Least Tern Nests Under Watch in Sian Ka’an Reserve as Threats Mount

Sian Ka’an Biosphere Reserve, Quintana Roo — Community monitors recorded 141 nests, 235 eggs and 87 chicks of the least tern (Sternula antillarum) during the first half of the year at the Boca Paila nesting site inside the Sian Ka’an Biosphere Reserve, part of a program aimed at conserving the threatened shorebird.

The results were presented by Amigos de Sian Ka’an (ASK) during the Second Meeting for the Exchange of Experiences on Shorebirds and Seabirds Nesting in the Yucatan Peninsula, organized by the office of the Yum Balam Flora and Fauna Protection Area.

ASK executive director Rocío Moreno said the organization devotes part of its work to conserving the least tern, a migratory species considered the smallest tern in North America.

Monitors who walk the beaches to locate nesting sites, register nests and follow the development of eggs and chicks achieved a hatching rate of 39 percent per nest, according to the season’s records.

Threats on the Beach

Moreno said the monitors’ work generates information on the species’ reproductive behavior and on conditions at its nesting sites — data she described as essential for setting protection measures.

The least tern is listed as threatened under Mexico’s NOM-059-SEMARNAT-2010 standard and faces several factors that can affect its reproduction and survival.

“Among the main threats are the movement of people and dogs, as well as motorcycles and bicycles passing over the beaches, activities that can disturb or destroy the nests,” she said.

Natural pressures add to those problems, including storms and storm surges, along with predation by species such as raccoons and crabs.

The bird is closely tied to coastal environments and rarely strays from the sand. It is distinguished by its small size, rapid wingbeats and beach-oriented habits, measuring between 21 and 24 centimeters long and weighing roughly 40 to 55 grams.

The species nests directly on the ground or on gravel surfaces, scraping out a shallow depression that can end up partly covered with small stones, grasses or debris.

Why the Monitoring Matters

“Community monitoring at Boca Paila is a key tool for identifying breeding sites, understanding nesting success and detecting the threats the species faces,” Moreno said.

The findings presented at the meeting underscore the importance of keeping up surveillance and protection of the beaches in the Sian Ka’an Biosphere Reserve, particularly during the least tern’s breeding season.