Radio-tracking urban breeding birds: The importance of native vegetation

As urban areas continue to expand globally, a deeper understanding of the functioning of urban green spaces is crucial for maintaining habitats that effectively support wildlife within our cities. Cities typically harbor a wide variety of nonnative vegetation, providing limited support for insect populations. The resulting scarcity of arthropods has been increasingly linked to adverse effects at higher trophic levels, such as the reduced reproductive success of insectivorous birds in urban environments. However, the responses by which urban breeding birds cope with the challenges of food limitation remain largely unexplored. To address this knowledge gap, in a Central European city, we employed radiotelemetry tracking and real-time observations on urban-breeding female great tits' habitat use, combined with detailed plant surveys and video recordings of nestlings' diet. This integrated approach enabled us to establish direct links between great tits' foraging behavior, vegetation preferences, and nestling diet. We found that besides tree canopies, great tits also frequently foraged on the ground and that the availability of bird feeders notably affected birds' habitat use. Foraging great tits generally avoided nonnative plants, particularly broadleaved species. When searching for nestling food, great tits were most time-efficient on conifers, albeit these trees provided low amounts of caterpillars (a preferred prey type). Great tits were more likely to forage on and deliver nestling food from large native trees and foraged less on and collected fewer prey items from the most abundant tree species. Our results underscore the importance of several factors that may help improve habitat quality for urban insectivorous birds, with preserving large trees and increasing diverse native vegetation being key elements in this endeavor.