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4.4    Increasing species

Those species that have increased by greater than 50% over the past 31 years on CBC plots and 24 years on WBS plots are shown in Tables 4.4.1 & 4.4.2 respectively. Three identifiable groups stand out: the corvids - Jackdaw, Crow and Magpie; the doves - Woodpigeon, Stock Dove and Collared Dove; and birds of prey - Sparrowhawk and Buzzard. Corvids appear to have benefited from relaxation and decrease of game keeping activities in the countryside in recent years and the increased use of brassica (particularly oilseed rape) crops has probably been beneficial to the doves. The birds of prey have been expanding with the decline of organochlorine pesticides in the environment (which affected productivity and survival) and have also benefited from declines in persecution (e.g. Ratcliffe 1993).

The population size of some resident insectivorous species has also increased. The majority of these are associated with woodland: Green Woodpecker and Great Spotted Woodpecker, Nuthatch, Long-tailed Tit, Great Tit and Wren. The reasons for these increases are presently unclear. Pied Wagtail have increased in number by 78% on CBC plots over 31 years, but declined by 48% on WBS plots over the past 24 years – although neither survey may be entirely representative of the UK population as a whole.

Two migrant insectivorous species have also exhibited large increases in abundance: Reed Warblers and Blackcaps. CBC data indicate that both species have more than doubled in number over the last 31 years. Reed Warblers have also increased by 77% on WBS plots over the last 24 years, although their numbers have fallen by 10% at CES sites over the last 15 years. Again, the reasons for these population increases are currently unclear.

Table 4.4.1 >50% population increases for CBC all habitats 1968-1999

Species Period
(yrs)
Plots
(n)
Change
(%)
Lower
limit
Upper
limit
Comment
Great Tit 31 210 58 . .  
Long-tailed Tit 31 130 65 . .  
Wren 31 220 67 . .  
Pied Wagtail 31 84 78 29 160 Unrepresentative
Jackdaw 31 76 79 17 194  
Coot 31 31 87 23 292 Unrepresentative?
Woodpigeon 31 98 90 14 218  
Crow 31 167 94 . .  
Mallard 31 112 110 61 166  
Magpie 31 157 110 . .  
Reed Warbler 31 24 113 45 277 Unrepresentative?
Nuthatch 31 65 113 57 177  
Blackcap 31 156 127 . .  
Green Woodpecker 31 80 136 86 230  
Great Spotted Woodpecker 31 98 142 89 239  
Little Grebe 31 15 153 2 849 Unrepresentative? small sample
Stock Dove 31 75 183 108 306  
Sparrowhawk 31 37 193 67 490  
Mute Swan 31 20 216 66 487 Unrepresentative? small sample
Shelduck 31 18 300 94 787 Unrepresentative? small sample
Buzzard 31 22 404 236 1040 Unrepresentative?
Collared Dove 31 71 1389 631 3524  
Tufted Duck 31 16 2141 941 5175 Unrepresentative? small sample

See Help for information on category definitions.

Many species associated with freshwater habitats are also becoming more abundant.  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 be affecting the whole population.  We can be confident that Grey Heron populations have increased in England and Wales over the past 70 years and that Mallard populations have increased on both CBC and WBS plots over the last 31 and 24 years respectively. The increases recorded for Mute Swan on both CBC and WBS plots are likely to be the result of banning the use of lead weights by anglers. The factors responsible for these population increases displayed by Coot, Tufted Duck and Shelduck are currently unclear. The increase of Little Grebe on CBC plots contradicts the rapid decline that this species has exhibited on WBS plots, although neither scheme is likely to provide representative monitoring for a species that prefers still water bodies. Two waders have increased in number on WBS plots over the past 14 years: Curlew and Oystercatcher. The forthcoming Survey of Breeding Waders of Lowland Wet Meadows should provide more information on the size of the lowland breeding populations of these species.

Table 4.4.2 >50% population increases for WBS waterways 1975-1999

Species Period
(yrs)
Plots
(n)
Change
(%)
Lower
limit
Upper
limit
Comment
Coot 24 39 62 3 214  
Curlew 24 20 63 4 364 Small sample
Mute Swan 24 44 76 12 152  
Reed Warbler 24 19 77 16 181 Small sample
Oystercatcher 24 23 110 73 164  
Mallard 24 93 192 116 294  

See Help for information on category definitions.

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This report should be cited as:
Baillie, S.R., Crick, H.Q.P., Balmer, D.E., Beaven, L.P., Downie, I.S., Freeman, S.N., Leech, D.I., Marchant, J.H.,
Noble, D.G., Raven, M.J., Simpkin, A.P., Thewlis, R.M. and Wernham, C.V.
(2002) Breeding Birds in the Wider
Countryside: their conservation status 2001. BTO Research Report No. 278. BTO, Thetford. (http://www.bto.org/birdtrends)

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