| |
| |
| 4.2 |
Latest
long-term alerts |
| |
| 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 satisfy criteria for UK decline,
but amber-listed birds may be listed for other reasons (see
Help on species accounts). |
| |
| 4.2.1 |
Long-term trends of PSoB 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 4.2.1, over the
maximum period available (usually the 41 years 1967–2008)
and over 25 years (1983–2008). The table thus provides
updates to the figures that were used to produce the current
BoCC3 red list. |
| |
| The 19 species in Table 4.2.1 are listed in descending
order 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 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. |
| |
|
|
See
PSoB pages for information
on red and amber criteria |
| |
4.2.2 |
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 4.2.2 in descending order of longest-term percentage
change (normally over the 41 years 1967–2008). Where available
the 25-year change (1983–2008) is also shown. |
| |
|
|
See
PSoB pages for information
on red and amber criteria |
| |
| Three species
raise high alerts, having shown significant declines of greater
than 50%. Whitethroat shows a massive decline
over the 41-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 less clear, but show shallow declines over the
ten-year period to 2008. 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. 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 been changed little since 1994, however. |
| |
| Bullfinch was moved from the
red to the amber list at the 2009 review. Its 41-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, Meadow Pipit
and Mistle Thrush 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 41-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 apparently surpass red or amber criteria but
which are not recognised in the current listings. Even though
a review of the red and amber lists took place in 2009, there
are a few species that remain in this category (Table 4.2.3). |
| Snipe |
33 |
WBS/WBBS waterways |
-93 |
-99 |
-78 |
>50 |
Small sample |
| Snipe |
25 |
WBS/WBBS waterways |
-94 |
-98 |
-86 |
>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 |
41 |
CBC/BBS UK |
-50 |
-69 |
-22 |
>25 |
|
| Little Owl |
25 |
CBC/BBS UK |
-54 |
-67 |
-39 |
>50 |
|
| Dipper |
33 |
WBS/WBBS waterways |
-31 |
-47 |
-12 |
>25 |
|
| Goldcrest |
25 |
CBC/BBS England |
-26 |
-41 |
-2 |
>25 |
|
|
See
PSoB pages for information
on red and amber criteria |
| |
| 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, and was not
presented in our previous report. 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 meets amber-list criteria
for population decline but, as an introduced species, is not
eligible for any conservation listing. 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. The UK Goldcrest
population has historically shown very wide fluctuations but
is currently at a relatively low level, marginally raising an
alert in England for the 25-year period. |
| |
4.2.4 |
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 trend are now available, allowing
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 WBBS trends for species 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 section of this report. |
| |
| 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 4.2.2 or 4.2.3,
as appropriate. Where WBS/WBBS is not the headline trend for
a species, however, the waterways data nevertheless provide
valuable supplementary information from this sensitive habitat. |
| |
| Table 4.2.4 lists all statistically
significant declines of greater than 25% recorded from the full
period of waterway monitoring (nominally 1975–2008). It
does not include Little Grebe, for which the decline is not
statistically significant (Table 4.2.2). Four species are included
for which WBS/WBBS is not the headline trend and so are not
listed in Tables 4.2.2 or 4.2.3. |
| |
|
|
| The trends for Yellow Wagtail
and Reed Bunting are consistent in direction
with the 41-year trends reported from CBC/BBS, but in each case
the declines on waterways have been more severe. For Reed Bunting,
recovery along waterways has also been weaker than in the countryside
as a whole. 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 Sedge Warbler, the headline
trend is a non-significant 41-year decrease of 21% 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. |
| |
| A full set of alerts raised by WBS/WBBS,
and long-term increases detected by that index, are tabulated
in Appendix 7.2. |
| |
4.2.5 |
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 24 years (Table 4.2.5). |
| |
| |
| |
| 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
4.2.1). Similarly, Willow Warbler, Reed
Bunting, and Whitethroat are amber
listed. |
| |
| 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 Appendix
7.3. |
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| Return to previous
page |
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| Next page –
4.3 Ten-year trends and evidence of species recovery |
