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 - Pearly-eyed Thrasher
 - Pearly-eyed Thrasher

Pearly-eyed Thrasher Margarops fuscatus

Wayne J. Arendt
Version: 1.0 — Published November 17, 2017

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Few would argue that, even for a mimid, Pearly-eyed Thrasher is a very successful species. It is a stalwart nest predator and competitor for nest sites. It has been called an "intrepid poacher", and is partially blamed for the depleted faunas on numerous Caribbean islands. Its belligerent nature and rapacious habits have earned it the title "insidious thrasher". Indeed, any species that poses a threat to the mere existence of coinhabiting species will be looked upon disdainfully by some but venerated by others.

In all aspects of its distribution and ecology, Pearly-eyed Thrasher is a classic example of an avian "supertramp". Of the two known, mutually exclusive, competitive strategies (colonizers vs. competitors) that have evolved in insular landbirds, the pearly-eye is a superior colonizer. Superior colonizers have the ability to fill vacant or underexploited niches and are capable of undergoing marked shifts in altitudinal range, habitat type, diet, foraging techniques and even morphology. This plasticity: (a) permits extensive regional dispersal; (b) successful establishment and rapid population growth by propagules (colonizers) in areas less suitable, and thus more sparsely populated, by the more competitive species already established; and (c) fosters density compensation on small islands and in species-poor habitats. The pearly-eye is a mobile species with a strong homing ability. It regularly undergoes inter-island natal dispersal, is omnivorous and, most importantly, it is a prolific breeder, characterized by extended breeding seasons (8–11 months), multiple broods (2–6 per season), rapid recycling within seasons (within 1–2 weeks), asynchronous hatching, multiple recruits (up to ca 50) into the breeding population by single breeders, and rapid population recovery after major habitat disturbances.

Having evolved superior colonizing traits at the expense of strong competitive characters, the pearly-eye is confined to about 80 generally small, often disturbed, species-poor islands and habitats throughout the Caribbean archipelago over a north-south geographical range of almost 3,000 km. With the exception of the island of Puerto Rico (895,000 km2), on which it is common only in species-poor habitats, the pearly-eye is noticeably absent from the larger islands, such as Cuba, Hispaniola, and Jamaica, inhabiting only their species-poor satellite islands.

Pearly-eyed Thrasher generally does not colonize islands less than about 1 km2, or with three or fewer resident landbird species. Nor does it inhabit large islands greater than 1,000 km2 unless the islands are species-poor and contain extensive, disturbed habitats. Although the pearly-eye is resident on small islands with as few as four landbird species, it is found most often on islands, and or within habitats, with about 16 resident species. It reaches its highest relative abundance in wet-forest habitats. On Caribbean islands, wet forests are generally more depauperate in bird species than are dry forests. The pearly-eye is considered a species of "Least Concern", owing to its wide geographic range, fluid subspeciation and ample ecological distribution.

The pearly-eye’s future depends on its ability to adapt to the ever-changing conditions in natural and anthropogenic environments. It is unlikely that Pearly-eyed Thrasher ever will expand its range onto the continents, at least in the near future. However, if the pearly-eye secures a foothold on either nearby continent, its large size, combative nature, and predatory habits would certainly enhance its chances of success, especially in species-impoverished environments resulting from today’s burgeoning human populations, increasingly coming into conflict with landowners and natural resource stewards. As a result, management actions may be necessary to moderate its numbers and mitigate its impact on other animals, plants and a variety of environmental resources.

Distribution of the Pearly-eyed Thrasher - Range Map
  • Year-round
  • Migration
  • Breeding
  • Non-Breeding
Distribution of the Pearly-eyed Thrasher
Pearly-eyed Thrasher (subspecies fuscatus).

Guana Island, British Virgin Islands. 8 May 2008.

© Michael Pazzani

Recommended Citation

Arendt, W. J. (2017). Pearly-eyed Thrasher (Margarops fuscatus), version 1.0. In Neotropical Birds Online (T. S. Schulenberg, Editor). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/nb.peethr1.01