The latest review of the conservation status of birds in Wales. The report assessed all 220 bird species which regularly occur in Wales. There are now 60 species of bird on the Red List, with 91 on the Amber List and just 69 - less than a third of the total number of species - on the Green List. The latest review of the conservation status of birds in Wales comes 20 years after the first, when the Red List was less than half the length it is today. The report assessed all 220 bird species which regularly occur in Wales. There are now 60 species of bird on the Red List in Wales, with 91 on the Amber List and 69 on the Green List. The Birds of Conservation Concern in Wales report assesses the status of each species against a set of objective criteria. Data sources include the BTO/JNCC/RSPB Breeding Bird Survey and the BTO/RSPB/JNCC Wetland Bird Survey, as well as Bird Atlases and other BTO-led monitoring schemes and citizen science initiatives. These are used to quantify the changing status of the species’ Welsh population. The UK, European and global conservation status of the species is also considered, placing the Welsh population into a wider context. The Red ListSwift, Greenfinch and Rook – familiar breeding species in steep decline across the UK – are among the new additions to the Welsh Red List, which now also includes Purple Sandpiper, on account of a rapidly shrinking Welsh wintering population, and Leach’s Petrel, an enigmatic seabird in decline across its global range. These species now sit alongside well-known conservation priorities, such as Curlew, Hen Harrier and Turtle Dove as birds at risk of being lost from Wales for good. Uplands and woodlands Many of the species on the Red List are found in upland and farmland habitats. Starling, Tree Sparrow, Yellow Wagtail and Yellowhammer can no longer be found in much of Wales, while iconic species of mountain and moorland, such as Ring Ouzel, Merlin and Black Grouse, remain in serious trouble. Wales is well known for its populations of woodland birds; however, many of these – including Lesser Spotted Woodpecker, Willow Warbler and Spotted Flycatcher – also feature on the Red List. Goldcrest, which has seen its Welsh population shrink alarmingly in recent decades, is another new addition. On the coast The assessment for Birds of Conservation Concern Wales 4 took place before the impacts of avian influenza could be taken into account. Breeding seabird species have been struggling in Wales for many years, however, and most were already of conservation concern before the outbreak of this disease. Kittiwake, Puffin, Black-headed Gull, and Common, Arctic and Sandwich Tern remain on the Red List. Wales holds internationally significant numbers of breeding seabirds, making the decline of these colonies a global concern. The Amber ListDeclines in Wheatear, Garden Warbler and House Martin - all migrants which breed in Europe and winter in sub-Saharan Africa - mean these species have moved from the Green List to the Amber List. Many other ‘Afro-Palearctic' migrant species are also in decline, but the potential reasons for this, such as habitat loss and reduced availability of invertebrate prey, are not well understood. Closer to home, the declines in the Welsh Chaffinch population, linked to the disease trichomonosis, have seen the species Amber-listed. A number of other species have been placed on the Amber List because of the wider importance of their Welsh populations, which in each case make up more than half the UK total. Wales is home to more than three-quarters of the UK’s Choughs, for example, so recent declines are cause for concern. The nation’s breeding populations of Manx Shearwater, Pied Flycatcher, Goshawk and Hawfinch also account for more than half the UK total, as does its wintering population of Spotted Redshank. It’s not all bad news, though: some species now on the Amber List have moved up from the Red List, indicating some positive change in their population trends. These include Common Sandpiper, Great Black-backed Gull, Bullfinch, Goldcrest and Pied Flycatcher. The Green ListWhile the report contains much cause for alarm, several conservation success stories shine through. Red Kite was almost lost as a British bird during the first half of the 20th century, when only a handful of pairs remained in remote Welsh valleys. Since then, a sustained conservation effort has brought the species back from the brink. Wales is now home to more than 2,500 pairs of Red Kite and the species has now been moved to the Green List, reflecting this incredible change in fortunes. Song Thrush, Reed Bunting, Long-tailed Tit, Redwing and Kingfisher are among the other species to have gone Green, providing much-needed hope that things can go up as well as down.

New research from BTO investigates the effects of climate change on Willow Warblers. The findings, based on volunteers’ ringing and nest recording data, help to explain why birds breeding in different parts of Britain are being affected in different ways.

BTO research has examined the effects of climate change and habitat loss on the population trends of Willow Warbler and Chiffchaff. These closely related songbirds, tricky to distinguish by eye, share breeding grounds across the UK but migrate to different wintering grounds. While Chiffchaffs mainly migrate to south-west Europe and north-west Africa, with a small number remaining in the UK, Willow Warblers head across the Sahara to the humid zone in central Africa.

Populations of many species of migratory bird are declining in Britain. However, the picture is not equally gloomy across the country. Many species are doing much better in northern Britain than they are in the south. Recent research, led by Cat Morrison at the University of East Anglia in collaboration with BTO staff, has used BTO data to understand why this difference occurs. Among the species faring better in the north is the Willow Warbler. This tiny inter-continental traveller used to be one of our commonest species, but it is now very scarce indeed in some places in the south-east of England. This work combined data from several BTO schemes to better understand the demographic causes of these patterns. By constructing an integrated population model (IPM) for each region, the authors untangled the different effects that productivity (from nest record visits) and survival (from CES captures) have on the number of breeding birds (from the BBS counts). This work shows that while changes in the number of breeding birds are primarily affected by the survival between years, the difference in the overall population trend between the two regions arises as a consequence of differences in productivity. Between 1994 and 2012, annual survival and productivity rates ranged over similar levels in the two regions, but years of good productivity (i.e. lots of chicks fledged) were rarer in the south, where the population is declining. In particular, years of good productivity never coincided with years when the survival rate was also high. In contrast, population growth in the north was fuelled by several years in which good productivity coincided with high survival rates. To assess the importance of this difference we modelled what the population changes might have been in the south using a realistic range of productivity values (including those achieved by birds in northern Britain). This showed that, with productivity similar to their northern cousins, populations in the south would have recovered. Consequently, actions to improve productivity on breeding grounds, for example improving the size and quality of available habitat, especially in areas (such as southern Britain), where there are currently population declines, are likely to be a more fruitful and achievable means of reversing migrant declines than actions to improve survival on the breeding, passage or African wintering grounds.

New BTO research shows a recent imbalance in Willow Warbler sex ratios, with 60% of adult birds being male. Such a skewed ratio has implications for the conservation of this migrant species. Male-biased sex ratios have been documented in a number of bird species, in particular those whose breeding populations are small or in decline. Various reasons have been put forward for why the sex ratio in a population should move away from one-to-one, with sex-related differences in mortality or dispersal behaviour two of the most likely. Understanding which of these factors are important, particularly in the context of why it is that small and/or declining populations show more strongly skewed sex ratios, has important consequences for conservation. One way to establish the importance of potential sex-related differences in mortality, recruitment (the number of young that survive and join the breeding population) and dispersal for small populations is to look at a single species. This should be a species for which we have good information on the local variation in abundance across a wider spatial scale. Using information from the Constant Effort Site Scheme (CES) and the Breeding Bird Survey (BBS), a new BTO study has looked at Willow Warbler – a summer migrant, which winters in Africa and for which there are strong regional differences in both abundance and population trend here in Britain. CES data, which come from standardized mist-netting across a network of study sites, were used to examine sex ratio and the survival rates of male and female birds. BBS data, which come from survey transects monitored in a standardized manner by volunteers, were used to predict the relative abundance of Willow Warblers at each CES site. Sex ratios were found to vary markedly among sites, with more male-biased sites occurring towards the south and east of Britain. Sex ratios, which were closest to equality at those CES sites with the highest levels of Willow Warbler abundance, became significantly more male-biased as relative abundance declined. Interestingly, across Britain, sex ratios have also become significantly more male-biased since 1994, when BBS began; in 1994, similar proportions of males and females were estimated to occur at CES sites, but more recently males comprised roughly 60% of the adult population at these sites. Male survival rates were typically higher than those of the females but, while the results suggest that higher levels of female mortality could be occurring in low-density, skewed populations, this difference is unlikely to explain the widespread occurrence of skewed sex ratios. This suggests that sex-related differences in dispersal and recruitment are likely to also be involved. It is possible that females may preferentially recruit into sites with a high abundance of males, perhaps attracted by high levels of song or by the presence of large amounts of suitable habitat. The results of this work, a collaboration between BTO and the University of East Anglia and part of a wider study, suggest that conservation efforts for this species should focus on maintaining and enhancing those sites capable of supporting those populations that are larger and which have more equal sex ratios. It could be that the fragmentation of suitable habitat is leading to small populations with skewed sex ratios, something that might have profound consequences for this particular Afro-Palaearctic migrant.

Populations of many of the UK-breeding birds that migrate to Africa for the winter are falling rapidly. These trends could be linked to conditions experienced during breeding, over winter, or on migration. Since the early 1990s, the abundance of Willow Warblers, one of Europe’s most numerous long distance migrants, has fallen sharply in the south and east of England, but decreases are less marked or absent in the north and west of England and Scotland. Could these contrasting population trends be explained by differences in the conditions birds are experiencing outside of the UK? New research by the BTO, the University of East Anglia and the Scottish Universities Environmental Research Centre has used stable isotope analysis to answer this question. Stable isotope ratios of elements such as carbon, nitrogen and hydrogen vary across the environment in predictable ways, and therefore provide an indication of large-scale variation in geographic location and environmental conditions (e.g. latitude, precipitation, distance from sea) or smaller-scale variation in local environmental conditions (e.g. habitat, soil type). When animals eat or drink, they incorporate these isotopes into their growing body tissues, such as hair, feathers and claws. Since Willow Warblers moult during the non-breeding season, collecting small samples of these winter-grown feathers during the breeding season allows stable isotope analysis to be used to look for differences in location and timing of moult between and within breeding populations. During the summers of 2008 and 2009 feather samples were taken by ringers at several Constant Effort Sites throughout the UK. Results demonstrated that Willow Warblers breeding in Scotland had different feather stable isotope signatures to those breeding in eastern England. BirdTrack shows that Willow Warblers breeding in southern Britain arrive approximately a fortnight earlier than those breeding in the north. If Willow Warblers breeding in the south moult at different times in Africa than later-arriving northern birds, then this could contribute to the regional variation in isotope signal. While pinpointing exact wintering locations of Willow Warblers is not possible from these data, the regional stable isotope differences may reflect variation in the trophic composition of birds’ diet and location during moult, and/or the timing of it. Such differences could mean that British-breeding Willow Warblers are exposed to non-uniform environmental conditions, which could influence subsequent breeding success and survival rates.