| |
 |
| 4.2 |
Latest
long-term alerts |
| |
| 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 35 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 and Song Thrush
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. |
| |
| Table 4.2.1
Long-term population changes over the longest available period
(usually 35 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. |
|
|
See Help
for information on category definitions. |
|
|
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 35 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. |
| |
| Table
4.2.2 Long-term population changes over the longest available
period (usually 35 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. |
|
|
See Help
for information on category definitions. |
| |
| 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 on-going 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 only from
England. The serious nature of the Yellow Wagtail
decline is supported by both WBS (-92% over 25 years) and
BBS (-17% over 9 years) data. BBS data indicate that for the
UK as a whole Willow Warblers and Cuckoos
have continued to decline over the last 9 years, but both
species now appear to be stable or increasing in Scotland. |
| |
| 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. Therefore it is
probably best to regard this species as being data defficient
rather than as a potential candidate for red listing. BBS data
indicate that House Martin numbers have been
stable or increasing since 1994. |
| |
| Grey Wagtails have been increasing
since the late-1990s, and as a result of this their 25-year
decline is now only 12%, although the decline over the longest
period for which we can measure changes in their populations
(27 years) remains 26%. 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 35 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
45% over 35 years but declined by 29% over 25 years. More recently
numbers have approximately doubled over the last 10 years and
it is doubtful that the status of this species should be of
particular concern. |
| |
|
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 10 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), with numbers having shown limited
signs of recovery over the last 25 years. |
| |
| Table 4.2.3 Long-term
population changes over the longest available period (usually
35 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. |
|
|
