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Despite advancements through satellite telemetry, knowledge of the behaviour and ecology of large raptors during natal dispersal is still poor, even though this transience phase is important in understanding the population dynamics and conservation of these keystone species. After this phase, which can take several years, the subsequent rapid transitional event on first territory settlement is less studied. It apparently occurs earlier without competition from existing territory occupants. The time of year when young large raptors settle on a territory has rarely been addressed empirically. Our study of seasonal timing of first settlement used data from 46 golden eagles GPS-tagged as nestlings in Scotland which were tracked to their first territory settlement, as adjudged by a robust algorithmic method. We show that when young golden eagles occupied their first territory, their settlements were uncommon in summer and most common in late winter/spring, but also occurred in autumn into early winter. The significant seasonal pattern was consistent, regardless of the probable prior occupancy status (vacant/occupied) of the settled territory (respectively, the likely absence or presence of defending territorial birds). This showed that seasonal territory settlement was unlikely to be related to any response from territory occupants. It infers further that seasonality in first territory settlement was underpinned by innate behaviours in dispersing eagles. Seasonal distribution of settlement dates was significantly different between sexes, with males more likely to settle in autumn, predominantly in prior vacant territories. We speculate on potential causative drivers behind our results and conclude that more research is clearly needed in this field of study. [ABSTRACT FROM AUTHOR]

Natal dispersal of large raptors is poorly understood, despite being a crucial transitional life-cycle phase affecting gene flow and population dynamics. A research-gap rarely examined concerns how young dispersing raptors strategize movements towards first settlement on a prospective breeding territory. First territory settlement is a critical decision for a lifetime and can take several years. With such importance, large raptors should theoretically devote considerable effort to acquire accurate information during prospection. Nevertheless, when discovery of territorial opportunities may be difficult, but easier in vacant territories, we posit two extremes in strategizing prospection behaviours: (1) "Quick, grab it when available with limited reconnaissance," as opposed to (2) "Slow, waiting game with frequent reconnaissance". We analysed pre-settlement data from 37 GPS-tagged nestling golden eagles, later recorded as having settled on their first territory. The number of eagles' unique daily visits to their later settled territories was a measure of prospection intensity. We documented substantial variation in prior visits, between less than 10 to several hundred. Analyses considered several potential predictors. We expected a positive association between number of prospecting visits and natal dispersal duration, since with more time to gather information there should be more visits. We also expected fewer prospecting visits in prior vacant territories. Neither of these expectations were supported. There was a non-significant tendency for more prospection visits by males. Our study provides novel information on a seldom-studied behaviour in a large raptor. It illustrates substantial variation in prospecting behaviour, but expectations of potential drivers behind this variation were not confirmed, urging further study. [ABSTRACT FROM AUTHOR]

Background Dispersal comprises three broad stages - departure from the natal or breeding locations, subsequent travel, and settlement. These stages are difficult to measure, and vary considerably between sexes, age classes, individuals and geographically. We used tracking data from 24 golden eagles, fitted with long-lived GPS satellite transmitters as nestlings, which we followed during their first year. We estimated the timing of emigration from natal sites using ten previously published methods. We propose and evaluate two new methods. The first of these uses published ranging distances of parents as a measure of the natal home range, with the requirement that juveniles must exceed it for a minimum of 10 days (a literature-based measure of the maximum time that a juvenile can survive without food from its parents). The second method uses the biggest difference in the proportion of locations inside and outside of the natal home range smoothed over a 30 day period to assign the point of emigration. We used the latter as the standard against which we compared the ten published methods. Results The start of golden eagle dispersal occurred from 39 until 250 days after fledging (based on method 12). Previously published methods provided very different estimates of the point of emigration with a general tendency for most to apparently assign it prematurely. By contrast the two methods we proposed provided very similar estimates for the point of emigration that under visual examination appeared to fit the definition of emigration much better. Conclusions We have used simple methods to decide when an individual has dispersed - they are rigorous and repeatable. Despite one method requiring much more information, both methods provided robust estimates for when individuals emigrated at the start of natal dispersal. Considerable individual variation in recorded behaviour appears to account for the difficulty capturing the point of emigration and these results demonstrate the potential pitfalls associated with species exhibiting complex dispersal behaviour. We anticipate that coupled with the rapidly increasing availability of tracking data, our new methods will, for at least some species, provide a far simpler and more biologically representative approach to determine the timing of emigration. [ABSTRACT FROM AUTHOR]