One-third of English breeding bird species show evidence of population responses to climatic variables over 50 years

Climate change is widely regarded as a major threat to the functioning of natural systems and to the maintenance of species’ populations. Birds are one of the taxa where climate change impacts have been most studied, the research demonstrating a range of documented responses, including advancement in the timing of migration and breeding, poleward shifts in distribution, and changes in community structure. While such work highlights some of the effects of climate change, the attribution of specific changes in species’ populations to a changing climate remains challenging.  The research reported in this paper examines the potential impacts of climate change on individual species for as wide a component of England’s breeding avifauna as is currently possible.

The study used data from the BTO’s Common Bird Census and the BTO/JNCC/RSPB Breeding/Bird Survey to generate annual indices of population change for 68 species, from 1966 to 2015. These data were then examined in relation to changes over time – and differences between regions – in a series of climatic variables derived from the National Oceanic and Atmospheric Administration / Earth System Research Laboratory, Physical Sciences Division series. This enabled Pearce-Higgins and Crick to consider climatic variables across the different geographical regions of relevance to individual species. For example, climatic conditions in England, Iberia and the Sahel region of Africa needed to be considered when examining population changes in those migrant species breeding in England but wintering in Africa’s arid-zone and migrating via Spain and Portugal.

The results of the statistical analyses suggest that climate change has had a measurable effect on the population fluctuations of about a third of the breeding species considered, resulting in notable positive impacts on the abundance of 13 species and notable negative impacts on three species. The majority of the effects found related to climatic conditions within England, which were particularly apparent for resident species during summer and winter. These findings support previous BTO work, highlighting the role of winter temperature as a key driver of resident bird populations, including Goldcrest, Long-tailed Tit and Dunnock.

With the exception of Common Whitethroat, Reed Warbler and Spotted Flycatcher, the study failed to find strong evidence for significant effects of climatic conditions away from the UK impacting on migratory species, something that may reflect the difficulty of assessing climate changes impacts on migratory birds, brought about in part by our incomplete knowledge of the migration routes and wintering areas for many of these species. This emphasizes that research seeking evidence for climatic impacts on species must also include a mechanistic understanding of the potential links between climatic variables and the population of interest. Gaining such understanding is an important component of current BTO work on migrant bird populations, with the knowledge gained on migration routes, wintering areas and differences between regional breeding populations key to future work.

Notes

This work was funded by BTO and Natural England. The annual population trend estimates for England used in this study originate from the BTO Common Bird Census and more recently, from the BTO/JNCC/RSPB Breeding Bird Survey. The latter is supported by a Partnership jointly funded by the BTO, RSPB and JNCC, with fieldwork conducted by volunteers, to whom we are very grateful.