As was noted in my previous blog, our Peregrines laid their first egg this year on 15 March, considerably earlier than we have seen before. I did speculate then that the general trend towards earlier laying dates, especially in urban locations, may be linked to a slight general warming in our climate. Having discussed this with an acquaintance who has an almost unrivalled knowledge of urban Peregrines, he suggests that the much earlier laying date may be due to a new female at the site, but, as she is unringed, we have of course no reliable way of knowing whether this is the case or not. Whatever the reason for the early laying of eggs, with the normally quoted incubation period of between 28 and 32 days, it was anticipated that we would have our earliest ever hatching of chicks this year. This has indeed proved to be the case, as the first two chicks hatched and were first seen on the morning of 23 April which indicates an incubation period of around 32 days in this instance. The two chicks were joined by a third which was first seen on 24 April, and the fourth hatched on the 25 April.
Hatching takes quite a long time with Peregrines, and it can be up to about 72 hours between the chick within the egg first making the first ‘chip’ in the egg shell and it actually fully emerging from the egg. During this time the adults will be aware that hatching is in progress as the unborn chicks call from within the egg even before hatching commences, but this becomes more audible once hatching actually begins. Unlike with many smaller birds, Peregrines do not usually carry the pieces of the hatched eggshell away from the nest, instead they are normally left lying around the nest and eventually get trampled into little bits as the chicks grow. Sometimes the adults, particularly the female who mostly tends the newly hatched chicks, can be seen nibbling at the discarded eggshells. It has been speculated that she does this to replenish her calcium levels following egg laying.
Newly hatched chicks are still wet and often quite exhausted after the rigours of emerging from the egg, and are closely brooded by the female at this stage. They soon dry out however and within a few hours appear fluffy in their familiar white down. As incubation in Peregrines does not normally start until all or perhaps the third out of a clutch of four eggs have been laid, the chicks do tend to hatch quite close together and thus do tend to be of a similar size during their time in the nest. This is in contrast with many owl species who start incubating as soon as the first egg is laid and hence the chicks hatch over a relatively long period of time and do vary considerably in size. This asynchronous hatching in owls is considered to be a survival strategy to ensure that, in times of poor food supply, at least the largest and strongest of the chicks survive.
As regular watchers of the webcam from previous years will know, the newly hatched falcon chicks are not at all aggressive to one another, and between regular feeds spend most of their time asleep. In the early days this is mostly beneath a brooding adult, usually the female, but a little later, especially on warm days, all huddled together in the open so to speak in a white ‘heap’, perhaps to help keep warm. They exhibit none of the’ Cain and Abel’ syndrome found for example in some of the larger Eagle species, including Golden Eagle, where the more aggressive of the (normally) two chicks mercilessly attacks and in most cases kills the weaker chick. This seems to happen in most cases even where there seems to be sufficient food for two chicks to be raised; quite why it happens seems not yet to be fully understood.
Regular food supply has never seemed to be a problem with our cathedral Peregrines, and I have watched several feeds in the last couple of days, the adult female feeding her tiny chicks in a wonderfully gentle and patient way, taking care to give them only the tiniest of morsels at a time. Whilst it may be just a coincidence of when I have been watching the webcam, but it does seem to be the case that in the early days of hatching, this year and in previous years, prey items brought in do tend to be relatively small birds; I think I identified a Blackbird being in brought in yesterday for example. Later as the chicks grow, larger birds like Pigeons and Gulls appear more frequently on the menu. This is understandable as larger prey items are needed to sustain the larger chicks at that stage. Quite why larger birds like Pigeons are not brought in so often when the chicks are small is something of a puzzle; the adults are presumably very capable of tearing off tiny pieces of food irrespective of the size of the prey item. As I say, maybe it is just a coincidence, and larger items might have been brought in whilst I have not been glued to the computer screen!
Having hatched, the chicks will now develop fast, and if all goes well, they should fledge in perhaps the first week of June. Fine dry weather in the first week or so after hatching is very important; cold wet weather in the first week or so after hatching can lead, despite the best efforts of the adults to shelter them, to chicks becoming chilled and ultimately dying. Bad weather is perhaps the major cause of chick mortality in the nest for Peregrines. Luckily, the weather forecast for the next week or so is set fair, so whilst your garden may not be enjoying this continuing dry weather, rest assured that the Peregrines will really appreciate it!
Granville Pictor 25 April 2021.