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
4.3 Alerts over shorter time periods
 
With the introduction of the new system, alerts are raised over shorter time periods of 25 years (for direct comparison with the original conservation listing process), 10 years and 5 years, to allow a ready assessment of the pattern and timing of the rates of declines among species.
 
4.3.1 Common Birds Census Alerts
 
There are relatively few major differences between the alerts raised at 25 years and those at 30 years already discussed. Four additional species raise alerts at 25 years:
 
  • House Sparrow (>50%): has been incompletely monitored by CBC because of its strong urban component to its population and because data were not gathered systematically before 1973. However, the BTO's Garden Bird Feeding Survey also shows large population declines in the suburban population (Glue 1994).
  • Lesser Spotted Woodpecker (>50%): shows a population increase in the late 1960s and early 1970s, followed by sustained decline. The increase may have been due to the increase in dead wood due to the effect of Dutch Elm Disease, but the decline is similar to that shown by a variety of other woodland specialists, such as Marsh and Willow Tits.
  • Kestrel (>25%): this is discussed above in section 4.2.3.
 
In addition,
  • Goldcrest (>50%): Although this might be viewed with some scepticism because its population is subject to large annual fluctuations due to the weather, its smoothed population trend shows a sustained decrease which contrasts it strongly with the population recoveries shown by two other small-bodied resident insectivores: Wren and Long-tailed Tit. However, it should be noted that the CBC monitors relatively few pure conifer woods and that most Goldcrests are recorded in relatively small numbers on plots that consist mainly of non-conifer habitats.
 
Complete tables of those species triggering alerts at 25, 10 and 5 years are given in Appendix 1.
 
4.3.2 Waterways Bird Survey Alerts
 
The WBS has only been in operation for 23 years and 5 species trigger alerts over that time period (Table 4.3.2).
 
  • Yellow Wagtail: the decline of this species by 81% over 23 years is extremely serious and may reflect a deterioration of the riverine habitat quality and management, or of the suitability of any adjacent farmland for foraging. This supports the more widespread impression of a decline in this species, which has been linked to the loss of wet meadows. Among other initiatives, the BTO, in conjunction with Anglia Water, are to begin an investigation into the ecology of this species in 2001.
  • Reed Bunting: the decline of this species along linear waterways (63%) is similar to that measured by the CBC in other habitats over a similar time period. Although the main decline is linked to declines in survival rates, it is possible that declines in breeding success might be holding back recovery (Peach et al. 1999).
  • Little Grebe: although the WBS does not monitor Little Grebes on still waterbodies and the sample sizes monitored are relatively small, the decline on linear waterways of 51% is considerable and suggests that an investigation of the potential cause of the decline and of its ecology is required.
 
In addition to these rapid declines, two species show declines of between 25-49%:
 
  • Pied Wagtail: although not generally considered to be a bird associated closely with linear waterbodies, this species is relatively common on WBS plots and has declined substantially (by 49%) over the past 23 years. Such a decline has not affected the main part of the population, which occurs in drier habitats, but it may reflect a potentially important decline in riparian conditions.
  • Grey Wagtail: this is the third wagtail species to show substantial declines along linear waterways (-48%). Grey Wagtail is the species most closely associated with rivers and streams, feeding alongside and over them, and is perhaps the strongest indicator that some serious decline in habitat quality has occurred over the past 23 years.
 
Of these species, only Yellow Wagtail triggers alerts at 10 years and 5 years, suggesting a continuing and rapid decline. In addition, Redshank triggers an alert at 10 years because of a 32% decline. The decline in waders on wet meadows is of some conservation concern and a resurvey of sites surveyed in England & Wales was due to be carried out in 2001, but has been postponed until 2002 because of the outbreak of foot-and-mouth disease and consequent restrictions on access to the countryside.
 
Table 4.3.2 Alerts for WBS waterways 1975-1998

Species

Period
(yrs)

Plots
(n)

Change
(%)

Lower
limit

Upper
limit

Alert

Comment

Yellow Wagtail

23

22

-81

-94

-70

>50

 

Reed Bunting

23

53

-68

-76

-56

>50

 

Little Grebe

23

18

-51

-79

-4

>50

Small sample

Pied Wagtail

23

67

-49

-62

-35

>25

 

Grey Wagtail

23

57

-48

-61

-30

>25

 

See Help for information on what the categories mean.
 
4.3.3 Constant Effort Sites Alerts
    
The majority of species that trigger alerts from the CES over the last 14 years are also the subject of alerts from the CBC. However, these alerts are useful because they cover a very different set of habitats, wet and dry scrub and reedbeds, not covered by CBC. Thus there are >50% alerts for Linnet, Redpoll and Yellowhammer, and >25% alerts for Spotted Flycatcher, Reed Bunting, Song Thrush, Willow Tit, and Willow Warbler. (But it should be noted that the CES does not necessarily monitor a representative portion of the populations of Spotted Flycatcher and Redpoll).
 
Interestingly, the CES finds a substantial decline (31%) for Whitethroat that is not shown by CBC over the same sort of time period, perhaps confirming that this species is not recovering, as it perhaps should have done after the sub-Saharan drought-induced decline of 1968.
 
Only one additional species triggers an alert on the CES: Lesser Whitethroat. It has declined by 44% over the past 14 years. This is rather an enigmatic species that winters in eastern Africa, in contrast to most of the UK's other long-distance migrants that winter in western or southern Africa. The population decline coincides with an alert raised by the CBC over the past 10 years (31% decline) and perhaps indicates a more general decline than in habitats additional to those covered by the CES.
 
Comparison between CES and CBC over the past 10 years shows that some species have declined much faster on CES than on CBC plots: This is especially so for Linnet, which declined by 76% on CES but increased by 9% on CBC plots. Indeed, much of this decline on CES has occurred over the past 5 years, with a 53% decline over that period. Reed Bunting has also declined more rapidly on CES (by 41%) than on CBC plots (-23%) or WBS plots (-12%), which is worrying because the CES reebed and wet scrub habitats are likely to be the preferred habitat for this species. Song Thrush has also declined faster on CES (-30%) than on CBC plots (-10%), as has Lesser Whitethroat (CES -53%; CBC -31%). The opposite has only occurred for Redpoll (CES -67%; CBC -80%); Yellowhammer (CES -35%; CBC -44%); and Willow Tit (CES -49%, CBC -69%).
Table 4.3.3 Alerts for CES adults 1984-1998

Species

Period
(yrs)

Plots
(n)

Change
(%)

Lower
limit

Upper
limit

Alert

Comment

Linnet

14

21

-87

.

.

[>50*]

 

Lesser Redpoll

14

20

-75

.

.

[>50*]

Small sample

Yellowhammer

14

23

-58

.

.

[>50*]

 

Spotted Flycatcher

14

18

-49

.

.

[>25]

Small sample

Reed Bunting

14

58

-47

.

.

[>25*]

 

Lesser Whitethroat

14

44

-44

.

.

[>25*]

 

Song Thrush

14

79

-39

.

.

[>25*]

 

Willow Tit

14

25

-36

.

.

[>25]

 

Whitethroat

14

56

-31

.

.

[>25]

 

Willow Warbler

14

90

-31

.

.

[>25*]

 

See Help for information on what the categories mean
 
4.3.4 Breeding Bird Survey Population Changes
 
The BBS has been designed to provide a properly representative coverage of the whole of the UK. However, it has only been in operation since 1994, so only 5-year population changes are reported here. These measures of change have been derived from simple annual indices and have not been subject to the same analytical approaches (smoothing etc) as the longer-running schemes. The results should therefore be interpreted with this limitation in mind.
 
Several of the species with population changes of greater than 25% on BBS in the UK (as well as in individual countries) have been in long-term decline, as measured by the CBC and WBS:
 
  • BBS - UK & England: Grey Partridge, Willow Tit and Yellow Wagtail.
  • BBS - UK & Scotland: Kestrel.
  • BBS - UK & Wales: Bullfinch and Cuckoo
  • BBS - UK: Corn Bunting.
 
Several others that have been declining in the long-term on CBC plots show declines greater than 25% in particular countries of the UK but not in the UK as a whole:
 
  • BBS - England: Redpoll and Tree Pipit.
  • BBS - Scotland: Lapwing.
  • BBS - Wales: Starling and Yellowhammer (Wales).
  • BBS - Northern Ireland: Mistle Thrush and House Sparrow.
 
The alert raised for Lesser Whitethroat over 14 years on CES is also reflected by a decline of greater than 25% on BBS in UK and England over the past 5 years. Similarly the alert raised for Redshank on WBS plots (over the past 10 years) is reflected by a decline of greater than 25% also raised on BBS plots in UK and Scotland over the past 5 years.
 
New species declines that aren't apparent in the more established schemes are found in:
 
  • UK for: Wood Warbler (and in England), Shelduck, Common Sandpiper.
  • England for: Snipe.
  • Scotland for: Golden Plover.
  • Wales for: Mallard.
 
For many of these species, long-established BTO monitoring schemes have not provided sufficient coverage of their distributional ranges and so the rapid declines reported from BBS may be important indicators of potentially new conservation problems, although some will turn out to be part of the natural range of fluctuation.
 
Table 4.3.4 Population Changes for BBS UK 1994-1999

Species

Period
(yrs)

Plots
(n)

Change
(%)

Lower
limit

Upper
limit

Alert

Comment

Wood Warbler

5

58

-45

-60

-24

(>25)

 

Grey Partridge

5

222

-43

-53

-32

(>25)

 

Willow Tit

5

60

-42

-58

-18

(>25)

 

Shelduck

5

110

-40

-51

-27

(>25)

 

Redshank

5

63

-36

-51

-16

(>25)

 

Black-headed Gull

5

425

-36

-43

-28

(>25)

 

Lesser Whitethroat

5

195

-31

-42

-17

(>25)

 

Kestrel

5

502

-30

-38

-21

(>25)

 

Common Sandpiper

5

63

-29

-46

-7

(>25)

 

Yellow Wagtail

5

155

-29

-41

-14

(>25)

 

Bullfinch

5

432

-28

-37

-19

(>25)

 

Cuckoo

5

744

-27

-33

-20

(>25)

Corn Bunting

5

148

-26

-37

<-13

(>25)

See Help for information on what the categories mean.
 

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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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