The maintenance of gene flow in species that have experienced population contractions and are geographically fragmented is important to the maintenance of genetic variation and evolutionary potential; thus, gene flow is also important to conservation and management of these species. For example, the Reddish Egret (Egretta rufescens) has recovered after severe population reductions during the 19^th and 20^th centuries, but population numbers remain below historic levels. In this study, we characterized gene flow among management units of the Reddish Egret by using ten nuclear microsatellite markers and part of the mitochondrial (mtDNA) control region from 176 nestlings captured at eight localities in Mexico (Baja California, Chiapas, Tamaulipas, and Yucatan), the U.S.A. (Texas, Louisiana, and Florida), and the Bahamas. We found evidence of population structure and that males disperse more often and across longer distances compared to females, which is congruent with previous banding and telemetry data. The maternally inherited mtDNA and biparentally inherited microsatellite data supported slightly different MU models; however, when interpreted together, a four MU model that considered population structure and geographic proximity was most optimal. Namely, MU 1 (Baja California); MU 2 (Chiapas); MU 3 (Yucatan, Tamaulipas, Texas, and Louisiana); and MU 4 (Florida and the Bahamas). Regions outside our sampled localities (e.g., the Greater Antilles and South America) require additional sampling to fully understand gene flow and movement of individuals across the species’ entire range. However, the four MUs we have defined group nesting localities into genetically similar subpopulations, which can guide future management plans.

Blood samples were collected from nestling Reddish Egrets (one nestling per nest) at eight breeding sites in Mexico (Baja California, Chiapas, Yucatan, and Tamaulipas), the U.S.A. (Texas, Louisiana, and Florida), and the Bahamas. DNA from whole blood samples was extracted by using the Gentra Puregene kit (Qiagen) following the manufacturer’s protocol. To genotype individuals, microsatellite primers designed by Hill & Green (2011) were used. Samples were amplified via a semi-nested PCR. Primers designed by Bates et al. (2009) were used to amplify the mtDNA control region (d-loop). PCRs were carried out in using the same reaction concentrations as above but also using the thermal profile suggested by Bates et al. (2009).

From 176 total birds, 123 individuals from Yucatan, Louisiana, Florida, Chiapas, and Texas had not been previously analyzed genetically. The remaining 53 samples were chosen randomly from a previous study to serve as a reference data set (Hill et al., 2012).