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BBWC Home > Contents > Discussion > Increasing species 4.4 Increasing species Population changes of 25 species for which our best trend estimate from CBC/BBS (usually over 38 years) or from WBS (usually over 30 years) shows an increase of more than 50% are shown in Table 4.4.1. Four identifiable groups stand out: corvids - Jackdaw, Carrion Crow and Magpie; doves - Woodpigeon, Stock Dove and Collared Dove; insectivores; and some waterbirds. Corvids appear to have benefited from relaxation and decrease of gamekeeping activities in the countryside in recent years, and the increased use of Brassica crops (particularly oilseed rape) has probably been beneficial to the doves. Numbers of Pheasants have also increased but the index for this species is difficult to interpret because it may be influenced by releases of captive-reared birds. The majority of increasing insectivores are species that are associated with woodland but also common in gardens: Great Spotted Woodpecker, Green Woodpecker, Nuthatch, Blackcap, Wren, Long-tailed Tit, Great Tit and Coal Tit. The reasons for these increases are presently unclear. Pied Wagtail has increased in numbers by 87% on CBC/BBS plots over 38 years, but declined by 52% on WBS plots over the past 30 years. The former survey is likely to be more representative of the UK population as a whole. See Help for information
on category definitions 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. The CBC and WBS cannot be said to provide monitoring of a representative portion of the population for most of these species but these results are interesting indicators of changes that may nevertheless be affecting the whole population. We can be confident that Mallard populations have increased greatly as CBC/BBS recorded a 167% increase over 38 years while WBS recorded a 166% increase over 30 years. The growth of this population is still continuing with CBC/BBS recording an 18% increase over the last ten years. 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 Survey of Breeding Waders of Lowland 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 17% increase over the last 25 years. Nevertheless this population has undergone a sustained increase of 63% over the last 76 years (1929–2005). Two widespread raptors have shown strong recoveries from low population levels caused by pesticides, and perhaps also persecution, in the 1950s and 1960s. Buzzards increased by a remarkable 422% between 1967 and 2005, with a rapid increase of 51% over the last 10 years alone. Sparrowhawks showed a 179% increase over the 30-year period from 1975 to 2005. 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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