Month: April 2014

Unexpected excitement

An e-mail from Phil Riley in the University’s Estates Dept on Wednesday afternoon gave details of some electrical work required at St George’s, to start the following morning.  Needless to say, this raised concern as to potential disturbance of the sitting adults with the risk of the eggs becoming damaged if the adult was spooked from the nest or getting cold if disturbance was ongoing.  By very happy coincidence, the SBSG monthly indoor meeting was to take place that Wednesday evening and the speaker was to be Mark Thomas, the RSPB Senior Investigations Officer, a national specialist on raptors and the law.  I had a good chat with Mark about the situation at St George’s and went down myself the following morning to see if we could find the best way forward.

After a good deal of discussion with the project manager and others we agreed that most of the work (replacing lights around the lower elevation of the church) would be able to go ahead without disturbance to the bird sitting in the nest platform.  However, work on the N elevation, under the platform, was to be postponed until a later date, a very good outcome that allows a key part of the work to go ahead immediately while respecting the protection that Peregrines enjoy as Schedule 1 species.

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The work involves a cherry picker to reach the light fittings and with work under way on the light furthest from the platform, the female took up station on the corner of the tower (circled in red above) overlooking the contractors, who were in clear sight of her while the male incubated.  To my surprise – and relief – she did not seem bothered by their presence and continued to sit there for quite a while.  As can be seen, there is a considerable amount of equipment in the area, and they seem to have become accustomed to such things, which were in place well before the start of this year’s breeding season.  And when the crane swings round, it can look as if it has almost passed over the nest!

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So, scare over, the birds have continued to incubate as normal yesterday and today, with turns of around a couple of hours and some great views when takeovers happen.

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In the photo above, taken as the female came off after an extensive stint on the eggs, it looks as if the sternum is visible just where the barring on the chest begins, with indented patches of feathers to either side suggesting the brood patches where the eggs had been nestled.  Peregrines have two brood patches, through which body heat can be transferred from the adult to the eggs, or vice versa if necessary.  Watching the birds settle onto the eggs on various occasions, they always seem to settle N-S or E-W with two eggs on either side of the sternum.  Might this explain why a clutch size of 4 is pretty standard for Peregrines – an optimal size of clutch to be able to incubate two eggs at each brood patch and maximise success?  Looking at the male when he moves onto the clutch, it would certainly be hard to imagine him adequately covering 5 or even 6 eggs.

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Again, in the overhead shot here you can see the disturbed feathers in the same area, or am I imagining it?!

A quick visit this morning confirmed all was well, with work on the lighting continuing at the E end of the church, out of sight of the platform and regular perching spots.  With no Peregrines on view, a Woodpigeon flew onto the stonework half way up the church and then flew up to the ledge where the platform is, where it started to walk towards the nest!  

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When it got to within about 20 centimetres of the nest I was expecting some excitement!  It looked for a while as if it was going to hop up onto the box, but in the end decided against it.  It’s a bit of a puzzle what the Pigeon was doing, but it seemed very curious about the platform.  I’ve posted before about Peregrines apparently not predating birds breeding in the vicinity of their nest, but this Pigeon seemed intent on testing that to the limit, and survived the experiment.

So an apparently routine few days became ‘interesting’, but thankfully all seems to be proceeding securely, with the halfway point in incubation just about here.

One third: two thirds

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.

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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.

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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.

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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.

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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.

 

Settling down

A few days on from the appearance of the fourth egg and things have settled into the expected pattern of the adults incubating the clutch between them.  We didn’t expect any more eggs to be laid, and a fifth now would break all known records for gap between eggs in a single clutch!  So four it is.

Things have quietened down in more ways than one, with the adults far less vocal around the church than had been the case in the preceding days and weeks.  Whichever adult is not incubating has been less evident around St George’s, though they can still be seen at times perched on the stone ornaments on the corners.  It seems that they are keeping a low profile while they incubate, drawing little attention to their presence.  Indeed, a couple of visits over the weekend made this clear, with fleeting views as the male arrived from the E, only to disappear onto one of the upper ledges.  A few minutes later he flew off, carrying a previously stored Feral Pigeon, without once calling or approaching the nest platform.  This is apparently typical, as food is usually kept at a distance from the nest during incubation, perhaps to reduce risk of infection (see flies below).

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The only other time any movement was apparent over the course of a couple of hours was when the male attacked a Buzzard that passed S over the area, diving repeatedly at it until it moved some distance from the church.  The views were not very close, but in the picture below you can see how the Buzzard flipped upside down to defend itself with its talons from the Peregrine as it attacked from above, something it had to do several times.

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So a lot of the time there’s not much to see at present if you do visit St George’s in terms of the Peregrines, though other species are making their preparations for the breeding season, including the pair of Mistle Thrushes mentioned in a previous post, now busy building a nest within 50 metres or so of the nest.

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Once things liven up in terms of activity, particularly when the eggs hatch later in April, there will be a lot to see at St George’s, and Sheffield Bird Study Group will be organising some Peregrine watches to share information if you want to be able to find out more.

In the meantime, settle down to enjoy watching the webcam, which continues to show some fascinating insights.  Today, for example, on one of the rare occasions when the eggs were left uncovered it was noticeable that a couple of flies immediately appeared, settling on the eggs.  No doubt the eggs were warmer than other surfaces, or were they looking to feed on tiny bits of organic matter on the shells?  One of the flies is just about visible on the top left of the eggs in the image below.

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And when the male did arrive to take over incubating duties there was a moment of concern as he trod on one of the eggs, something both birds are very careful to avoid doing on the whole when they move onto and off the eggs.

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Last year the egg that failed to hatch suffered a fate similar to the image above.  Jim Lonsdale, who oversaw construction of the platform, saw the male tread on one of the eggs when arriving at the platform last spring, and sure enough the unhatched egg was found to have a tiny puncture hole when the platform was taken down over the winter.  Jim’s design is also in place at Wakefield cathedral, where a platform has also been installed.  If anyone needs a Peregrine nest platform building, to a tried and trusted design, let me know and I’ll put you in touch!

Finally, thanks to those who have sent messages of support and appreciation for the Peregrine Project here in Sheffield – it’s great to know the enjoyment it’s bringing.  I can’t find time to reply individually, but I am grateful for your comments and input and hope the webcam and blog continue to provide good viewing.