2016 Kirtland's Warbler Winter Survey Update

February 23, 2016 by Nathan Cooper


March is just around the corner and that means we are getting closer and closer to another series of Kirtland's warbler surveys on the wintering grounds.

Kirtland's warbler with geolocator on its back. Photo by Nathan Cooper.

As you may remember from previous blog posts, Kirtland's warblers spend the winter primarily in The Bahamas, especially on the central islands (Eleuthera, San Salvador, Cat and Long Islands). However, recent evidence from our geolocator study indicates that perhaps as much as 15% of the population winters in the extreme eastern Bahamas or on Turks and Caicos.

Figure 1 (below) shows the migratory path of one male Kirtland's warbler, from his breeding grounds in northern Michigan to his wintering grounds.

Figure 1. Relative probability of residency for one male Kirtland's warbler. Beige indicates the least time spent, while blue indicates the most time spent relative to the full year. Solid red line = spring migration. Dashed red line = fall migration.

Light-level geolocators collect information about the intensity of light to determine the time of sunrise and sunset. Because sunrise and sunset times vary depending on one's location on the planet, we can then use this information to infer latitude and longitude throughout the year. While incredibly useful, this type of data is noisy and can only pinpoint locations to within ~200 kilometers (~ 120 miles).

As a result, this male could have wintered anywhere in the eastern part of the Bahama Archipelago, with the most likely islands found within the blue oval (Figure 1). This particular male had one of the longest spring migrations of all the males we tracked, flying over 3000 km (~1800 miles) in just 16 days.

There are a few sightings of Kirtland's warblers from Turks and Caicos but no formal surveys have been done there. Joe Wunderle, one of our wintering Kirtland's experts, actually saw his first ever Kirtland's warbler on North Caicos, well before he knew he would spend much of his career working with them. Because so many birds appear to be wintering in this region, we have planned a trip to Turks and Caicos to carry out surveys.

The team consists of long-time Kirtland's researchers Dave Ewert (The Nature Conservancy) and Joe Wunderle (U.S. Forest Service), as well as Scott Johnson, a colleague from the Bahamian National Trust, and myself.

We will spend two weeks in late March and early April surveying for Kirtland's warblers in any good looking habitat we can find down there. We hope it will be a productive trip and that we'll find lots of Kirtland's warblers. I'm sure we'll spot lots of other interesting wildlife along the way.

Look for an update on these surveys sometime in late March or early April!