A common issue that many analysts of biological data encounter is that of detectability. For a human population we can (in principle) count every individual. For wildlife though, things are trickier, and only rarely is this possible. Bird’s nests are a good example of this - we cannot find every nest. Some are well hidden, some are out of reach, and some we just miss. When we do find a nest, it is rarely right at the start of egg-laying, mostly we find them when they already have eggs or chicks in them. This makes coming up with unbiased estimates of nest survival and success tricky, especially when considering that the chances of a nest surviving differ depending on whether it contains eggs, or noisy chicks. Fortunately, there are statistical methods that enable us to overcome many of these problems, but they suffer from one problem. They assume that the dates when the eggs were laid and the chicks hatched and subsequently fledged are known. This though is rarely the case, since most nests are not visited every day. Recently our statistician Mark Miller has developed an extension of these statistical methods that enable one to account accurately for this imperfect information. This new method was applied to the thousands of Blackbird nest record cards collected by BTO volunteers between 2003 and 2011. The study particularly focused on whether there was a difference between Blackbirds nesting in gardens and those nesting in the countryside. The results showed that the nest survival of Blackbirds nesting in suburban habitats was higher than in either urban or rural areas. There was also an effect of rainfall. In both town and countryside nests survived better when it was wetter, presumably reflecting better conditions for birds to find the soil invertebrates which make up much of their diet. However, in towns, nest survival was related to rainfall in the weeks preceding nest-laying, so a very immediate effect. In the countryside, by contrast, overall wetness of the soil, which is influenced by rainfall several months previously, was more important. This difference probably reflects the much greater run-off and drainage of surface water in urban areas (because of tarmac), whereas in the countryside moisture is much more evenly distributed in the soil. As rainfall patterns are expected to alter as part of wider climate changes birds in different habitats are likely to respond differently, and some may be constrained in how they are able to do this. Nest recorders will continue to gather data to help understand these changes as we devise solutions to help our birds adapt to the changing environment.

Climate change is a much discussed topic. There has been significant warming in the UK since the 1960s, with land temperature from 2005-2014 0.9°C higher than the 1961-1990 mean, and detectable shifts in rainfall patterns. During this time, there have been significant changes in biodiversity too, with long-term declines in some of our bird species, such as on farmland and in woodland, and in our moths. Other taxa have seen increases however, including some of our mammal species like deer. An important component of our work at BTO is to identify the causes of population changes in our biodiversity. Here, we consider the role that climate change may have played in driving some of these long-term trends. In a collaborative project led by BTO, we analysed data on population trends from the Rothamsted Insect Survey (aphids and moths), the National Bat Monitoring Programme, the UK Butterfly Monitoring Scheme, and the Breeding Bird Survey (birds and mammals). We modelled annual changes in the abundance of over 500 species from these schemes as a function of monthly variation in temperature and precipitation, summarised into a small number of principal components. These models were then used to identify the extent to which long-term population trends were consistent with the trend expected from changes in temperature and precipitation. We used this approach to infer the potential role of climate change in driving these population trends, although a proportion of this contribution may have been related to natural variability in the weather. Our results suggest that climate change may have had a significant impact on the long-term trend of 79 species since the 1970s. Trends of eight rapidly declining species matched the negative impacts of climate change expected from our models, including two birds (Lesser Redpoll and Common Snipe) and six moths (Mottled Umber, Little Emerald, Northern Winter Moth, Twin-spot Carpet, Broom Moth and Minor Shoulder-knot). Positive population trends of four species were consistent with the modelled increases in abundance expected from climate change (Greylag Goose, Canada Goose, Lesser-spotted Pinion and Reeves Muntjac). Across species, moth populations declined by an average of 1.4% per year, half of which was consistent with the expected impact of climate change. Conversely, winged aphid abundance increased annually by 0.7%, of which over 60% may have been caused by climate change. Although it is difficult to definitively attribute long-term trends to climate change, this study suggests that at least some long-term trends in terrestrial biodiversity may have been caused by climate change. Although overall changes in bird, mammal and butterfly populations were not strongly related to climate change, matching the results of previous work on farmland birds, and suggesting that other drivers of change have probably been more important for these groups, our results strongly suggest that climate change may have significantly contributed to the decline of moths, particularly in southern Britain, and to increases in winged aphids. This information helps identify the species that may be most vulnerable to future impacts, and importantly suggests that we need to be closely monitoring trends in the abundance of bird species that rely on moth caterpillars for food.

The State of Nature report is an assessment of how nature is doing across the UK. As well as an overarching assessment of UK flora and fauna, there are separate reports for England, Scotland, Northern Ireland and Wales to look at each country in more depth. The reports pool data and expertise from 53 nature conservation and research organisations, a partnership unparalleled in UK conservation. The BTO is proud to be a founding member of the State of Nature Partnership and our long-term volunteer-based monitoring schemes are key to such assessments. It is extremely important that well-structured monitoring to track changes in biodiversity continues and that good evidence is collected to identify the causes of change. Publicising the results and engagement with the public as well as policy-makers is essential to the success of any project based on citizen science. Report is available in six different versions. The main report covers the whole UK, with the other reports focussing on England, Scotland, Wales (in both English and Welsh) and Northern Ireland (to be published shortly). The report offers: Key findings A comparison of the most important drivers of change Summaries by habitat Case studies Emerging themes for conservation action An explanation of the methodologies used to produce the report