Contents of report
Breeding Bird Survey
Common Birds Census
Constant Effort Sites
Nest Record Scheme
Waterways Bird Survey
Alerts
Summary
What the categories mean
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4. DISCUSSION
4.2 The 30-year alerts
 
There are 25 species that have declined by greater than 25% over the 30-year period from 1968-98, 16 of which have declined by greater than 50% (see table 4.2.1 and 4.2.2).  The majority are these are on the JNCC’s Conservation Importance List and on the conservation Non-Governmental Organisations’ (NGO) Birds of Conservation Concern List (see section 6 for a description of the categories), although there have been some changes.
 
The species which have not changed status are: Tree Sparrow, Grey Partridge, Corn Bunting, Spotted Flycatcher, Turtle Dove, Song Thrush, Linnet and Skylark, all with declines of greater than 50%; and Dunnock and Blackbird, which have population declines of between 25-49%.
 
4.2.1 New 50% alerts
 
Here we highlight those species which are not on the current JNCC Conservation Importance List or NGO Birds of Conservation Concern List as having a >50% decline (see section 2.7).
 
 
Three other species trigger alerts, but it should be noted that the CBC does not necessarily provide monitoring coverage of a representative portion of their populations.
 
  • Redpoll: was not included on previous conservation listings because the CBC does not cover the centres of its distributional range, particularly in Scotland and Wales.  However, it has shown the second largest population decline, after the Tree Sparrow, and indicates a potential problem in at least a part of its range (lowland England): this is why it has been given an alert here.   Furthermore, it showed substantial range contraction between the two breeding bird atlases (Gibbons et al. 1993).  The causes of these declines are unknown and certainly warrant conservation attention.
  • Tree Pipit: this was not included on previous conservation listings for the same reason as the Redpoll but, again, this upland woodland species has shown substantial population declines in lowland England and may justify an investigation into its ecology.
  • Woodcock:  The Woodcock was previously put on the conservation listings because of a 50% range contraction (between the two breeding bird atlases – Gibbons et al. 1993).  Although the CBC does not cover its distributional range well, its sizeable decline in lowland England may necessitate further investigation.
 
Table 4.2.1  >50% population alerts for CBC all habitats 1968-1998

Species

Period
(yrs)

Plots
(n)

Change
(%)

Lower
limit

Upper
limit

Alert

Comment

Tree Sparrow

30

60

-95

-98

-88

>50

 

Lesser Redpoll

30

43

-90

-95

-84

>50

Unrepresentative?

Grey Partridge

30

60

-83

-88

-77

>50

 

Corn Bunting

30

24

-83

-91

-68

>50

 

Spotted Flycatcher

30

70

-79

-86

-72

>50

 

Tree Pipit

30

33

-77

-88

-65

>50

Unrepresentative

Woodcock

30

20

-70

-85

-48

>50

Unrepresentative? small sample

Starling

30

127

-70

-78

-61

>50

 

Turtle Dove

30

60

-69

-81

-57

>50

 

Willow Tit

30

32

-69

-82

-46

>50

 

Marsh Tit

30

55

-66

-76

-53

>50

 

Song Thrush

30

204

-60

-65

-50

>50

 

Linnet

30

123

-59

-69

-45

>50

 

Whitethroat

30

118

-57

-68

-39

>50

 

Yellowhammer

30

133

-54

-63

-45

>50

 

Skylark

30

121

-53

-62

-45

>50

 

See Help (link to http://www.bto.org/birdtrends/help.htm) for information on what the categories mean

 
4.2.2 New 25% Alerts

 

Here we highlight those species that are not on the current JNCC Conservation Importance List or NGO Birds of Conservation Concern List as having a 25-49% decline (see section 2.7).
 
  • Mistle Thrush: this is the third Turdus thrush species to have declined sufficiently rapidly to be given an alert. The declines of these widespread and closely related species are of considerable conservation concern.  Research on Song Thrush (Thomson et al. 1997) and Blackbird (Siriwardena et al. 1998a) suggests that declines in survival have driven their declines and this may apply to Mistle Thrush too.  The decline of Mistle Thrush has been greater on farmland CBC plots (-59%) than in woodland (-22%), which is presumably its preferred habitat. 
  • Willow Warbler: Detailed analysis of population data, survival rates and breeding performance showed that the decline in the mid-1990s was largely related to a fall in survival rates of adult Willow Warblers in the southern part of its range in the UK (Peach et al. 1995).  Interestingly, its decline is greater on woodland CBC plots (-50%) than on the presumably less preferred habitat found on farmland plots (-21%).
  • Cuckoo: This species has declined more rapidly on woodland plots (-60%) than on farmland CBC plots (-20%).  The reasons for its decline have not been investigated but may be linked to declines in the populations of two key host species: Dunnock and Meadow Pipit.
  • Bullfinch and Reed Bunting: were both on the 50% conservation listing, but over the 30-year period, their declines are just under the 50% mark.  The decline of Bullfinch has been greater on farmland CBC plots (-64%) than on woodland plots (-38%), which presumably reflects its habitat preference.
 
Two other species trigger alerts, but it should be noted that the CBC does not necessarily provide monitoring coverage of a representative portion of their populations.
 
  • Meadow Pipit: this is another essentially upland species, which is not covered adequately by the CBC.  However, unlike Redpoll and Tree Pipit, it is a species of open moor and heathland and its decline in lowland England is worrying, given its key position as the prey of many open country raptors.
  • Lapwing: was originally included on the conservation listings because the UK holds greater than 20% of Europe’s wintering population.  Although the CBC does not monitor Lapwing strongholds in the north and west of the UK, its substantial population decline on lowland England is of conservation concern, especially when combined with information from periodic national surveys (see Lapwing Survey; Wilson et al. 2001).
 
Table 4.2.2  >25% population alerts for CBC all habitats 1968-1998

Species

Period
(yrs)

Plots
(n)

Change
(%)

Lower
limit

Upper
limit

Alert

Comment

Bullfinch

30

137

-50

-59

-40

>25

 

Reed Bunting

30

85

-49

-60

-35

>25

 

Dunnock

30

205

-46

-54

-37

>25

 

Mistle Thrush

30

143

-43

-51

-33

>25

 

Willow Warbler

30

190

-39

-52

-21

>25

 

Lapwing

30

53

-34

-62

-3

>25

Unrepresentative

Meadow Pipit

30

44

-34

-65

-3

>25

Unrepresentative

Cuckoo

30

105

-32

-48

-14

>25

 

Blackbird

30

225

-26

-34

-19

>25

 

See Help (link to http://www.bto.org/birdtrends/help.htm) for information on what the categories mean
 
4.2.3 No longer triggering alerts
 
Three species would no longer need to appear on the current JNCC Conservation Importance List or NGO Birds of Conservation Concern List because they don’t show population declines of >25% over the past 30 years:  Kestrel, Swallow and Goldfinch. 
 
Although the Kestrel doesn’t trigger an Alert over the 30-year period, it still warrants a 25% alert over the 25-year period.  During the first few years of the CBC, the species was increasing from a relatively low point, possibly indicating a recovery from the likely detrimental effects of organochlorine pesticide poisoning.  Its population decline over 25 years is still a concern, given the species’ position at the top of one of the open-farmland food-chains.
 
Swallow and Goldfinch have both now recovered from their population declines, which may have been a consequence of medium-term fluctuations driven perhaps by climatic events or other factors.  In addition, the previous reports used a less sophisticated method of analysis than is employed now, and may have indicated a decline mistakenly.
 
4.2.4 Alerts in farmland and woodland
 
In general, more species raise alerts on farmland plots (17 species) than on woodland plots (12 species) (see Appendix).  Two species have declined sufficiently rapidly to trigger alerts in farmland alone, although not over all CBC plots.  Sedge Warbler declined by 48% on CBC farmland plots over the past 30 years.  Although this is a secondary habitat for Sedge Warblers (and the index is probably unrepresentative of the population as a whole), they nest in crops alongside damp ditches and in oilseed rape fields.  Moorhens have also declined on farmland plots (by 32%), which might be a reflection of the loss of farm ponds.  The trends of both species might reflect the impact of increased drainage on farmland that has impacted on other birds of wet meadows.
 
For a number of species, sufficient samples of plots are censused to allow the comparison of trends on woodland and farmland habitats. For two species the rate of decline has been similar in both habitats: Spotted Flycatcher, Turtle Dove.  Both are Palaearctic-African migrants and it is likely that the declines have been driven by factors acting outside of Britain. 
 
For some, the declines have been greater in farmland than woodland:
 
  • Song Thrush (farm –71%; wood –50%);
  • Bullfinch (farm –64%; wood –38%);
  • Mistle Thrush (farm –59%; wood -22%);
  • Blackbird (farm –42%, wood -12%). 
 
For others, the declines have been greater in woodland than farmland:
 
  • Starling (farm –60%; wood –83%);
  • Linnet (farm –50%; wood –87%);
  • Whitethroat (farm –43%; wood –82%);
  • Yellowhammer (farm –42%; wood –74%);
  • Dunnock (farm –44%; wood –58%);
  • Willow Warbler (farm -21%; wood –50%);
  • Cuckoo (farm -20%; wood –60%). 
 
For the most part these are likely to reflect the habitat preferences of the species, with declines being more rapid and slower to recover in the less preferred habitat. 
 

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The report should be cited as: Baillie, S.R., Crick, H.Q.P., Balmer, D.E., Bashford, R.I., Beaven, L.P., Freeman, S.N., Marchant, J.H., Noble, D.G., Raven, M.J., Siriwardena, G.M., Thewlis, R. and Wernham, C.V. (2001) Breeding Birds in the Wider Countryside: their conservation status 2000. BTO Research Report No. 252. BTO, Thetford. (http://www.bto.org/birdtrends)

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