CES 2022

In 2022 we completed our second year of the constant effort site at Thornwick.
CES (Constant Effort Site) is a BTO (British Trust for Ornithology) led project aimed
at monitoring bird populations through time, in order to aid effective conservation. It
looks to monitor numbers of birds (abundance), the number of births (breeding
success or productivity) and deaths, usually recorded as the number that don’t die

This data enables the BTO to calculate expected changes in numbers, and at what
stage in their lifecycle birds may be affected by environmental changes. They can
then try to find out causes for any decline in numbers.

The CES scheme uses comparisons of the numbers of birds caught each year to
provide indices of population change, looking at 24 species in particular. This is
done by standardised mist-netting through the breeding season, consisting of 12
visits between May and August.

We completed 10 out of the 12 sessions, with one of those sessions being cut short
by rain.

A total of 408 birds were caught with 221 of these newly ringed and 187 being
retraps. Retraps are vital as they provide valuable information on the longevity and site fidelity of adult birds.

267 adult birds were ringed alongside 141 juveniles, comprising of 22 species.
For comparison in 2021 we completed 9 sessions and caught 352 birds of which
169 were new and 183 retraps.

240 adults were ringed alongside 112 juveniles, comprising of 27 species.

Juvenile Warblers caught :
– Willow Warbler 31 (2021=11)
– Blackcap 14 (2021=3)
– Lesser Whitethroat 9 (2021=15)
– Whitethroat 13 (2021=19)
– Reed Warbler 10 (2021=15)
– Sedge Warbler 1 (2021=5)
– Chiffchaff 5 (2021=4)

No juvenile Garden Warblers this year, 1 was caught in 2021.