Breeding bird communities on Scottish farms

The Common Birds Census, begun by the British Trust for Ornithology has now been monitoring bird population levels on a nationwide basis since 1962. Separate indices were constructed for Scotland and the rest of Great Britain for 12 of the commonest species. Of the species examined blue tit (Parus caeruleus), wren (Troglodytes troglodytes), song thrush (Turdus philomelos), lapwing (Vanellus vanellus), chaffinch (Fringilla coelebs) and skylark (Alauda arvensis) have increased since 1963 and show very similar population trends to the rest of Great Britain. Whitethroat (Sylvia communis), willow warbler (Phylloscopus trochilus) and swallow (Hirundo rustica) have all declined nationally, the decline in the swallow appears to have begun earlier in Scotland. The blackbird (Turdus merula) and dunnock (Prunella modularis) showed similar upward trends until 1972 when the Scottish population started to decline; a much more noticeable decline in the Scottish robin (Erithacus rubecula) population began in 1966. The total density of territory-holding males has not increased but the biomass has and this is due to more, bigger birds but fewer passerines. The species diversity measured by the Shannon Wiener index (H.) has improved a little since 1971 and it is concluded that during the study period the farmland plots censused in Scotland have on average not shown evidence of deterioration as habitats for territory-holding birds.