Eleven days on from completion of the clutch, we’re a third of the way through the incubation period and all looks to be going well with both adults continuing to take turns on the eggs throughout the day. The male was doing his one-eyed dozing again this afternoon, moving his head to look around while keeping his left eye firmly closed, so giving a rest to the right side of his brain.
The male is still spending a good proportion of the time on the eggs, and continues to be reluctant to hand over duties to the female. This was evident this afternoon, when she arrived and called persistently at him from the edge of the platform, before dropping onto the gravel and advancing towards him, which finally encouraged him to come off the eggs. They remained uncovered for only a few seconds before she moved onto them, with all four clearly visible and apparently unharmed by the male having stood on one of them last week.
Katklaw asked if the Peregrines might be measuring the temperature of the eggs with their feet, something I’ve not come across, though she comments that Barn Owls do this. A bit of a search has come up with some information on the temperature of Peregrine eggs, which are incubated at 35.7 degrees C (most birds incubate at 30-38 degrees), but no mention of testing with the feet. Whatever the case, the birds are clearly sensitive to keeping the temperature of the eggs regulated and turn them on a fairly regular basis, especially at takeover times, as below. I previously referred to Tim Birkhead’s fascinating book Bird Sense in relation to the one-eyed sleeping mentioned again above, but he also states that touch receptors in birds are concentrated on the beak and feet so testing temperature with the feet would be quite feasible.
Looking back at some photos I took of the third Peregrine that’s been in the area, I’m pretty sure it’s one of the females that fledged from St George’s last year. The photo below is of the bird at some distance as it flew over, so far from the best posted, but you can make out the peachy colour below, and there’s no sense of the bill or flesh around the eye being the bright yellow that can be very obvious, even in flight. Seeing that as the pale blue of immatures is pushing it in the image below, but zooming it right up from the original image suggests that is the colour of the base of the bill.
I’ve witnessed the adult female see off this young female twice from around St George’s, but on both occasions the chase was not particularly violent and certainly less aggressive than what the Buzzard endured recently. Females can breed at 2 years old in immature plumage, and it is very unlikely that the immature could be seen as a territorial rival, especially if the adults continue to recognise their offspring, as appears to be the case. When territory is at stake, fatal combats have been recorded, especially in males, so things can get extremely violent. At the other end of the behavioural spectrum is the care taken with the eggs, which is what is on view 24/7 at present and should continue to be so for another couple of weeks.