Month: May 2016

Four Weeks Old

It’s been great to see the positive comments about Nicola’s post: delighted others have found it as interesting as I have.  As part of her research, Nicola would be keen to analyse other failed Peregrine eggs, so if anyone with connections to other Peregrine nests where failed eggs have been removed is reading this, do get in touch!

Despite the disappointing weather, a quick post to mark four weeks since the chicks hatched.  They’re increasingly left to their own devices between feeds, and are starting to take a greater interest at feed times.

May 21

Something to look out for in the days ahead is them beginning to look to feed themselves.  They’ll also continue to change their appearance apace as the down is lost and replaced by the emerging feathers that are already visible when they stretch their wings.

As ever, even when the chicks are left (apparently) alone, one or other of the adults is nearby.  The female likes to perch on top of the church’s turrets, from where she can crane her neck and look down into the nestbox.  Behind you!

May 22 4

A visit early in the morning on Sunday (with sun!) allowed for some observation of behaviour and a few photos.  The female flew in with a loose primary feather.

May 22 2

As she preened on the perch, the feather fell out and dropped.  It looked as if it was going to fall to the ground, which would have enabled a direct DNA sample, but it didn’t quite make it over the lower wall and dropped onto the lower roof of the church.

May 22 3

As she left, there was no discernible gap (unlike in the immature bird that visited recently) and it didn’t affect her flight in the slightest, as you’d expect.

May 22 1

The panoramic camera has come into play as a perch too, as occasionally in previous years, and it appears to have left a bit of a smudge on the lens, judging by the atmospheric effect created in the evening drizzle.

May 23 dusk

The Fourth Egg Explained

For today’s blog post I’m handing over to Dr. Nicola Hemmings, from the Department of Animal and Plant Sciences here at the University of Sheffield.  Nicola, to whom I give a really big vote of thanks for her work here, is an expert on the causes behind hatching failures and has had a look at the fourth egg removed (under licence) during the ringing…   Over to Nicola:

Those of you who followed the Sheffield Peregrines last year (2015) will remember that two out of four eggs didn’t hatch. These eggs were collected during chick ringing, and I was able to examine them in my lab at the Department of Animal & Plant Sciences, University of Sheffield, to determine the causes of hatching failure. To learn more about my findings last year, you can look at the archived post here

This year, things went a little better for the peregrine eggs – three out of four hatched, leaving only one egg left behind.

Nicola Hemmings 1

When the chicks were ringed (Monday 16th May), the egg was collected so that we could once again try to identify why it failed to hatch.

I received the egg in rather amusing protective packaging –this was one egg you certainly wouldn’t want to bite into!

Nicola Hemmings 2

As I opened the container, I could smell that familiar stench. Remember, this egg had been sat in a warm, humid nest for about seven weeks. It had undergone a full incubation period, followed by several weeks of being sat (and excreted) on by the chicks and their parents. It was covered in faeces, feathers, and other debris. There was no doubt its contents would be severely degraded.

Nicola Hemmings 3

Despite this, I wasn’t quite ready for extreme level of deterioration I encountered on opening the egg – even I have rarely seen such putrid egg contents! As the rich green soup poured out, my eyes began to water. My research colleagues were repulsed by the foul fumes that filled the lab.

Nicola Hemmings 4

I must admit I was concerned this egg was beyond examination. However, with characteristic determination, I began steadily to sift my way through the gunk, pouring subsample after subsample of the soup into a new dish and diluting it with saline solution to help clear the fluid.

I wasn’t simply filled with blind hope; I had good reason to think I might find something interesting or useful in among this smelly concoction. I’ve examined many unhatched eggs – probably several thousand – over the years, as part of my research into the causes of hatching failure in birds, so I am used to finding golden bits of information among a rotten mess! I also conducted an experiment a few years ago (using turkey eggs) to see how long non-developing eggs could be incubated before I was no longer able to get useful information from them. Even after several weeks of intensive incubation, I was still able to find degraded embryonic tissue, as well as sperm cells embedded in the layer surrounding the egg yolk. It’s amazing how much you can learn from a rotten egg!

Unhatched egg examinations are an important tool for bird conservation. Across species, around 10% of all eggs fail to hatch, but in some critically endangered species the failure rate is over 70% – that’s almost three-quarters of all potential chicks never hatching! By looking at unhatched egg contents, we can diagnose fertility problems (i.e. insufficient sperm), detect egg infections, and identify abnormalities in developing embryos that may be linked to genetic problems or environmental factors. Understanding these causes of hatching failure allows rapid and effective measures to be put in place to improve success in the next breeding season.

Back to the peregrine egg. Despite the extreme degradation, my long-practiced egg examination skills didn’t fail me. In one diluted subsample, I suddenly noticed a tiny lump, surrounded by what looked like a thin membranous sack.

Nicola Hemmings 5

Nicola Hemmings 6

On closer inspection, the “lump” was very obviously a tiny peregrine embryo that had begun developing, but then died at a relatively early stage. The photo below shows the embryo, separated from its “sack”, next to a 1 cm square grid for scale (each of the smallest squares on the grid = 1mm). The “sack” is in fact a glycoprotein layer that surrounds the yolk, called the perivitelline layer. When you dunk a bread soldier into your fried egg, it’s the perivitelline layer that ruptures to allow the yolk to ooze out. The perivitelline layer attaches the yolk to the embryo, which is important because the yolk is the embryo’s only source of nutrition throughout the entire developmental period. Remains of the other extra-embryonic membranes may also be present: the amnion, which surrounds the embryo and secretes amniotic fluid to prevent the embryo from drying out; the allantois, which provides a gas-exchange surface so the embryo can breathe, and also removes waste; and the chorion, which serves as a protective membrane for all the embryonic structures.

Nicola Hemmings 7

It is possible to roughly estimate the “age” at which an embryo died (i.e. how long it had been incubated for before death) based on its developmental stage. The developmental stages of the domestic chicken embryo are well-established, having been described by Hamburger & Hamilton (1951) using morphological landmarks. You can see the full developmental series  here, and read the original paper if you are interested. These stages have also been described for a few other bird species – in general, early development proceeds at a very similar rate across species. I therefore used Hamburger & Hamilton’s staging series as a guide when examining the peregrine embryo.

If you look closely at the embryo, you can clearly see that the eye is pigmented and the limb buds are slightly elongated. This corresponds with stages 20-23 of Hamburger & Hamilton’s series i.e. approximately 3-4 days development. It is difficult to give a more precise estimate of the developmental stage, because some of the fine morphological structure of the embryo had degraded.

Embryo mortality in birds is most common very early (first three days) or very late (just before hatching) in incubation. This peregrine embryo died at the tail-end of the critical early development period. In these early stages, death mainly results from problems with the formation of organs and the respiratory system, which may result from interference during incubation (e.g. eggs being exposed to abnormal temperatures for prolonged periods). It would be interesting to look back at the nest camera footage (and weather conditions) 3-4 days after incubation started, to see if there are any clues about what went wrong [ed – the temperature dropped to 1.5ºC on the early morning of 28th March and the night of March 30th, with the clutch haivng been completed on March 26th ; the cold tempratures do coincide with this 3-4 day timeframe, but it’s not possible at present to look back to see if there was a period when an egg was left uncovered for any length of time].

It is worth noting that prior to the onset of incubation eggs remain in a state of suspended animation. The embryo undergoes some development (rapid cell division) inside the mother’s body before the egg is laid, but assuming ambient temperatures are below ~24ºC, development pauses after egg-laying until incubation begins. In birds, 24ºC is considered to be to “physiological zero” – below this threshold no development occurs. For UK breeding birds, this makes timing of incubation and chick hatching fairly straightforward. For example, blue tits (Cyanistes caeruleus) can lay up to 16 eggs (usually 8-12) at a rate of one egg per day. However, the female only begins incubating after the ultimate or penultimate egg is laid (as do the Peregrines), ensuring that all the chicks hatch over the course of just one or two days. The pre-incubation period poses a bigger problem for birds in hotter climates, where ambient temperatures frequently exceed physiological zero. If the egg temperatures rise above 24ºC, but do not reach full incubation temperature (36-38ºC), developmental abnormalities will occur and the embryo is likely to die. As a result, birds that breed in hot environments often have smaller clutches and begin incubating as soon as the first egg is laid, leading to asynchronous chick hatching.

I have now stored the embryo, along with some other samples from the egg, in 100% ethanol for DNA analysis. The molecular lab here in Sheffield are hoping to find funds to pay for this work, which may reveal whether or not we have a new peregrine female this year.

For now, I will leave you with a stark reminder about why you should always store your eggs somewhere cool and dry, and avoid leaving them too long before eating them. This is what was left of the once-nutritious yolk, after seven weeks of being sat on by a peregrine falcon. Delicious.

Nicola Hemmings 8

Ringed (II)

A few days on from the successful ringing on Monday, a chance to respond to a few questions people have posted.  One thing we’ll certainly consider next year is to use coloured darvic (plastic) rings in addition to the metal rings from the British Trust for Ornithology (BTO).  Both types of rings used are very lightweight and have no impact on the birds’ ability to fly or live their normal lives, but coloured plastic rings would make it easier to identify the birds away from the nest once they fledge and disperse.  The current arrangement of the metal rings allowed us to identify the young male that was taken into care a couple of summers ago, and was sadly picked up dead subsequently.  To find out more about the BTO’s ringing programme, look here .  There are some amazing stories that have resulted from all of this, and the good work of the Sorby Breck Ringing Group always results in some fantastic data for the Sheffield Bird Study Group annual report.

May 15 imm Jeff Allesbrook

Above, for example, is a picture taken by Jeff at St George’s last Sunday (thanks Jeff!).  The damage to the primaries on the right wing (how would that have come about??) reveals it’s clearly a different bird to the resident pair.  And the streaking that runs down the breast – rather than across it – tells us that it’s an immature bird, one that hatched last spring.  It could well be that this is one of the birds that fledged from St George’s last year, though it could also be a wanderer from another nest in the Midlands or Yorkshire.  Even at the distance in Jeff’s photo a coloured ring would probably be visible, allowing us to know for sure and mapping the movements of the Sheffield birds.

While I was up St George’s during the ringing, Andy D was on the ground and took a series of great photos, showing Simon removing the chicks from the nest (one by one) and then returning them all together from the bag in the top right image.  Simon’s an experienced climber, but even so it gets the adrenalin pumping: rather him than me!

May 16 ringing AD 4

Andy also got some terrific images of the female as she circled the tower, including the one above in dive mode and a couple more below.

May 16 ringing AD 5

May 16 ringing AD 3

Dr Nicola Hemmings of the University’s Department of Animal and Plant Sciences has been examining the unhatched egg and is preparing a report to explain why it didn’t hatch.  That will follow soon: her piece in a similar vein last year was fascinating, so don’t miss it!


Monday (16th) had been identified by members of Sorby Breck Ringing Group as a good opportunity to ring the chicks/ eyasses, and with good weather conditions this went ahead as planned.  Consequently, the webcams were switched off for a while (thanks Ian), we gained access to the church tower (thanks Jim) and climbed up and out onto the roof.  Once all the ropes had been secured, Simon went over the edge and placed the chicks in a bag that was then passed back for the rings to be located on the chicks’ legs.


Given that Peregrines are a Schedule 1 species, for which it is a criminal offence to disturb the nest (let alone remove or injure the birds), it was vital that Steve Samworth has the necessary permit – and experience – to ring Peregrines.   Together with Steve were Simon, Paul and Helen, all of whom are ringers based at the University: a great team!   The rings serve a dual purpose as a security measure that indicates that these birds were ringed in the wild and also enables the monitoring of movements if the rings are read at any point.

Helen has taken the unhatched egg and a tiny amount of down for analysis so that we can have a DNA sample from each of the chicks, matched to their ring number.   Hopefully it will also be possible to sex the chicks, as well as determine whether or not this is a different female to last year’s bird.  Steve felt there were at least two females, based on thickness of the legs, but in order to reduce the disturbance to the absolute minimum no weighing or measuring was carried out, which might have helped to confirm this.  The whole process was completed in around 20 minutes from start to finish, which saw Simon go back over to return the chicks to the nest: note how the bag containing the chicks has its own safety rope!


As expected, the adults became agitated while we were out on the roof, and the female in particular circled the tower at close quarters, calling repeatedly.  Below are a few pictures taken from virtual eye level.

PG May 16 5

PG May 16 3

PG May 16 9

PG May 16 4

PG May 16 6

PG May 16 1

The male circled at more of a height, but also called repeatedly, the difference in tone (male markedly higher pitched) readily apparent.

PG May 16 12

Once we had got down to the bottom of the church, the female had landed back on the perching pole on the nextbox, and things quickly returned to normal.  By the afternoon a good feed saw one of the chicks walking around the box rather than shuffling, and standing on its feet as opposed to resting on its tarsals (lower legs).

May 16 feed

At one point it pecked at the female’s wing and looked as if it was going to feed itself on the feral pigeon that had been brought in, but thought better of it.  It won’t be long, however, before they start to feed themselves and the feather that are just starting to peep through from their shafts (visible below) will begin to emerge and result in a rapidly changing appearance.


I’ll end by giving a big vote of thanks to everyone involved in making the ringing possible: Ian, Jim and Phil from the University’s Computing and Estates Departments; and Simon, Paul, Helen and – especially – Steve for their ringing expertise.

PG May 16 10



Half-way to fledging?

Eighteen days have now passed since the first chick hatched, and they continue to grow well, increasingly left to their own devices in the box, though at least one of the adults is typically in attendance nearby.

May 12 chicks

The chicks (proper name eyasses when talking of downy raptor chicks) can now shuffle around the box, but are not yet standing.  What they are resting on is their tarsus, which connects the foot to the ankle – it’s the ankle (and not the knee) joint that you can see on a bird’s leg.  They’ll soon gain the strength and balance to be able to stand and start to become more mobile.  As it is, they can already move about enough to hide in the corner (almost) out of sight: they’ve definitely not fledged yet!

May 14 chicks hiding

In the last three years that we have known dates for the laying and hatching of the eggs, the eyasses have taken 38 days (2013 and 2014) days from hatching to leaving the nest, though in 2015 that was just 35 days, the result of one juv getting blown off the edge of the box in strong winds!  So we are approximately half-way to fledging.

May 12 feed

They are very well fed, as is evident from the full crop (throat) in the bird being fed above, so the adults are being excellent parents and even though the chicks are unbrooded tonight, there’s an adult on the perch.

May 14 dusk

A visit this morning gave a chance to observe both adults head off to hunt in tandem, though I didn’t see them bring in any prey.

May 14 5

The female left the male to it as he drifted off further away from St George’s, and went into a terrific stoop that brought her several hundred metres back to the nestbox in a couple of seconds.

May 14 6

As they came and went, it gave the chance to capture some photos, which I’ll leave you with below.

May 14 4May 14 3May 14 2May 14 1

And finally, a word of warning: the cameras will be going off on Monday morning for an hour – entirely scheduled and nothing to panic about.






Ten Days Old

The three chicks are growing well and all appears to be progressing nicely for them.  The unhatched fourth egg is beginning to be forgotten by the adults, squeezed out by the growing chicks as they’re brooded, as seen below (screengrab on Thursday 5th May).

May 5 egg 1

At one point on Thursday  the egg was set aside with no warmth from the adult’s body, which looked like a decisive moment (below) in the female turning her back on the final egg.

May 5 egg 2

The adults continue to find plenty of food locally to support the chicks’ growth, with Feral Pigeons still the usual prey item, though a Yellow Wagtail – presumably passing over Sheffield – was a notable exception.  Also on Thursday 5th, the male passed morsels of food to the female, who then fed the chicks, something that is a change from the usual pattern.

May 5 male feeding female

His smaller size allows her to take food from him if necessary, though this particular male always seems ready to hand over whatever he’s brought in to the nest.  The male Peregrine is known as a tiercel, which comes from his being about a third smaller (in weight) than the female.  His size is evident in the screengrab below, and means that he can no longer do much in the way of brooding the chicks.

A visit to St George’s this morning, Sunday 8th, coincided with a changeover as the male brought in a prey item for an early morning feed.  The female departed and took up station on the Arts Tower, one of her favoured perches.

May 8 female

The male left some 10 minutes later, no doubt having fed the chicks, but neither adult returned to the nest as I’d expected.

May 8 male lift off 1

With the male’s (and even the female’s) ability to brood now limited, the weather (finally!) having taken a turn for the better and the chicks having grown considerably, the need for constant protection is ever less pressing, even at this early stage.

The comparison above shows just how much the chicks have grown over the last 10 days, but there’s still a long way to go in that department and they will continue to grow and develop rapidly over the next three weeks or so.

And finally, for those who’ve never been to St George’s, I thought an image of the church showing the nest platform and webcams might be of interest.  You can just about make out the female on the top right-hand turret, stretching her wing, typically keeping a close eye on things, even when she’s not in sight on the webcams.

St George's

Three it is

With chicks having hatched on successive days over 26th, 27th and 28th April, there seems no chance of the fourth egg now hatching, so we’ll have to hope our brood of three makes it through to fledging successfully.  In 2014, the only year to have seen all four eggs hatch here in Sheffield, there was a gap of a couple of days between the third and fourth eggs hatching, after the first three all hatched on the same day (more on that later), but at the end of 2nd May we’re now a good four days since the third egg hatched on 28th April.

April 29 chicks

In each of the past breeding seasons, the number of chicks known to have hatched has been the number to have fledged, so there’s good reason to be optimistic on that front, especially now we seem to have moved past the cold spell that saw them hatch to temperatures just above freezing.  On the brief occasions when the chicks are left unattended, they tend to huddle together, which will help keep them warm.  However, it won’t be enough to have any effect on the remaining egg, which is still being brooded by the adults, as evident below.

April 29 handover

As is also evident in this screengrab, the egg is finding itself pushed out from prime position under the brood patch by the chicks that have hatched and will grow rapidly.  Whatever the reason behind the failure of the fourth egg to hatch, it’s likely that over the next few days it will start to be pushed aside and will eventually be abandoned.

The webcam has allowed insights into some fascinating behaviour over the last few days, something I’ve never seen (or heard of) before.  My suspicion that the female is a new mate has re-surfaced as a result of some clumsy incidents, which have seen her scatter the chicks when she’s stood up to leave the nest.  One such occasion occurred on Friday 29th when she got up from brooding and left the nest to allow the male to feed the chicks, spilling one of the chicks to the back of the nestbox, its head just visible begging below on the far right-hand side of the inside of the box.

April 29 spill 2

Given their age and stage of development, they cannot walk or move themselves any distance.  The male fed the two chicks in the scrape, but noticed the movement at the back of the box and approached the ‘lost’ chick, which is began pecking at.  I feared the worst and thought that as it had left the nest it might be seen as a food item.  After a few seconds, the male stopped pecking at it and left it alone.  Was it still alive?

April 29 spill 1

The female then replaced the male and took over feeding the two chicks before also noticing the displaced chick and also moving over to it, also proceeding to peck at it.  My concern suddenly changed to astonishment as she picked it up by the wing and carried it back to the other two chicks and put it down in the centre of the scrape.  In the heavily cropped screengrab below, you can make out the chick’s open beak facing upwards as it’s carried.

April 29 spill 3 blow up

The female then left the nest with the three chicks back in place, but the third chick missed out on the feed.  Subsequently, it seems to have got back into the feeding routines.

April 29 post-spill

Perhaps others know of this behaviour, but it’s not something I’ve ever seen myself nor read about.  It may not be as unusual as I thought, for Wendy Bartter, one of the devoted webcam watchers, captured the same behaviour in the middle of the night (!) just prior to the incident I saw.  Her terrific video capture can be seen online via the Twitter feed, or here

Back to the question of the eggs hatching at the same time, mentioned at the outset.  Another of the fascinating things I’ve learned from Tim Birkhead’s book on eggs is that the eggs in a nest ‘talk’ to each other shortly before hatching, making a series of sounds that are audible to other chicks in eggs in the brood, though it seems this depends on the eggs touching each other, so the cues may also be sensory.  This is what enables many species to synchronise the emergence of their broods, and is another reason to feel that the fourth egg had not developed and will not hatch.

I made a couple of visits to St George’s on Saturday and saw the male perched on the church for most of the time, out of sight of the webcam but in earshot of the female as she brooded the chicks and keeping an eye out for potential threats (a passing Crow was of particular interest).  A picture from below as he circled back to his watchpoint.

PG April 30