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Latest long-term alerts

This report uses a standardised system for setting 'alerts' that has been agreed between the providers and users of population monitoring information in the UK. The system provides alerts to population declines of 25–50% and of >50% over short, medium and longer terms (5 years, 10 years and 25+ years respectively). These help to highlight the scale and timing of declines, and act as an aid to interpreting the trend graphs presented. Our main emphasis is on long-term declines measured over the longest period available (usually 42 years) and over 25 years, which is one of the periods used to determine red and amber listing (Eaton et al. 2009). Alerts triggered over the short term for individual species should be considered as early warnings, indicating that conservation issues may be developing for these species. Some short-term declines might stem, however, from chance 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 alerts and methodology used in this report are given in the methods section.

These alerts are therefore important for conservation practitioners who need to set priorities for conservation action, but we hope that they will also prove of interest to more general readers of the report. Similar alerts for wetland birds are provided by the Wetland Bird Survey (Thaxter et al. 2010). 

Where this section discusses conservation-listed species, it uses the now-current version of these lists, introduced in 2009 and abbreviated as BoCC3. The full paper (Eaton et al. 2009) details the criteria by which each listed species qualifies for its red or amber status. All of the red-listed species that breed in the UK have automatically satisfied criteria for UK decline, but amber-listed birds may be listed for other reasons (see Help on species accounts).

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

The species considered in this section are red-listed wholly or partly because of severe UK population declines revealed by annual census data, amounting to more than 50% either over the 25-year period 1981–2006 or, in four cases (Skylark, Song Thrush, Marsh Tit and Linnet), over the 37-year period 1969–2006. 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 42 years 1967–2009) and over 25 years (1984–2009). The table thus updates the figures that were used to produce the current BoCC3 red list.

The 19 species in Table A1 are listed in descending year=2011&s= of longest-term percentage change. Tree Sparrow heads the table once again, despite significant increases in numbers recorded by BBS over the shorter term. 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.

For Linnet, Marsh Tit, House Sparrow and Skylark, the latest 25-year change is less than 50%, indicating that, while these species meet red-list criteria for long-term change, their recent rate of decline has been lower overall than for most other red-listed birds. On the data we present here, Song Thrush fails to meet any red-list criteria, but by only a narrow margin: its 25-year trend is effectively stable. The 25-year trend for Lapwing is a significant decline of 50% but, as for Lesser Spotted Woodpecker, data quality does not allow us to be 90% confident that a decline occurred over the longer period.  

Table A1 Latest trends for red-listed species

Species Period
(yrs)
Source Change
(%)
Lower
limit
Upper
limit
Alert Comment
Tree Sparrow 42 CBC/BBS England -96 -98 -93 >50  
Tree Sparrow 25 CBC/BBS England -81 -91 -64 >50  
Grey Partridge 42 CBC/BBS UK -91 -93 -87 >50  
Grey Partridge 25 CBC/BBS UK -79 -83 -71 >50  
Turtle Dove 42 CBC/BBS UK -90 -95 -86 >50  
Turtle Dove 25 CBC/BBS UK -86 -91 -81 >50  
Willow Tit 42 CBC/BBS UK -90 -96 -83 >50  
Willow Tit 25 CBC/BBS UK -87 -93 -80 >50  
Spotted Flycatcher 42 CBC/BBS UK -89 -93 -84 >50  
Spotted Flycatcher 25 CBC/BBS UK -81 -87 -74 >50  
Lesser Redpoll 42 CBC/BBS England -89 -96 -74 >50  
Lesser Redpoll 25 CBC/BBS England -93 -97 -87 >50  
Tree Pipit 42 CBC/BBS England -87 -94 -76 >50  
Tree Pipit 25 CBC/BBS England -88 -93 -78 >50  
Starling 42 CBC/BBS England -87 -90 -82 >50  
Starling 25 CBC/BBS England -80 -83 -76 >50  
Corn Bunting 42 CBC/BBS UK -87 -94 -76 >50  
Corn Bunting 25 CBC/BBS UK -76 -88 -61 >50  
Yellow Wagtail 42 CBC/BBS UK -78 -89 -52 >50  
Yellow Wagtail 25 CBC/BBS UK -75 -84 -64 >50  
Linnet 42 CBC/BBS England -76 -82 -70 >50  
Linnet 25 CBC/BBS England -34 -47 -21 >25  
Cuckoo 42 CBC/BBS England -73 -80 -62 >50  
Cuckoo 25 CBC/BBS England -73 -77 -67 >50  
Marsh Tit 42 CBC/BBS UK -72 -80 -62 >50  
Marsh Tit 25 CBC/BBS UK -43 -57 -27 >25  
House Sparrow 32 CBC/BBS England -71 -79 -60 >50  
House Sparrow 25 CBC/BBS England -49 -61 -28 >25  
Skylark 42 CBC/BBS England -63 -69 -58 >50  
Skylark 25 CBC/BBS England -39 -45 -28 >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
Yellowhammer 42 CBC/BBS UK -57 -66 -48 >50  
Yellowhammer 25 CBC/BBS UK -54 -60 -48 >50  
Song Thrush 42 CBC/BBS UK -50 -57 -42 >25  
Song Thrush 25 CBC/BBS UK -2 -15 9    
Lapwing 42 CBC/BBS UK -34 -61 4    
Lapwing 25 CBC/BBS UK -52 -62 -35 >50  

Long-term trends of declining amber-listed species

There are 40 amber-listed species that are included in this report, of which about half (19 species) are listed because of UK population declines over the periods 1981–2006 or 1969–2006. Long-term trends are available from annual census data for 13 of these species, which are listed in Table A2 in descending year=2011&s= of longest-term percentage change (normally over the 42 years 1967–2009). Where available the 25-year change (1984–2009) is also shown.

Table A2 Latest trends for declining amber-listed species

Species Period
(yrs)
Source Change
(%)
Lower
limit
Upper
limit
Alert Comment
Redshank 34 WBS/WBBS waterways -69 -90 -41 >50  
Redshank 25 WBS/WBBS waterways -68 -86 -52 >50  
House Martin 42 CBC/BBS England -64 -89 23    
House Martin 25 CBC/BBS England -66 -90 52    
Whitethroat 42 CBC/BBS UK -61 -73 -49 >50  
Whitethroat 25 CBC/BBS UK 117 80 165    
Willow Warbler 42 CBC/BBS England -60 -71 -49 >50  
Willow Warbler 25 CBC/BBS England -62 -68 -56 >50  
Mistle Thrush 42 CBC/BBS UK -52 -61 -43 >50  
Mistle Thrush 25 CBC/BBS UK -42 -49 -35 >25  
Meadow Pipit 42 CBC/BBS England -50 -77 -23 >25  
Meadow Pipit 25 CBC/BBS England -35 -56 -17 >25  
Bullfinch 42 CBC/BBS UK -45 -57 -31 >25  
Bullfinch 25 CBC/BBS UK -16 -27 -3    
Little Grebe 34 WBS/WBBS waterways -40 -71 15    
Little Grebe 25 WBS/WBBS waterways -22 -58 48    
Common Sandpiper 34 WBS/WBBS waterways -40 -56 -27 >25  
Common Sandpiper 25 WBS/WBBS waterways -44 -55 -32 >25  
Curlew 42 CBC/BBS England -38 -81 16    
Curlew 25 CBC/BBS England -28 -61 18    
Grey Wagtail 34 WBS/WBBS waterways -35 -50 -15 >25  
Grey Wagtail 25 WBS/WBBS waterways 26 9 49    
Dunnock 42 CBC/BBS UK -33 -42 -21 >25  
Dunnock 25 CBC/BBS UK 12 -1 26    
Reed Bunting 42 CBC/BBS UK -20 -40 3    
Reed Bunting 25 CBC/BBS UK 24 4 50    

Four species raise high alerts, having shown significant declines of greater than 50%. Whitethroat shows a massive decline over the 42-year period, since this includes the extraordinary population crash that occurred between 1968 and 1969, but the 25-year period has seen a partial reversal of this decrease. English Willow Warblers meet the red-list criterion for population decline, but it is likely that the overall UK decline has been less severe: Scottish and Welsh trends are not as clear, but show shallow declines over the ten-year period to 2009. 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. Continuing decline for Mistle Thrush has taken its 42-year trend over the 50% threshold for rapid decline. It now joins the list of potential red-list candidates.

Our best estimate of long-term change in the English House Martin population also shows a decline of more than 50%, but statistically it is not significantly different from no change and therefore no alerts are raised for this species. This species is best regarded as data deficient, but may possibly be a future candidate for red listing. BBS data indicate that its numbers have changed little since 1994, however.

Bullfinch was moved from the red to the amber list at the 2009 review. Its 42-year trend is only marginally below the red-list threshold, but the 25-year trend, although significant, is not large enough to raise any alert. Common Sandpiper and Meadow Pipit continue to meet amber-list decline criteria in both periods. Data for Little Grebe and Curlew suggest a similar overall rate of decline but should be treated with caution, as the confidence intervals are very wide. For Little Grebe there is poor agreement since 1994 between WBS/WBBS data and BBS, which may cover a more representative set of habitat types for this species: BBS results show a non-significant increase.

Populations of Dunnock, Grey Wagtail and Reed Bunting are recovering and show stable or increasing trends over the shorter, 25-year period. Reed Bunting now shows only a shallow decline over the 42-year period and has ceased to raise any alerts for population decline.

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 2009 listings (Table A3). These species may be candidates for conservation listing 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 34 WBS/WBBS waterways -92 -98 -81 >50 Small sample
Snipe 25 WBS/WBBS waterways -93 -98 -82 >50 Small sample
Woodcock 31 CBC to 1999 -74 -88 -49 >50 Small sample
Woodcock 25 CBC to 1999 -76 -88 -51 >50 Small sample
Little Owl 42 CBC/BBS UK -54 -71 -25 >50  
Little Owl 25 CBC/BBS UK -60 -72 -45 >50  
Tawny Owl 25 CBC/BBS UK -33 -47 -17 >25  
Dipper 34 WBS/WBBS waterways -32 -49 -15 >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 it is a Species of European Conservation Concern (SPEC category 3) through its moderate decline on the European scale (BiE04). There is ample evidence, however, that its breeding range has contracted sharply, especially in lowland England.

Similarly, Woodcock is currently amber-listed solely because it is a Species of European Conservation Concern (SPEC category 3) through its moderate decline on the European scale (BiE04). The only UK census data indicating a trend are from CBC, which recorded steep declines. Samples were small, however, and the CBC's mapping method was not well suited to monitoring this species: for these reasons, the CBC trend is no longer used to support the species' conservation listing.

Little Owl now meets red-list criteria for population decline but, as an introduced species, is not eligible for any conservation listing. Tawny Owl has newly passed the criteria for amber listing, with a decline >25% over the 25-year period. Although the trends are statistically significant, it should be borne in mind that neither CBC nor BBS field techniques cater well for nocturnal and crepuscular species.

Fluctuations in the UK Dipper population since 1974 appear to be underlain by decrease. The current estimate of long-term change clearly raises an alert but decrease over the 25-year period has been moderate and not statistically significant. 

Declines along linear waterways

The Waterways Bird Survey and Waterways Breeding Bird Survey supplement the results from CBC and BBS, which are more broadly-based surveys, by measuring trends in bird populations alongside rivers and canals. Joint WBS/WBBS trends allow trend assessment to be continuous since 1974 for up to 25 species that were covered by WBS. WBBS, ongoing since 1998, includes all bird species but waterways trends are presented here only for waterway-specialist species, for which joint WBS/WBBS trends are available. A full set of up-to-date WBS/WBBS trends can be obtained from the Table generator.

For several species, such as Canada Goose, Goosander and Kingfisher, that are abundant in waterway habitats, the WBS/WBBS trend provides our headline information on population trends. For Redshank, Little Grebe, Common Sandpiper, Grey Wagtail, Snipe and Dipper, which are also in this category and are in decline, details appear in Tables 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 1975–2009). It does not include Little Grebe, for which the decline is not statistically significant (Table A2). Four species are included for which WBS/WBBS is not the headline trend and so are not listed in Tables A2 or A3. These are discussed briefly below.

The trends for Yellow Wagtail and Reed Bunting are consistent in direction with the 42-year trends reported from CBC/BBS, but in each case the declines on waterways have been more severe. The Pied Wagtail declines along waterways, which are significant in all the periods assessed, are intriguing because they contrast markedly with the fluctuating but generally upward trend as measured by CBC/BBS. The cause of the decline along waterways is currently unknown. For Reed Bunting, recovery along waterways has also been weaker than in the countryside as a whole.

For Sedge Warbler, the headline trend for the UK is a non-significant 42-year shallow decline, from CBC/BBS. Large fluctuations make trends difficult to determine in this species, but the WBS/WBBS data add firmer evidence for a long-term moderate decrease.

 

Table A4 Population declines of greater than 25% recorded by the joint Waterways Bird Survey/Waterways Breeding Bird Survey (WBS/WBBS) between 1975 and 2009

Species Period
(yrs)
Source Change
(%)
Lower
limit
Upper
limit
Alert Comment
Yellow Wagtail 34 WBS/WBBS waterways -94 -98 -89 >50  
Snipe 34 WBS/WBBS waterways -92 -98 -81 >50 Small sample
Redshank 34 WBS/WBBS waterways -69 -90 -41 >50  
Pied Wagtail 34 WBS/WBBS waterways -67 -76 -59 >50  
Reed Bunting 34 WBS/WBBS waterways -58 -69 -40 >50  
Common Sandpiper 34 WBS/WBBS waterways -40 -56 -27 >25  
Sedge Warbler 34 WBS/WBBS waterways -37 -56 -12 >25  
Grey Wagtail 34 WBS/WBBS waterways -35 -50 -15 >25  
Dipper 34 WBS/WBBS waterways -32 -49 -15 >25  

 

 

A full set of alerts raised by WBS/WBBS, and long-term increases detected by that index, are tabulated in WBS/WBBS alerts and population increases.

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 25 years (Table A5).

Most of the species that are declining on CES sites show broadly similar trends to those from CBC/BBS or WBS/WBBS data. Linnet and Willow Tit are red listed on the strength of their CBC/BBS declines (Table A1). Similarly, Willow Warbler, Reed Bunting, and Whitethroat are amber listed.

 

Table A5 Population declines of greater than 25% recorded by the Constant Effort Sites scheme between 1984 and 2009

Species Period
(yrs)
Source Change
(%)
Lower
limit
Upper
limit
Alert Comment
Linnet 25 CES adults -94 -98 -83 >50 Small sample
Willow Warbler 25 CES adults -68 -75 -60 >50  
Lesser Whitethroat 25 CES adults -66 -82 -51 >50  
Reed Bunting 25 CES adults -61 -72 -49 >50  
Willow Tit 25 CES adults -53 -82 -9 >50 Small sample
Sedge Warbler 25 CES adults -40 -58 -24 >25  
Reed Warbler 25 CES adults -35 -49 -13 >25  
Whitethroat 25 CES adults -35 -52 -11 >25  

 

For reasons unknown, CES trends for Lesser Whitethroat, Sedge Warbler and Reed Warbler are considerably more negative than those from census data. Both CBC/BBS and WBS/WBBS show strong increases for Reed Warbler, in clear contrast to the CES data.

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

 

This report should be cited as: Baillie, S.R., Marchant, J.H., Leech, D.I., Renwick, A.R., Eglington, S.M., Joys, A.C., Noble, D.G., Barimore, C., Conway, G.J., Downie, I.S., Risely, K. & Robinson, R.A. (2012) BirdTrends 2011. BTO Research Report No. 609. BTO, Thetford. http://www.bto.org/birdtrends