The change in behaviour is one of the most remarkable signs yet of the warming world being caused by climate change, according to the BTO’s Chief Executive, Juliet Vickery, “It is indeed remarkable. We haven’t got to go back too far to remember winters when it would have been impossible for Swallows to survive the freezing temperatures, but as our winters get milder it is something we may see more and more.” Swallows head south at the end of summer because the European winter is too cold for the flying insects on which they feed. And for thousands of years, the return of the bird from its winter quarters in Africa has been one of the key signs of the coming of spring all across Europe. It is greeted with delight and celebrated in the folklore of many countries. A famous Greek vase from 500 BC shows three men looking up at a returning swallow with the caption Spring already! But with the run of mild winters in recent years, a small number of swallows have been able to attempt to spend the winter months here. This year – 2022 – the BTO’s BirdTrack survey of birdwatchers’ regular observations has received almost a hundred reports of up to 12 individual swallows between January 1 and February 1. Most have been seen in the warmer south and south-west of Britain, and also in Ireland. Professor James Pearce-Higgins, the BTO’s Director of Science, said, “To suggest that our winters would be warm enough for swallows to survive would have been unthinkable a few decades ago, but the evidence that our climate is changing is building year by year.” Although the return of the Swallows has been celebrated for thousands of years, until the 20th century it was not known where they went, when they disappeared in the autumn. Some people, even some scientists, thought that they hibernated in the bottom of ponds. Their true destination was only revealed in the early 20th century with the introduction of bird ringing. In December 1912, a Swallow was caught on a farm in Natal, South Africa, bearing a ring which had been placed on its leg 18 months earlier by John Masefield, a solicitor and amateur naturalist, in the porch of his house at Cheadle in Staffordshire. This proved that a bird not much bigger than a matchbox could undertake an immense annual journey that included crossing the Sahara desert. The Swallow is not the only bird being affected by climate change. The BTO’s recent report Climate Change and the UK’s Birds indicated that a quarter of British breeding species might be negatively affected – with one of the British public’s favourite birds, the Puffin, likely to disappear completely. Visit BirdTrack for information about how you can submit your bird observations.

Thanks to the efforts of nearly 10,000 'citizen scientists' we now have a much greater understanding of the UK's breeding Tawny Owls, together with much-needed information on their calling behaviour, that will help future surveys of the species. The results of this study have just been published in the journal Bird Study. Despite being reasonably common, widespread, and easily identifiable from its vocal behaviour, we know surprisingly little about the changing fortunes of the UK's breeding Tawny Owl population. There is evidence for an ongoing but shallow long-term decline in the population since the mid-1980s, but this evidence comes from studies that involve daytime surveys by volunteers. Better information is likely to come from dedicated surveys, carried out at night during the Tawny Owl’s breeding season, when territorial vocal activity is at its peak. Such dedicated surveys typically rely on the use of call playback to elicit responses from territorial birds, a labour-intensive method that limits survey coverage. An alternative approach has been tested using nearly 10,000 volunteer 'citizen scientists' and the results are extremely encouraging. The BTO Tawny Owl Calling Survey set out to establish the factors that influenced Tawny Owl calling behaviour (such as weather conditions and local habitat) and to determine whether the approach could reveal changes in Tawny Owl populations over time. The BTO Tawny Owl Calling Survey was carried out over two separate survey periods (October to March in 2005/06 and 2018/19) and had a particular focus on the impact of urbanisation. Volunteers carried out surveys across each winter period, avoiding evenings that were wet, windy or had poor visibility. They were asked to record whether they heard Tawny Owls calling during the survey period, and to specify the types of Tawny Owl calls heard. The volunteers also collected data on the amount of cloud cover, which was used alongside environmental data from other sources to identify factors that might influence calling behaviour. Some 9,452 volunteers took part in the survey in 2018/19 and 3,465 took part in 2005/06, collectively covering 9,567 sites. Overall, Tawny Owls were reported at least once from 86.8% of sites in 2005/06 and 84.3% of sites in 2018/19, suggesting that Tawny Owl populations have been largely stable over this period. Dr Hugh Hanmer, lead researcher on the project, says, “The data generated by our volunteers inform our understanding of Tawny Owl calling behaviour and of the types of sites where they occur. Importantly, these data can be used to shape the design of future surveys. For example, the results of the volunteers' weekly efforts imply that five or six survey visits would be needed within a survey season to determine with confidence whether Tawny Owls are present at a site or not.” Surveys carried out in the autumn and early winter were more likely to detect an owl at occupied sites than those carried out in the middle of winter, but there was an upturn in activity in early spring. Such patterns almost certainly reflect the changing territorial behaviour over this period, with Tawny Owls likely to be more vocal in the autumn as established adults respond to the settlement of dispersing juveniles, and increase their vocal activity again in spring when breeding begins in earnest. Tawny Owls were less vocal on cloudy nights and when it was raining, but more active on nights when the moon was fuller. The two strongest factors influencing whether or not Tawny Owls were present at a site were the amount of broadleaf woodland cover locally and the amount of artificial light at night, the latter a measure of the degree of urbanisation. Occupancy increased with woodland cover, but declined as the degree of urbanisation (and artificial light at night) increased. Michelle Reeve, BTO Garden BirdWatch Manager (and whose volunteers played an important role in the study), says, “The study demonstrates the tremendous value in being able to use citizen scientists to capture data on Tawny Owls and engage both new and existing volunteers with active participation in science. This is a bird that many of us will know; even if we have never seen one its hooting call is likely to be familiar.”

A passive bat detector, left outside to automatically trigger and record bat calls as they fly over, set up in a garden in West Sussex as part of the Chichester Bat Recording Project, has recorded the social calls of the extremely rare Kuhl’s Pipistrelle. Normally found around the Mediterranean, Kuhl’s Pipistrelle is believed to be a rare visitor to Britain with only a handful of records to date. Kuhl’s Pipistrelle can easily be overlooked because it produces echolocation calls that are very similar to Nathusius’ Pipistrelle, which is commoner in the UK, but its social calls are different and diagnostic. Over three nights this summer, a bat detector used in a garden as part of the citizen science project logged 55 audio recordings that contained the social calls of Kuhl’s Pipistrelle. It is likely that these would have been missed if it wasn’t for the BTO’s Acoustic Pipeline, which identified these automatically as Kuhl’s Pipistrelle, and so flagged that something special had been recorded at this location. Reactions to the discovery Ken and Linda Smith, co-ordinators of the bat recording project for Chichester Natural History Society, said, “We started using the bat detector four years ago, leaving it overnight in the gardens of Society members and their friends and have been amazed by the number of bat records at every garden. Coming across this rare bat is very exciting and shows how much more there is to learn about these fascinating animals.” Dr Stuart Newson, lead scientist on bat monitoring at BTO, said, “I am really excited by this finding. It is thought that the range of Kuhl’s pipistrelle is expanding northwards, so it is interesting to speculate whether this represents a vagrant or an establishing population.”

In the latest report looking at the size of our bird populations the Wren tops the list with 11 million pairs across the UK. The latest report, Population estimates of birds in Great Britain and the United Kingdom shows that the Wren continues to hold the title of our commonest bird – the last report in 2013 also had Wren at the top of the list but with a population of just over 8.5 million pairs. Wren numbers are known to fluctuate according to environmental conditions and it may be that generally milder winters are benefitting one of our smallest birds. The top five are made up of Wren, Robin (7,350,000 pairs), House Sparrow (5,300,000), Woodpigeon (5,150,000) and Chaffinch and Blackbird share the number five spot at 5,050,000 territories each. It is estimated that there are around 85 million breeding pairs of birds in the UK altogether, just over one and a quarter pairs for each of us. This is similar to the last estimate calculated in 2013. There are also 20 species whose populations are more than 1 million pairs. As always there have been winners and losers. One of the most shocking falls in numbers is that seen by the Turtle Dove, down from 75,000 pairs in 1997 to an estimate of just 3,600 pairs in the latest report, and, there are now no breeding waders in the UK that have a breeding population greater than 100,000 pairs, with Lapwing and Oystercatcher falling below this for the first time. Almost as surprising is the fall in number for one of our most familiar of birds, the Chaffinch. Since the last report, seven years ago, the Chaffinch breeding population has fallen by 1.15 million pairs - the drivers of which are unclear and need further investigation. Lead author of the paper, Ian Woodward of the British Trust for Ornithology (BTO), said, “It is great to have these latest estimates of the numbers of our birds. Knowing how many of which species we have is important for many reasons, not least of which is the ability to make better informed decisions when it comes to conservation policy and site management. It is thanks to the thousands of volunteers that take part in a variety of bird surveys that we have the data and are able to produce these figures at all.” There have been three other avian population estimates all published in the journal British Birds, the first in 1997, followed by others in 2006 and 2013. For more on the report