In the current report, there are 29 species for which our best long-term trends show statistically significant population declines of greater than 50% over periods of 31–46 years (see Latest long-term alerts).
These are Grey Partridge, Little Grebe, Lapwing, Redshank, Woodcock, Snipe, Turtle Dove, Cuckoo, Little Owl, Willow Tit, Marsh Tit, Skylark, House Martin, Willow Warbler, Whitethroat, Starling, Song Thrush, Mistle Thrush, Spotted Flycatcher, Nightingale, House Sparrow, Tree Sparrow, Yellow Wagtail, Grey Wagtail, Tree Pipit, Linnet, Lesser Redpoll, Yellowhammer and Corn Bunting (taxonomic order). Nightingale, for which a CBC/BBS index has not previously been calculated, is a new addition to this list since BirdTrends 2014.
One further species shows a non-significant decline greater than 50% over a long timescale. Change for Lesser Spotted Woodpecker is non-significant over the longest period but only because its monitoring period ceased in 1999: further strong decline has since been logged by Atlas data.
The steepest long-term populations declines we have measured are for Turtle Dove, Tree Sparrow, Willow Tit, Snipe and Grey Partridge, which have all declined by more than 90% since 1967, as almost certainly has Lesser Spotted Woodpecker. Turtle Dove shows the biggest decline of any species in this report and its rate of decline appears to be accelerating towards extinction in the UK.
These 29 species that have halved outweigh the 19 species found to show an equivalent increase, i.e. a doubling of population size, over similar periods, though six further species in this report have more than doubled over shorter periods (see Positive changes). The gap between the numbers of species halving and doubling has widened in recent years.
Except for Little Owl, which as an introduced species is not eligible, and two species moved from amber to green in 2015, all these rapidly declining species already benefit from listing as either red or amber Birds of Conservation Concern (PSoB/BoCC4). The two species moved to green, despite strong decline over the longest term, are Little Grebe, for which monitoring results are conflicting, and Whitethroat, which has shown considerable recovery following losses in the late 1960s.
A further eight species raise lower-level concern, as a result of statistically significant long-term declines of between 25% and 50%. These are Common Sandpiper, Dipper, Garden Warbler, Dunnock, Meadow Pipit, Bullfinch, Greenfinch and Reed Bunting. All of these species are already on the amber list on account of their population declines, except for Garden Warbler and Greenfinch which remain for now on the green list.
In addition, Curlew (now red listed) has also declined by more than 25%, but raises no formal long-term alert because the confidence intervals around its change estimates are too wide.
Three scarcer species with much shorter monitoring histories have also decreased by more than half during just an 18-year period and are already red listed: Pied Flycatcher, Wood Warbler and Whinchat. Six species in this report have more than doubled over equivalent shorter periods (see Positive changes).
This report should be cited as: Robinson, R.A., Marchant, J.H., Leech, D.I., Massimino, D., Sullivan, M.J.P., Eglington, S.M., Barimore, C., Dadam, D., Downie, I.S., Hammond, M.J., Harris, S.J., Noble, D.G., Walker, R.H. & Baillie, S.R. (2015) BirdTrends 2015: trends in numbers, breeding success and survival for UK breeding birds. Research Report 678. BTO, Thetford. www.bto.org/birdtrends