Realising that I haven't yet written up the results of last winter's egg survival project I am posting a brief summary now before a much more satisfactory post with the results of our annual foreshore transect last month. The chosen survey site was on the north side of top field, adjacent to the reserve’s small car park
The original aim of the survey was to try to assess the number of eggs predated by ‘unknown’ predators over the winter months, in order to establish base information for future surveys, including identification of possible predators.
The survey was begun in September 2014, with fortnightly then monthy checks. By March 2015 40 of the established 196 eggs were missing or predated, with a further 17 eggs found without tags. (A further 100 eggs were lost under different circumstances - see below).
The overall total of eggs surviving therefore was established as 78%.
This compares well with survival counts carried out by David Redhead in the Midlands where survival rates appear to be slightly lower, being in the region of 75%.
Could these be possible predators?
This survey was flawed and after 2 months there was a serious problem.
- horses that graze the field broke managed to 'predate' several eggs along with the tender twigs they were on.
- 85+ eggs were lost when the ‘over-enthusiastic’ contractor employed to top the meadow failed to see the young tagged Blackthorn and removed them too. These numbers were not included in the 196 eggs surveyed mostly by David Redhead, in a much denser area of blackthorn inside the fence.
This is an important learning curve, and the next egg predation survey will be carried out with tighter limits and guidelines. Loss by horse and machine were not anticipated.
Encouragingly we established that the predation/egg loss was steady over the months from October to March. In the past one of the 3 small sample survival counts had indicated that increased predation may have taken place very soon after the earliest eggs were laid i.e. possibly taken by Warblers.
These 3 old studies had resulted in a higher survival percentage than the current study – they were all in the 80% band.