The Influence of Population Growth and Wind on Vagrancy in a North American Passerine

摘要: Understanding the causes of vagrancy among migratory bird species is increasing importance as climate change threatens species' survival. Vagrancy may serve to safeguard populations from environmental through expansion their geographic ranges. To dissect underlying vagrancy, we analysed data on occurrence vagrant Ash-throated Flycatchers Myiarchus cinerascens east coast North America and population growth within core breeding range, test what extent driven by production young that have a proclivity explore new places. We also tested related drift prevailing winds, analysis synoptic weather maps America. Our analyses aimed quantify which factors most strongly influence interannual variation in number reaching obtained records vagrants ‘North American Birds’, Breeding Bird Survey (BBS), reproductive success Monitoring Avian Productivity Survivorship (MAPS) databases, NOAA NCEP Regional Reanalysis database. found was predominantly explained growing size indexed BBS data. In addition, significant effects annual well three measures air circulation across models indicated an important role growth, with additional predominant airflow affecting incidence vagrancy. Years high bring larger numbers east, this enhanced when conditions are especially favourable.