Movements and survival of juvenile reddish egrets Egretta rufescens on the Gulf of Mexico coast

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 characterized the remainder of the tracking period, suggesting that surviving birds were able to establish 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 combination 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.

Survival of adult reddish egrets Egretta rufescens marked with satellite transmitters

“…Bates et al (2015) estimated juvenile survival of reddish egrets at 78% for the first 6 mo after hatch. Geary et al (2015) found similar results for the first 6 mo after hatch at 83%; yet survival decreased to 53% by 17 mo after hatch.…”

Bringing back the dead: Genetic data from avian carcasses

“…Furthermore, we performed 2–3 replicate amplifications for each sample, and results were consistent among tissues from the same individual. Previous studies of reddish egrets have reported skewed sex ratios in small samples of hatch‐year and adult birds (Geary et al , Koczur et al ), which may be due in part to the timing or methods of capture. In addition, these carcasses represent mortalities, which may indicate sex‐bias in survival.…”

Juvenile Sandhill Cranes exhibit wider ranging and more exploratory movements than adults during the breeding season

“…Recent reductions in the mass of satellite transmitters and advances in other technology (e.g. light-level geolocators, McKinnon et al 2013) have made it more feasible to study movements of juveniles (Bridge et al 2011, Margalida et al 2013, Geary et al 2015, Flack et al 2016, Harel et al 2016. As a result, several studies have demonstrated differences in the foraging patterns of juveniles vs. adults (Riotte-Lambert & Weimerskirch 2013, Weimerskirch et al 2014, de Grissac et al 2017).…”