Many long-distance migratory bird species are experiencing severe population declines. These declines are being caused by human-driven changes, such as habitat loss and climate change, but the relative severity of these varies in space and time. Understanding this variation is key to understanding where species might be most exposed to population-limiting effects. This study used 10 years’ worth of satellite data from birds tagged as part of the BTO Cuckoo Tracking Project alongside data on human impacts on the environment (including the location of infrastructure, habitat change and climate change) collected via remote sensing to address these information gaps.
The results showed that although the actual amount of change had been greatest on the breeding grounds, cumulative exposure to changes in direct mortality risk and climate were highest during the Cuckoos’ autumn migration through Europe and the period on their wintering grounds, due to the longer duration of these phases.
There were no clear between-flyway differences in overall exposure during European migration stages but more easterly autumn migratory routes were significantly associated with lower subsequent exposure to anthropogenic impacts in the winter stage, which included migration through tropical Africa to the forests of central Africa and from there through West Africa in spring
This study demonstrates the value of integrating tracking data with remote-sensing data in providing detailed insights on the potential impacts of environmental change and pressures for vulnerable migratory species. Further work is required, however, to establish how exposure to change relates to impacts on birds, since relationships are unlikely to be either linear or proportional.
Identifying when and where organisms are exposed to anthropogenic change is crucial for diagnosing the drivers of biodiversity declines and implementing effective conservation measures. Accurately measuring individual-scale exposure to anthropogenic impacts across the annual cycle as they move across continents requires an approach that is both spatially and temporally explicit—now achievable through recent parallel advances in remote-sensing and individual tracking technologies. We combined 10 years of tracking data for a long-distance migrant, (common cuckoo, Cuculus canorus), with multi-dimensional remote-sensed spatial datasets encompassing thirteen relevant anthropogenic impacts (including infrastructure, hunting, habitat change, and climate change), to quantify mean hourly and total accumulated exposure of tracked individuals to anthropogenic change across each stage of the annual cycle. Although mean hourly exposure to anthropogenic change was greatest in the breeding stage, accumulated exposure to changes associated with direct mortality risks (e.g., built infrastructure) and with climate were greatest during the wintering stage, which comprised 63% of the annual cycle on average for tracked individuals. Exposure to anthropogenic change varied considerably within and between migratory flyways, but there were no clear between-flyway differences in overall exposure during migration stages. However, more easterly autumn migratory routes were significantly associated with lower subsequent exposure to anthropogenic impacts in the winter stage. Cumulative change exposure was not significantly associated with recent local-scale population trends in the breeding range, possibly because cuckoos from shared breeding areas may follow divergent migration routes and therefore encounter very different risk landscapes. Our study highlights the potential for the integration of tracking data and high-resolution remote sensing to generate valuable and detailed new insights into the impacts of environmental change on wild species.
Notes
The BTO Cuckoo Tracking Project was funded by the A. G. Leventis Foundation, BBC Wildlife Fund, Dulverton Trust, BTO including from much appreciated gifts in Wills, Ernest Kleinwort Charitable Trust, Essex and Suffolk Water, Mark Constantine, Tobit Trust and ‘Cuckoo Sponsors and Champions’. The authors thank everyone who provided assistance in the field, Paul and Russell Howey for assistance with PTTs, and BTO Fundraising and Communications teams for vital contributions to the project. CB was funded by a PhD studentship from the Natural Environment Research Council, grant number NE/L002582/1. IC was funded by contract 2021.03224.CEECIND from FCT (Fundação para a Ciência e Tecnologia).
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