A few weeks ago, I took a trip to Eleuthera Island in the Bahamas to visit the Kirtland’s Warbler Research and Training Project.
The Kirtland’s warbler (Dendroica kirtlandii) is an endangered species that spends the summer breeding season in north-central Michigan and is only known to winter in the islands of the Bahamas. This warbler breeds exclusively in fire-controlled jack pine forests. Nest parasitism by brown-headed cowbirds is greatly threatening the Kirtland’s breeding success, but a control program to reduce the effects of cowbirds helped boost the population from as few as 167 singing males in 1987 to roughly 2,000 individuals at latest count.
While a great deal is known about these warblers’ ecology and behavior on its breeding grounds, until recently they had not been studied at all during the winter. Basic questions regarding the bird’s habitat use, movement patterns, and diet have been unanswered.
The Kirtland’s Warbler Research and Training Project, now in its fourth year, is finally studying the bird’s little known habits on the wintering grounds in order to better promote conservation efforts. Led by Joe Wunderle, an ornithologist from the United States Forest Service, a team of five biologists, including Peter Bichier, a long-time technician at SMBC, Wunderle is studying different aspects of the wintering biology of the Kirtland’s warbler on Eleuthera Island in the Bahamas. The team is capturing and following Kirtland’s warblers around the island using radio transmitters.
The warblers primarily forage on the ground, and arthropods (insects and spiders) in the leaf litter are suspected to make up a large part of their diet. Most of the arthropods seen are ants and spiders, but a major focus of the team’s efforts will be to study leaf litter arthropods found in the Kirtland’s scrub habitat. They will examine the natural variation in the size of arthropod populations and try to determine how factors such as temperature, water, shade cover, and plant diversity in the scrub habitat influence the arthropod distribution and abundance.
Additionally, the team is mist-netting other commonly seen migrant and resident species in the same habitats.
Some of the common migrants captured in Eleuthera included the black-throated blue Warbler, palm warbler, prairie warbler, thick-billed vireo, white-eyed vireo, common yellowthroat, ovenbird, gray catbird, indigo bunting, and northern mockingbird. The most common Bahamian resident was the Bahamian yellowthroat.
Team members have also been collecting blood samples from the Kirtland’s warblers and other birds they capture. Measuring hormone levels in the samples will let them determine how stressful migration is to the birds. Further, analysis of isotopes in the blood will reveal where exactly the birds spend the summer and winter as well as components of the birds’ diets.
Staff of the Kirtland’s Warbler project are also very involved in training and outreach to Bahamian students. This year, two students are participating in mist-netting and radio tracking in the Bahamas and will travel during the summer to work with the Kirtland’s warbler in the Michigan breeding grounds.
The project, supported by the Nature Conservancy, is striving to train and educate local biologists to work on conservation and ecology projects to protect birds and the rest of the biodiversity of the Bahamas over the long term.
Of course, one of my personal goals during the visit was to see this endangered warbler. After a few days of getting out to the study sites at 5:00 a.m., opening the mist-nets, and working through the day, I came up with an impressive list of migrants and Bahamian residents, but no Kirtland's.
By the last day, I was convinced that the star of the show would elude me. I was packed and ready to catch the five-seater plane back to Nassau. But a half-hour before leaving, I heard Wunderle say the magic words over the walkie-talkie, “We’ve got a Kirtland’s.” After watching the team affix a radio transmitter to the bird, I was off to the airport—but not without seeing this rare bird.
Stacy Philpott is a postdoctoral fellow at the Smithsonian Migratory Bird Center (SMBC).