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When natal dispersal ends: using satellite telemetry to quantify territory settlement in a long-lived raptor

Citation

Whitfield, Douglas (2019), When natal dispersal ends: using satellite telemetry to quantify territory settlement in a long-lived raptor, Dryad, Dataset, https://doi.org/10.5061/dryad.573n5tb3g

Abstract

Breeding territory settlement, as the end point of natal (juvenile) dispersal, is a key juncture in the life history and population dynamics of long-lived raptors. It spatially identifies natal dispersal distance and temporally identifies first recruitment to a breeding population. Its determination can be confused by similar temporary settlement behaviour during dispersal or by post-occupation territorial birds’ excursions. Satellite telemetry provides potentially for a method to ascertain location and date of territory settlement without field observer limitations. Prior field-observer estimates are likely biased towards older ages. Telemetry has previously ascertained first territory settlement, but not via a quantified repeatable measure based solely on telemetric records. Our primary goal was to derive analytical rules, via an algorithm based on satellite telemetric data to determine when a dispersing Golden Eagle Aquila chrysaetos had settled on (occupied) a prospective breeding territory, using 83 birds tagged as nestlings in Scotland.  Our algorithm derived median record locations during a night, also compared median values over a longer time span, and processed records to confirm the spatial and temporal stability that was expected when a territory was occupied. All 17 birds deemed as algorithmically settled were confirmed by visual plot checks. Field work further validated territory occupation in all 14 of the 17 territories where field observations were possible; confirming egg-laying and chick-rearing in some instances. Many tagged birds were not deemed algorithmically to have settled on a territory, despite comparable or greater age. As a research tool, any current telemetric method is skewed away from older settlement ages due to technological lifespans which will hopefully improve.

These files provide 16 example datasets as shapefiles: eight for birds deemed to have settled on a territory and eight deemed not to have settled on a territory. Due to required confidentiality on locations of nest sites actual coordinates have been geometrically processed to mask their true locations but the scaling is unaffected.