Over the last several decades, anthropogenic emissions (primarily of carbon dioxide (CO2)) have rapidly increased global temperatures and altered climate patterns. Widespread and rapid changes in the atmosphere, ocean, cryosphere and biosphere have occurred, affecting both average conditions and annual variability, in particular the frequency of extreme events. Climate change has already caused substantial damage and increasingly irreversible losses to most species groups in terrestrial, freshwater and marine ecosystems.

Migratory species are vulnerable to a wide range of threats, both climate-related and non-climate- related, as they move between countries and ecosystems on a seasonal basis. This potentially

exposes them to the impacts of climate change at multiple locations along their migration route, with possible interactions and divergence in the timing of cues at these locations. The aim of Part 1 of this review was to critically evaluate the current evidence on the impacts of climate change on migratory species, with regard to the size of those impacts at a population level and the strength of evidence for each. We also use the evidence base to assess migratory species responses and potential adaptations to a changing climate, in order to help identify where international conservation actions are most needed. To achieve this, we carried out a review of the literature on the impacts of climate change on each class of species within the Convention on the Conservation of Migratory Species of Wild Animals (CMS) Appendix I and Appendix II from 2005 to present, to identify new research that has been undertaken since the previous reviews of climate change impacts on migratory species (Robinson et al. 2005; McNamara et al. 2010). The results of this review build on the findings of these previous reviews, highlighting a range of climate change impacts on migratory species, associated adaptations and responses to climate change, and key research gaps. This review finds that the impacts of climate change are becoming increasingly apparent across a range of scales, from species genetics to entire ecosystems. There is now particularly strong evidence of the impacts of climate change on migratory species in aquatic environments, and migratory marine predators across a range of taxa are particularly vulnerable to the negative impacts of warming. Current evidence suggests the effects of warming will be greatest at mid- and high latitudes, whilst changes in precipitation will have the greatest impact at low latitudes. Increases in the severity of extreme events, particularly storms, are having large, but localised, negative consequences on some migratory species groups.

Climate change and migratory species: a review of impacts, conservation actions, indicators and ecosystem services Part 1 – Impacts of climate change on migratory species 5

Overall, there is widespread evidence of changes in the distribution and phenology of migratory species. In particular, poleward range shifts and earlier migration and breeding are already occurring in temperature-driven medium and high latitudes, and more mixed directional shifts are apparent in the tropics, depending on changes in rainfall. The results of this review suggest that evidence on the impacts of climate change is lacking for several species groups, particularly bats, fish, South American grassland birds, and sharks and rays, as well as regionally for species residing in the tropics and Global South.