Post-release movements of translocated White-tailed eagles (Haliaeetus albicilla) during the first year of juvenile dispersal.

Abstract

Conservation translocations are increasingly being used as an effective means of species recovery. In order to address the loss of White-tailed eagle (WTE) (Haliaeetus albicilla) from its historic range, a conservation translocation commenced with the aim to re-establish a viable breeding population of WTE to the Isle of Wight and across southern England. This project offered the unique opportunity to investigate the initial stages of juvenile dispersal and post-release movements of translocated WTE, using satellite telemetry, from release, up until the end of their first year. Data was utilised from nine birds from two groups during analysis (Cohort 1 and Cohort 2). The aim of this research was to increase our understanding of what the birds did within the initial post-release period; when did dispersal onset begin, where did they travel and settle, how far away from the release site and on what temporal scale? Ultimately, what insight can this information give us into juvenile dispersal, the translocation process so far and importantly, how could we use this information to support WTE recovery in the UK going forward? There are a limited number of studies that have investigated aspects of natal dispersal and the ecology of adult WTE but few focus specifically on Juvenile WTE during juvenile dispersal. Prior to this study, first year WTE telemetry data derived from this translocation project had not been investigated in this way. Movements were characterised by moderately sedentary behaviour in the initial post-release period, with movements away from the release site following dispersal from the Post-Fledgling Area (PFA). Cohort 1, released in 2019, tended to reach dispersal onset quicker than cohort 2, released in 2020, 23 days earlier than cohort 1. Most individuals continued to reside in and move between multiple Temporary Settlement Areas (TSAs) ranging from 1-6, mostly across England and Scotland with a single individual travelling into mainland Europe. Four areas of overlap were identified whereby at least 2 birds used in part the same TSA (spatially if not temporally). Size and residency times for each PFA/TSA varied but a higher proportion of time was spent residing in areas identified as TSAs overall (85%) as opposed to continuous exploratory travel (15%). High levels of inter- individual variation in travel distances were detected, demonstrating some individuals moved greater distances more often than others. Intra-individual travel distances also varied greatly, with a far greater frequency of short than long distance movements. When long distance movements and wider distancing variation did occur (including maximum daily distance and maximum dispersal distance), it was almost exclusively in the final months of the 12-month study period. Juvenile dispersal in WTE is a long and complex process and has important implications for the conservation of the species. It is likely that there are many influencing factors affecting movements during the transient period and this research adds to the growing body of information relating to juvenile dispersal in raptors. The outcomes from this project could also be utilised to support future translocation projects, as well as highlight areas in the juvenile dispersal process that may require further conservation consideration to ensure juvenile WTE continue to thrive within the landscape and reach recruitment into the breeding population.