The Kirtland’s Warbler is one of the rarest of the temperate New World warblers. It is listed as a federally endangered species and Near Threatened by BirdLife International. Nearly its entire population (current estimates of more than 3600 individuals) breeds in north-central Michigan in young Jack Pine forests. These forests were once naturally fire-maintained ecosystems, but they are now heavily managed through controlled burns and harvesting.
Brown-headed Cowbirds, though native to the Great Plains, spread into Michigan in the 1880s following the felling of eastern forests, which acted as a natural break to the expansion of this species eastward. Cowbird parasitism rates on Kirtland’s Warbler were once as high as 70%, but with control measures that began in the 1970s, this rate dropped to a low of 3%, and warbler productivity tripled. The population of Kirtland’s Warbler has continued to grow since the 1990s, so much so that the federal government is beginning to think about de-listing it. Pairs are now breeding in the Upper Peninsula of Michigan, in Ontario, and most recently in central Wisconsin. Despite still being very rare in migration, birds are being found with more frequency, including at least two seen in northwest Ohio in May 2010. I was fortunate to see a female on migration in late September 2006 on Folly Island (Charleston County), South Carolina.
Surprisingly though, my experiences with Kirtland’s have not occurred where most people are likely to see them. I mentioned the bird in migration (my lifer), but I have now had the pleasure of seeing Kirtland’s Warbler on its wintering grounds in the Bahamas. In late April 2008, I made my first visit to the island of Eleuthera in the Bahamas to scout the area for a Field Guides tour there. Eleuthera is one of just two islands in the archipelago where visitors can see Great Lizard-Cuckoo, though I must admit I had Kirtland’s on my mind as well. I searched extensively throughout the island but didn’t find a one. I suppose the late date of my trip may have had something to do with this. Kirtland’s generally arrive on their breeding grounds in mid-May, which would mean that many of them have probably left or are beginning to leave the islands by late April.
It was the following year in early April 2009 while leading the tour that I got my first look at a wintering Kirtland’s Warbler. We had spent the previous day on Eleuthera tracking down the Great Lizard-Cuckoo, eventually finding several individuals around our hotel grounds on the north end of the island near Gregory Town. These oversized Coccyzus cuckoos spend much of the day in the shadows of tall coppice hunting Anolis lizards. Occasionally they like to come out and sun themselves. They also make amazing cackling or growling sounds. However, on this day I knew I needed to find some good low scrub or coppice if we had any chance of locating a Kirtland’s, our remaining target bird. We set out and after driving several kilometers south of Governor’s Harbour I eased the van over to the right shoulder at a spot where the habitat looked good—a mix of low open scrub with visible bare ground between bushes. No sooner had we gotten out of the van than we began hearing a rich call note, tsip!, coming from the vegetation. All of a sudden, a bird popped up in front of us in the closest small scrub. A little surprised, I remember saying to the group, “Hey guys, that’s a Kirtland’s Warbler!”
We ended up finding a total of five Kirtland’s that day at two different sites. In April 2010 our tour group found another female. That totals six sightings of Kirtland’s in two years. Not bad, I believe, considering the paucity of records on the wintering grounds. All our sightings were of unbanded birds and most appeared to be females or first-year birds. It is surprising to me that we didn’t find any males, but perhaps males prefer a slightly different habitat type or maybe we just missed them. Adult male warblers typically leave the wintering grounds before females, but early April is still probably too early for migration of either sex.
It is exciting when tour leading and science can mix. I know our participants enjoy being a part of something that is not well studied—a feeling that every little photo or written note is helping us to learn a bit more about a species, in this case the Kirtland’s Warbler.