Warmer Summers and Drier Winters Correlate with More Winter Vagrant Purple Gallinules (Porphyrio martinicus) in the North Atlantic Region

Abstract

Individuals from a diverse array of bird species sometimes occur well outside of their historic distributions. These vagrants, and their patterns of occurrence, may yield valuable insights regarding how birds respond to environmental change. Among the Rallidae, which are champion dispersers, the Purple Gallinule (Porphyrio martinicus) disperses exceptionally long distances. Whereas most Purple Gallinule vagrants occur from April to October, a much smaller number of records represent a more enigmatic vagrancy pattern that occurs from November to February. Using eBird, a global bird-monitoring project, we compiled 77 occurrences of vagrant Purple Gallinules from 1957–2014 during this seasonal window and examined how those occurrences correlated with environmental conditions and population trends. Average temperature anomalies showed significant correlations with patterns of records, with warmer late summer temperatures in particular in Florida and Puerto Rico correlating with more vagrants. Drier conditions in eastern Mexico, especially during winter, showed similar significant relationships. Our results indicate the potential utility of studying vagrants to understand relationships between bird populations and environmental changes, and more importantly highlight the potential for understanding how vagrancy may relate to changes in this species’ distribution under new climate regimes.