State of Nature report - RSPB

Watchlist indicator
Between 1995 and 1999, 577 species were identified as
priorities for conservation, under the UK BAP. The list was
reviewed in 2007, and doubled in length to 1,150 species.
This list has been superseded by priority species lists for the
UK’s four nations individually, but remains a good indication
of species that have been conservation priorities in the UK
since the 1990s and remain so now.
We have developed a new Watchlist Indicator, showing
the overall trend in population of 155 conservation
priority species – about 13% of those listed as UK BAP
priorities. The species included were all those where
information was available on changes in population
abundance over time, and do not represent a random
sample of those on the UK BAP list.
Annual estimates of relative abundance were available
for 51 birds 4–9 , 77 moths 16 , 19 butterflies 15 and eight
mammals 7,10,11,12 . For many of these species, data were
available from the 1970s to the present day. However,
for some species, the time series available was
substantially shorter.
In order to combine the species into a composite indicator,
we first scaled the data for each species so that the estimate
for each year was expressed as a proportion of the estimate
in the first year. The composite index shown in the report
is the geometric mean of the scaled species-level data.
The index has been adjusted to take into account the
different starting years for different species, with “new”
species entering the index scaled to the overall index value
for the year of entry. The 95% confidence intervals around
the composite index were generated by bootstrapping the
species-level trend data.
CaveaTS
The datasets presented in this report are a summary of
the information available: this is the first time that these
data have been brought together and assessed as a whole.
However, the datasets have not been selected to reflect a
representative sample of UK species, either within or between
taxonomic groups or habitats. This means that we should be
cautious about extrapolating findings beyond the species
assessed. Additionally, although there are numerous studies
investigating the underlying reasons for these changes in
abundance or distribution, it is difficult to interpret the
observed patterns for many species.
Here we have put together datasets collected using different
methods, measuring different aspects of species status
on a variety of spatial scales and analysed using different
statistical techniques.
There are two points to note about this. Firstly, how a species
has been monitored – the method, effort and extent of
surveying – can influence whether the results were suitable
for our analyses, and indeed the species’ trend itself. Whether
trends in abundance or range are reported can be influential.
For example, when a widespread species begins to decline,
changes in abundance may be detected before changes in
distribution. Conversely, increases in distribution in an already
widespread species may be difficult to detect. The scale at
which trends in range are measured can also be influential,
with range loss at a fine spatial scale not detected if mapping
is done at a coarser resolution.
Many of the monitoring schemes that produce the datasets
included in this report have a wide range geographically,
but may not have sufficient sampling density locally to pick
up changes in localised or particularly rare species. As a
result, trends for relatively few of these species are reported.
Our measures of the balance of increasing and decreasing
species may therefore be biased towards the more common,
widespread and generalist species.
Secondly, although official guidelines are used to produce
national Red Lists, there is room for variation in interpretation
of these guidelines and so there are small differences in the
way different authors have compiled the national Red Lists
summarised here. This is particularly true in defining which
species are not threatened (of Least Concern).
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