Winter habitat use by Blackburnian Warblers (Dendroica fusca) in Los Amarillos, Colombia

Abstract

Blackburnian Warblers (Dendroica fusca) were observed in their wintering grounds in a High Andean native secondary forest in Colombia between September 1993 and May 1994. The main objective of the study was to determine the relationships between the Blackburnian Warblers and the habitats where they were found. Size and composition of the mixed-species flocks joined by Blackburnian Warblers were also compared to habitat features. Habitat variables were measured in circular plots centered where a Blackburnian Warbler was first seen. The same set of variables was measured in randomly located paired plots to compare the two sets. The results obtained in Colombia (wintering grounds) were compared to similar data available from North America (breeding grounds).

Ninety-six mixed-species flocks with Blackburnian Warblers were detected. Some of the habitat variables measured differed between plots used by the birds and the random plots. Density of trees in all dbh (diameter at breast height) categories, density of snags and density of native trees and shrubs were higher at the bird-centered plots. Percentage vegetation density (understory foliage volume) from O-1m, 1-2m and 2-3m were lower at bird-centered plots. There was no significant difference for maximum and mean canopy height between bird-centered and randomly selected paired plots. At Los Amarillos, Blackburnian Warblers avoided Eucalyptus spp. trees. They preferred the higher part of the trees and trees in the middle and high abh classes. They avoided the smallest dbh size class (3-8cm dbh). Comparisons were made between the data from Los Amarillos and data available from northern central Minnesota (Collins et al. 1982). Percent ground cover, densities of trees 15.1-23, 23.1-38 and 38.1-53 cm dbh and total density of trees were significantly higher in Minnesota. Trees 7.5- 15, 53.1-68 and > 68.1 cm dbh were higher in Los Amarillos. Percent canopy cover was not different between the two Sites. Blackburnian Warblers selected for closed canopy cover (about 75%) and large trees in each individual site. They selected larger trees in Minnesota. This selection may be related to nesting requirements of the species.