2021 saw the FBOT ringing group trialling a CES 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 (survival).

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.

The 24 species are:

  • Song Thrush
  • Willow Tit
  • Dunnock
  • Willow Warbler
  • Bullfinch
  • Reed Bunting
  • Wren
  • Robin
  • Blackbird
  • Cetti’s Warbler
  • Sedge Warbler
  • Reed Warbler
  • Whitethroat
  • Lesser Whitethroat
  • Garden Warbler
  • Blackcap
  • Chiffchaff
  • Long-tailed Tit
  • Blue Tit
  • Great Tit
  • Treecreeper
  • Chaffinch
  • Greenfinch
  • Goldfinch

Of these 24 species, 22 are known breeding birds within the Flamborough Bird Observatory recording area.

Despite some poor weather conditions the FBOT team managed to complete 9 out of the 12 visits.

Some 169 birds of 27 species were ringed.

Of the 24 species of concern the following were caught:

                                     ADULTS            JUVENILES

Song Thrush                      4                        2                           

Dunnock                              3                        6

Willow Warbler                   11                        8

Bullfinch                               6                        4

Reed Bunting                      4                        0

Wren                                     7                        6

Robin                                    0                        2

Blackbird                              7                        0

Sedge Warbler                   6                        3

Reed Warbler                      3                      13          

Whitethroat                         16                      10

Lesser Whitethroat           10                        6          

Garden Warbler                  0                        1

Blackcap                              4                        3

Chiffchaff                             4                        3

Long-tailed Tit                   3                        2                          (+3 un-aged birds)

Blue Tit                                 5                        6

Great Tit                               6                        2

Greenfinch                            3                        1

Goldfinch                              4                        0

Particularly rewarding was the numbers of warblers, including juveniles of every species that we caught.

A special highlight was the stunning male Ring Ouzel we caught right at the start of the CES season, other birds species caught include Meadow Pipit, Redwing, House Sparrow, Tree Sparrow, Linnet and Yellowhammer.

The CES site has been visited this year by members of the team with some adjustments to the positions of net rides made to try and maximise the numbers of birds caught. The team are looking forward to our second year and hoping to re-catch some of the birds we ringed last year in order to gather valuable data on survival and site fidelity.

Look out for more CES updates on the blog from May.