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To Catch a Willet

New technology is transforming the study of migratory birds


Willet Slideshow

See what it takes to catch a willet!

By Darci Palmquist

Consider this: an eastern willet returns to the same location to nest year after year, to a site about the size of your living room.

But even when you know exactly where a willet is, catching it is another matter—requiring at least 4 different nets and traps, 2 scientists and 1 decoy bird.

How hard can it be? To find out, I join ecologist Joe Smith and research assistant Ashley Green for a day of catching willets at The Nature Conservancy's Gandys Beach Preserve in southern New Jersey. We don knee-high wading boots and forge across the salt marsh, striding through short grasses known as "salt hay," tall cord grasses, shallow streams and lots of mud.

To make matters more challenging, we're not looking for just any willet. We're hoping to catch participants in Smith's 3-year study of willet migration. Which means catching willets wearing tiny ankle bracelets called geolocator tags—a new type of tagging device that's transforming the field of migratory bird research.

Wily Willets Be Warned: We're Looking for You


We start at a known nest marked by a small "goal post" placed during a previous field outing. Smith and Green sound like wide receivers as they discuss their offensive strategy:

"You want to go wide and left?"

"Sure, wide left and then go in for it?"

"Yeah. And go single file down the left side of this stream."

They hold long poles strung with 40 feet of black netting. Called a mist net, it lets the researchers take a wide berth around the nest so they're less likely to startle the bird into flight. Slowly they creep up. Using eye contact and silent nods to communicate, they drop the net on top of the nest. A quick flutter emerges in the web of string—they've nabbed a willet!

Back at the truck, they take the bird's diagnostics: weight (245 grams), tarsus (ankle) and bill length, feather samples (one from each side for symmetry)and blood (for sex ID,  mercury levels and isotopes). They note all these details plus the location of the nest and number of eggs (4).

Unfortunately, this willet isn't wearing a geolocator tag.

Geolocators calculate longitude and latitude by sensing light, weigh just a few grams and are fairly cheap to produce—all of which have made them a boon for scientists studying bird migration. Originally developed to track seabirds, geolocators are now being used on shorebirds like willets, songbirds and other birds previously excluded from tracking by larger, more expensive satellite tags.

There's only one catch (literally): Unlike satellite tags, geolocators have to be retrieved from the bird in order to collect the data.

"Last year we collected 9 tags out of 30, this year we're hoping for more," says Smith.

The tags are crucial because they're helping pinpoint the primary wintering location of willets, something scientists had only guessed at before. Based on the data Smith has gathered so far, the secret spot turns out to be an estuary on the northeastern coast of Brazil that boasts the largest track of mangroves in the western hemisphere.

This knowledge—combined with the feather and blood samples that Smith's team collects—is helping paint a fuller picture of the birds' year-round life.

One emerging concern is pollution at the wintering grounds. While the estuary in Brazil is considered relatively pristine due to its low human population, the feather samples indicate otherwise.

"We're finding that the willets have mercury in their systems," says Smith. He suspects the source is from nearby gold mining in the Amazon. Another concern is the growth of shrimp farming in the area, which is destroying coastal mangrove forests at a rapid rate.

What impact this pollution might have on the willets is still unknown, but Smith's research will undoubtedly add to the scientific understanding of this unique shorebird and shed light on the secrets of bird migration.

"Let's Start a Fight"

It's been a long day—we've used the mist net and Smith's self-made "reaper net" with only one successful catch so far and no geolocators.

On our final attempt, we walk out along the beach past dozens of horseshoe crabs laying tiny green eggs in the sand. Wading through a shallow tidal pool, we end up at a little spit of beach where hundreds—maybe thousands—of shorebirds are circling and squawking, feeding on the plentiful eggs.

We're in the "living room" of a willet the researchers call Mac n' Cheese.
 
"Let's start a fight," says Smith.

Willets are territorial, so in this spot the researchers decide to use a decoy bird to lure Mac n' Cheese into a box-and-stick trap. When the stick is triggered, a whoosh net will spring down and catch him. Smith is hopeful this will be the one: half the birds with geolocators have been caught with the box trap and whoosh net this season.

After everything is set up, we sit a short distance away and watch with binoculars. Green occasionally plays willet calls from the decoy by remote control.

It's a magical spot to wait. Besides willets, we see short-billed dowitchers, ruddy turnstones, red knots, semi-palmated sandpipers, sanderlings, black-bellied plovers and more, all stopping here for a quick feast of horseshoe crab eggs before continuing on to the Arctic.
 
But the willets are the stars. With a sleek white stripe stretching across the top of each wing, willets exude cool charisma. Of all the shorebirds, willets are the only ones that don't go to the tundra to nest.

"Willets are unique, they're creatures of the estuary," says Smith.

"And they're tricky birds to catch," he grins, clearly pleased by their ingenuity and the challenge. "I've never had to pull out so many different kinds of traps."
 
After an hour it's clear that Mac n' Cheese is not going to take the bait. We call it quits and trudge back across the beach. I'm beat, but Smith and Green are heading out once more with a "secret weapon"—a bow net that they will set out on an unattended nest and trigger by remote control.

It requires guesswork—you can't see if the bird is on the nest or not—but a nesting willet will only leave his or her eggs unattended for a short time. And it's worth a try. After all, calculated guesswork is often at the root of scientific discovery.

Author's postscript: Smith and Green did not catch a willet with the bow net that day. However, by the end of the field season they had collected a total of 12 geolocator tags. Next step: retrieving and analyzing the tags' data.

Darci Palmquist is a senior science writer for The Nature Conservancy.

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