The State of the UK’s Birds (SUKB) report for 2017 reviews the impact of climate change. What is the evidence for those impacts, and how may our bird communities change in the future?

The State of the UK’s Birds (SUKB) 2017.
Hayhow D.B., Ausden M.A., Bradbury R.B., Burnell D., Copeland A.I., Crick H.Q.P., Eaton M.A., Frost T., Grice P.V., Hall C., Harris S.J., Morecroft M.D., Noble D.G., Pearce-Higgins J.W., Watts O. & Williams J.M. 2017. RSPB, BTO, WWT, DAERA, JNCC, NE and NRW, Sandy, Bedfordshire View

Long-term data are required to document the impact that climate change has had upon birds. The best way to provide the scale of data for national reporting is through citizen science. In the UK, volunteer schemes such as the BTO/JNCC/RSPB Breeding Bird Survey (BBS) or BTO/JNCC/RSPB Wetland Bird Survey (WeBS) enable changes in bird populations to be documented across the country, whilst the rise of online systems such as BirdTrack, provide a means for capturing large numbers of observational records from birdwatchers throughout the year (Figure 1).

Figure 1. The reporting rate of Chiffchaff from BirdTrack data, measured by the percentage of complete lists they were recorded in, shows that they arrived earlier in spring 2017 compared to the mean from previous years (historical).

It was analyses of the BTO/JNCC Nest Record Scheme data, where volunteers monitor the timing and fate of individual nesting attempts, that first documented the impact of climate change upon the timing of breeding (Crick et al. 1997). As spring temperatures increase, birds nest earlier (Crick & Sparks 1999). Warming has similarly driven advances in the timing of spring bird migration. A comparison of historical and BirdTrack data has shown that the timing of spring arrival of 14 species of long-distance migrants has advanced by an average of 10 days since the 1960s (Newson et al. 2016). As the timing of autumn migration has become slightly delayed by an average of five days, many of our migrants now remain in the UK for two weeks longer than they did five decades ago. These changes could have population level consequences; the species which have failed to shift their timing of arrival have tended to show long-term population declines (Newson et al. 2016).

Figure 2. Nuthatch populations have increased in recent years, probably as a result of warmer temperatures, driving a significant expansion in the species’ range as it has colonised southern Scotland. Image: Sławek Staszczuk GFDL via Wikimedia Commons

What is the evidence that climate change has affected bird populations in the UK? Long-term population monitoring schemes such as BBS, and its forerunner, the Common Bird Census (CBC) provide the data to answer this question and reveal strong evidence of impacts. During the last 50 years, many of our resident species have increased in abundance, which is at least partly due to a reduction in the severity of winter weather and increases in spring temperature that probably boost breeding success (Pearce-Higgins et al. 2015). Conditions for species, such as the Wren, Robin or Nuthatch, have generally improved through time as the frequency of cold weather events, which can cause high levels of mortality in winter (Robinson et al. 2007), has declined. The same is probably also true for the Grey Heron, the subject of our longest running dataset, which extends back to 1928, and whose population fluctuates in response to severe winter weather (Pearce-Higgins 2017). These increases have driven expansions in the size of many species ranges within the UK (Massimino et al. 2015), and accompanying northward shifts of range margins (Gillings et al. 2015).

Figure 3. In common with many of our resident species, populations of Grey Herons, subject to annual monitoring from 1928, fluctuate in response to winter temperature. Image © JJ Harrison ( CC-BY-SA-3.0 via WIkimedia Commons

Conversely, populations of many of our long-distance migrants have declined during this period (Thaxter et al. 2010, Sullivan et al. 2015). They do not benefit from warmer winter temperatures in the UK, and are more negatively impacted by warming during the spring and summer than residents (Pearce-Higgins et al. 2015), potentially through impacts upon their food resources. Migrant populations are also strongly affected by weather conditions on their African wintering grounds. Those that winter in the Sahel fluctuate in response to the length and intensity of the rainy season there (Ockendon et al. 2014), which affects their overwinter survival rates (Johnston et al. 2016). A wet rainy season in the Sahel, which runs from May to October, ensures high vegetation productivity and abundant insect and fruit resources through the overwinter period for our migrants. Conversely, in a dry year, there is much less food, reducing overwinter survival rates. As a result, UK breeding populations of migrants that winter in the Sahel have fluctuated strongly in relation to changes in Sahel rainfall, declining during the 1970s and 1980s during an extensive drought, but then recovering somewhat as rainfall levels have subsequently increased (Pearce-Higgins & Green 2014). There is even evidence that weather conditions in Africa may affect the timing of breeding and productivity in the UK, although the magnitude of such carry-over effects appear to be small for most species, relative to the impact of weather conditions on the breeding grounds (Ockendon et al. 2013), or on passage (Finch et al. 2014).

Migrants have long-been regarded as particularly vulnerable to climate change. In particular, given that in warmer springs, the peak availability of invertebrate food sources, such as caterpillars, has become earlier, relative to the timing of bird migration and breeding (Thackeray et al. 2010), it has been widely suggested that one of the causes of long-distance migrant decline may be that they are not able to arrive back in the UK sufficiently early to adapt to these earlier springs, causing a phenological mismatch. As outlined above, there is correlative evidence to support this; the migrant species that have failed to advance their timing of arrival have tended to decline in abundance more than those which have arrived earlier (Newson et al. 2016). However, a newly published study suggests that long-distance migrants are not more likely to be affected by such mismatch. Further, the most sensitive species to potential changes in the timing of spring, have not suffered the long-term declines in breeding success that would be expected based upon warming trends (Franks et al. 2017). This either suggests that contrary to expectations, negative impacts of mismatch may operate through reduced post-breeding survival rates rather than breeding success, or that a failure to advance the timing of breeding and population declines are both symptoms of another underlying environmental pressure, rather than cause-and-effect. Despite this, there is widespread evidence that the most important climate change impacts will occur as a result of biotic, rather than abiotic, mechanisms (Ockendon et al. 2014). For example, in the UK, there is growing evidence from both marine (Frederiksen et al. 2006) and terrestrial (Pearce-Higgins et al. 2010) environments that climate change affects bird species by reducing prey populations. There may also be a potential impact of extreme events (Palmer et al. 2017), although more research is required to test this further.

Figure 4. Golden Plover populations in the Peak District respond to changes in cranefly populations, which decline following hot, dry summers. As a result, they may be threatened by future climate change. Image: Dagur Brynjólfsson CC-BY-SA-2.0 via Wikimedia Commons

The future magnitude of climate change in the UK is likely to be much greater than that already experienced. For the reasons outlined above, rising temperatures are likely to have an increasingly negative impact on upland bird species associated with cooler climates (Pearce-Higgins et al. 2017). These, along with our breeding seabirds (Johnston et al. 2013), may be amongst some of the most vulnerable to climate change. Modelled effects of climate change upon the density of breeding birds suggests that it is the species that are already of conservation concern which will be most vulnerable to future change (Massimino et al. 2017). This is probably because they tend to be more climatically limited, as with northern or upland species, or because their ability to respond positively to climate change is more likely to be restricted by habitat availability (Oliver et al. 2017).

Through volunteer citizen science schemes, we have learned a great deal about the impacts that climate change has already had on the breeding bird community in the UK. This enables us to assess the likely future direction of travel that future climate change will cause (see also Ausden et al. 2015). However, predicting the future is difficult, and whilst these projections generally paint a relatively consistent picture, our ability to make specific predictions about any one species is less certain. For this reason, the importance of our long-term monitoring schemes must grow in the future, in order for us to document and understand the future changes that will inevitably occur, and to use that understanding to inform potential management and policy responses.

References and further reading

Ausden, M., Bradbury, R., Brown, A., Eaton, M., Lock, L. & Pearce-Higgins, J. 2015. Climate Change and Britain’s Birdlife: What might we expect? British Wildlife Feb 2015: 161-175. View
Crick, H.Q.P., Dudley, C., Glue, D.E. & Thomson, D.L. 1997. UK birds are laying eggs earlier. Nature 338: 526. View
Crick, H.Q.P. & Sparks, T. H. 1999. Climate change related to egg-laying trends. Nature 399: 423–424. View
Finch, T., Pearce-Higgins, J.W., Leech, D.I. & Evans, K.L. 2014. Carry-over effects from passage regions are more important than breeding climate in determining the breeding phenology and performance of three avian migrants of conservation concern. Biodiversity and Conservation 23: 2427-2444. View
Franks, S.E., Pearce-Higgins, J.W., Atkinson, S., Bell, J.R., Botham, M.S., Brereton, T.M., Harrington, R. & Leech, D.I. 2017. The sensitivity of breeding songbirds to changes in seasonal timing is linked to population change but cannot be directly attributed to the effects of trophic asynchrony on productivity. Global Change Biology DOI: 10.1111/gcb.13960. View
Frederiksen, M., Edwards, M., Richardson, A.J., Halliday, N.C. & Wanless, S. 2006. From plankton to top predators: bottom-up control of a marine food web across four trophic levels. Journal of Animal Ecology 75: 1259-1268. View
Gillings, S., Balmer, D.E. & Fuller, R.J. 2015. Directionality of recent bird distribution shifts and climate change in Great Britain. Global Change Biology 21: 2155–2168. View
Johnston, A., Ausden, M., Dodd, A.M., Bradbury, R.B., Chamberlain, D.E., Jiguet, F., Thomas, C.D., Cook, A.S.C.P., Newson, S.E., Ockendon, N., Rehfisch, M.M., Roos, S., Thaxter, C.B., Brown, A., Crick, H.Q.P., Douse, A., McCall, R.A., Pontier, H., Stroud, D.A., Cadiou, B., Crowe, O., Deceuninck, B., Hornman, M. & Pearce-Higgins, J.W. 2013. Observed and predicted effects of climate change on species abundance in protected areas. Nature Climate Change 3: 1055–1061. View
Johnston, A., Robinson, R.A., Gargallo, G., Julliard, R., van der Jeugd, H., Baillie, S.R. 2016. Survival of Afro-Palearctic passerine migrants in western Europe and the impacts of seasonal weather variables. Ibis 158: 465-480. View
Massimino, D., Johnston, A., Gillings, S., Jiguet, F. & Pearce-Higgins, J.W. 2017. Projected reductions in climate suitability for vulnerable British birds. Climatic Change DOI 10.1007/s10584-017-2081-2. View
Massimino, D., Johnston, A. & Pearce-Higgins, J.W. 2015. The geographical range of British birds expands during 15 years of warming. Bird Study 62: 523-534. View
Newson, S.E., Moran, N.J., Musgrove, A.J., Pearce-Higgins, J.W., Gillings, S., Atkinson, P.W., Miller, R., Grantham, M.J. & Baillie, S.R. 2016. Long-term change in spring and autumn migration phenology of common migrant breeding birds in Britain: results from large-scale citizen science bird recording schemes. Ibis 158: 465-695. View
Ockendon, N., Baker, D.J., Carr, J.A., Almond, R.E.A., Amano, T., Bertram, E., Bradbury, R.B., Bradley, C., Butchart, S.H.M., Doswald, N., Foden, W., Gill, D.J.C., Green, R.E., Sutherland, W.J., Tanner, E.V.J. & Pearce-Higgins, J.W. 2014. Mechanisms underpinning climatic impacts on natural populations: altered species interactions are more important than direct effects. Global Change Biology 20: 2221-2229. View
Ockendon, N., Johnston, A. & Baillie, S.R. 2014. Rainfall on wintering grounds affects population change in many species of Afro-Palaearctic migrants. Journal of Ornithology 155: 905-917. View
Ockendon, N., Leech, D. & Pearce-Higgins, J.W. 2013. Climate effects on breeding grounds are more important drivers of breeding phenology in migrant birds than carry-over effects from wintering grounds. Biology Letters 9: 20130669. View
Oliver, T.H., Gillings, S., Pearce-Higgins, J.W., Brereton, T., Crick, H.Q.P., Duffield, S., Morecroft, M.D., Roy, D.B. 2017. Large extents of intensive land use limit community reorganisation during climate warming. Global Change Biology 23: 2272-2283. View
Palmer, G., Platts, P.J., Brereton, T., Chapman, J.W., Dytham, C., Fox, R., Pearce-Higgins, J.W., Roy, D.B. & Thomas, C.D. 2017. Climate change, climatic variation and extreme biological responses. Philosophical Transactions of the Royal Society B 372: 20160144. View
Pearce-Higgins, J.W. 2017. Birds and Climate Change. British Birds: 388-404. View
Pearce-Higgins, J.W., Beale, C.M., Oliver, T.H., August, T.A., Carroll, M., Massimino, D., Ockendon, N., Savage, J., Wheatley, C.J., Ausden, M.A., Bradbury, R.B., Duffield, S.J., Macgregor, N.A., McClean, C.J., Morecroft, M.D., Thomas, C.D., Watts, O., Beckmann, B.C., Fox, R., Roy, H.E., Sutton, P.G., Walker, K.J. & Crick, H.Q.P. 2017. A national-scale assessment of climate change impacts on species: assessing the balance of risks and opportunities for multiple taxa. Biological Conservation 213: 124-134. View
Pearce-Higgins, J.W., Dennis, P., Whittingham, M.J. & Yalden, D.W. 2010. Impacts of climate on prey abundance account for fluctuations in a population of a northern wader at the southern edge of its range. Global Change Biology 16: 12-23. View
Pearce-Higgins, J.W., Eglington, S.M., Martay, B. & Chamberlain, D.E. 2015. Drivers of climate change impacts on bird communities. Journal of Animal Ecology 84: 943-954. View
Pearce-Higgins, J.W. & Green, R.E. 2014. Birds and Climate Change: Impacts and Conservation Responses. Cambridge University Press, Cambridge. View
Robinson, R.A., Baillie, S.R. & Crick, H.Q.P. 2007. Weather-dependent survival: implications of climate change for passerine population processes. Ibis 149: 357-364. View
Sullivan, M.J.P., Newson, S.E. & Pearce-Higgins, J.W. 2015. Using habitat-specific population trends to evaluate the consistency of the effects of species traits on bird population change. Biological Conservation 192: 343-352. View
Thackeray, S.J., Sparks, T.H., Frederiksen, M., Burthe, S., Bacon, P.J., Bell, J.R., Botham, M.S., Brereton, T.M., Bright, P.W., Carvalho, L.C., Clutton-Brock, T., Dawson, A., Edwards, M., Elliott, M., Harrington, R., Johns, D., Jones, I.D., Jones, J.T., Leech, D.I., Roy, D.B., Scott, W.A., Smith, M., Smithers, R.J., Winfield, I.J. & Wanless, S. 2010. Trophic level asynchrony in rates of phenological change for marine, freshwater and terrestrial environments. Global Change Biology 16: 3304–3313. View
Thaxter, C.B., Joys, A.C., Gregory, R.D., Baillie, S.R. & Noble, D.G. 2010. Hypotheses to explain patterns of population change among breeding bird species in England. Biological Conservation 143: 2006-2019. View

Image top right: Wood Warbler © Steve Garvie CC-BY-SA-2.0 via Wikimedia Commons

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