In Patagonia, survey reveals Magellanic Plovers are becoming rarer

“Many of the surveyed sites have been visited [by shorebird scientists] for approximately 30 years, always recording a similar number of individuals and evidence of active breeding at these sites,” says Santiago Imberti, vice president of Ambiente Sur, who spearheaded the binational survey efforts in Argentina. “So, the low number does not necessarily mean the species is in decline, but rather that the total population of the species has likely been overestimated to date.”

Studies in the 1970s by Joseph R. Jehl showed that the Magellanic Plover breeds along shores of lagoons with sufficient water, avoiding shallow lagoons that can dry up quickly during the summer. In December, several of the surveyors noted that a number of the lagoons they visited were already dried up or contained very little water. It is not known what this species might do when their breeding habitat is suddenly unavailable. They might move to another lagoon, or skip breeding altogether, the team says.

“Climate change [has] a negative impact on the specific habitat characteristics of the [Magellanic Plover], and thus could have a negative effect on its population,” says Ricardo Matus, director of CRAL, who led the bi-national survey on the Chilean side. “With the information we collected during the surveys, we will be able to better direct any effort for its conservation.”

An extraordinarily rare bird

The Magellanic Plover is unique in that it is the only species of shorebird that feeds its young by actively regurgitating meals from its well-developed crop, a muscular pouch inside the esophagus that stores food until the birds can feed their young. Other shorebirds like oystercatchers (Haematopus) and sheathbills (Chionis) also deliver food to their chicks straight from their bills, but do not gather food in a crop. Despite its name, the Magellanic Plover is not genetically related to other plovers, and instead makes up a taxonomic family all of its own, Pluvianellidae. Among other shorebirds, it is believed to be the most closely related to sheathbills (Chionidae). 

After the breeding season, Magellanic Plovers move away from the Patagonian Steppe and are found on mudflats and pebble beaches along Argentina’s Atlantic coast from Tierra del Fuego up to southern Buenos Aires Province. One of its wintering sites is Argentina’s Estuario del Rio Gallegos in Santa Cruz Province, a site of international importance within the Western Hemisphere Shorebird Reserve Network (WHSRN), a designation earned in part due to the site’s importance to this species. In 2003, biologists observed almost 200 Magellanic Plovers within this one area. 

Although a count of 264 birds was a lower than expected number found during the December 2021 binational survey of over 180 sites, the team says more data needs to be gathered to accurately estimate the species population size.

“If we can confirm these data during the [South American] autumn and winter months, when the species is concentrated at sites along the coast, we would [find that we now] have an enormous task ahead of us,” Imberti says. “We would be facing a species with a very small population size, which would put it in a much more critical category of conservation.”

The binational team is now planning winter surveys for May 2022. Together with Manomet’s shorebird monitoring specialists, Ambiente Sur and CRAL will develop a survey protocol to obtain comprehensive data to compare to the population numbers found during the December 2021 breeding season. If the results are similar, it would mean we are dealing with one of the rarest species of shorebird in the world–and that conservation actions aimed at this species would become a top priority.

Manomet is looking ahead to support additional surveys during the next breeding season in December 2022. Ambiente Sur and CRAL also are planning to use tracking devices on the Magellanic Plover to better understand the species’ movements. There is currently no data on how the birds move between the breeding and wintering sites, nor how they respond to events–like the drying up of lagoons–when their habitat becomes unavailable.

Data gathered from tracking studies will provide valuable information that can be fed into targeted conservation actions. In the future, more advanced technologies (like using sound-monitoring devices to estimate populations of bird species based on their calls) could boost scientists’ ability to survey shorebirds in some of the world’s most remote regions.