Full Annual Cycle Tracking Of Black-Crowned Night-Herons Suggests Wintering Areas Do Not Explain Differences In Colony Population Trends

An understanding of the full annual cycle distributions of bird populations is a prerequisite to elucidating the drivers of differing trends among breeding populations. In the United States, Black-crowned Night-Herons (Nycticorax nycticorax) are listed as threatened or endangered in some states where they breed, but populations are stable in others. Outside of the breeding season, little is known about the species, including migratory routes and wintering areas. We used transmitters to track 28 Black-crowned Night-Herons from breeding colonies with stable (Washington, D.C.) and declining (Ohio) populations. For breeding populations across North America, we used band encounter data to estimate the movement of populations between breeding and wintering latitudes and the strength of migratory connectivity metric among latitudes. The first full annual cycle tracking of Black-crowned Night-Herons revealed diverse wintering strategies, including broad geographic distributions, within-winter movements, and between-year site fidelity. We found that over 80% of tracked individuals from the two breeding populations shared similar wintering areas, including the southern United States, Cuba, Honduras, and Nicaragua. Black-crowned Night-Herons exhibited weak breeding to wintering migratory connectivity (MC = 0.001 +/- 0.03) across the latitudinal extent of their North American breeding range, including some degree of partial migration. High overlap in the winter distributions and within-winter relocations of Black-crowned Night-Herons tracked from breeding populations in the two regions, as well as weak migratory connectivity across their range, suggest that localized conditions during the winter period may not be driving different trends in breeding populations.