Consequences of migratory strategies in the context of anthropogenic threats

Buchan, Claire (2021) Consequences of migratory strategies in the context of anthropogenic threats. Doctoral thesis, University of East Anglia.

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Migratory species – particularly long-distance migrants – are facing global population declines. Ongoing anthropogenic transformation of the environment may be disrupting the balance of fitness outcomes thought to drive the evolution and maintenance of migratory behaviours. In this thesis, we use partially migratory systems as natural experiments by which to explore the effects of migration on fitness parameters, and take a spatially explicit approach to quantifying the threats faced by Afro-Palaearctic migratory birds. In a meta-analysis of fitness consequences of migratory strategies, we find a persistent benefit to residency in birds, and across taxa, that fitness benefits of residency are more likely to come from survival than from breeding success. In a case study using long-distance partially migratory lesser kestrels (Falco naumanni), we find weak evidence for carryover effects of migration, with fitness instead better predicted by breeding site. Using risk-vulnerability composite threat-mapping algorithms, we combine remote-sensed maps of anthropogenic risk with distribution ranges of 103 Afro-Palaearctic migratory bird species to relate range-level exposure to population trends. We find evidence that threats relating to direct mortality – particularly in non-breeding ranges – may contribute to the population declines seen in these species. Finally, we use GPS tracking of common cuckoos (Cuculus canorus) as a case study by which to quantify spatiotemporal risk exposure using relevant risk surfaces. Despite greater anthropogenic transformation in Western Europe leading to higher mean hourly risk levels in the breeding season, accounting for temporal exposure reveals that total accumulated risk exposure is greatest in the non-breeding seasons in this species. Overall, this thesis provides evidence to support that the hypothesised fitness benefits conferred to individuals by migrating may be decreasing with spatiotemporal exposure to anthropogenic risks – in some cases possibly mediated by breeding season conditions – and provides a framework for quantifying spatiotemporal threat exposure.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Environmental Sciences
Depositing User: Chris White
Date Deposited: 22 Mar 2022 09:54
Last Modified: 30 Sep 2022 01:38


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