NOTE: Species accounts are no longer included within the BirdTrends report and all links to individual species in this BirdTrends report now point to the relevant species page in BirdFacts. Species trends can now be viewed in the "Trends Explorer" which allows you to view a range of temporal trends for each species.

Waterbirds

Most waterbird species are increasing in the UK. It is likely that increased water quality and warmer winter temperatures, reducing mortality, are at least partly responsible but there is little direct evidence on the causes of change for most species. For Mute Swan a ban on the use of lead weights substantially reduced mortality in the late 1970s and 1980s, particularly in England, resulting in a population increase (Wood et al 2019). Ingestion of lead shot similarly appears to be associated with population declines in wintering ducks (Green & Pain 2016).

Both Greylag Goose and Canada Goose extensively exploit urban habitats where low mortality rates of adult birds and a relatively high reproductive rate may both contribute to the population increases.

Study of breeding populations of ducks is difficult, the adults are not easy to catch and nest are hard to find and access, so less is known about these species than almost any other group of British birds.

Until the 1990s the Little Egret was a relatively uncommon species, but since the first nesting attempt in 1996 the population has increased rapidly (Musgrove 2002). There is little direct evidence as to why this might be, but a combination of warmer winters, increased water quality and provision of new habitat, in the form of remediated gravel pits may all have played a part. It is likely other species, such as Purple Heron, Great White Egret and Cattle Egret may join the Little Egret as British breeding species in the near future, all have successfully bred for the first time in recent years. Herons and egrets, though, are susceptible to cold winters reducing prey availability and increasing mortality (Holt 2012), and the effects of the recent cold winters can be seen in downturns in the trend of both Little Egret and Grey Heron.

Raptors, Owls and Raven

In the last few decades, most birds of prey have increased in number as a result of reduction in the use of certain pesticides, reductions in persecution and, for some species, changes in habitat availability.

During the 1950s and 1960s the widespread use of organochlorine and organophosphate pesticides reduced population numbers of many raptor species, of which the Peregrine and Sparrowhawk were perhaps best studied, by reducing breeding success (Newton 2013). Following a ban on their use, numbers gradually increased. Being towards the top of the food chain, though, birds of prey remain vulnerable to the risk of secondary poisoning, and there are current concerns more recently around the use of anticoagulant rodenticides which bear further investigation (Christensen et al. 2012; Walker et al. 2013, 2014, 2019).

Concurrent with these changes, increased legal protection of these species led to a reduction in levels of control and persecution, particularly in lowland areas for species such as Buzzard, further contributing to increased numbers (Elliott & Avery 1991). Illegal persecution, in particular of Hen Harrier, remains a problem in some areas though (Murgatroyd et al. 2019). Similar considerations apply to the Raven, which has more also recently been subject to increased licenced control in Scotland; for this species understanding of population dynamics is therefore vital for licencing decisions (Wilson et al. 2019) .

Positive conservation measures have been particularly successful for two species. Provision of nest boxes for Barn Owl increased population numbers from a low-point in the 1960s, however numbers of this of this species fluctuate widely in response to cycles in vole abundance complicating quantification of this effect. Much more clear-cut has been the successful program of re-introductions of Red Kite into areas where they were formerly absent and whose numbers continue to increase (Carter 2001).

The two species found most commonly on farmland (Kestrel and Little Owl) are faring less well, probably due, at least in part, to changes (and intensification) in land management reducing the availability of prey. Habitat availability has apparently played a more positive role in Peregrine populations as they have (re-)colonised urban areas, where individuals have higher breeding success than those nesting in rural areas (Kettel et al 2018b).

Waders

Breeding populations of most waders in Britain are declining, mostly as a result of habitat loss/intensification. They are also among the species most vulnerable to nest predation.

A key reason for the decline in breeding wader species, particularly Lapwing, Redshank, Curlew and Snipe has been the loss of wet grassland through drainage (Wilson et al. 2005a) and more intensive grassland management (Smart et al. 2008). As they nest on the ground, waders are vulnerable to nest predation and densities of generalist predators are higher in UK than elsewhere in Europe (Roos et al. 2018). Some species may also be vulnerable in some habitats to nest trampling from livestock, such as Redshank in saltmarsh (Norris et al. 2003, Malpas et al. 2012).  Habitat loss has concentrated breeding populations into smaller areas increasing their vulnerability (Bolton et al. 2007). Predation of nests is also an issue in other habitats, such as in the Uists where populations of Ringed Plover and other species are declining due to predation by (introduced) hedgehogs (Calladine et al. 2017).

Woodland Residents

Most resident species of woodland habitats are increasing, with the exception of those that have specialised habitat requirements, notably Lesser Spotted Woodpecker, Willow Tit and Marsh Tit.

In part, these increases are due to flexible, generalist nature of the habitat requirements of these species. Most are species of the woodland edge and leafy suburban habitats, in particular, provide a suitable alternative habitat for many, with the extensive provision of food in gardens being an additional attraction. Indeed, those species that have increased their use of gardens the most, such as Great Spotted Woodpecker, Nuthatch and Siskin, have also shown the most positive population trends (Plummer et al. 2019).

In many species this has led to relatively high survival, perhaps particularly overwinter, although warmer winters will also have played a role, contributing to the population increases. One notable recent exception is the Greenfinch, where the population has declined recently as a result of reduced survival induced by a pathogen which is likely to be transmitted at garden feeders (Lawson et al. 2018).

The causes of decline in the woodland specialist species are less clear, but the scale of the changes, especially in Lesser Spotted Woodpecker (which is now so uncommon that we can no longer monitor its population through BBS), Lesser Redpoll and Willow Tit suggest fundamental changes in woodland habitat quality in the last few decades.

Woodland Migratory Species

Population trends in migratory species in woodland habitats depend largely on migration distance: those with shorter migratory journeys (wintering in Europe or North Africa) tend to be increasing, while those with longer journeys (wintering in central Africa) tend to be decreasing (Thaxter et al. 2010).

Increases in the short-distance migratory species are likely a result of climate change and warmer winters, with species such as Chiffchaff and Blackcap able to winter successfully further North than previously, reducing the distance of their migratory journey (Plummer et al. 2015).

Reasons for the declines in the longer distance migratory species are less well known, although in at least some species, such as Nightingale, changes in breeding habitat are thought to be important (Hewson et al. 2005), although this may not be true for all species (Mallord et al. 2016). Conditions on migration (or in the wintering destination) are likely to be important for some species, for example spatial variation in Cuckoo population declines has been linked to the proportion of birds migrating through Spain (Hewson et al. 2016), a route taken by many of our migratory species. However, spatial variation in population trends of Willow Warbler seem more strongly linked to breeding conditions (Morrison et al. 2016), indicating a mix of factors may be involved.

Farmland Resident Species

Most resident species on farmland are declining, or have declined in the past, with these trends generally reflecting fluctuations in food supply.

The declines in farmland bird are well studied and generally relate to the reduced availability of food resources, especially in seeds in winter for species like Yellowhammer and Corn Bunting (e.g. Robinson & Sutherland 2002). These declines generally reverse earlier increases in the 1950s and 60s as agriculture (particularly arable) expanded in extent from a previous low. Food availability in grassland habitats has also likely reduced affecting those that feed primarily on soil invertebrates such as Song Thrush and Starling. Implementation of agri-environment schemes to address these declines has resulted in some positive benefits, but the overall impact has been less clear-cut (Baker et al. 2012; Dadam & Siriwardena 2019). Recent research has also focused on the relative benefits of 'land sparing' (which combines highly intensive agriculture with land set aside for nature) and 'land sharing' (wildlife-friendly farming over a wide area); this suggests that 'land sparing' may promote greater avian diversity than 'land sharing' but that an intermediate approach may be best (Finch et al. 2019).   

In contrast, those species that are increasing have adapted to using other food resources, such as gardens in the case of Goldfinch, Greenfinch and Chaffinch, or oilseed rape in the case of Woodpigeon. Gains in population size of Chaffinch and Greenfinch have largely been reversed in recent years due to the increased incidence of trichomonosis (Lawson et al. 2018).

Farmland Migratory Species

All migratory species living on farmland, with the possible exception of Lesser Whitethroat, are declining in both numbers and range and some (Whinchat, Wheatear) are now restricted to marginal habitats in more upland areas.

The declines have generally been caused by intensification of agricultural practices in both grass (Whinchat, Wheatear, Yellow Wagtail) (e.g. Vickery et al. 2001) and arable (Turtle Dove) (Browne & Aebischer 2001) habitats. The catastrophic decline of the Whitethroat in the late 1960s was caused by drought conditions on its wintering grounds in the Sahelian region of Africa from which it is yet to recover.