Golden Eagle Satellite Tag Review
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Scottish Natural Heritage Commissioned Report No. 982 Analyses of the fates of satellite tracked golden eagles in Scotland COMMISSIONED REPORT Commissioned Report No. 982 Analyses of the fates of satellite tracked golden eagles in Scotland For further information on this report please contact: Professor Des Thompson Scottish Natural Heritage Silvan House 231 Corstorphine Road EDINBURGH EH12 7AT Telephone: 0131 316 2630 E-mail: [email protected] This report should be quoted as: Whitfield, D.P. & Fielding, A.H. 2017. Analyses of the fates of satellite tracked golden eagles in Scotland. Scottish Natural Heritage Commissioned Report No. 982. This report, or any part of it, should not be reproduced without the permission of Scottish Natural Heritage. This permission will not be withheld unreasonably. The views expressed by the author(s) of this report should not be taken as the views and policies of Scottish Natural Heritage. © Scottish Natural Heritage 2017. COMMISSIONED REPORT Summary Analyses of the fates of satellite tracked golden eagles in Scotland Commissioned Report No. 982 Project No: 015542 Contractor: Natural Research Year of publication: 2017 Keywords Golden eagle; satellite tagging; Scotland; juvenile dispersal; wind farms; grouse moor; persecution; illegal killing. Background The Cabinet Secretary for Environment, Climate Change and Land Reform requested a thorough investigation of the fates of satellite tagged raptors, especially golden eagles. This report provides a major review of the movements and fates of golden eagles satellite tagged during 2004 - 2016. Of 131 young eagles tracked, as many as 41 (31%) have disappeared (presumably died) under suspicious circumstances significantly connected with contemporaneous records of illegal persecution. These disappearances occurred mainly in six areas of the Highlands (predominantly in the central and eastern Highlands). Some, but not all, areas managed as grouse moors were strongly associated with the disappearance of many of the tagged eagles. Tagging revealed that the persecution of young eagles is suppressing the golden eagle population in the central and eastern Highlands, and hampering overall recovery from historic, widespread persecution. Wind farms were not associated with any recorded golden eagle deaths, and there were very few records of tagged young golden eagles near wind farms. Operations associated with tagging had no discernible adverse effects on the welfare, behaviour or survival of the birds. Main findings Purpose 1. This report addresses the question: is there a pattern of suspicious activity surrounding the ‘disappearance’ of many satellite tagged golden eagles? i Methods 2. The movements and fate of many raptors in Scotland are being studied through the use of satellite transmitters attached to birds. For golden eagles, tags were deployed between 2004 and 2016, with increasing activity in recent years, as transmitters have improved in reliability and ease of attachment. Studies are on-going on golden eagles, white-tailed eagles, ospreys, red kites, hen harriers, peregrines and kestrels. Many of these studies are undertaken by a range of individuals and organisations across the UK, and currently data are at varied stages of being prepared for publication. 3. This report details a comprehensive analysis of the fate of 131 satellite tagged golden eagles (tagged in the nest, and subsequently tracked). 4. Tag fates were cast into eight classes based on a combination of location data, transmitted engineering data and the results of searches for ‘downed’ birds or ‘dropped’ tags at and around the last transmissions’ locations: Still Tracking; Died Natural; Stopped Malfunction; Battery Drained; Dropped Not Suspicious; Dropped Suspicious; Killed (found dead, most were poisoned); and Stopped No Malfunction. 5. Tag deployments are summarised by type, fate-class, year and region (NHZ) of deployment. Last fixes of potentially or known ‘suspicious’ tag fates are illustrated by calendar month. Potentially ‘suspicious’ tag fates almost entirely involved the ‘stopped no malfunction’ class of tag. These fates, involving many birds, were potentially suspicious because of sudden cessation of transmissions but also because no bird or its tag was discovered at or around the location of the last transmission(s). 6. Spatial maps summarise over half a million locations recorded to 15 January 2017 from the transmissions received from the tagged birds in Scotland. Grid references for final fixes of all tags which were not still transmitting as of that last date are presented. Broad spatial patterns in the fates of tagged eagles 7. Tagged eagles ranged widely over most of upland Scotland (especially the Highlands). There was a broad association between last known fixes and the background density of utilisation from the tagged birds’ locations. At a finer scale, however, it was apparent that several potentially suspicious tag fates were unusually concentrated. 8. A cluster analysis of the final locations of ‘stopped no malfunction’ and known ‘killed’ tagged birds fell into two broad areas: a broad ‘Highland’ grouping (four clusters) distinctly central-easterly and heavily populated with relatively concentrated clusters and many records; and a more westerly, looser grouping with four clusters. 9. Within these groupings, six broad geographical clusters were identified, with the most intense concentrations of potentially or actually ‘suspicious’ records in the central/eastern Highlands. These clusters were indicative of an unusual concentration of potential or known suspicious final fixes from many tagged young eagles. This was indicative of external human influences, as no other factor could account for such concentrations. 10. The final locations of these ‘stopped no malfunction’ and killed birds’ tags were unexpectedly spatially connected, suggesting further a human influence. These 39 locations are referred to as ‘stopped no malfunction last fixes’ (snmlfs). There were up to 73 non-snmlf tags in these analyses. ii 11. Nearest neighbour distances (NNDs) were calculated between snmlfs and contrasted with NNDs for a ‘virtual’ set of last fixes drawn randomly from the locations of all tagged birds. Ten analyses were conducted, examining various alternative potential datasets to ensure that the results were robust. 12. The snmlfs were spatially clustered at up to five spatial scales in comparison to what was expected from randomly selected locations of last fixes. Thus, this clustering was not because birds spent more time in the areas where snmfls were recorded. The same results were apparent when the following were analysed: the snmlfs tags; the more reliable 70GPS/GSM tags; and when up to 20 of the 33 snmfls tags were assumed to have actually malfunctioned. Hence, even if many of the latter were undetected malfunctions (and so misclassified) the spatial clustering was still evident. 13. In marked contrast, for the non-suspicious tags there was no difference between their final fixes and randomly selected ‘virtual last fixes’. This provided a robust test of the approach, but also provided further evidence that the snmfls were spatially associated and thereby suspicious. 14. The presence of clusters of snmlfs indicated localised activities that increased the probability that a tag would cease transmitting in those locations. The results strongly indicated that this was due to human influences operating primarily in six clusters, mostly in the central and eastern Highlands. 15. In answer to the question ‘was there a suspicious pattern in the sudden failure to transmit for many tagged eagles?’ The answer was: ‘Yes’. Reliability of different tags 16. Other research deploying the same MTI GPS PTT model tags had not found the same level of the ‘stopped no malfunction’ fate class as recorded in Scotland. A large sample from the USA for golden eagles classified a low rate (c. 2 %) of ‘stopped no malfunction’ fate (the comparable rate for Scotland was about 25 times higher), but for both the USA and Scotland there was a very similar (low) rate of definitely identified malfunction fate (c. 2 %). 17. The MTI GPS PTT tags which formed the backbone of the present project appeared to be intrinsically reliable, similarly so in Scotland and elsewhere, with a very low rate of unexpected malfunction. 18. An analysis of ‘survival rates’ of Scottish 70GPS/GSM tags revealed that ‘stopped no malfunction’ tags had relatively poor ‘survival’ compared to other tags, and was below the tag manufacturer’s expected longevity of ≥ 3 years. Again, this was not consistent with sudden, failed tags suffering an undetected malfunction. 19. A few MTI GPS PTT tags classed as ‘stopped no malfunction’ may have been due to malfunction, but this number would appear to be very small, and not clustered. The results do not indicate a substantive contribution of ‘tag reliability’ to the scale and spatial pattern indicated by the many sudden, ‘stopped no malfunction’ tag fates in Scotland. iii Inferences on human influences on the fate of tagged eagles 20. The results consistently point to a particularly high level of human-caused interference with tagged eagles in Scotland. The following six points are relevant to the human related fate of tagged eagles: a) Physical harm (e.g. lesions and inflammation) and contribution to further disease and possible death through ill-fitting harnesses have been recorded in 22% of 18 red kites in England. However, these results appear illustrative of a specific problem through