In my previous blog date dated 13 March 2021, I mentioned that in 2020, the first egg was laid on 22 March 2020, and wondered when the first egg would be laid in 2021. We certainly did not have long to wait, as just before midnight on 15 March 2021 we saw the first egg laid. This is by some margin the earliest we have seen our cathedral pair lay their first egg, in the early years of occupation the first egg was laid in late March or very early April. This trend towards earlier egg laying seems to be reflected nationally, and is of course much easier to monitor nowadays as so many urban nests are covered by nest cams. There is speculation that this is perhaps because of a slightly warming climate, but, as they say, the jury is probably still out on that one. As I type this note, we have four eggs and it seems likely that this will be the complete clutch. The normal clutch size is three or four eggs, occasionally just two, and very rarely five. Clutches of five do seem to have become a little more common in recent years, especially in urban locations, helped perhaps by have a very plentiful supply of prey nearby. I am aware of a clutch of six eggs laid in a nest box on the outskirts of London in 2018 although only three eggs actually hatched. Regular cathedral watchers will recall that one of our previous females called Sally (colour ringed blue SY) laid five eggs in 2017, but alas only one egg hatched. That said, it is not unknown for a clutch of all five eggs to be hatched and all five chicks survive to fledging; indeed this has happened recently on a neighbouring cathedral site at Winchester.
Regular watchers will have noticed that there is quite a variation in the colouration of the four eggs. Whilst it is true that the colour of the eggs tends to fade somewhat as incubation proceeds, the first one laid this year was very pale from the moment it was first laid, in fact to my eye it did not seem much different in colour to a rather uniform chicken egg. There are now two of these pale eggs, one very handsomely blotched with brown markings, and one somewhat of a ‘halfway house’ between the two. The attractiveness and variation in colour between clutches was one of the reasons that nests were robbed so prolifically by egg collectors before bird protection laws made this practice illegal. There are a number of really good books on Peregrine Falcons on the market, including an excellent one on urban Peregrines by Ed Drewitt who, as regular watchers of our site will recall, has kindly ringed our chicks in past years. The ‘bible’ for most enthusiasts however remains ‘The Peregrine Falcon’ by the late Dr Derek Ratcliffe. A really beautifully written book and featuring a colour plate of twelve clutches of eggs from the British Museum which show the richness and variation of the colours between and within clutches. It perhaps explains why the eggs were so coveted by egg collectors. A book for the ‘birthday wish list’ in lockdown perhaps?
Length of incubation with Peregrines tends to vary a little, but seems to be generally between about 28 and 32 days, and thus it is anticipated that, all going well, our eggs should hatch towards the end of April. Whilst the adults may cover the earliest laid eggs from time to time, incubation does not normally start in earnest until the third or fourth egg is laid. In a clutch of four eggs, incubation can thus sometimes start perhaps two days before the final egg is laid. This explains why sometimes one chick hatches a couple of days later than the others. It has been speculated that this may be a survival strategy should food become scarce and the fourth and last hatched chick is thus the first to perish in such situations. That said, in many urban locations, including Salisbury, where local prey is apparently quite abundant, the last hatched chicks seem to fare very well. It is interesting to note that in 2014, the year in which the birds first bred successfully in recent times on the cathedral, that we had our first and only clutch of three eggs in the nest box, and all hatched very close together.
As I type this on 26 March, whilst at the same time keeping an eye on the nest cam, it is raining steadily in Salisbury, and the adult female is sitting on the eggs keeping them warm and dry. In some years the adults have looked very wet and bedraggled in the rain, but today at least her plumage looks remarkably well oiled and droplets of water can be seen very clearly on her head and back. Let us hope she and her mate can, like the rest of us, enjoy better weather soon.
Granville Pictor 26 March 2021.