse nests by avian and mammalian predators in two contrasting boreal forest landscapes by the use of artificial nests

Egg predation is an important determinant of breeding success among boreal forest grouse, but the relative roles of mammalian and avian predators are poorly known. During spring/early summer of 2010, predation on artificial nests was studied by placing nests on the ground and on 1.5-m tall poles at two forested areas. One study site was highly fragmented due to intensive forestry (Varaldskogen, Norway) and the other site was a pristine, natural forest in north-western Russia (Pinega Forest Reserve). The nests on poles were subject to predation by birds and those on the ground by both mammals and birds. Total predation was significantly higher in Varaldskogen than in Pinega. Ground nests suffered ca. 2.5 times higher losses than nests on poles. In Pinega, predation did not differ between the two nest types. The difference between the two areas was probably due to different predator guilds: mammalian generalist predators, such as the Red Fox (Vulpes vulpes) and Badger (Meles meles), were common in Varaldskogen but scarce or absent in Pinega. Canopy cover explained most of the variation in predation rate in Varaldskogen, but no significant relationship with canopy or nest concealment was detected in Pinega. Predation on pole nests varied across habitat types in a similar manner at the two areas, but predation on ground nests did not. As Raven (Corvus corax) and Hooded Crow (Corvus corone cornix) were rare in both areas, these findings suggest similar searching and predatory behaviour of the two main (smaller) corvids, the Eurasian Jay (Garrulus glandarius) in Varaldskogen and the Siberian Jay (Perisoreus injaustus) in Pinega. Although the study design allowed a comparison between avian and mammalian nest predators, the lack of a clearer relationship between predation and certain variables suggests that nest predation is a complex process involving components of predator behaviour.