Data from the Wetland Bird Survey have contributed to new research showing how Europe's winter population of Smew has redistributed north-eastwards due to milder winter conditions in the last 25 years. The study, involving scientists in 16 countries, also demonstrated that population growth has been twice as fast inside protected areas compared to outside. Many bird species are showing distributional change in response to global warming. New research using data collected by volunteers taking part in the Wetland Bird Survey shows that Europe's winter population of Smew has redistributed north-eastwards due to milder winter conditions in the last 25 years. In the UK, a small population of typically less than 200 Smew (and in mild winters just a few dozen birds) can be found in winter at favoured gravel pits and reservoirs in lowland England. This UK population has approximately halved since the late 1990s. This study, compiled by scientists in 16 countries (including BTO staff) shows that Special Protection Areas (SPAs) scheduled under the EU Birds Directive, facilitate such distribution change across a species’ entire range. Currently, one third of the total population winters in north-eastern Europe, compared to 6% two decades ago. Furthermore, population growth rate in this region was also twice as fast inside EU Birds Directive’s SPAs compared to those outside over the last 25 years. Thus, well designed protected area networks can mitigate the effects of climate change on biodiversity by safeguarding high quality habitat as species adopt new distributions. These findings confirm that the existence of Special Protection Areas assists species to cope with climate change. However, the results also highlighted severe gaps in the EU Special protection Area network, especially in northern parts of the wintering range. Many countries designated their SPAs more than 20 years ago, when no account was taken of the rapid environmental changes now occurring. More than eight out of ten Smew wintering in Latvia and Sweden do so in currently unprotected areas, and in Finland nearly all individuals winter outside the SPA network. Despite this range shift, it is still important to maintain the network at the southern end of the birds’ range, so that they have somewhere to retreat during particularly harsh winters. Studies such as this can help policy makers review protected area networks to ensure they keep pace with the conservation needs of Smew and other species.

BTO research has used information collected by bird ringers to investigate large-scale differences and flexibility in the timing of feather moult across 15 passerine species that breed in the UK. Different moult strategies were found between migrant and resident species, alongside within-species regional variation in moulting schedules. Most passerines replace their 10 primary flight feathers in sequence after breeding, and ringers are encouraged to score the progression of this moult in the birds they catch. This study found significant differences in when species begin to moult, with Blue Tits, which commence this process earliest in the season, replacing feathers more than two months before Bullfinches, the latest moulting species. Data from the Nest Record Scheme showed that these differences can be completely explained by the time at which species finish breeding, and consequently, species that produce only a single-brood each year start moult earlier in the season than multi-brooded species. There was also significant variation in how long species take to complete their post-breeding moult, with long-distance migrants replacing their feathers at a faster rate than the resident species. Migrants achieved this by moulting a greater number of feathers simultaneously than residents. For example, migratory Whitethroats moutled faster than any other species in the study, replacing their primary feathers in about two months by moulting an average of three and a half feathers per wing at one time. Conversely, resident House Sparrows, the slowest moulting species, took nearly four months to complete their moult by only moulting two feathers simultaneously. It is likely that these differences in moult strategies are governed by the constraints each species faces at the end of the breeding season. Residents are unlikely to travel very far from breeding grounds during the winter and can consequently take their time over moult, but a rapid post-breeding moult, although energetically costly, may allow migratory species to undertake their perilous southerly journeys as early and quickly as possible. Within species, there were clear regional differences in the commencement of moult that seemed to influence moult duration. This was particularly apparent in the multi-brooded species, in which moult started later but progressed faster in southern Britain (where the duration of the breeding season was longer) than in the north. This finding demonstrates flexibility within birds’ moult schedules so that a later end to breeding can be compensated for by a faster post-breeding moult. Such flexibility might allow species to change their moult schedules in response to prevailing breeding season conditions. However, this may be constrained by the requirement to complete post-breeding moult prior to migration or the onset of winter, which may be especially limiting for later nesting species.

Aerial surveys that capture high quality photos are increasingly being used to monitor bird populations, but these images are not always good enough to identify birds to species-level. A new study led by the BTO investigates how best to resolve this issue. In certain habitats, aerial surveys can monitor bird populations by taking high quality photos or videos. This is an example of how new technology is revolutionizing monitoring. Such passive survey techniques can often cover a larger area faster than human surveyors can, and may cause less disturbance to the animals concerned. However, these advantages may be offset by the loss of accuracy in identifying species or individuals, as the human ability to take in aspects of size, colour, behavior, habitat and group dynamics (all of which contribute to identification) has not yet been surpassed by technology. A new study led by the BTO has analysed aerial photos of birds at sea taken to estimate species’ population sizes at a site where an offshore wind farm has been proposed. Traditionally birds at such sites have been counted by observers on boats, but digital aerial snapshots are quicker, and therefore avoid the issue of double counting that can arise from boat surveys. However, these aerial photos do not always create an image that is good enough to identify birds to species-level. Only 23% of photographed birds were identified to species-level with any confidence in this study, with some individuals classed only by family, e.g. “auk”. This low proportion identified presented a major hurdle to estimating population sizes. To overcome this problem, the study incorporated data from boat surveys carried out at similar times and places to the aerial surveys. On boat surveys, observers routinely identify the species of up to 95% of the birds they record. Sophisticated statistical models were used to compare the proportions of different species observed on boats with that from planes, allowing “intelligent guesses” to be made on the species identification of birds in the aerial surveys. This is the first time population estimates have been calculated for individual species with uncertain identification. This approach could be applied in a range of situations that do not identify species with certainty, resulting in large-scale, quick, efficient and non-invasive monitoring that has obvious conservation benefits in today’s rapidly changing world.