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Magnificent frigatebird. Photo by Mark Vance CC BY-NC 2.0.

Luring magnificent frigatebirds back to Key West National Wildlife Refuge

Magnificent frigatebirds are magnificent in many ways. The wingspan of these birds reaches more than seven feet, and has the largest wingspan-to-body weight ratio of any bird in the world. They also are one of the only seabirds in the world that is unable to get wet, as they lack sufficient oil glands to maintain waterproofing of their feathers. Because of this trait, magnificent frigatebirds are kleptoparasites, also known as pirates in the animal kingdom, stealing food from other seabirds. These birds will often exhaust other seabirds in-flight until they regurgitate their most recent meal, which the frigatebirds will willingly take.

Prior to each nesting season, adult males congregate at nesting locations in what is known as a lek, in an effort to attract females to the nesting site. As the nesting period draws nearer, the males will compete for their mates through an elaborate display. While female frigatebirds are soaring over the lek, the males will display from the top of the mangrove canopy by inflating their bright red throat pouch, roughly to the size of a volleyball, and flail their wings, all while tilting their bill towards the sky and calling out to the females above. Females use this display to select their mate, and will begin nest building soon after. Fledgling frigatebirds will stay in the care of their mother for six to nine months after hatching.

A dark grey bird with a long curved beak perched on a shrub.
Magnificent frigatebird roosting on a mangrove island within Key West National Wildlife Refuge. Photo by USFWS.

While thousands of non-breeding magnificent frigatebirds can be found across the coastlines of Florida and the Caribbean during many months of the year, there is now only one known breeding frigatebird colony in North America. Historic accounts have documented breeding activities within the Key West National Wildlife Refuge on Marquesas Key from the 1960’s through the late 1980’s, when the nesting colony was abandoned. These birds were thought to have left their colony due to human disturbance, and were soon after observed nesting within Dry Tortugas National Park, 45 miles west of Marquesas Keys.

Current efforts are in place to re-establish nesting frigatebirds within select islands of Key West National Wildlife Refuge through a social attraction and monitoring study. Refuge staff members and volunteers have partnered with Avian Research and Conservation Institute personnel to place fleets of frigatebird decoys within the mangrove canopy of each study site, mimicking the stages of pre-breeding and breeding behaviors. Each artificial colony has the added realism of audio from recorded frigatebird calls projected through a broadcast caller.

This is the first season of a four-year study in the Florida Keys, and interest from frigatebirds has already been observed. Refuge and Avian Research and Conservation Institute staff members will continue to monitor sites for several years. Through periodic observations, we hope to gain a better understanding of the nest site selection characteristics that these birds require, and potentially produce a new nesting colony.

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