GPS Tracking of Endangered Black-capped Petrels Could Reveal New Nesting Sites

By Elizabeth Serrano
June 28, 2019
Black-capped Petrel, white-faced, by Brian Sullivan/Macaulay LIbraryBlack-capped Petrel (white-faced form) by Brian Sullivan/Macaulay Library.

In May 2019, five scientists accomplished a long-held goal: to catch at sea and track one of the rarest seabirds of the Atlantic, the Black-capped Petrel. Now, after placing GPS transmitters on 10 birds they caught off Cape Hatteras, North Carolina, they’re hoping the birds will lead them back to an undiscovered nest site.

New self-paced course: Learn How to Identify Bird Songs, Click to Learn More

“That’s sort of what the dream is, that they’re going to take you to a whole new island that no one knew about,” is how Patrick Jodice, of Clemson University’s South Carolina Cooperative Fish and Wildlife Research Unit, describes the tracking project. Finding new nest sites could be a major step forward in conservation of this endangered bird. As the story unfolds, we can all follow along via a real-time map of where the birds are going.

Once an abundant nesting bird on several Caribbean islands, the Black-capped Petrel was almost made extinct by introduced predators and hunting. Today, Hispaniola (home to Haiti and the Dominican Republic) is the only known nesting island left—though research led by Adam Brown of Environmental Protection in the Caribbean suggests they may also nest on the island of Dominica.

distribution of black-capped petrelBase map from Neotropical Birds Online; map data originally provided by BirdLife International.

Here’s the mysterious part: these endangered seabirds are fairly commonly seen in the Gulf Stream, supporting a global population estimate of about 1,500 breeding pairs. But scientists know of only about 50 nest sites—so where are the remainder? Some are probably elsewhere on Hispaniola—the birds nest in hard-to-reach burrows, and they visit their nest sites only in complete darkness, so they’re hard to find. But scientists believe there must also be nesting areas on other islands that we don’t know about.

“Once you see where they nest and how secretive they are,” Brown says, “It wouldn’t be surprising to find them in an entirely new place.”  Tagging the birds at sea may finally give researchers an answer.

That’s how Jodice found himself 30 miles off Cape Hatteras, bobbing among 6-foot swells in an inflatable motorboat along with collaborators Brad Keitt of the American Bird Conservancy, Clemson research associate Yvan Satgé, Chris Gaskin of the Northern New Zealand Seabird Trust, and pelagic birding guide Brian Patteson.

The team used a net gun designed by Gaskin to snare the birds as they flew close to the boat. The satellite tags are solar powered and weigh only 6 grams (less than 3% of a petrel’s weight). Once a tag is placed on a petrel, it sends the bird’s location back to Jodice’s team for 6 hours at a stretch, after which it goes offline to recharge for 28 hours (during which time the bird can travel up to 360 miles) before turning back on.

Once the team started catching petrels, they were relieved to find some with dark faces and others with white faces. This color variation may reflect the existence of two groups of Black-capped Petrels that nest in different locations (a pattern that’s known in other seabird species). All the currently known nest sites are of the dark-faced morph, so the team will be watching especially closely the movements of the four white-faced individuals they tagged.

The banding expedition took place toward the end of the petrels’ nesting season, which runs from November to June. So far, all 10 birds have stayed in the Gulf Stream about 1,000 miles (at least 2 days’ flight) north of the Caribbean islands, indicating they are probably not currently breeding. According to Jodice, they may have already fledged chicks, their nests might have failed early, or some of the birds may not have bred at all this year. Black-capped Petrels spend at least 4 years as subadults before beginning to breed, so it’s possible some were still too young to nest.

Dark-faced Black-capped Petrel. Photo by Brian Sullivan/Macaulay Library.The "dark-faced" form of the Black-capped Petrel has sooty black completely surrounding the eye. All known Black-capped Petrel nest sites are for this dark-faced form. Photo by Brian Sullivan/Macaulay Library.
White-faced Black-capped Petrel. Photo by Steve Kelling/Macaulay LibraryThe "white-faced" form of the Black-capped Petrel has more white in front of and above the eye. There are currently no known nesting sites of the white-faced form. Photo by Steve Kelling/Macaulay Library.

“We’re still very much in the pilot phase of understanding this species,” Jodice said. By following these 10 petrels, his team will learn how the species uses the western North Atlantic, and could identify critical foraging areas, he said. As an example, in 2014 researchers put satellite tags on nesting Black-capped Petrels and learned for the first time that some individuals forage in parts of the Caribbean, the Gulf of Mexico, and an area off Venezuela. And the GPS tags have a potential life of 6 months, so it’s possible that some of these little devils (to use a colloquial name) will lead Jodice and his team back to their nest sites this November.

If a new nesting island is discovered, it will open up a new chapter in conservation of the species. Human encroachment into the forests where petrels nest poses the number one threat, according to Jennifer Wheeler of Birds Caribbean. “Petrel conservation can’t happen outside the human context,” she says. But new efforts will be able to take cues from a decade of work in Boukan Chat, Haiti, home to many known Black-capped Petrel nests. There, strategic local outreach has resulted in successful coexistence between petrels and the community. And if it can happen in Haiti, one of the poorest countries in the Americas, it can happen elsewhere, Wheeler says.

Elizabeth Serrano ’20 is an Animal Science major at Cornell University. Her work on this story was made possible by the Cornell Lab of Ornithology Science Communication Fund, with support from Jay Branegan (Cornell ’72) and Stefania Pittaluga.

All About Birds is a free resource

Available for everyone,
funded by donors like you

Donate