Dietary Niches and Their Consequences for Five Insectivorous Passerines in a Seasonal Boreal Setting

ABSTRACT

To understand the effects of climate change and other disturbances on ecosystems, methodologies capable of unravelling the complexity of biotic interactions are vital. Here, we present a dietary study on five passerines nesting in boreal forests: the crested tit Lophophanes cristatus , willow tit Poecile montanus , blue tit Cyanistes caeruleus , great tit Parus major , and pied flycatcher Ficedula hypoleuca . We used metabarcoding to describe their arthropod prey during the breeding season, and linked diets' properties with breeding success to understand birds' dependence on particular prey. The birds' diets contained hundreds of arthropod taxa, showing considerable richness and interannual variation. Most prey identities were resolved to species level. The most common prey were Lepidoptera, followed by Diptera, Coleoptera and Araneae. Dietary overlap was low to middling, conformed to temporal overlap, and fluctuated across the three studied years. Higher consumption of lepidopterans and their larvae was strongly associated with higher breeding success in blue tits and, to a lesser extent, great tits. In contrast, crested tits, willow tits and pied flycatchers had a more constant breeding success without relying on specific prey. The results suggest that the more recently settled blue tits and great tits are less capable of optimally utilizing the comparatively resource‐poor boreal environments. The apparent good adaptation to local foraging conditions contrasts to declining population trends in the Red‐Listed crested tits and willow tits. Our study highlights the complexity of arthropod communities and insectivore food webs, and showcase how molecular methods can be used to study ecological interactions.