The Secret Life of the Kirtland’s Warbler

Page 3

Clearly, this was a bird worth traveling to see. “Something’s happening here,” Wunderle told me when I finally got to Tarpum Bay. “Something exciting.”

We were standing beside a field table erected in a clearing in an expanse of fruit-bearing shrubs and low trees. Two of the project’s field assistants, Ingeria Miller and Keith Philippe of Nassau, had just returned from a nearby line of mist nets and were measuring, weighing and banding birds that the nets had snared. Over the course of the project, Bahamian students had begun cataloging their native land’s abundant vegetation and wildlife, especially its birds. Their efforts were yielding data on the distribution of other migratory species, such as the Cape May warbler, American redstart and painted bunting, as well as resident birds, such as the Bahama yellowthroat, Bahama woodstar and greater Antillean bullfinch. And together with Wunderle, Ewert and Currie, the young scientists were finally describing the winter habits of the Kirtland’s warbler.

Using handheld Global Positioning System receivers to pinpoint the location of every Kirtland’s warbler they spotted on the island, they had produced detailed maps of the areas that the birds preferred. Then they studied the plants growing at the most-used locations and reached a tentative but revealing conclusion: The warblers were congregating in areas where edible fruit was growing on low, drought-tolerant shrubs such as wild sage.

The birds eat their share of insects and spiders, the researchers learned, but in the winter they also feed on fruit. What’s more, observations made at the beginning, middle and end of the season suggested that the availability of fruit decreases as the season progresses, probably because the amount of rain that falls on the island declines dramatically as October yields to November and then remains low through April. By the time March rolls around, Eleuthera is quite dry. Bushes that once were full of berries are bare, and only the hardiest plants offer fruit. To find food, the warblers have to move around.

To get a handle on where they go and how frequently they move, Currie outfitted each of a handful of Kirtland’s warblers with an assembly consisting of a tiny radio transmitter and battery and one wispy 5-inch-long antenna. Each assembly weighed only 0.5 grams in all, or about 3 percent of a typical warbler’s body mass, and was held like a backpack between the wings by nothing more than cotton threads looped around the legs, so the birds could fly unencumbered. Each unit broadcast on a separate frequency. For as long as the battery held out—about 21 days, if researchers were lucky—each Kirtland’s warbler could be tracked wherever it went.

Among the radio-tagged birds, I learned, was the one I most wanted to see: PXGO.

The next morning, I stood with Wunderle, Ewert and Philippe at the end of a rocky lane carved through a parched, low thicket. Wunderle told me the bird was a chipper, not a sneaker. The names have to do with how different warblers respond when a tape recording of their call or song is played: Chippers respond aggressively and chirp loudly to defend their territory; sneakers approach silently and cautiously.

Hoping for a chipper, we arranged ourselves in a line and started walking down the path. Philippe took the lead, carrying a portable cassette tape player. I went second, and Wunderle and Ewert brought up the rear.

As we set out, Wunderle reminded me to look low. Eight in 10 of the Kirtland’s warblers they had observed were either on the ground or less than a meter above it.

He also mentioned that it’s usually the second person in line who sees a warbler.

And wouldn’t you know it, a bird called immediately after Philippe started playing his tape. The sound came from a spot in the brush to my right. When I looked that way, a bird flew across the road between Philippe and me, about head high, and disappeared into an opening in the scrub to my left.

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