|Feathers added by a pair of Swifts to a concave|
Photo Judith Wakelam
This year we put 18 new nest boxes in Worlington church, again with a concave in every other box. So 9 with and 9 without a concave. We have checked the boxes and 6 boxes were occupied, 5 with a concave and just 1 without. The probability of this result by chance is even higher at 16.7%.
Neither of these experiments passed the statisticians test for 'certainty' of 5%, but together, they do.
The probability of both of these results occuring by chance is 10.7% x 16.7% = 1.8%
So now we can be sure that Swifts do prefer boxes with concaves.
Not only that, but 2 of these boxes contained chicks, supporting the assertion that breeding in the first year of occupancy is more likely in a nest-box with a concave. So, on our next visit to St Mary's we will insert a concave in all nestboxes.
We need more experiments like this e.g.:
Dark interior versus light interior
Oval entrance versus rectangular entrance
Rough exterior versus smooth exterior
Large box versus small box
[For the technically minded, for the statistics I used the Excel HYPGEOMDIST() function.]