Renewable energy is a key part of strategies to reduce the effects of climate change. However, there are concerns about the potential impacts of large renewable developments, such as offshore wind farms, on wildlife. A significant amount of research has been directed at understanding how these developments may affect marine wildlife, particularly seabirds. Key impacts on seabirds are likely to include increased mortality through collisions with wind turbines, and displacement from preferred foraging areas. However, whilst we can estimate what impact any development may have at an individual level, understanding what this means for the population as a whole is more complex. New research led by Aonghais Cook of the BTO has tested a variety of analytical tools, or models, to assess the likely population-level consequences of the impacts arising from any individual wind farm development. These include tools predicting the likelihood of a given outcome (e.g. the probability of a 25% decline) and those that compare scenarios with and without the development. The results demonstrate that conclusions about the significance of any population-level consequences differ according to the initial assumptions made about a seabird species’ survival, breeding success and population trend. The effect of these assumptions is particularly noticeable for approaches that predict the likelihood of a given outcome. In a world where our knowledge of wildlife populations is often imperfect, this may lead to situations where conclusions about the significance of any population-level impacts are driven by how knowledgeable we are about the population concerned, rather than by the magnitude of any impact. This research suggests that future assessments should compare the outputs of models considering scenarios for wildlife with and without any wind farm development. However, given that our knowledge of the population concerned can influence our conclusions, it is important that all assumptions used in the modelling are clearly stated. Judgement of whether any population-level consequences can be deemed acceptable should then be made with reference to our knowledge of the species concerned and its local, regional, national and international populations, ensuring that decisions about offshore wind farm development are made in the best possible way for wildlife.

The BirdTrends 2020 report is a one-stop shop for authoritative information about the population status of the common breeding birds of the wider UK countryside. The report is based on data gathered by the many thousands of volunteers who contribute to BTO-led surveys.

As the effects of climate change are becoming ever more evident and widespread, methods to measure the impact on ecological communities and to understand how such impacts occur are more valuable. Recently published research, led by the BTO in collaboration with the Centre for Ecology and Hydrology, BioSS, Butterfly Conservation and Rothamsted Research, describes the development of a new indicator for detecting the effect of climate change in British butterflies and moths, which also provides new insights into when species are most sensitive to change. Data from the UK Butterfly Monitoring Scheme and the Rothamsted Insect Survey were used to calculate population trends over a 35 year period and to model each species’ population response to seasonal temperatures. These estimates of species’ responses to temperature can be used to describe communities according to how they have been shaped by temperature - the Community Temperature Response (CTR). A rise in CTR occurs when populations of species which ‘do better’ in warmer conditions increase in abundance more than populations of species whose populations ‘like’ it cold. Using twenty years of butterfly and moth data from twelve UK Environmental Change Network sites run by the Centre for Ecology and Hydrology we tested whether this indicator could track spatial and temporal climate-driven community change. The authors, led by Blaise Martay, predicted that moth and butterfly communities in warmer sites and years would contain more individuals of species that increase in response to rising temperatures, than those in the colder sites and years. Although they didn’t find this relationship if species’ response to annual temperature was used to describe the community, they instead found that communities were shaped by seasonal temperatures. In particular, moth communities were influenced most by summer temperature while winter temperature was the strongest driver of butterfly communities. Importantly, this shows that the CTR indicator can effectively indicate the biological impacts of climate change over time. Seasonal as well as annual temperatures must therefore be considered when predicting species’ vulnerability to climate change. It has been previously assumed that British butterflies will be fairly resilient to climate change because temperatures in Britain are colder than in much of their European range and populations tend to increase in response to warmer summer weather. However, as winter temperatures were found to be the main driver of butterfly community change, British butterflies may be more vulnerable to climate change than previously thought.

As the number of offshore wind farms increases, it is important to correctly assess the impact that these developments can have on wildlife. New research led by the BTO examines this situation for seabirds, considering the current environmental impact assessment process in light of the key factors that determine seabird population dynamics. The construction of offshore wind farms is rapidly increasing as governments aim to reduce carbon emissions. However, since there is a growing body of evidence linking offshore wind farms to increased rates of mortality and displacement in seabirds, many countries require a full assessment of any potential impacts to seabird populations before giving consent for wind farm development. These impact assessments follow the precautionary principle, so that consent decisions are based on estimates of the maximum harm that could be caused to seabird populations. Such assessments typically exclude any consideration of density-dependent processes on the population concerned. Density-dependence can be both positive and negative. Negative density-dependence occurs when, for example, the death of breeding adults frees up space in the population for young birds to join it and become breeders themselves. This process can therefore offset the loss of individuals from a breeding population. Positive density dependence can take place once a population falls below a critical threshold. Small populations might not have the ‘safety in numbers’ benefits of seeing off predators, or have a sufficient numbers of potential mates to make the population sustainable. Populations can change from negative to positive density-dependence should they become too depleted. Seabirds are one of the most threatened bird groups in the world, so understanding the implications of wind farm impact assessments for their breeding populations is crucial. New research by the BTO and the JNCC collated evidence for density-dependent population processes in 31 species. The results found widespread evidence for negative density-dependence, especially amongst the large gulls and auks, meaning that populations may be able to withstand small and infrequent losses associated with renewable energy developments. However, extinctions will still occur if the number of losses is greater than the number of new breeding recruits, and species that are highly vulnerable to wind farm developments include large gulls, small gulls, Gannets, seaducks and divers. The study also showed that positive density-dependence was prevalent in the smaller species that breeding in colonies, such as terns, small gulls and auksThese species are likely to experience accelerated rates of population decline at low densities due to increased predation from large gulls and corvids. For such populations impact assessments that ignore density-dependent processes will underestimate the projected impact of a wind farm and could therefore overlook potential extinction events. Scientifically robust estimates of the expected impacts of wind farms on seabird populations are critical. The evidence for density-dependence in seabird populations indicates that the current impact assessment process does not offer a fully precautionary approach. A more robust approach would be to compare the projected population size with and without the expected population changes associated with the proposed development, and test how this changes under a range of density-dependent scenarios. For more information about this research, please see this blog for the Journal of Applied Ecology.

BTO has been providing advice about the potential ornithological impacts of renewable energy schemes since the 1980s, with BTO scientists working to improve our understanding of the impacts of wind farms on birds in order to help minimise any negative effects. This short BTO Research Note highlights key projects that BTO scientists have been involved in which have helped to improve our knowledge of the interactions between birds and wind farms.