Modeling Population Dynamics of Roseate Terns (Sterna dougallii) in the Northwest Atlantic Ocean

Abstract

The endangered population of roseate terns (Sterna dougallii) in the Northwestern Atlantic Ocean consistsof a network of large and small breeding colonies on islands. This type of fragmented population poses anexceptional opportunity to investigate dispersal, a mechanism that is fundamental in population dynam-ics and is crucial to understand the spatio-temporal and genetic structure of animal populations. Dispersalis difficult to study because it requires concurrent data compilation at multiple sites. Models of popula-tion dynamics in birds that focus on dispersal and include a large number of breeding sites are rare inliterature. In this work, we propose a stochastic simulation model that captures the dispersal dynamics ofthis population of roseate terns. The colonization and decolonization (abandonment) of breeding coloniesare modeled as discrete events that follow different dynamics than dispersal. We show that our modelreproduces the properties of this population that have been observed in field data. We also analyzed thesensitivity of our model to alterations in different variables, and study the impact of these alterations inthe model dynamics. Our results suggest that large colony population size exhibits a threshold sensitivityto adult survival, and that regional persistence is maintained by the larger populations.