Caribbean Wintering Grounds

This is the non-breeding period of its annual cycle, and VCE’s long-term commitment to Bicknell’s Thrush conservation demands that we pay careful attention to issues on its winter range. Since 1994, VCE biologists have followed the birds there, committed to studying and conserving these important, high-elevation, tropical habitats.

© Pedro Genaro Rodriguez on iNaturalist. Some rights reserved CC-BY-NC

A Mostly Caribbean Bird

In the 1990s, the Bicknell’s Thrush wintering habitat was largely unexplored. Historical records, while scant, suggested that the Bicknell’s Thrush winter range was restricted to the Caribbean Greater Antilles, and an exploratory trip to the Dominican Republic by Chris Rimmer in 1994 confirmed the presence of Bicknell’s Thrush in high- elevation, broadleaf forests of Sierra de Bahoruco.

This catalyzed a three-year study of the species’ distribution and habitat use. Although Bicknell’s Thrush have been found in the Blue Mountains of Jamaica, the Sierra Maestra of Cuba, and Puerto Rico’s Luquillo Mountains, VCE’s research has shown convincingly that at least 90% of the species’ global population overwinters on Hispaniola.

We’re currently trying to get more detail on when they arrive and leave. In January 2025, Vermont Center for Ecostudies deployed the first Motus station within the Bicknell’s Thrush wintering distribution, at Reserva Privada Zorzal. BITH that we have fitted with small radio receiver backpacks will ping this and other towers, giving us data on their whereabouts.

With help from generous private donors, we are setting up more towers along the coast so we can further track BITH’s arrival and departure to the island, and understand where in their migration they are running into obstacles and dying.

© Yolanda M. Leon on iNaturalist. Some rights reserved CC-BY-NC

Preferred Habitat and Human Disturbance

Montane forests in the Dominican Republic and Haiti constitute the primary winter refugia for Bicknell’s Thrush. They prefer wet, broadleaf forests with a dense understory. Although we have documented Bicknell’s Thrush in humid forests at sea level, extremely few of these habitats have escaped loss or alteration by humans. But even remote habitats on the island face unrelenting loss from intense human population pressures.

Remotely sensed data suggest that from 1996 to 2022, both Haiti and the Dominican Republic experienced rapid primary forest loss, inside and outside protected areas. Forest agriculture such as shade grown coffee or cacao production have increased rapidly. Cacao production, especially along the northern coast, has exploded in recent years as the price for cacao beans has nearly tripled.

Climate change is also expected to decrease rainfall, which doesn’t bode well for a species that prefers wet rainforests. Adding insult to injury is our discovery that introduced rats may cause significant mortality during winter, even in the relatively pristine forests of Sierra de Bahoruco.

Male and female Bicknell’s Thrush appear to segregate by habitat type. In undisturbed, primary forests of Sierra de Bahoruco, males outnumber females by a 4:1 ratio. Both sexes maintain discrete territories throughout the winter, and insect food resources are relatively rich in these forests, which we believe represent “optimal” winter habitat.

A different situation exists at our study site in the Cordillera Septentrional, a mid-elevation, much wetter area that features more disturbed, secondary broadleaf forest with a relatively open understory. Here females slightly outnumber males, and birds appear to feed more heavily on fruit, a generally lower quality food than insects. We suspect that these forests constitute “suboptimal” habitat, and that, because suitable habitat is limited islandwide on Hispaniola, females may have few options but to inhabit them. The consequences for female survival could be pronounced, with effects on the entire species’ viability.

© Jim Goetz

Building Conservation Capacity in the Caribbean

Training of our local partners in the Dominican Republic and Haiti is among the most important facets of VCE’s overall conservation program on Hispaniola.

For over two decades we have worked closely with local biologists, students, and amateur ornithologists, helping to build their capacity in becoming ecological stewards of Hispaniola’s unique biodiversity.

In the Caribbean, Jim Goetz leads field training for the next generation of biologists. The students install pitfall traps which will collect leaf litter insects at each survey point, and measure the structure of the forest and the amount of fruit in the regenerating habitat of the reserve, comparing it to a non-sustainably-managed nearby plantation.

They conduct surveys for Bicknell’s Thrush, using audio playback to call in Bicknell’s Thrush from the regenerating forest of the private reserve. Mist nets are hung to catch birds so they can be measured, banded, and fitted with a backpack receiver for tracking.

Hopefully, the tagged BITH will pass close to one or more Motus receiving stations, so we can track their movements to the U.S. mainland, up the coast, and to its breeding grounds in the Northeast.