Abstract
Understanding natal dispersal patterns of animals is critical to development of effective species conservation plans, as it ensures that population management takes place at appropriate scales. The reddish egret Egretta rufescens is a threatened waterbird species lacking documentation on many aspects of its ecology, including movement behaviors at all life stages. We attached satellite transmitters to 25 juvenile reddish egrets on their natal colonies and observed their dispersal patterns and subsequent movements over a period of 115 wk (May 2010-August 2012). Birds exhibited the greatest movement rates in the remainder of the first breeding season (through July 2010, ~10 to 13 wk of age, 11.07 km d �1 ) and steadily decreased in the post-breeding period (4.87 km d �1 ) and winter (1.96 km d �1 ) of their first year. Movements of 1 to 2.5 km d �1 char- acterized the remainder of the tracking period, suggesting that surviving birds were able to estab- lish local territories. Of the 25 tagged birds, 8 (32%) survived throughout the observation period, based on transmitter failure rates, with losses increasing each winter. The majority of birds remained on the Texas/ Mexico coast of the Gulf of Mexico, indicating that the population is largely resident and therefore vulnerable to coastal habitat alterations in the region. Due to a com- bination of infrequent long- distance migration, specialized behaviors, and apparent limited gene flow, habitat maintenance should be of primary importance for management of this rare species. This is among the first published studies of heron movement ecology using telemetry, and should be followed by further tracking with developing technologies to characterize high-resolution movements and habitat associations.
Highlights
Natal dispersal is defined as movement of an individual from its place of birth or a center of population density (Koford et al 1994)
Our cohort of reddish egrets appears to exhibit the typical pattern of post-fledging winter dispersal after a nomadic first summer, as seen in many bird species (Rydzewski 1956, Boddy 1983, Stahl & Sagar 2006)
After an initial bout of exploration, they settled in areas that have been previously identified as key wintering areas for adult reddish egrets, in the coastal regions of Tamaulipas, Mexico
Summary
Natal dispersal is defined as movement of an individual from its place of birth or a center of population density (Koford et al 1994). Information on the life history of juvenile reddish egrets is limited, with many aspects of their ecology completely lacking documentation. This is troubling given the species’ threatened status in the states of Texas and Florida, and designation as a species of concern at the federal level (Kushlan et al 2002). If a nearby area that contains abundant resources becomes locally available, it is assumed that a nonbreeding individual will establish itself there, remaining stationary for a period of time (as long as optimal conditions hold and prey remains) and conserving energy (Smith 1978, Greenwood & Harvey 1982, Lowther & Paul 2002). Persistent movement during non-migratory periods could be indicative of a lack of consistency in quality habitat, or intense competition in which an inexperienced juvenile is subordinate to more established adults (Greenwood et al 1979)
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