Ecological and Genetic Monitoring of a Recently Established Osprey (Pandion haliaetus) Population in Wales

ABSTRACT The Osprey (Pandion haliaetus) experienced severe declines in Europe over the past centuries, including extirpations from large parts of its range. After Ospreys began naturally recolonizing Wales, United Kingdom (UK), in 2004, the Dyfi Osprey Project initiated an extensive ecological (ringing, satellite tracking, and nest video recordings) and genetic (microsatellite genotyping) monitoring program alongside artificial nest platform construction. From 2004 to 2019 there were 40 reproductive events (i.e., eggs laid in a nest) across six nests, resulting in a total of 95 fledglings and a yearly average of 2.35 ± 0.8 (SD) fledglings per nest-with-eggs. Video recording at one nest documented high hatching success and survival to the fledging and dispersal phases, as well as mate- and nest-fidelity across multiple years. Collectively these breeding parameters suggest high productivity associated with artificial nest structures and limited density-dependent effects for the Welsh population due to its small size and low density at this stage of recovery. Satellite tracking of four migrating individuals revealed that Ospreys used a western European migratory flyway and wintered in sub-Saharan western Africa. Genetic analysis of nestlings from five nests indicated single paternity in all cases, in agreement with evidence of social monogamy. Genetic analysis of geographical outgroups (Scottish, Swedish, and Latvian) provided preliminary evidence of cryptic population structure among UK (Welsh and Scottish) populations. The novel combination of loci show Welsh Osprey retain high levels of variation and more broadly direct reconsideration of the hitherto inferred genetic poverty of the species compared to other raptors. We recommend implementation of similar long-term ecological and genetic monitoring programs for other populations.