Tracking the long-distance migrations of Arctic Skuas from their north-east Atlantic breeding grounds revealed complex migration strategies, with mixing of individuals from different populations at important staging areas before the birds reached their southern wintering grounds. Arctic Skuas are long-distance migrant seabirds that have seen large declines in breeding numbers across areas of the north-east Atlantic. Part of these declines has been attributed to poor food availability during the breeding season, exacerbated by predation from Great Skuas, particularly in years where food availability is low. However, Arctic Skuas only spend around a third of the year at their breeding grounds. Therefore, they likely also face a range of threats during the non-breeding season. To shed light on the migration routes and strategies of Arctic Skuas, researchers, including BTO scientists, tracked 131 individuals with small tracking devices called geolocators between 2009 and 2019, collecting information from four breeding populations: Scotland, the Faroe Islands, Norway and Svalbard. This collaboration revealed extensive mixing of Arctic Skuas from different breeding populations during migration in several discrete staging areas. An area of high marine productivity, part of which has recently been designated as a high seas Marine Protected Area, was particularly important to the skuas during both their south-bound (autumn) and north-bound (spring) migrations. Because of their predictable food sources, such staging areas are vital, fuelling long flights to the wintering areas and, during spring, enabling individuals to build up reserves for the upcoming breeding season. This considerable mixing of individuals means that if adverse conditions affect the skuas in these important staging areas, then it has the potential to negatively impact multiple breeding populations through reduced survival or productivity. However, the data also revealed some differences in the migration routes and staging areas of individuals from the different breeding populations. Specifically, during southbound migration, skuas from Scotland largely migrated south through the North Sea and along the Iberian Peninsula, whilst those from the other more northerly populations tended to head west towards the mid-Atlantic staging area. Individuals from Svalbard staged much further west in the Atlantic during both migrations, where they may have encountered different, potentially more favourable, conditions given that the Svalbard population appears to be declining less severely than other populations in the north-east Atlantic. Understanding where long-distance migrants, such as Arctic Skuas, are distributed during migration and the strategies they use is a vital first step in identifying threats that individuals may encounter en route, and how this may affect their survival, productivity and therefore population trends. This new knowledge will help us prioritise future research and conservation actions for this declining charismatic seabird. View the Press release associated with this publication

Seabird populations face many different challenges, from the impacts of a changing climate through to the risks posed by offshore wind farms. Understanding how environmental conditions influence seabird distributions at sea, and therefore interactions with potential threats, at the individual level, can help improve our understanding of the population-level impacts of these challenges. During the 2021 breeding season, BTO scientists tracked 20 Kittiwakes, fitted with small GPS devices, from Whinnyfold – part of the Buchan Ness to Collieston Coast Special Protection Area – in Aberdeenshire. There are several existing offshore wind farms within the vicinity of this Kittiwake colony, with several more proposed for the future. The study found no evidence of habitat selection when averaging across all individuals tracked, with large uncertainty in how the environmental conditions (proxies of prey availability, and including sea surface temperature, sea depth, and the presence and location of ocean fronts) were linked to where the Kittiwakes foraged. Instead, the results revealed considerable variation among individuals. This was not only in the response of individuals to local environmental conditions, but also in the extent to which they visited areas where wind farms had either already been built or are proposed. However overall, the amount of time spent by individual birds within the existing and proposed offshore wind farms’ footprints was relatively low. The study’s results emphasise the importance of understanding individual variation when measuring the impact of specific pressures on Kittiwake, and other seabird populations. By averaging across individuals to focus on population responses, we may be under- or overestimating the impact of potential threats, such as offshore wind farms, on some individuals. This could lead to potential unforeseen consequences on demographic rates, such as survival and breeding success, especially where individual differences are driven by factors such as sex, age or breeding stage.

Protected areas are a key part of the nature conservation toolkit, as shown by recent BTO evidence. Climate change is also having an increasing impact on species. Those impacts will vary between species and habitats, with some likely to be at particularly high risk, and others having the potential to benefit from changing conditions. Protected areas can play a major part in helping protect species and habitats from detrimental climate change impacts, and to promote positive changes, such as providing areas of semi-natural habitat for range-expanding species to colonise. To guide what this means for particular sites, it is important to assess the likely future impacts of climate change on that site, for example by undertaking a climate vulnerability assessment. In this paper, two approaches commonly adopted by Natural England for climate change vulnerability assessments were used to assess the vulnerability to climate change of Special Protection Areas (SPAs) for birds in England; one focused on species, and the other on the habitats. Importantly, the study set out to test whether these two approaches would provide similar results, suggesting that climate vulnerability for habitats and species were linked, or whether they would differ, potentially indicating different aspects of climate vulnerability. Climate vulnerability of birds is different between protected sites, with bird communities in upland habitats the most vulnerable, whilst communities in other habitats had a lower vulnerability. When separating vulnerability between breeding and wintering bird communities, freshwater wetland, heathland and woodland communities were regarded as having a particularly low vulnerability, with many species regarded as potentially expanding in range or abundance in response to climate change. Habitat vulnerability showed a different pattern, with coastal habitats identified as the most vulnerable, and upland habitats the least vulnerable. This comparison shows that measuring climate vulnerability in different ways can help provide additional information to land managers about how best to adapt to climate change. For example, whilst many coastal bird species are not regarded as having high vulnerability to climate change, their habitats are vulnerable, particularly due to climate driven sea-level rise and greater risk of storm surges. The species models did not take account of changes in habitat extent, highlighting the value of this twin assessment. Conversely, many upland species are cold-associated and declining in response to climate change, but their habitats are regarded as having a low vulnerability because they are large, continuous and have heterogeneous topography with potential for microclimates to provide refugia. By comparing species and habitat vulnerability, different responses to climate change can be prioritised. For example, habitat management to increase resilience should be prioritised on SPAs where bird species are projected to respond positively to climate change, but yet their habitats are likely to be adversely impacted. Conversely, targeted species interventions may be required on SPAs where the habitats have low vulnerability, but species are at risk; such interventions are increasingly recognised as having positive impacts on climate vulnerable species. Sites with high species and habitat vulnerability may require a twin approach, but ultimately are most likely to require off-site action at the network rather than individual site level. This study shows the value of using large-scale and long-term data, such as those collected by BTO’s long-term monitoring schemes, to undertake climate vulnerability assessments, and how the results can be used by conservation organisations such as Natural England, to inform the management of protected sites.

Habitat loss and climate change are two major threats to birds and other species globally. To plan effective conservation, we need a good understanding of what is driving declines across different species. There are many examples of research that identifies whether population declines in vulnerable species are primarily driven by habitat change or climate change. However, how these two threats interact to drive biodiversity change is very poorly understood. Without this understanding, conservation measures run the risk of being ineffective, for example, by not planning for the impacts of climate change when deciding where to carry out habitat creation. This collaborative research involving BTO attempted to start understanding how habitat change and climate change interact. The study examined changes in over 1,000 bird, butterfly, moth and plant distributions across the UK over the past 75 years, combined with climate and land-use data, to identify whether long-term (50+ years) and short-term (20 years) community changes, such as to species richness and diversity, were linked to changes in land-use, climate change and the interaction between them. They research also considered whether community changes were linked to the land-use or climate seen in the 1930s. In the short- and long-term across all UK 10-km squares, species richness increased for birds, butterflies and plants. However, warm-adapted species such as Nuthatch generally became more prevalent relative to cold-adapted species (e.g. Kestrel) and species assemblages became more homogenous across the UK, decreasing the overall diversity. The long-term changes were most strongly linked to land-use change. Warming temperatures and wetter conditions also contributed to the long-term trends. Short-term community changes were more associated with baseline conditions than the changes to these conditions, which could suggest a time-lag in observed community changes. The interactions between climate and land-use change were relatively minor. Such interactions had the biggest impact on long-term community changes, with arable habitats enhancing the link between temperature and bird community change, while forest habitats reduced the probable impact of temperature. In the short-term, the link between rising temperatures and the decline of cold-adapted birds was strongest on farmland and in urban habitats compared to in woodland. One of the key findings of this paper was the protective effect of semi-natural grasslands, as these habitats were where community changes were lowest. This indicates the importance of these habitats for maintaining diversity. This project has shown the diversity in species’ responses to drivers of change, highlighting the importance of biological recording and the inclusion of species-level information when devising plans to maintain biodiversity. It also suggests that while accounting for interactions between land-use change and climate change may be less important than predicted, examining how the impacts of climate change may vary on different habitats is an important line of future research to make the best decisions for conservation.

The UK government has pledged to build much-needed new housing that also honours a legal requirement to improve biodiversity. Currently, this is often achieved by compensatory measures ‘off-site’, but BTO research is investigating how biodiversity improvements could be integrated into new developments instead. This study used data from 160 urban sites in England, collected by volunteers taking part in the Wider Countryside Butterfly Survey, in which BTO is a partner. Butterflies were chosen as the species group to investigate because they can be sensitive to small changes in habitat, are commonly seen in urban settings, and can reflect the responses of other insects. The percentage of survey sites covered by different types of land, such as housing, roads, and private gardens, was assessed alongside the connectivity and diversity of green spaces and the quantity of broader habitats in the wider landscape, such as waterbodies and farmland. The resulting analysis quantified how 18 butterfly species responded to 32 different measures of urban environments. Most butterfly species were shown to respond more positively to urban green spaces where management is less frequent, such as grass verges and railway embankments. Higher butterfly counts were also found at urban sites with larger areas of semi-natural grassland, other managed green spaces, and adjacent arable land. Fewer butterflies were seen where the land was highly built up, and the green spaces were more fragmented. Species-specific relationships were also found, for example Holly Blue and Red Admiral thrived in areas with a larger number of smaller, private gardens. These results could be used alongside related BTO research on birds in urban spaces as a new urban-environment biodiversity prediction tool. Practitioners could receive digestible species information, based upon the nature of their development site and the configuration of habitats in their plan. When used over multiple plans, the user should see which support the most species or have the highest likelihood of encounters with particular species or species groups. This could help support developers in creating biodiverse spaces for people to live in, and reduce the reliance on off-site offsetting schemes, meeting the demand for new homes in a way that benefits humans and the natural world alike.