Priorities for Future Research

In Light of Global Climate Change and Increased Climatic Disturbances – Although several studies document the predicted effects of global climate change on the timing of amphibian and avian reproduction, most have been done in temperate climates and ecosystems. There remains a dearth of quantitative studies from the tropics, especially on islands. As more and more Caribbean islands switch from agrarian to commercial- and tourism-based societies, particularly in light of the currently changing global climate, Pearly-eyed Thrasher will continue expanding into anthropogenic environments and ever shrinking natural habitats and thus will increasingly come into conflict with landowners and natural resource stewards. As a result, management actions will be needed to moderate its numbers and mitigate its impact on other animals, plants and a variety of environmental resources.

A prime example involves the diminutive island of Montserrat allied to the United Kingdom. Ongoing volcanic eruptions have forced the bulk of the island’s biota into cramped living spaces within the Centre Hills, a secondary mesic forest covering an area of c. 14 km² within the island’s interior. Owing to the pearly-eye’s predatory habits and its omnivory, including a penchant for cultured fruits such as guava, mangos, and bananas, all of which are remnants of past agriculture and remain common throughout the hills, several non-invasive control measures, including the removal of exotic fruit trees and banana plants, have been put into place (Young 2008). Undoubtedly, many more islands will be forced to take a variety of management steps necessary to regulate thrasher numbers and to lessen its deleterious impact on other biota and sundry natural and human-induced resources.

Research During Disturbance Interims – Facultative brood reduction (or FBR) is a “bet-hedging” adaptation practiced by many avian taxa to increase reproductive success in response to a fluctuating resource base as a result of stochastic environments. Pearly-eyed Thrasher populations throughout the Caribbean endure volatile and sometimes extreme physiographic, climatic and edaphic conditions (e.g. erratic topography, droughts, hurricanes, volcanism, inconsistent evapotranspiration, and variable soil pH). Owing to a rapidly changing global climate, an increase in the frequency and intensity of regional cyclonic disturbances in recent decades has made survival even more precarious for the pearly-eye as well as other insular animals and plants. In response to these extreme and unpredictable conditions, the Luquillo Experimental Forest (LEF) pearly-eye population has adopted FBR as a means of increasing breeding success and, consequently, has maintained a fairly stable population over the past 2.5 decades (Arendt 2011). Future thrasher research should continue investigating FBR among thrasher populations inhabiting other islands and diverse habitat types during disturbance interims to compare results with those extracted from the existing database. Such comparative, temporal studies should reveal potential changes attributable to global climate change.

Specific research questions might include: (1) How does FBR affect various pearly-eye reproductive parameters in the interim between major climatic disturbances? (2) What is the extent of FBR and its temporal effects on eggs and hatchlings within and among seasons? (3) Is there disparate resource allocation to eggs among lay and hatch orders? (4) Does greater egg mass increase hatching probability, nestling survival, hatching interval, as well as body mass and size at hatching?

Research Following Major Habitat Disturbances – In addition to research focusing on FBR during the hiatuses between cyclones and other major habitat disturbances, several challenging biological and ecological questions need to be addressed in the wake of major habitat destruction: (1) How are cause-and-effect mechanisms of resource availability and allocation among thrasher adults, eggs, nestlings, and fledglings, connected to the direct and indirect effects of major tropical cyclonic events, which are becoming more frequent and intense in a changing climate (Goldenberg et al. 2001, Webster et al. 2005)? (2) How does egg number and mass vary following disturbance? (3) Does greater egg mass increase hatching probability, hatching interval, nestling body mass and size at hatching, as well as nestling survival? And vice versa; (4) How do small egg dimensions and mass influence these same parameters?

Genetic Research – Various studies, including Ricklefs and Bermingham (1997, 2007) and Hunt et al. (2001), have treated the molecular systematics and phylogenetics, biogeography, and evolutionary radiations of West Indian birds, including pearly-eyes. Also warranted would be a thorough review and workup from museum specimens of the species’ genetic profile at the subspecific level from collections worldwide, noting especially the subspecies of dispersers collected on islands rarely reached by Pearly-eyed Thrasher. It is quite possible that such a review would shed even more light on the spatiotemporal aspects of the biogeographical radiation of the species.