Cerulean Warbler (Setophaga cerulea) spring migration stopover in northern Middle America
The Cerulean Warbler (Setophaga cerulea) has one of the longest migrations of any small passerine, traveling approximately 4,000 km between breeding grounds in eastern North America and nonbreeding residency in northern South America. However, unlike many migratory birds, little is known about this aspect of the ecology of this species. In 2004 – 2009 teams of resident and foreign biologists conducted 181 line-transect surveys in Belize, southern Mexico, Guatemala, Honduras, and Nicaragua, during the last week in March and the first three weeks of April. Results generally confirm Parker’s (1994) hypothesis that Cerulean Warblers stop in low mountains on the Caribbean coast of northern Central America in early April. However, in contrast to Parker’s observations of Cerulean Warblers between 600 and 750 m in Belize, sightings in this project were evenly distributed at these and elevations above and below this range. The frequency of encountering Cerulean Warblers was higher in Belize, southern Mexico and central Guatemala than elsewhere. The relatively low numbers of Cerulean Warblers encountered during spring migration (134 individuals during 701 h of surveys) call into question Parker’s suggestion that the entire population of Cerulean Warblers stops over in the Caribbean-facing mountains of northern Middle America. We suggest a new hypothesis consistent with results to date, that many of these birds fly directly from South America to North America in the spring.