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4.4    Increasing species

Population changes of species for which our best trend estimate from CBC/BBS (usually over 39 years) or from WBS (usually over 31 years) shows an increase of more than 50% are shown in Table 4.4.1 below. There are 25 species included, of which 17 have at least doubled their population size over the decades under review. Four groups of species stand out: 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 80% on CBC/BBS plots over 39 years, but declined by 53% on WBS plots over the past 31 years. The former survey is likely to be more representative of the UK population as a whole. The increase in Pheasants is driven largely by the scale of releases for shooting.

A number of species associated with freshwater habitats are also 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 increase of 165% over 31 years. The growth of this population is still continuing, with CBC/BBS recording a 16% increase over the most recent ten-year period. The increases recorded for Mute Swan on both CBC/BBS and WBS plots are likely to be the result of banning the use of lead weights by anglers. Oystercatchers have increased by 122% on WBS plots over the last 30 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. Grey Heron is not listed in Table 4.4.1 because it is covered by a separate survey that spans a much longer period. The population of this species is probably not increasing quite as fast as the species listed in the table, with only a 16% increase over the last 25 years. Nevertheless this population has undergone a sustained increase of 58% over the last 77 years (1929–2006).

Two widespread raptors have shown remarkable recoveries from low population levels caused by pesticides in the 1950s and 1960s, assisted by a relaxation of predator control. Buzzards increased by a remarkable 419% between 1967 and 2006, with a rapid increase of 39% over the last ten years alone. Sparrowhawks, too scarce for CBC to monitor until the mid 1970s, showed a 166% increase over the 31-year period from 1975 to 2006. However, their recovery appears to have been completed earlier than for Buzzard, with the population having been relatively stable since the early 1990s.

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This report should be cited as:
Baillie, S.R., Marchant, J.H., Leech, D.I., Joys, A.C., Noble, D.G.,
Barimore, C., Grantham, M.J., Risely, K. & Robinson, R.A. (2009).
Breeding Birds in the Wider Countryside: their conservation status 2008.
BTO Research Report No. 516. BTO, Thetford. (http://www.bto.org/birdtrends)

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