Conservation Science in the RSPB 2006

37
Climate change and ring ouzels
Ring ouzel
Jan Halady (rspb-images.com)
The ring ouzel, with a population
of only 6,000–7,500 breeding pairs,
is rapidly declining in the UK.
Declines have previously been
explained in terms of topography
and habitat, although large-scale
processes, such as climate change,
may also be involved. Ring ouzel
data from four study populations
in Scotland and northern England
were analysed to examine
whether breeding success and
population change could be
related to climate on both the
upland breeding and Moroccan
wintering grounds.
The mean laying date of first
clutches was later in years when
rainfall in March and April on the
breeding grounds was high.
However, overall nesting success
was not affected either by the
timing of laying or by weather in
May and June, when most nests are
active. Instead, most of the variation
in nesting success was explained by
population size, being higher where
population density was low.
Breeding success did not therefore
appear to be much affected
by climate.
Analysis of data from southern
Scotland showed that population
declines were greatest in years that
followed warm summers with
intermediate levels of rain. Declines
were also greater two years after
high spring rainfall in Morocco. Such
rainfall is known to reduce juniper
pollination and hence the abundance,
18 months later, of berries on which
wintering ring ouzels feed. Recent
changes in British summer
temperatures have been strong
enough to account for the observed
population decline, which could be
linked to reduced post-breeding