Having been away over Easter, I followed developments from a distance and was pleased to see a fourth egg laid on Saturday morning, after a further gap of another two days.
So it took a week (Saturday to Saturday) for the clutch of to be complete, as another egg at this stage looks extremely unlikely. With the same size clutch as every previous year at St George’s, there’s nothing to suggest a different female on that front, and the colour is also very similar to the deep ruddy shade of the eggs in each previous year. Views are mixed as to whether the screengrabs show the same female as last year or a different bird, and at present everything is proving inconclusive as to her identity.
As the male took over brooding duties earlier today, it was evident again how he struggles to cover the four eggs. In Tim Birkhead’s excellent new book on eggs, The Most Perfect Thing, shortly to be available in British bookstores, he discusses both the shape and number of eggs in a clutch. Many waders lay four quite pointed eggs that can fit – pointed-end inwards – into a neat group that can be easily brooded. Both the images above show that the Peregrines do not do this, partly because their eggs are much less pointed and more spherical than in the waders; and, as a result, it is not possible for the four eggs to fit together so neatly.
The other thing that more pointed eggs allows for is that a greater percentage of the egg’s surface area can be in contact with the adult’s body for the transfer of body heat to the eggs. So on this count too Peregrines are less ‘efficient’ in their brooding. And why do different species (or families) of birds lay eggs of different shapes? It seems this is one in which is still much to learn, although it may be related to pelvis shape (right-angled in raptors), which in turn bears a superficial correlation to the shape of the bird overall.
Raptors and their relatively rounded eggs are not, then, optimally efficient in their brooding, but with few natural predators and relatively secure nest sites perhaps this is less of an issue than for ground-nesting waders whose young are born at an advanced stage of development. Whatever the merits of the Peregrines’ strategy, these particular eggs will take between 30 and 32 days to hatch from completion of the brood, so we can expect them to hatch some time around 26-28 April all being well. In the meantime, there will be a lot of time during which the adults will be sitting tight, punctuated by handovers every few hours. Not the most exciting stage perhaps, but an absolutely vital one nonetheless.
A quick update on the laying of the third egg this morning, with another gap of around 60 hours between eggs. One egg was left out in the (not so) cold by the brooding female late morning, but this is not a cause for concern as the eggs are quite hardy and can be left uncovered for several hours at a time. Even when they are left uncovered, rest assured that the adults will be nearby to protect the nest from Crows or gulls, both of which could potentially take an egg. If you’re down at St George’s and see the Peregrines chasing either of these, that’s why it is.
The male flew in several times during the morning and screeched at the female, apparently looking to take over brooding duties. At around midday she moved aside and he took over, the three eggs already proving a challenge for his smaller size.
After some rolling of the eggs into place with his bill he settled down for a stint. At the current rate, it’ll probably be the weekend before any more eggs are laid, although a brood of three would also be quite normal. Ratcliffe’s seminal study (1993) found an average brood size of 3.65 based on over 400 clutches, with four eggs representing about 15% of a female’s body weight. Whether or not any more are laid we’ll have to wait and see!
It’s taken a little longer than anticipated, but the second egg was laid this afternoon at around 16:45, so around 58 hours after the first.
Prior to that, both adults took turns to brood the single egg. There was a lot of interaction during the day, with some courtship bowing on the nest.
Shortly after that, the male returned to the ledge with a prey item, which attracted the female’s attention. She flew round and did the classic snatch from the male, showing the clear benefit of the difference in size. The male seemed a little spooked and flew off, circling in the background, just visible in the screengrab below.
Another screengrab captured one about to land on the perch. Must get down some time to try and get some pics from below.
One of the things that’s puzzled me is how or why – as in the picture below – the eggs look entirely pale at night. Nothing else in the box undergoes this transformation: dark pebbles continue to look dark, so why do the eggs change colour? Is it the lighting or something in the surface of the shell that reflects the light in a certain way? Perhaps I’ll ask Professor Tim Birkhead, whose new book on eggs is about to come out.
And the other puzzle: is this the same female as in the last few years? They’re certainly similar, but I reckon that there are differences in the length of the hook on the upper mandible, in the shade and extent of the yellow at the base of the bill (and around the eye), and in the degree to which the white patch on the ‘cheek’ extends up behind the moustachial stripe. I’ve put together a side-by-side comparison from January 2015 and today so you can see what I mean.
You can come to your own conclusions while I keep looking into it!
Following an eventful autumn, in which we feared the worst when the female was seen looking very poorly on the nest platform on 11th Sept, things have happened very quickly. After her illness, the adult female seemed to recover and was subsequently seen looking well around Sheffield, but before Christmas what looked to be a new female had taken up residence with the original male at St George’s. Whether the original female had died or been usurped is not clear, but the new pair has been in evidence for the last couple of months, showing pair-bonding behaviour and nest-scraping.
However, they caught me by surprise by laying the first egg on Saturday 19th, a day earlier than the first egg last year and just over a week earlier than in 2014. Thanks to Helen for sending through a screengrab shortly afterwards.
The egg was unattended for much of the day, which is quite normal, but was brooded overnight, and the female is again brooding tonight, which is no bad thing given the relatively low temperatures.
Peregrines usually lay between 3 and 5 eggs, and if this is indeed a new female she may have a different clutch size to the previous four eggs that were laid in each of the previous years at St George’s. They typically leave up to 48 hours between each egg laid, so it may well be that another appears early tomorrow morning, with early mornings the favoured time for laying over recent years.