Demographic and spatial responses of resident bird populations to the arrival of migratory birds within an urban environment

Long‐distance migration allows many bird species to overcome the severe climatic changes that occur in seasonal environments. Migration is highly demanding, and given its cyclical nature, we currently know that it has substantial effects on the population parameters of migratory birds during both breeding and wintering seasons. However, the potential effects of the presence of migratory birds in their wintering grounds on populations of resident birds have remain largely unexplored. Here, we propose the hypothesis that migratory birds negatively affect the habitat occupancy and population abundance of resident birds because of the arrival of numerous individuals during the most limiting months of the year. Here, we studied different species of migratory and resident birds that coexist during winter in an urban ecological reserve located within Mexico City. We used single‐species multiseason occupancy models, two‐species occupancy models, and distance sampling techniques to evaluate changes in occupancy and population density of resident bird species during three consecutive winters. We found an aggregation pattern between two resident species (Psaltriparus minimus and Thryomanes bewickii) with three migratory warblers (Cardellina pusilla, Setophaga coronata and Setophaga townsendi). Thus, our results provide evidence of the formation of mixed‐species flocks in our study area. We also conclude that resident birds experience different demographic and behavioral processes during winter that not necessarily result from interspecific interactions with migratory birds. We used occupancy models and distance sampling techniques to evaluate changes in occupancy and population density of resident bird species in response to the presence of migratory birds within an urban ecological reserve. We found an aggregation pattern between two resident species with three migratory warblers. Our results provide evidence of the formation of mixed‐species flocks in our study area, and suggest that some of the observed demographic changes were not necessarily derived from interspecific interactions.