Scientists deploy ‘nanotags’ to study shorebirds
Tiny tracking devices help identify population pressure points
Scientists with the New Jersey Audubon are using some of the world’s smallest tracking devices to solve one of the biggest conservation mysteries: What is driving the precipitous decline in shorebird populations, and where is that happening?
By gluing tiny “nanotags” – button-sized radio transmitters trailing delicate wire antenna – to the backs of semipalmated sandpipers, researchers hope to identify exactly where the birds are running into trouble as they migrate back and forth between the Canadian arctic, the United States and northern South America.
“It’s critical that we understand the threats to these species at each link of the chain,” said David Mizrahi, vice president for research at New Jersey Audubon. “They face challenges everywhere along their migration route, but the weakest link is going to be the place putting the greatest pressure on those populations. These pressure points are driving the decline of the species overall.”
The New Jersey Audubon project, supported by a grant from the National Fish and Wildlife Foundation (NFWF), is designed to pinpoint these pressure points. Then conservation groups can direct resources and actions to address whatever issues are causing populations declines.
“This is how you get the most bang for your buck, in terms of conservation dollars,” Mizrahi said.
Semipalmated sandpipers can fly more than 3,000 miles without stopping. No resting, no eating, no drinking – just six straight days of constant flight above a seemingly endless ocean.
These small, brown-and-white shorebirds make such epic journeys twice a year, stopping along beaches and lakeshores across the United States. Many well-known sites serve as critical migration stepping stones, where the birds can recover and fuel up before the next leg of their journey.
But the sandpipers never stay for long.
“The general perception is that these are North American species, but that’s not really the case,” Mizrahi said. “These birds are only here for four months out of every year. They’re really a South American bird that visits North America to breed.”
In the fall, sandpipers head south from summer breeding grounds in the arctic. Many of them fly directly from New England or eastern Canada to wintering grounds in the coastal marshes of French Guiana, Suriname and northeastern Brazil.
What happens to them when they finally reach this wintertime destination, with depleted fat reserves, after one of the natural world’s most grueling journeys? Scientists aren’t exactly sure.
Over the past few decades, the populations of semipalmated sandpipers and other shorebirds have fallen dramatically. Recent studies suggest that several Atlantic Flyway shorebird species have experienced declines of between 50 percent and 90 percent within the past three decades.
Scientists theorize that loss of habitat, pollution and other factors in South American wintering grounds may be playing a major role.
“We know a lot about what happens to these birds when they come to North America, but very little about what happens when they go to Central and South America in the winter,” Mizrahi said. “Here in the United States, we tend to take for granted the availability of information and financial resources for conservation. We assume that’s happening in other places in the world, but in places like Suriname and Brazil, limited resources tend to be focused on protecting endemic species – like keeping parrots from being captured and sold on the black market.
“We’re trying to make sure there are also continuing investments in migratory species, the birds that we share across the hemisphere.”
TINY TAGS, BIG IMPACT
Scientists use many methods to track animal movement, including simple leg bands, radio and satellite telemetry, and geolocators. Radio telemetry is one of the oldest forms of wildlife tracking technology; in its early days biologists would attach collars with large radio transmitters to animals and then track their movements with hand-held antennas.
Technological advances have made it possible to shrink the size and cost of radio tracking devices. The current generation of nanotags, designed specifically to work on small birds that migrate long distances, can weigh less than a gram.
Signals from nanotags are detected by receivers scattered along their migration routes; information on bird movements are uploaded to a central database located in southern Ontario. This international network, called Motus, alerts researchers when tagged birds pass within about 10 miles of a tower.
Thousands of tags can be simultaneously deployed and tracked within the system, which currently includes more than 300 receiving stations throughout the Western Hemisphere.
A 2016 NFWF grant for nearly $100,000 supports an effort by Mizrahi and his colleagues to set up seven new tracking stations along the coasts of Suriname, French Guiana and northern Brazil. The team plans to nanotag about 300 semipalmated sandpipers captured near the stations.
The nanotags have a limited lifespan – about four months of battery power. But that’s enough time for Mizrahi’s team to track the sandpipers while they winter in northern South America.
“We are hoping to learn whether a bird tagged in November is it still alive in March,” Mizrahi said. “This is a key missing piece in our understanding about the relative importance of threats on the wintering grounds. Once we have these data, we can fill in the gaps in our population models.”
Once researchers and conservation groups develop a more complete population model, they will be able to determine which factors affecting semipalmated sandpipers on their wintering grounds are driving the bird’s decline. Then parallel efforts to support the U.S. Fish and Wildlife Service and other partners to address these factors could help alleviate this stress and boost the population of the transcontinental shorebirds.
PART OF A LARGER EFFORT
Effective conservation efforts for shorebirds such as the semipalmated sandpiper require a wide-ranging approach to identify and ameliorate threats at multiple locations throughout their flyways. Such an approach must coordinate research, conservation, and management efforts of many groups across many political boundaries, focusing resources to generate the best measurable outcomes.
Building on its success to reverse declines in American oystercatcher along the U.S. Atlantic coast, NFWF and the U.S. Fish and Wildlife Service are expanding their efforts to a broader, multi-species approach – the Atlantic Flyway Shorebird Initiative. This new program, launched in 2015, aims to increase population levels for 15 focal shorebirds: American oystercatcher, semipalmated sandpiper, red knot, whimbrel, Wilson’s plover, marbled godwit, piping plover, purple sandpiper, red-necked phalarope, ruddy turnstone, sanderling, snowy plover, American golden plover, greater yellowlegs and lesser yellowlegs.
The initiative includes partnerships with and support from a broad range of contributing organizations, including Manomet, the National Audubon Society, the College of William and Mary, The Nature Conservancy, and dozens of other groups leading the field of shorebird conservation.
In 2016, the Initiative awarded more than $515,000 in grants, leveraging another $564,000 in matching contributions for conservation projects along the Atlantic Flyway.