Nest Sites seem to fall into 2 categories, pairs that are able to breed on a structure/building (core sites) and are territorial all year round, and those that have to move to an alternative nest site as the core site does not offer nesting opportunities.
Some vacated core sites do not offer nesting opportunities, the O2 for one, they are resident on this most of the year but as soon as breeding season arrives, there off to the nest site. From then on, and as soon as the juveniles have fledged and are flying strongly enough, the adults will then, usually with prey enticement lure them back to the O2.
Parliament is another, although a nest box has been placed for them by Brunel University, it is unfortunately a little too low, additionally for all the magnificence of Victoria Tower, it unfortunately does not offer them a ‘ natural scrape’ for breeding.
By mid February they leave Victoria Tower, Westminster Abbey and Big Ben and head off to the nest site, much the same pattern and times as the O2 pair. Breeding and fledging takes place at the nest site and they all then come back to Parliament, usually around July 10th.
|Falcon seen hunting recently successfully|
Of the 11 pairs that I monitor, 4 pairs are core site ‘vacators’ with the remaining 7 being 365 days a year on territory. The all year round territorial birds not surprisingly have nest boxes or trays.
I am not sure how it works in rural cliff dwelling pairs, do they become nomadic after breeding and follow a solitary winter existence forever searching for prey, do they retain the pair bond out of breeding and away from the nest site? Or do they remain territorial with enough prey available locally to sustain them through the non breeding months?
In London prey has never been a problem, I know where the ‘vacators’ go and the pairing is retained, not surprisingly as Peregrines do mate for life, or at least until one is usurped.
What is a perfect nest site, usually older buildings/structures with a good clear approach all round with large exercise areas for juveniles beit roofs or ledges.
Ideally they should have a number of ledges/knolls below for fledging juveniles, the more the merrier, if they lose height on that 1st flight they will have somewhere relatively safe to land.
From lower ledges/knoll’s they can then hedge hop their way back up, short flights back up to a height where the adults will feed them, if they stay too low unfortunately the adults will not come down.
Nowadays modern buildings, in particular glass built skyscrapers, like the Shard or the Gherkin and many others are totally unsuitable for peregrines or little else, they would be a fledging nightmare for juveniles, that's not forgetting the glass/reflection issue, it kills birds both night and day.
In short these type of buildings are unsuitable for any birds, possibly Swifts but unfortunately nature is simply bypassed. I am not a fan of modern architecture as you have probably guessed, unless they have Brown or Green Roofs or Walls how and where does nature fit in?
Give me an old Building/Structure any old day.