Population changes of species for which our best trend estimate from CBC/BBS (usually over 42 years) or from WBS/WBBS (a maximum of 34 years) shows an increase of more than 50% are shown in Table C1, below. There are 30 species listed: this is three more than last year, with Greylag Goose, Goldfinch and Chiffchaff now added. Twenty of the 27 species have more than doubled their population size over the periods under review.
Two of the fastest-increasing species in this report are, however, not included in Table C1, because their monitoring data cover too short a period. Both are introduced. The population of Ring-necked Parakeet is estimated to have risen by 842% (more than a ninefold increase) over the 14 years 1995–2009. Arguably, however, this is more a conservation problem than a success. An unmitigated success is the growth of the reintroduced Red Kite, now estimated through BBS at 475% during 1995–2009. Attention should also be drawn to the rise of Cetti's Warbler, which has increased by an estimated 267% over the recent ten-year period.
Four groups stand out among the increasing species: corvids – Carrion Crow, Magpie and Jackdaw; doves – Collared Dove, Stock Dove and Woodpigeon; insectivores; and some waterbirds. Corvids appear to have benefited from the decrease of predator control by gamekeepers in recent years, and the increased use of brassica crops (particularly oilseed rape) has probably been beneficial to the larger doves.
The majority of increasing insectivores are woodland species that are also common in gardens: Great Spotted Woodpecker, Green Woodpecker, Nuthatch, Blackcap, Great Tit, Wren, Long-tailed Tit and Coal Tit. The reasons for these increases are presently unclear. Pied Wagtail has increased in numbers by 63% on CBC/BBS plots over 42 years, but declined by 67% on WBS/WBBS plots over the past 34 years. The former index is likely to be more representative of the UK population as a whole. Reed Warbler, also an insectivore, has been expanding its range northwards and westwards and might be benefiting from climate change.
Table C1 Long-term population increases of greater than 50% from CBC/BBS (1967-2009) or WBS/WBBS (1975-2009), using the best survey for each species
Great Spotted Woodpecker
CBC to 1999
|Table C1 Long-term population increases of greater than 50% from CBC/BBS (1967-2009) or WBS/WBBS (1975-2009), using the best survey for each species|
|Greylag Goose||16||WBS/WBBS waterways||461||126||1247|
|Great Spotted Woodpecker||42||CBC/BBS UK||403||264||693|
|Collared Dove||37||CBC/BBS UK||400||240||674|
|Shelduck||31||CBC to 1999||300||94||787||Small sample|
|Mute Swan||42||CBC/BBS UK||234||58||625|
|Green Woodpecker||42||CBC/BBS England||214||132||341|
|Canada Goose||28||WBS/WBBS waterways||169||47||710|
|Stock Dove||42||CBC/BBS England||166||99||302|
|Carrion Crow||42||CBC/BBS England||119||76||175|
|Long-tailed Tit||42||CBC/BBS England||117||60||191|
|Great Tit||42||CBC/BBS UK||110||86||139|
|Reed Warbler||42||CBC/BBS UK||107||15||312|
|Tufted Duck||34||WBS/WBBS waterways||104||-16||426|
|Coal Tit||42||CBC/BBS UK||68||1||190|
|Pied Wagtail||42||CBC/BBS UK||63||24||125|
A number of species associated with freshwater habitats are becoming more abundant, although differences between their ecological requirements make it unlikely that a common causal factor is involved. For Mallard, the CBC/BBS increase was matched by a WBS/WBBS increase of 159% over 34 years. The long-term increases recorded for Mute Swan on both CBC/BBS and WBS/WBBS plots are likely to be the result of banning the use of lead weights by anglers, which took effect in 1986. Greylag Goose, Shelduck, Canada Goose, Tufted Duck, Coot and Goosander are other wildfowl among this report's increasing species. Oystercatchers have increased by 73% on WBS/WBBS plots over the last 34 years. This finding is consistent with the results of the most recent survey of Breeding Waders of Wet Meadows which found that numbers of Oystercatchers using these habitats in England and Wales increased by 51% between 1982 and 2002 (Wilson et al. 2005).
Two widespread raptors have shown remarkable recoveries from low population levels caused by pesticides in the 1950s and 1960s, assisted by a relaxation of illegal predator control by shooting interests. Buzzards increased by a remarkable 652% between 1967 and 2009, with a rapid increase of 88% over the last ten years alone. Sparrowhawks, too scarce for CBC to monitor until the mid 1970s, showed a 147% increase over the 34-year period from 1975 to 2009. However, their recovery appears to have been completed earlier than the Buzzard's, with the population having been relatively stable since the early 1990s.
While Pheasant holds a place in this table, its increase has been driven largely by the hugely increasing scale of releases for shooting, from which the corvids may also have benefited.
This report should be cited as: Baillie, S.R., Marchant, J.H., Leech, D.I., Renwick, A.R., Eglington, S.M., Joys, A.C., Noble, D.G., Barimore, C., Conway, G.J., Downie, I.S., Risely, K. & Robinson, R.A. (2012) BirdTrends 2011. BTO Research Report No. 609. BTO, Thetford. http://www.bto.org/birdtrends