About This Project

Ask the Scientists

What is the context of this research?

The White-breasted Thrasher (WBTH) is a moderately sized songbird of the family Mimidae, restricted in geographic range to less than 13 square kilometers on the Lesser Antillean islands of St. Lucia and Martinique. Considerable development for tourism and agriculture has severely reduced the habitat available for the WBTH, as pressure from introduced predators such as mongoose and feral cats have increased as well. At last estimate, only 200-400 individuals remain on the island of Martinique, and approximately 1300 individuals on St. Lucia. Despite the small geographic range, and population size, greater natural history and conservation efforts remain poorly informed regarding the habits of this species. Our aim is to collect information regarding nesting habits and juvenile success rates of the WBTH.

What we do know about the WBTH is intriguing: WBTH are particularly attentive parents, providing considerable care to young. Additionally, young WBTH often act as nest helpers, providing a "third-parent" role to rear young and practice parenting. And in response to reduced nesting habitat, WBTH may breed cooperatively. Although attention has been paid to WBTH reproduction, comparatively little has investigated what happens once juveniles fledge (leave the nest).

What is the significance of this project?

Once WBTH nestlings fledge (leave the nest), they may remain dependent upon parental care for several months. Currently however, ecological songbird studies often incorrectly define nest success by assessing the success of the nest, i.e. getting nestlings to fledge. However, this is just one more step on the road to independence for juvenile WBTH. And using this standard may erroneously draw conclusions regarding population strength and viability.

By attaching radio transmitter "backpacks" to fledgling WBTH, we hope to improve conclusions about reproductive success and population stability of the WBTH on St. Lucia. This will hopefully include information about natural history and movement patterns of fledglings, duration of the fledgling period, and the impact of predation—particularly by introduced mammalian predators. As a West Indies endemic species, the WBTH evolved in the absence of introduced predators such as feral cats and mongoose. Considering the majority of extinctions worldwide have involved island-endemics this research is particularly pertinent to insular species such as the WBTH, and may hopefully be applied to conservation efforts of other Caribbean birds.

Increasing the accuracy of WBTH juvenile survival estimates by tracking survival from fledging to independence will improve understanding of population growth—information that can be applied to conservation and management of other avian species. Juvenile survival has not been studied in an insular and cooperatively breeding species, such as WBTH. Investigation of WBTH juvenile behavior will increase understanding of nest-helper effects in buffering small populations of island-endemic species from extinction. Knowledge of helper behavior may apply to other threatened cooperative breeders, many of which are also Neotropical island species.

Understanding the behavior and response of island birds such as the WBTH is tantamount to conservation efforts, particularly in the Caribbean. The West Indies are of particular concern due to the high number of endemic species, deforestation, and rapid, unregulated tourism development.

What are the goals of the project?

We aim to investigate several aspects of WBTH behavior and maturation through a number of ecological questions:

1. Is there a discrepancy in
survival estimates for WBTH nests and fledglings? If nest survival estimates are different than fledgling survival estimates this will suggest nest survival alone can be a misleading indicator of seasonal productivity. If fledgling survival is high while nest survival is low, population growth could be more sensitive to fledgling survival than nest survival and conclusions about population viability should not be based solely upon nest success.

2. Are there differences in post-fledgling survival between cooperative vs. single-pair groups? If cooperative groups have higher fledgling survival, extent of fragmented habitat may be an important factor in territory and nest-site selection. Cooperative WBTH may be optimizing disturbed habitat through increased post-fledgling care. Conservation measures should seek to manage both nesting habitat and post-fledgling habitat.

3. Do helpers play an anti-predator role in post-fledging care? If helpers play an anti- predator role in post-fledgling survival then the effects of post-fledgling care may be amplified for cooperative species.