Predation Risk and Shifts of Foraging Sites in Mixed Willow and Crested Tit Flocks

Abstract

Field studies have demonstrated interspecific niche separation between the Willow Tit Parus montanus and the Crested Tit P. cristatus in mixed-species flocks using mature coniferous forest. The dominant Crested Tit prefers the upper parts in pine, while the Willow Tit forages lower in the canopy. Foraging niche shifts of these species were studied when they foraged alternately in mature pine forest and in areas with saplings. In the saplings, where flying predators are unable to attack prey in the lower part of the canopy because of the dense branch structure there, Crested Tits switched to forage in the lower parts. As the subordinate species, Willow Tits foraged lower in the mature forest and higher up in the saplings, thus in both cases using more exposed parts of the canopy. Predation risk from Sparrowhawks Accipiter nisus seemed to be high. Since Crested Tits used the safest sites in both habitats, tits seem able to evaluate predation risk and adjust their habitat use. The spatial segregation of foraging niches in flocks of wintering tits can be explained by their response to habitat gradients in predator exposure.