The
Constant Effort Sites Scheme |
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Constant Effort Sites (CES) scheme is the first national standardised
ringing programme within the BTO Ringing
Scheme and has been running since 1983. Ringers operate
the same nets in the same locations over the same time period
at regular intervals through the breeding season at 120 sites
throughout Britain and Ireland. The Scheme provides valuable
trend information on abundance of adults and juveniles, productivity
and also adult survival rates for 25 species of common songbird. |
CES
Information |
| Preliminary
results - 2009 |
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2009 results
Following the two very poor breeding seasons in 2007 and 2008,
this summer saw many species have a much more productive year. The
preliminary results were released in December, and can be seen here.
The headlines results included:
Adult numbers
- 18 species showed a decline
vs 2008 (this is a consequence of the previous two poor breeding
seasons)
- Significant decline
for Robin, Reed Warbler, Blackcap, Long-tailed Tit, Blue Tit,
Great Tit and Linnet
- Lowest ever adult
numbers for Blue Tit and Linnet
- Significant increase
only for Whitethroat and Bullfinch
Productivity
- Significant increases
(vs 2008) for 18 species
- Significant increases (vs
long-term) for 15 species
- Highest ever productivity
for Reed Warbler and Chaffinch
- Significant decrease
only for Willow Tit (and lowest ever)
2007 and 2008 seasons
| The previous two
years were the worst we have seen since the start of the CES
scheme, with productivity significantly lower than the long-term
average for 11 of the 25 core species. The range of species
affected was rather different in the two years though, and
it looks like the timing of heavy rainfall in the breeding
season was responsible for this.
The results for the 2007 season featured in major newspapers
in the autumn (The Times and Telegraph are
shown to the right) and we hope the better news in 2009 will
be equally popular!
Full results for the last two years can be found in the relevant
copy of CES News which can be downloaded here. |
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Why do we need CES?
We need to monitor bird populations through time in order to conserve
them effectively. Firstly, we need to know whether numbers are stable
or changing, whether decreasing or increasing. If there is a change
in numbers, particularly a decrease, we need to know why. Conservation
action can then be targeted appropriately.
The key things that we need to monitor are numbers (abundance),
the number of births (breeding success or productivity) and the
number of deaths, usually recorded as the number that do not die
(survival). Once we have this information, we can calculate expected
changes in numbers and look for the stage of the life cycle which
is most affected by environmental change. We can then find, or
at least narrow down, the possible cause(s) of a decline. This
is the philosophy behind the BTO
Integrated Population Monitoring (IPM) programme. The CES scheme
uses comparisons of the numbers of birds caught each year to provide
indices of population change for 28 species. This information complements
that from other BTO census schemes, such as the Breeding
Bird Survey (BBS) and Common
Birds Census (CBC), particularly for songbirds breeding
in wetland and scrub habitats. Changes between years in the proportion
of juveniles in catches are used as an index of productivity for
the 28 species, complementing information from the Nest
Record Scheme (NRS). Information on breeding success from CES
is particularly valuable because it integrates success through the
whole season (including the outcomes of multiple broods and early
post-fledging mortality), whereas the NRS only monitors the results
of single nesting attempts. Between-year recaptures of individual
birds in the CES scheme are used to determine adult survival rates.
This information complements that from general ringing from the
BTO Ringing Scheme. For the species
monitored by CES, higher quality information on adult survival per
unit ringing effort is generated, compared with the low recovery
rates from the general ringing.
What is CES?
The CES Scheme uses catches from standardised mist-netting to monitor
key aspects of the demography of 25 common breeding songbirds. Around
120 sites are monitored through the breeding season, with twelve
standard visits between May and August. Changes in the total number
of adults caught provides a measure of changing population size,
whilst the proportion of young birds caught forms an index of breeding
success. Retraps of adult birds ringed in previous years are also
used to estimate annual survival rates.
CE
Sites
The popularity of CES ringing is increasing again after a drop-off
during 2001 (due to Foot and Mouth restrictions) and 117 sites operated
in 2008. Eight of these operated for the first time, including
our most northerly site now in Scotland. The majority of CE Sites
currently operated are in England (90 sites), but valuable contributions
are received from Scotland (15 sites), Ireland (5 sites) and Wales
(7 sites). The geographical spread of sites is impressive, but
still somewhat biased towards the south and east due to the higher
densities of ringers. Poor weather in the north and west can also
make regular ringing more difficult. The majority of CE Sites are
in scrub (shown as circles in the map on the right (wet sites are
blue and dry sites are green)) and reedbeds (light brown squares)
with a small number of sites in deciduous woodland (dark brown squares).
The sites are selected by the ringers themselves as those that are
are suitable for catching satisfactory numbers of birds at each
visit in habitats where successional changes can be managed. If
the habitat were to change too dramatically, the results would be
less meaningful because of changes in the chances of capturing individual
birds.
Species monitored
The CES Scheme monitors 25 species of common passerines. Of these,
three are on the 'Red list' of the Birds of Conservation Concern
(BOCC) document (Song Thrush, Willow Tit and Linnet) and
five are Amber-listed (Dunnock, Whitethroat, Willow Warbler, Bullfinch
and Reed Bunting). The other species are Wren, Robin, Blackbird,
Cetti's Warbler, Sedge Warbler, Reed Warbler, Lesser Whitethroat,
Garden Warbler, Blackcap, Chiffchaff, Long-tailed Tit, Blue Tit,
Great Tit, Treecreeper, Chaffinch, Greenfinch and Goldfinch.
Adult numbers
A full analysis of changes in abundance measured by CES has been
carried out for the years 1983-1995. Catches of most insectivorous
resident species either increased or remained stable, while catches
of resident thrushes, small finches, buntings and some trans-Saharan
migrants declined. The largest increase in catches of adult birds
were recorded for Robin, Wren, Greenfinch, Long-tailed Tit and Chaffinch,
while the largest decreases in adult catches were recorded for Linnet,
Redpoll, Spotted Flycatcher, Yellowhammer, Reed Bunting and Willow
Warbler (Peach, W.J., Baillie, S.R. & Balmer, D.E. 1998. Long-term
changes in the abundance of passerines in Britain and Ireland as
measured by constant effort mist-netting. Bird Study 45,
257-275)
As an example, here we show the trends
in the abundance of adults for Linnet, Long-tailed Tit and Wren.
Linnet
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| Adult numbers of Linnets on CE Sites
show a very worrying decline, generally consistent with those
shown by other BTO schemes; for example, the Breeding
Bird Survey (BBS) shows that the breeding population has
been declining since 1977. Linnet is already on the Birds
of Conservation Concern Red List (being of high concern).
Overall, Linnets numbers underwent a large decline between the
mid-1970s and mid-1980s, probably due to a loss of weed seeds,
but may have recovered since that time, perhaps due to the beneficial
effects of set-aside. More recently, oil-seed rape has probably
helped to compensate for losses of traditional foods. But CES
catches of both adults and juveniles suggest that the decline
of Linnets in scrubland continues, with productivity also in
long-term decline. |
Long-Tailed Tit
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| The population fluctuations shown
by Long-tailed Tit are likely to be due to variation in winter
weather conditions. The trend produced from the Breeding Bird
Survey shows the effects of the very cold winters in the 1970s
and early 1980s. CES information from 1983 onwards shows a
period of recovery following a series of mild winters with the
population increasing, though this has levelled off in recent
years. |
Wren
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| Like the Long-tailed Tit, winter weather
is the major determinant of population changes in Wrens in Britain.
Even a short spell of winter weather, severe enough to prevent
efficient feeding, results in high mortality. Throughout the
1980s and early 1990s, catches of adult Wrens have fluctuated
markedly, suggesting recoveries from cold winters until reduction
again in the next hard spell. |
Breeding success
We are also able to produce an index of productivity (a measure
of breeding success) from CES data. Information on individual nesting
attempts from the Nest Record Scheme allows a detailed investigation
of success at various stages of the breeding cycle for many species,
but cannot provide information on the number of breeding attempts
(and 'whole season' productivity). Productivity measured by CES
integrates success (or failure) across the whole breeding cycle,
including all breeding attempts and early post-fledging mortality.
We currently produce trends in productivity for all CES species
using generalised linear modelling methods. These will allow influences
of short-term weather variation on productivity to be controlled,
so that true long-term trends are revealed.
Survival
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| The Sedge Warbler is a common breeding species
throughout most of Europe, wintering south of the Sahara Desert
in West Africa (see Migration
Atlas). In Britain, numbers of Sedge Warblers breeding
in farmland and riparian habitats fluctuate markedly from
year to year but declined by about two-thirds between the
mid-1960s and mid 1980s. Survival rates of adult Sedge Warblers
were estimated for the period 1969-1984 using mark-recapture
data collected at two long-running CE Sites in southern England
(Marsworth Reservoir, Hertfordshire and Wicken Fen, Cambridgeshire).
(Peach, W.J., Baillie, S.R. & Underhill, L. 1991. Survival
of British Sedge Warblers Acrocephalus schoenobaenus
in relation to west African rainfall. Ibis133:300-305).
The results of the investigation showed that fluctuations
in the population levels and annual adult survival rates of
British Sedge Warblers since the late 1960s are strongly correlated
with indices of wet season rainfall in the West African winter
quarters, the higher the rainfall in West Africa the greater
the adult survival rate (graph). This suggests that the continued
expansion of the Sahara Desert due to droughts, land drainage
and over-grazing is a threat to our Sedge Warblers, as well
as to populations of many trans-Saharan migrants. |
How to get involved
If you are considering starting a new CES please first read the
instructions and complete a registration
form. For further information about the CES Scheme or setting up
a new site, please contact
. A newsletter, CES News,
is produced on an annual basis and is sent to all ringers involved
with the scheme.
The Constant Effort Sites Scheme is funded by a partnership of
the BTO, the JNCC (on behalf of Natural England, Scottish Natural
Heritage, the Countryside Council for Wales, and also on the behalf
of the Environment and Heritage Service in Northern Ireland), Duchas
the Heritage Service - National Parks and Wildlife (Ireland) and
the ringers themselves.
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