In the current report, there are 28 species for which our best long-term trends show statistically significant population declines of greater than 50% over periods of 31–48 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, Tree Pipit, Linnet, Lesser Redpoll, Yellowhammer and Corn Bunting (taxonomic order).
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 data are sparse and monitoring ceased in 1999; a 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, Grey Partridge and Nightingale, which have all declined by 90% or more since 1967, as, almost certainly, has Lesser Spotted Woodpecker. Turtle Dove shows the biggest decline of any species in this report (98%) and its rate of decline suggests it may soon disappear as a British breeding bird.
These 28 species that have halved in population size outweigh the 22 species found to show an equivalent increase, i.e. a doubling of population size, over similar periods, although seven 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 narrowed by one species in this year's report.
Except for Little Owl, which as an introduced species is not eligible, and two species that 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 sustained, though limited, recovery following considerable losses in the late 1960s.
A further seven species raise lower-level concern, as a result of statistically significant long-term declines of between 25% and 50%. These are Common Sandpiper, Sedge Warbler, Dunnock, Grey Wagtail, Meadow Pipit, Bullfinch and Greenfinch. All of these species are already on the amber list on account of their population declines, except for Grey Wagtail which is red listed, and Sedge Warbler and Greenfinch which for now remain on the green list. Populations of the first two of these species have fluctuated with little overall trend in recent decades, while recent declines in Greenfinch populations reverse a period of sustained increase. Dipper was listed in this section in the 2016 report, but the long-term decline has now dropped below 25% after a couple of years of increase and is also no longer statistically significant.
In addition, Curlew (now red listed) has declined by more than 25% (as also shown by atlas data), but raises no formal long-term alert because the confidence intervals around its change estimates are too wide.
Two scarcer species with much shorter monitoring histories have also decreased by more than half during just a 20-year period and are already red listed: Wood Warbler and Whinchat. Set against these two species are seven that have more than doubled over equivalent shorter periods (see Positive changes). Pied Flycatcher, also already red listed, declined by between 25% and 50% over a 20-year period.
This report should be cited as: Massimino, D., Woodward, I.D., Hammond, M.J., Harris, S.J., Leech, D.I., Noble, D.G., Walker, R.H., Barimore, C., Dadam, D., Eglington, S.M., Marchant, J.H., Sullivan, M.J.P., Baillie, S.R. & Robinson, R.A. (2017) BirdTrends 2017: trends in numbers, breeding success and survival for UK breeding birds. Research Report 704. BTO, Thetford. www.bto.org/birdtrends