The Accipiter - On The Park August 2005

On the Park - August 2005

The tasks that our 'flying' staff undertake are many and varied.

Incubating eggs is an extremely delicate and skilled process which the flying staff (along with some lucky volunteers) have been learning about from an expert in recent months. Mike Riley gives us the story...

Who would have thought that something like incubation could capture the hearts of so many of the staff and bring focus to one aspect of the work carried out behind the scenes in the hospital.

Let me take you back to the beginning... it all started at the end of May, when the male Griffon vulture, who we know from past experience tends to do most of the incubation, started to get fidgety and was on and off the egg throughout the day. Up until this time he had shown every care and attention and as we continued to watch we began to suspect that the egg was infertile and that the parents had given up on it.

Feeling somewhat disappointed, operation egg removal was put into action. Gary and I went up to the aviary with ladder and glove. Normally if the parents believe any egg to be fertile and due to hatch they will guard and defend the egg, however as we entered the aviary the male was off the nest ledge and showed no real signs of aggression and actually moved to the far side of the aviary, so up we went to find one egg sitting neatly in the middle of their nest.

Milky Eagle Owl chick

Gary and I exchanged a few words on how simple this was, very unlike a similar operation which had recently played out with the Milky Eagle owls. That particular removal took the combined efforts of four falconers attempting to retrieve the single chick from the nest when it was about two weeks old so that he could be used for demonstrations. Just like the boy scouts, always prepared, we were ready. Four grown men, one ladder, one dustbin lid and a glove, hold on that doesn't sound quite right as I write this down, shouldn't that be four gloves? Ok, so none of us have been in the boy scouts!

Once again Gary and I were sent up the ladder, Ash and Andy were lookouts on the ground to tell us if the parents looked like defending the chick, (to be honest Gary and I both really enjoy this side of the job immensely, we are always keen to be involved in the sort of work that involves catching the larger birds). It's quite a sight to see two grown men on a ladder, set at an acute angle with the second person, Gary this time, holding the dust-bin lid as a shield, not that easy or much of a shield when both of us are six foot tall and the bin lid is only two feet in diameter! Gary was brilliant in keeping the birds away from us as the parents were determined not to let their chick go without a fight. After the female’s first strike at us she flew kind of close to Ash and Andy, this resulted in a bit of a startled cry, no not the bird, Andy. However our combined efforts prevailed and as you can see when you next visit theTrust the procedure was a complete success and the baby Milky Eagle owl is now getting acclimatized to his new aviary and has been named Tolkein.

Griffon chick at 3 days

Sorry, I digressed a little there, back to the Griffons... so still hoping the egg was fertile, until we knew for definite we would follow our normal procedures for handling fertile eggs. Before we entered the aviary our hands were washed and scrubbed with an anti-bacterial wash and latex gloves were donned to avoid any cross contamination. Once at the top of the ladder the gloves were discarded, the egg was carefully removed and passed down to Gary.

Safely back in the incubation room we presented the egg to the candling machine, this is a device that emits a beam of light through a small hole which can be used to highlight the inner contents of eggs. On went the candling machine, lights were turned out and blinds drawn, once the rounded end of the egg was placed against the light beam the beam passed into the egg and enabled us to see what was happening within.

The moment of truth; a large dark mass could be seen inside the egg filling just over half of it. Due to the thickness of the Griffon egg shell we couldn't see any distinguishing features or indeed any movement, however a crude but true test was to place the egg on the work top and as it began to cool the chick inside started to twitch due to the drop in temperature. I say this is a crude method as it only works on chicks that are considerably well developed within the egg, however we now had a confirmed fertile egg with a well developed chick in it.

Mike with Griffon chick 14 May

We then marked one side of the egg with a number 1, turned it 180 degrees and marked it with a cross, these marks are put on the egg to monitor the half hourly turning cycle carried out automatically by the incubator. The incubator was then set at 37 degrees and the rotation observed to ensure the egg was turning 180 degrees from the start of incubation. Now was the time to call Simon who has been working with the staff teaching us about the incubation process.

Incubating an egg correctly is quite a scientific process; you need to know when the egg was laid, when the birds started to incubate the egg and how long incubation lasts for that species from start of incubation until the egg hatches. Once you have all these figures you can calculate how much weight the egg should lose each day and predict a date for the egg to hatch...easy! Unfortunately all the books that we read were quite vague on the incubation period, around 48-55 days, this left a large margin of error when calculating the weight loss, so in the end Simon opted for somewhere in the middle at 52 days.

Once the weight loss per day was calculated and the hatch date determined, it was just going to be a waiting game. Every day the egg was removed from the incubator, weighed and all results were recorded. If the egg was losing too much weight we would have to move it to a second incubator with a much higher humidity level which slowed the weight loss and vice versa; if the egg was not losing enough weight back it went into the first incubator with a lower humidity to maintain the steady daily loss.

Griffon chick developing well

As the hatch date approached we began to candle the egg again. When a chick gets close to pipping, (by that we mean just starting to crack the egg shell) it draws itself down into the pointed part of the egg and the air sac increases in size. At this point of the hatching process the automated turning mechanism on the incubator was switched off and we all waited eagerly for the chick to break through into the air sac to breath and to begin breaking out of the egg shell.

As we watched, waited and candled this failed to happen, the chick could be seen moving about in the egg when it was candled and then suddenly one morning his head had entered the air sac and the hatching process had begun. The egg was carefully examined for any fine cracks which would indicate that the chick was starting to pip, but no such cracks could be found so the egg was replaced in the incubator and was checked again that evening. Evening came but still no cracks, although we could hear the chick calling in the egg and tapping the shell.

Back on the phone to Simon for advice. Simon had mentioned that occasionally a chick would need outside help to hatch and that we might want to drill a hole into the egg and help it out. The chick had a tight timeline, only 36 hours to pip once he had entered the air-sac, if he didn't pip by then he would exhaust his air supply in the air sac and suffocate. Our expectations were that by the next day the egg would start to pip, however Saturday rolled around but still no sign of any cracks in the shell, so now it was a matter of time until Simon came to help. Once he arrived and washed up so he could examine the egg, he was in no doubt that the chick was in danger and the egg must be drilled to release the carbon dioxide build up and to let fresh air in.

Simon opening the Griffon egg

Video part 1 - 1m 41s, 2MB

Video part 2 - 1m 43s, 2MB

There was a sense of apprehension among the staff but also great excitement in seeing this delicate procedure carried out. A small drill was found and disinfected along with a pair of tweezers, all 10 pairs of eyes were on Simon either crowded in the room with him or watching through the window. You could actually see his hands shaking slightly as he placed the drill tip against the egg and then slowly started to turn the drill with his fingers. A fine dust started to appear as it worked against the shell and then very gently the drill was just through and Simon could see into the egg. If he had gone too deep with the drill he could have damaged the chick or ruptured a vein in the membrane which would have been fatal.

Once he could see through the hole and had established a clearer picture of what was going on inside the egg he started to enlarge the hole by breaking off very tiny pieces of shell with the tweezers until the hole was about 2 inches in diameter. We could all then see the fabulous sight of the baby Griffon vulture in the egg. His beak and a small part of his head had broken through the membrane so that he was able to breath.

We could also see the intricate network of blood vessels running throughout the membrane which are in turn connected to the chick, these vessels appeared not to have shut down completely and clearly still had blood flowing through them, if any were now damaged the chick could bleed to death. So the next plan of action was to keep the membrane through which the chick had thrust his head moist by very gently applying bottled water to it with a cotton bud. The new danger to the chick was that if the membrane was not kept moist the chick would dry out and the membrane could dry over his nostrils and cause suffocation. In addition the 2 inch diameter hole Simon had created in the top of the egg was gently packed with damp cotton wool to maintain a moist environment and a gap was left to allow fresh air in.

The chick, still in his egg was then placed into the high humidity incubator to prevent any further drying out. Damping of the membrane and replacing the moist cotton wool was repeated every three hours throughout the night and each falconer left a note on the chick’s progress for the next shift whilst we waited for the following day when Simon had said he would try to remove it from the shell.

The opening in a slide show
400KB (click the image)

Next afternoon Simon arrived, scrubbed up and removed the egg from the incubator. After an initial examination he slowly began to chip the shell away further to get a good look inside the egg. Unfortunately the membrane still appeared to have some viable filled blood vessels which would mean that the chick could not be extracted from the egg until the following day, however, as he began to examine the egg more closely and with a cotton-bud very gently moved the blood vessels it became apparent that the vessels had in fact closed down at both ends and had just trapped a small amount of blood in between. It was safe to continue and remove the chick.

Some more gentle chipping with the tweezers and within another 5 minutes the baby Griffon Vulture was laying in Simon's hand. After he was weighed he was placed back into the humidity incubator for a couple of hours and then put in a baby incubator. He is now rapidly gaining weight and can be seen in the baby incubator through the windows of the hospital.

On behalf of everyone at the Trust I would like to say a big thank you to Simon for sharing his expertise with us and for taking the time and effort to teach us his skills.

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