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| 4.2 |
Latest
long-term alerts |
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| 4.2.1 |
Long-term trends of PSOB red-listed species |
| The species considered here were
red-listed due to long-term
declines of more than 50% over 25 years. The latest long-term
population changes and alerts over the maximum period available
(usually 36 years) and over 25 years are shown in Table 4.2.1.
As expected the results confirm the decline status of all of
the 16 species concerned. All changes fire alerts except for
the 31-year change for Lesser Spotted Woodpecker
that has very wide confidence limits and is thus not statistically
significant. Marsh Tit, Song Thrush
and Bullfinch now show declines of less than
50% over 25 years, mainly reflecting the fact that their long-term
declines started more than 25 years ago. Reed Bunting
now has both long-term and 25-year declines of between 25% and
50%. Its population increased between 1967 and 1975 before the
rapid decline that gave rise to its current conservation listing. |
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| Table 4.2.1
Long-term population changes over the longest available period
(usually 36 years) and 25 years for species that are currently
on the PSOB red list. The table is ordered by decline over the
longest available time period. |
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See Help
for information on category definitions. |
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4.2.2 |
Long-term
trends of PSOB amber-listed species |
| The species considered here were amber-listed
due to long-term declines of between 25% and 49% over 25 years.
The amber list category also included a number of species where
the best trend estimates show declines of more that 50% but
the trend data are sparse or may be unrepresentative. The latest
long-term population changes and alerts over the maximum period
available (usually 36 years) and over 25 years are shown in
Table 4.2.2. As expected the results confirm the decline status
of most of the 16 species concerned. |
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| Table 4.2.2
Long-term population changes over the longest available period
(usually 36 years) and 25 years for species that are currently
on the PSOB amber list due to population declines. The table
is ordered by decline over the longest available time period. |
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See Help
for information on category definitions. |
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| Six species show
significant declines of greater than 50% and could thus be
candidates for future red listing. Three of these, Lesser
Redpoll, Tree Pipit and Woodcock,
are amber listed as a result of data limitations, and there
has been no substantial change in the information available
on their declines. Three others, Yellow Wagtail,
Willow Warbler and Cuckoo,
have been subject to ongoing declines that have now passed
the 50% threshold, although it should be noted that for the
latter two species the long-term trend data are from England
only. The serious nature of the Yellow Wagtail
decline is supported by data from both WBS (-92% over 25 years)
and BBS (-27% over 10 years). BBS data indicate that in England
and Wales Willow Warblers and Cuckoos
have continued to decline over the last ten years, but both
species have shown significant increases in Scotland. |
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| Our best estimate of long-term change in the English
House Martin population now also shows a decline
of over 50% but it is not significantly different from no change.
Thus no alerts are raised for this species. It is probably best
to regard it as being data deficient rather than as a potential
candidate for red listing. BBS data indicate that House
Martin numbers have been stable or increasing since
1994. |
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| Grey Wagtails have been increasing
since the late 1990s, and as a result of this their 25-year
change is now +3%, while the decline over the longest period
for which we can measure changes in their populations (28 years)
is down to 23%. If the positive trend continues they might be
removed from the amber list at a future revision. Kestrel
and Lapwing show an opposite pattern to Grey
Wagtail, with smaller declines over 36 years than 25
years, reflecting modest increases prior to the declines that
are now a cause of concern. Goldcrest is a
difficult species for status assessments because its populations
show wide fluctuations and may not have been well monitored
prior to the start of the BBS. Numbers actually increased by
46% over 36 years and declined by obly 16% over 25 years. More
recently BBS data show that numbers have increase by 60% over
the last ten years and it is doubtful that the status of this
species should be of particular concern. |
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Long-term declines of
species that are not currently red- or amber-listed (for declines) |
| We identified only five species that are currently
showing long-term declines of greater than 25% but are not currently
included on either the red or amber lists (Table 4.2.3). Two
species, Little Grebe and Whitethroat,
appear to have experienced declines of greater than 50%. The
Little Grebe data should be treated with caution
as they are based on a small sample from linear waterways. WBS
shows an ongoing decline over the last ten years while BBS shows
an increase for the UK as a whole. The long-term Whitethroat
decline results from the well-documented crash between 1968
and 1969 (Winstanley
et al. 1974), from which numbers have shown only
a limited recovery over the last 25 years. |
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| Table 4.2.3 Long-term
population changes over the longest available period (usually
36 years) and 25 years for species that have declined by more
than 25% but are not currently on the PSOB red or amber lists
(for declines). The table is ordered by decline over the longest
available time period. |
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See Help
for information on category definitions. |
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| Two other species, Common
Sandpiper and Lesser Whitethroat,
could all be candidates for future inclusion on the amber list.
Lesser Whitethroat should be of particular
concern because the 29% decline from CBC/BBS over the last 25
years is consistent with a 52% decline on CES sites over the
last 19 years and a 30% decline measured by the BBS over the
last 10 years. Red-legged Partridge declined
by 46% over the last 25 years but would not be a candidate for
amber listing because the species is not native to the UK. |
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4.2.4 |
Declines
on WBS plots |
| The Waterways Bird
Survey supplements the results from more broadly based schemes,
such as CBC and BBS, by measuring trends in the bird populations
of linear waterways. For a few waterways habitat specialists
such as Grey Wagtail and Common Sandpiper
WBS provides our best information on population trends but for
several others it provides supplementary information from this
sensitive habitat. Long-term declines of greater than 25% recorded
from WBS plots are listed in Table 4.2.4. |
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| Table 4.2.4 Population
declines of greater than 25% recorded by the Waterways Bird
Survey between 1975 and 2003. |
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See Help
for information on category definitions. |
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| The trends for Little Grebe,
Redshank and Common Sandpiper
have already been discussed above while those for Yellow
Wagtail and Reed Bunting are consistent
with those reported from CBC/BBS. The Pied Wagtail
decline of 47% is interesting because in contrasts markedly
with the position in the rest of the country where populations
have recently been increasing. Over the 25-year period 1978
to 2003 Pied Wagtails declined by 42% on linear
waterways compared with only an 8% decrease in the UK, as shown
by the CBC/BBS trend. The cause of the decline on waterways
is currently unknown. |
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4.2.5 |
Declines
on CES plots |
| The Constant Effort Sites Scheme
provides trends from standardised ringing in scrub and wetland
habitats. It is our best scheme for monitoring 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 19 years (Table 4.2.5). |
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| Table
4.2.5 Population declines of greater than 25% recorded by
the Constant Effort Sites Scheme between 1984 and 2003.
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See Help
for information on category definitions. |
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| Most of the species that are declining on CES
sites also show similar trends from CBC/BBS data. Linnet,
Spotted Flycatcher and Willow Tit are
already red-listed while Lesser Redpoll and
Willow Warbler are amber-listed. The declines of Lesser
Whitethroat and Whitethroat have also
been discussed above (section 4.2.3). Both
species are doing less well on CES sites than in the UK as a
whole. Over the ten-year period 1993 to 2003 Whitethroats
increased by 41% in the 41% in the UK but decreased by 21% at
CES sites. Similarly Lesser Whitethroats declined
by 17% in the UK as a whole but by 58% on CES sites. Longer-term
comparisons show a similar picture. Numbers of juveniles captured
at CES sites show very similar patterns of decline to adult
captures for both species. It is unclear why these two species
are doing so poorly on CES sites as many of these are located
in the good-quality scrub habitats that are preferred by these
species. |
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