 |
||
 |
||
|
||
|
||
|
BBWC Home > Contents > Discussion > Increasing species 4.4 Increasing species Those species that have increased by more than 50% over the past 35 years on CBC/BBS plots and 27 years on WBS plots are shown in Tables 4.4.1 & 4.4.2 respectively. Four identifiable groups stand out: corvids - Jackdaw, Carrion Crow and Magpie; doves - Woodpigeon, Stock Dove and Collared Dove; insectivores; and 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 resident insectivores are species that are associated with woodland but also common in gardens: Green Woodpecker, Great Spotted Woodpecker, Nuthatch, Long-tailed Tit, Great Tit and Wren. The reasons for these increases are presently unclear. Pied Wagtail has increased in number by 97% on CBC/BBS plots over 35 years, but declined by 47% on WBS plots over the past 27 years. The former survey is likely to be more representative of the UK population as a whole. Two migrant insectivorous species have also exhibited large increases in abundance: Reed Warbler and Blackcap. CBC/BBS data indicate that both species have approximately doubled in number over the last 35 years. Reed Warblers have also increased by 60% on WBS plots over the last 21 years, although their numbers have fallen by 20% at CES sites over the last 18 years. Again, the reasons for these population increases are currently unclear. Table 4.4.1 Population increases of >50% for CBC/BBS 1967-2002. The figures refer to UK indices unless otherwise stated.
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 nevertheless 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/BBS and WBS plots over the last 35 and 27 years respectively. 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. The factors responsible for the population increases displayed by Coot are currently unclear. Oystercatcher have increased markedly on WBS plots over the last 27 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. Table 4.4.2 Population increases of >50% for WBS waterways 1975-2002
See
Help for information on category definitions |
|
|
|
|
BTO
Home | JNCC
Home |
|
|