|Ph.D. student, The Ohio State University|
|Comparing Relative Suitability of Shade-Coffee Plantations and Primary Forest for a Neotropical Migrant|
|Location: La Azulita, Venezuelan Andes|
|Species: Cerulean warbler|
|Abstract: Although Cerulean Warblers (Dendroica cerulea) have shown some of the greatest population declines of North American birds, causes for declines remain uncertain. Current conservation efforts are limited by the paucity of information on their ecology and response to disturbance, especially on wintering grounds. Cerulean Warblers winter in a narrow elevational band of the northern Andes, an ecosystem that is among the most rapidly deforested zones in the Neotropics. One form of agriculture in these areas, shade coffee plantations, may support diverse Neotropical migrants including Ceruleans, though studies provide conflicting evidence regarding their suitability. This project will be the first to examine if shade coffee plantations may be an important resource to wintering Cerulean Warblers. Specifically, I will compare use, condition, and return rates of Cerulean Warblers in primary montane forest and shade-grown coffee plantations in Venezuela. This information is critically needed to develop effective conservation plans for this declining forest warbler.|
|View from a field site in a shade coffee plantation near La Azulita, Venezuela.
(Photo by Marja Bakermans)
Project Update: April 2006
This project worked in three primary forest sites and three shade coffee plantations on the western slope of the Andes Mountains. At each site, Cerulean Warblers were surveyed using a distance-based line transect protocol, migrants were mist-netted and banded, and flocking and foraging behavior was documented. Preliminary findings reveal a number of insights, which may aid in the conservation of this species.
Based on preliminary analysis, shade coffee plantations may provide important habitat for Cerulean Warblers on their wintering grounds. Densities of Cerulean Warblers were considerably higher in shade coffee plantations compared to primary forest sites. In fact, capture rates of all Neotropical migrants in shade coffee plantations were over 3.5 times greater than in primary forest.
During the first season, 20 individuals were banded to estimate survival. Although fewer numbers of males than females were banded, numbers of birds observed on line transects suggest that shade coffee plantations have a roughly even sex ratio (56.5% male and 43.5% female). One possible explanation for a higher capture rate for females is sex differences in foraging behavior. For instance, females and males may segregate foraging habitats by foraging at different heights, with females foraging lower than males. In fact, I found that females foraged at lower heights than males, which is consistent with their tendency to be passively captured in nets than males.
Few studies have examined persistence and site fidelity of migrants wintering in shade coffee plantations. Several advantages may exist for birds that remain or return to the same location throughout the winter period including dominance, familiarity with resource fluctuations, and increased ability to avoid predators. In this study, over-winter persistence was high, with the majority of birds staying at the same site throughout the 9-week season.
Finally, Cerulean Warblers were found to be a major component of mixed-species flocks in shade coffee plantations. In fact, Cerulean Warblers were the most common migrant found in mixed-species flocks ranging up to 8 Ceruleans in a flock. Foraging observations indicated that Cerulean Warblers use a variety of trees and bushes to forage. Inga trees, in particular, have been found to provide large numbers of canopy arthropods (Johnson 2000), which is the primary food resource for Cerulean Warblers. Although Ceruleans directed most foraging activity to Inga sp., this may simply be a reflection of birds using trees according to availability.
This is the first study to examine over-winter persistence and survivorship of Cerulean Warblers on their wintering grounds. This is a multi-year project and additional research is planned from November 2006 - February 2007. The opportunity of working in the Tropics is a dream of many field ecologists. The experience of walking through primary forest and shade coffee plantations with toucans, macaws, parrots and countless hummingbirds and tanagers is a tremendous experience. Working in primary forest gave me the opportunity to meet Venezuelan citizens active in conservation of a rapidly diminishing ecosystem. In shade coffee plantations, I had the chance to witness farmers working closely with the land and their plight to keep farming shade coffee in times of hardships (i.e., extremely low coffee prices)