Open- and cavity-nesting traits merge in the evolution of an avian supertramp, the Pearly-eyed Thrasher (Margarops fuscatus).

Abstract

There is a dichotomy between open- and cavity-nesting species in the quantitative and temporal aspects of most reproductive parameters. For example, parameters such as 1) breeding season commencement, length, and conclusion, 2) number of clutches per season, 3) length of recrudescence periods, and 4) incubation and nestling periods, usually reflect shorter times in open nesters. However, these parameters are not always comparable among species with a proclivity for similar nest placement strategies, nor are they mutually exclusive within a given species. The Pearly-eyed Thrasher (Margarops fuscatus), an insular, secondary cavity nester, has adopted several reproductive traits typical of both open and cavity nesters along its evolutionary highway to becoming a premiere avian supertramp. It has evolved superior colonizing abilities, extended breeding seasons, multiple broods, rapid recycling within seasons, asynchronous hatching, and a highly adaptive resiliency to major habitat disturbances. Its egg size and mass tend to decrease with the laying of each consecutive egg within a clutch as it does in several cavitynesting non-passerine species, which is just the opposite of the general trend found in many principally open-nesting passerines. Even though it is a secondary cavity nester, the Pearly-eyed Thrasher practices iteroparity and has adopted other egg-laying and incubation strategies characteristic of small, open-cup nesters to minimize the duration of the egg stage, renesting more quickly with each successive clutch. It maximizes reproductive yield, and thus increases its annual fecundity and, ultimately, lifetime reproductive success, all of which enhance its numbers and chances of continual survival in the region.

Citation

Arendt, Wayne J. 2004. Open- and cavity-nesting traits merge in the evolution of an avian supertramp, the Pearly-eyed Thrasher (Margarops fuscatus). Ornitología Neotropical 15 (Suppl.). 455–465.