Breeding forest birds of northeastern Connecticut show a long-term population increase and high species turnover

Abstract

North American birds have declined by 29% over 48 years, with declines occurring across species and biomes. To examine population patterns at a local scale, we investigated species and population shifts in a forest bird community in northeastern Connecticut. We did so in relation to its changing environments, focusing on patterns consistent with the effects of climate change and habitat manipulation. In 1985, we established survey routes primarily in the intensively managed Yale-Myers experimental forest, which we repeated in 2018 and 2019. Species richness varied little from the initial survey to the recent ones, although population density increased by 24% after 1985. Turnover in species composition exceeded 50%. The 5 most strongly declining species were northerly distributed, forest interior inhabitants, whereas the 7 most strongly increasing species were variously distributed forest interior and edge/successional-associated species. Some species experienced increases by invading new habitats, whereas at least one appeared to decline due to interspecific competition. Expected effects of climate change on populations were consistent with some findings, but habitat effects appeared related to a greater number of shifts. However, much contrary data indicated that these factors were not alone in driving community change. This bird community may best be thought of as a dynamic assemblage that represents the sum of individualistic responses to environmental and perhaps stochastic factors.