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Latest long-term alerts

A standardised system for setting 'alerts' in this report has been agreed between the providers and users of population monitoring information in the UK. Alerts are raised by population declines of 25–50% and of >50% over short, medium and longer terms (five years, ten years and 25+ years respectively) and noted in the 'Alert' column in the population change and demography tables. These help to highlight the scale and timing of declines, and act as an aid to interpreting the trend graphs presented.

These alerts are important for conservation practitioners who need to set priorities for conservation action, but we hope that they will also interest readers of the report more generally. Similar Alerts for wetland birds are provided by the Wetland Bird Survey (Cook et al. 2013).

Our main emphasis in this section is on long-term declines measured over the longest period available (usually 46 years) and over 25 years, which is one of the periods used to determine 'Birds of Conservation Concern' red and amber listing for the UK (Eaton et al. 2015).

Alerts triggered over the short term should be considered as early warnings, indicating that conservation issues may be developing for the species concerned. Some short-term declines might stem, however, from normal fluctuations in abundance, from which the population is able to recover without assistance. The steep decline of a suite of species of similar ecology should be considered as a stronger indication that potential problems may be developing. Details of the methodology used to raise alerts are given in the Methods section.

Where this section discusses red-listed or amber-listed species, it uses the current version of these lists, introduced in December 2015 and abbreviated as BoCC4. The full paper (Eaton et al. 2015) details the criteria by which each listed species qualifies for its red or amber status and these criteria are also summarised on our species pages under 'Conservation listings' (see Key to species texts). Our tables here of red and amber species include only those that met the criteria (red or amber, respectively) for UK breeding population decline.

Long-term trends of 'Birds of Conservation Concern' red-listed species

The species considered in this section are red listed under BoCC4 wholly or partly because of severe UK population declines revealed by annual census data, amounting to more than 50% over the 25-year period 1987–2012, the 43-year period 1969–2012, or both. The latest long-term population changes and alerts for these severely declining species are shown in Table A1, over the maximum period available (usually the 46 years 1967–2013) and over 25 years (1987–2013). This table thus updates the figures that were used to produce the new BoCC4 red list, though only by one year.

The 24 species in Table A1 are listed in descending order of their longest-term percentage change. Turtle Dove is once again the species with the strongest long-term UK decline. Tree Sparrow, which headed this table recently, has shown significant increases in numbers since 1995 and is now in second place. The figures for Lesser Spotted Woodpecker are likely to be a very large underestimate of the current population change, because the species had by 1999 become too rare for further annual monitoring. Were recent data available, this species might easily surpass Turtle Dove and Tree Sparrow in the strength of its decline. Similarly, there is strong evidence that the decline for Woodcock has continued since it was last included in CBC/BBS monitoring.

Table A1 Latest trends for red-listed species

Species Period
(yrs)
Source Change
(%)
Lower
limit
Upper
limit
Alert Comment
Turtle Dove 46 CBC/BBS UK -97 -98 -95 >50  
Turtle Dove 25 CBC/BBS UK -94 -95 -92 >50  
Tree Sparrow 46 CBC/BBS England -95 -98 -92 >50  
Tree Sparrow 25 CBC/BBS England -49 -77 -20 >25  
Willow Tit 46 CBC/BBS UK -92 -97 -86 >50  
Willow Tit 25 CBC/BBS UK -90 -95 -86 >50  
Grey Partridge 46 CBC/BBS UK -91 -94 -87 >50  
Grey Partridge 25 CBC/BBS UK -75 -81 -68 >50  
Nightingale 46 CBC/BBS England -90 -97 -41 >50  
Nightingale 25 CBC/BBS England -63 -76 -35 >50  
Spotted Flycatcher 46 CBC/BBS UK -89 -92 -83 >50  
Spotted Flycatcher 25 CBC/BBS UK -78 -83 -70 >50  
Starling 46 CBC/BBS England -89 -92 -86 >50  
Starling 25 CBC/BBS England -77 -81 -73 >50  
Corn Bunting 46 CBC/BBS UK -88 -94 -79 >50  
Corn Bunting 25 CBC/BBS UK -58 -76 -38 >50  
Tree Pipit 46 CBC/BBS England -86 -94 -76 >50  
Tree Pipit 25 CBC/BBS England -84 -91 -75 >50  
Lesser Redpoll 46 CBC/BBS England -83 -94 -66 >50  
Lesser Redpoll 25 CBC/BBS England -83 -92 -72 >50  
Cuckoo 46 CBC/BBS England -75 -81 -69 >50  
Cuckoo 25 CBC/BBS England -71 -75 -67 >50  
Woodcock 31 CBC to 1999 -74 -88 -49 >50 Small sample
Woodcock 25 CBC to 1999 -76 -88 -51 >50 Small sample
Marsh Tit 46 CBC/BBS UK -74 -83 -67 >50  
Marsh Tit 25 CBC/BBS UK -40 -52 -26 >25  
Linnet 46 CBC/BBS England -74 -81 -65 >50  
Linnet 25 CBC/BBS England -9 -24 12    
Yellow Wagtail 46 CBC/BBS UK -71 -87 -39 >50  
Yellow Wagtail 25 CBC/BBS UK -61 -74 -41 >50  
House Sparrow 36 CBC/BBS England -70 -78 -58 >50  
House Sparrow 25 CBC/BBS England -41 -57 -24 >25  
Skylark 46 CBC/BBS England -63 -70 -56 >50  
Skylark 25 CBC/BBS England -29 -38 -20 >25  
Lesser Spotted Woodpecker 31 CBC to 1999 -60 -81 40   Small sample
Lesser Spotted Woodpecker 25 CBC to 1999 -73 -86 -31 >50 Small sample
Mistle Thrush 46 CBC/BBS UK -59 -65 -50 >50  
Mistle Thrush 25 CBC/BBS UK -41 -49 -34 >25  
Lapwing 46 CBC/BBS UK -57 -78 -34 >50  
Lapwing 25 CBC/BBS UK -53 -64 -37 >50  
Song Thrush 46 CBC/BBS UK -57 -63 -49 >50  
Song Thrush 25 CBC/BBS UK -4 -13 5    
Yellowhammer 46 CBC/BBS UK -56 -64 -47 >50  
Yellowhammer 25 CBC/BBS UK -47 -53 -41 >25  
Grey Wagtail 38 WBS/WBBS waterways -54 -64 -38 >50  
Grey Wagtail 25 WBS/WBBS waterways -27 -40 -12 >25  
Curlew 46 CBC/BBS England -39 -77 26    
Curlew 25 CBC/BBS England -25 -49 1    

For nine species – Tree Sparrow, Marsh Tit, Linnet, House Sparrow, Skylark, Mistle Thrush, Song Thrush, Yellowhammer and Grey Wagtail – the 25-year change is less than 50%, indicating that, while these species meet red-list criteria for long-term change, their rate of decline in more recent years has been slower than for most other red-listed birds. For Linnet and Song Thrush, the 25-year trend is effectively stable. Though Curlew is red listed for its UK breeding population decline, its long-term CBC/BBS trends do not currently meet the >50% criterion: the key information for red listing comes from other surveys.

Long-term trends of declining amber-listed species

There are 25 amber-listed species under BoCC4 that are included in this report, of which about half (13 species) are listed because of UK population declines over the periods 1987–2012 or 1969–2012. Long-term trends are available from annual census data for 12 of these species (all except Swift); their trends are listed in Table A2 in descending order of longest-term percentage change (normally over the 46 years 1967–2013). Where a 25-year change (1988–2013) is available, this is also shown.

Table A2 Latest trends for declining amber-listed species

Species Period
(yrs)
Source Change
(%)
Lower
limit
Upper
limit
Alert Comment
House Martin 46 CBC/BBS England -69 -92 -3 >50  
House Martin 25 CBC/BBS England -54 -79 -11 >50  
Redshank 38 WBS/WBBS waterways -65 -90 -40 >50  
Redshank 25 WBS/WBBS waterways -65 -80 -49 >50  
Willow Warbler 46 CBC/BBS England -62 -72 -51 >50  
Willow Warbler 25 CBC/BBS England -58 -65 -52 >50  
Common Sandpiper 38 WBS/WBBS waterways -50 -63 -39 >25  
Common Sandpiper 25 WBS/WBBS waterways -51 -62 -44 >50  
Meadow Pipit 46 CBC/BBS England -46 -75 -17 >25  
Meadow Pipit 25 CBC/BBS England -30 -49 -7 >25  
Bullfinch 46 CBC/BBS UK -39 -50 -28 >25  
Bullfinch 25 CBC/BBS UK 3 -10 17    
Dunnock 46 CBC/BBS UK -34 -44 -25 >25  
Dunnock 25 CBC/BBS UK 15 4 25    
Dipper 38 WBS/WBBS waterways -31 -49 -5 >25  
Dipper 25 WBS/WBBS waterways -25 -39 -1 >25  
Reed Bunting 46 CBC/BBS UK -25 -43 -1 >25  
Reed Bunting 25 CBC/BBS UK 4 -12 26    
Kestrel 46 CBC/BBS England -22 -44 15    
Kestrel 25 CBC/BBS England -19 -29 -7    
Tawny Owl 46 CBC/BBS UK -11 -52 21    
Tawny Owl 25 CBC/BBS UK -24 -49 -12    
Shelduck 31 CBC to 1999 300 94 787   Small sample
Shelduck 25 CBC to 1999 12 -40 118    

Four amber-listed species raise high alerts, having shown significant declines of greater than 50%, and so potentially are red-list candidates:

  • The English House Martin population shows a statistically significant long-term decline of more than 50%. The species is still therefore a potential candidate for red listing, although BBS data indicate little change since 1995 in the UK as a whole and increases in Scotland and Northern Ireland.
  • Redshank has declined steeply in lowland Britain, according to waterways surveys, raising high alerts; a major decline is also documented for its breeding sites on saltmarsh, and BBS data show that decline has occurred recently across a wide range of habitats. BBS declines do not yet meet the red-list criterion, however.
  • English Willow Warblers clearly meet the red-list criterion for population decline, but there has been little change in Wales and overall change in Scotland and Northern Ireland since 1995 has been upward.
  • Common Sandpiper populations have approximately halved according to the 38-year and 25-year trends, but the long-term trend is marginally below the 50% threshold and only the 25-year trend raises the higher level of alert.

Five species raise only the lower level of alert. Meadow Pipit and Dipper meet the 25% criterion (equivalent to amber listing) in both periods. Populations of Bullfinch, Dunnock and Reed Bunting have been recovering and show stable or increasing trends over the shorter, 25-year period. Though amber listed for population decline, Kestrel, Tawny Owl and Shelduck do not formally raise alerts on the present data.

Long-term declines of species that are not currently red or amber listed (for declines)

This section of the report draws attention to declines which currently surpass red or amber criteria but which were not recognised in the BoCC4 listings (Table A3). These species may be candidates for conservation listing (for declines) at the next review.

Table A3 Long-term trends for declining species not on the red or amber list (for declines)

Species Period
(yrs)
Source Change
(%)
Lower
limit
Upper
limit
Alert Comment
Snipe 38 WBS/WBBS waterways -91 -98 -64 >50 Small sample
Snipe 25 WBS/WBBS waterways -87 -97 -73 >50 Small sample
Little Owl 46 CBC/BBS UK -70 -84 -55 >50  
Little Owl 25 CBC/BBS UK -64 -77 -52 >50  
Little Grebe 38 WBS/WBBS waterways -61 -81 -22 >50  
Little Grebe 25 WBS/WBBS waterways -41 -61 -4 >25  
Whitethroat 46 CBC/BBS UK -57 -68 -43 >50  
Greenfinch 46 CBC/BBS UK -34 -48 -15 >25  
Sedge Warbler 46 CBC/BBS UK -30 -61 1    
Red-legged Partridge 46 CBC/BBS UK -27 -56 11    
Garden Warbler 25 CBC/BBS UK -26 -37 -13 >25  

The WBS/WBBS trend for Snipe is based now on a very small sample of plots, the species having deserted so many of its former riverside haunts. It is currently amber-listed solely because its UK breeding range has contracted sharply, especially in lowland England, and not for UK population decline. BBS data indeed do not show any long-term decline at the UK scale, although numbers have dropped sharply in both Scotland and England during the most recent 10-year period.

Little Owl meets red-list criteria for population decline but, as an species introduced to the UK, is not eligible for any conservation listing. Whereas WBS/WBBS indicates a strong decline for Little Grebe over all timescales, relative stability on BBS squares casts doubt upon the true nature of this species' population trend. Whitethroat also raises a high alert over the long term, but the species is currently in recovery from its sudden losses in the late 1960s and therefore does not warrant a conservation listing.

Greenfinch, Garden Warbler and Sedge Warbler have all decreased by more than 25% and yet are green-listed, though the trend for Sedge Warbler is not quite statistically significant and so does not formally raise an alert. The apparent decline of Red-legged Partridge, which is not statistically significant, is of no conservation concern because the species is not native to the UK.

Declines along linear waterways

The Waterways Bird Survey and Waterways Breeding Bird Survey supplement the results from CBC and BBS, which include all habitat types, by measuring trends in bird populations alongside rivers and canals. Joint WBS/WBBS trends allow trend assessments to be continuous since 1974 for up to 25 species that were covered by WBS. WBBS, ongoing since 1998, includes all bird species but trends are presented here only for waterway-specialist species, for which joint WBS/WBBS trends are available.

For 13 species that are abundant in waterway habitats, WBS/WBBS provides the headline population trend for this report, generally because sample sizes exceed those from CBC/BBS. These species include one that is red-listed (Grey Wagtail), seven amber-listed species (Greylag Goose, Oystercatcher, Common Sandpiper, Redshank, Snipe, Kingfisher and Dipper) and four green-listed species Tufted Duck, Goosander, Little Grebe and Sand Martin), along with Canada Goose, which, as a non-native species in the UK, is excluded from the BoCC4 listings.

For six of the WBS/WBBS headline species that are in decline, latest trends appear also in Tables A1, A2 or A3, as appropriate. Even where WBS/WBBS is not the headline trend for a species, however, the waterways data provide valuable supplementary information from this sensitive habitat.

Table A4 lists all statistically significant declines of greater than 25% recorded from the full period of waterway monitoring (nominally 38 years, 1975–2013).

Table A4 Population declines of greater than 25% recorded by the joint Waterways Bird Survey/Waterways Breeding Bird Survey (WBS/WBBS) between 1975 and 2014

Species Period
(yrs)
Source Change
(%)
Lower
limit
Upper
limit
Alert Comment
Yellow Wagtail 38 WBS/WBBS waterways -97 -99 -94 >50  
Snipe 38 WBS/WBBS waterways -91 -98 -64 >50 Small sample
Redshank 38 WBS/WBBS waterways -65 -90 -40 >50  
Reed Bunting 38 WBS/WBBS waterways -64 -74 -47 >50  
Pied Wagtail 38 WBS/WBBS waterways -63 -72 -55 >50  
Little Grebe 38 WBS/WBBS waterways -61 -81 -22 >50  
Grey Wagtail 38 WBS/WBBS waterways -54 -64 -38 >50  
Sedge Warbler 38 WBS/WBBS waterways -51 -64 -33 >50  
Lapwing 33 WBS/WBBS waterways -50 -75 -9 >50  
Common Sandpiper 38 WBS/WBBS waterways -50 -63 -39 >25  
Moorhen 38 WBS/WBBS waterways -35 -51 -16 >25  
Dipper 38 WBS/WBBS waterways -31 -49 -5 >25  

Six species are included here for which the WBS/WBBS trend is not the headline one and so is not listed in Tables A1–A3. These species are discussed briefly below. The trends for Yellow Wagtail and Reed Bunting are consistent in direction with the 46-year trends reported from CBC/BBS, but the declines on waterways have been more severe. The Pied Wagtail declines along waterways are particularly intriguing because they contrast markedly with the fluctuating but generally upward trend as measured by CBC/BBS.

For Sedge Warbler, the headline trend for the UK is a non-significant 46-year moderate decline, from CBC/BBS. Large fluctuations make trends difficult to determine in this species, but the WBS/WBBS data add firmer evidence that a long-term moderate decrease is in progress.

In the early 1980s, population increase for Lapwing as detected by WBS/WBBS contrasted sharply with decline on CBC/BBS sites but long-term trends from both schemes agree there ha been steep decline. Moorhen numbers have dipped sharply by all measures over the last ten years, perhaps through extra mortality in cold winters, and its long-term WBS/WBBS change has tipped over the alert threshold.

Alerts raised by WBS/WBBS, and long-term increases detected by that index, are tabulated in WBS/WBBS alerts and population increases. A full set of this year's WBS/WBBS trends can be obtained from the Table generator.

Declines on CES plots

The Constant Effort Sites Scheme provides trends from standardised ringing in scrub and wetland habitats. It is possibly our best scheme for monitoring some bird populations inhabiting reed beds but its main objective is to collect integrated data on relative abundance, productivity and survival for a suite of species. The longest trends currently available from the CES cover a period of 29 years (Table A5).

Table A5 Population declines of greater than 25% recorded by the Constant Effort Sites scheme between 1984 and 2014

Species Period
(yrs)
Source Change
(%)
Lower
limit
Upper
limit
Alert Comment
Lesser Whitethroat 29 CES adults -72 -85 -58 >50  
Lesser Whitethroat 25 CES adults -78 -86 -70 >50  
Willow Warbler 29 CES adults -71 -77 -64 >50  
Willow Warbler 25 CES adults -70 -75 -64 >50  
Willow Tit 29 CES adults -64 -87 -17 >50 Small sample
Willow Tit 25 CES adults -68 -90 -34 >50 Small sample
Reed Bunting 29 CES adults -63 -75 -50 >50  
Reed Bunting 25 CES adults -57 -71 -43 >50  
Sedge Warbler 29 CES adults -48 -62 -32 >25  
Sedge Warbler 25 CES adults -62 -69 -52 >50  
Greenfinch 25 CES adults -46 -69 -7 >25  
Reed Warbler 29 CES adults -32 -49 -15 >25  
Song Thrush 29 CES adults -31 -44 -15 >25  
Song Thrush 25 CES adults -31 -42 -18 >25  
Whitethroat 29 CES adults -31 -54 -3 >25  
Whitethroat 25 CES adults -34 -51 -5 >25  

Most of the species that are declining on CES sites show broadly similar trends to those from CBC/BBS or WBS/WBBS data. Willow Tit and Song Thrush are red listed on the strength of their long-term CBC/BBS declines (Table A1). Willow Warbler and Reed Bunting are similarly amber listed (Table A2).

For reasons unknown, CES trends for Whitethroat, Reed Bunting, Sedge Warbler, Song Thrush and especially Lesser Whitethroat and Reed Warbler are considerably more negative than those from census data over similar periods. Both CBC/BBS and WBS/WBBS show strong increases for Reed Warbler, in complete contrast to the CES alert presented here.

Greenfinch and Whitethroat raise CES alerts for the first time this year.

A full set of alerts raised by CES and long-term increases are tabulated in CES alerts and population increases.

 

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