Captive breeding update
As reported last month, Durrell has been artificially incubating chough eggs this year. On 30th April our first egg hatched. Closely followed by a second then three more within a week. These eggs were from the first clutches of two different pairs.
It is always a worrying time waiting for an egg to hatch. It can take over 24 hours for a chough to hatch out of its shell and ours certainly were not in a rush. If a chick is strong and healthy it has no problems hatching. Occasionally, however, a chick is too weak and struggles. We encountered this in two of our eggs, the chicks began external pipping (chipping away at the egg shell) but were sadly too weak to break out and died in the shell.
The five chicks which did successfully hatch were still not in the clear. As mentioned in last month’s report one of these chicks had complications with a protruding yolk-sac and died within a few days. The other four did much better and grew bigger each day. Quite an achievement considering staff had never hand-reared a chough before and rearing from the egg stage is always the hardest.
The hand-rearing protocol used was based on our previous experience with rearing passerines. We also looked to Paradise Park for information, as they have tried artificial incubating and hand-rearing choughs in the past, as well as to other global institutions who have corvid experience.
We fed the chicks a diet of finely chopped mice and papaya with insects added from day 3. To start with they were fed every hour from 6am until 11pm. As they get older their energy demands change and they only need feeding every 90 minutes or two hours. We also cut back on the duration of feeds so that by the time they were a few weeks old they were fed from 7am until 7pm.
When we feed them we play back recordings of wild chicks begging, the noise the female makes at the nest when arriving with food and, in between feeds, we play adult flight calls. This helps the chicks to associate with chough voices and not the human ones around them. To aid this we also minimised the amount of human contact time and stopped taking them home in the evenings. At Durrell we usually take the hand-reared birds home with us to avoid making several trips back to the office at night and at 6am in the morning. This stops when the chicks are about to fledge. It becomes too hazardous to drive them home having them hop around in the brooder. For the choughs we stopped once their eyes started opening. This particular species is prone to imprinting and for the reintroduction project it is imperative that they don’t imprint on the wrong thing.
For this reason we also wore a black glove and used red tweezers when hand feeding the chicks. This presented the chick with the rough image of a parent’s head and not a human hand. We want the chicks to have a certain level of tameness for the release process, but we don’t want them taking food from a tourist’s hand. It seemed to do the trick. They never stopped eating anyway. Chicks were weighed daily and, on comparison with wild chick data, by the end of May they were exceeding all standards.
Double-clutching efforts 2014
Whilst we did show that choughs can produce a second clutch if the conditions are correct, we failed to glean anything of use from those clutches.
As mentioned last month there were problems with parents discarding eggs and the loss (escape) of Arthur disrupted Issy’s attempts. We managed to rescue three eggs to set in our incubator. Unfortunately these suffered from the same problems as the last clutches. Insufficient weight loss leading to embryonic deaths. Hopefully, we can look back through the data collected this year and work out improved incubation protocols for next year.
Summary of hand-rearing programme
Statistically a 33% success rate from 13 eggs is not a great achievement and there are definitely areas for improvement. However, it is still an incredible accomplishment to have hand-reared four chicks from eggs all taken before parental incubation had really begun. It takes a lot of commitment and emotional investment on behalf of the keepers. A lot has been learnt that will not only benefit the chough breeding programme but the other species hand-reared at Durrell too.
Chough chicks take about 6-7 weeks before they leave the nest. Normally the keepers are used to seeing their hand-reared chicks fly within three weeks. This is double the effort and double the wait to see if these four chicks successfully fledge into well adapted juveniles fit for release into Jersey.
Health screening and DNA sexing
Chough chicks are hard to sex visually. It is based on bone measurements and body weights although individuals can vary. Common practice in captivity is to take a pin-prick of blood dotted on blotting paper and send it off for DNA analysis. All four chicks had samples taken and we will await to hear the results in June.
They had their first visit to the vets this month. All routine. We screen faecal and blood samples for various parasites and bacteria whilst the birds are held at Durrell. We will screen again once they are out at Sorel. It allows us to make comparisons and highlight any concerns which may require treatment to increase their chances of survival.
Whilst in the hand, each chick was implanted with a transponder. This has a unique code which allows individuals to be identified if rings are lost or maliciously removed as can be the case in the pet trade. The chicks didn’t seem too phased by their visit as they were eating as soon as they went back to their housing.
Sorel soft-release update
April saw the start of the 2014 soft-release for eight choughs up at Sorel. Very quickly eight became six with the mysterious disappearance of Yellow and Cerise after the first week (see April’s report).
After a week or so of opening and closing hatches each day, Red and the young male White grew in confidence and decided to join the others when they flew out of the hatches.
By May the six had started to fly as a group, feed as a group, and play in the quarry buildings as a group. But, when it came to returning to the aviary they still had their own ideas. Sometimes they would fly back in twos or threes. We could, with relative ease, shut them in to the back sections and reopen hatches waiting for the remainder to return.
When they returned as a group of six it often made it impossible to shut the hatches. There might be at least one bird on the roof on lookout whilst the others fed inside. Any movement like a passing cyclist or friendly team member approaching the hatches and an alarm call would send the group fleeing.
We also encountered the same problem as last year with the pair, Green and Mauve, who don’t like being shut in. They would bolt at the first sign of a keeper. Unless of course they were really hungry in which case their motivation to be outside was overruled by their stomachs. On the odd occasion of one of them being shut in, the other would hang around the aviary begging to be let in with them.
It was quickly becoming apparent that not all of the choughs liked being shut in. We did not want them to start viewing the aviary as a negative experience. The soft-release method had to be adapted. Instead of locking them in as they returned we waited until roost. At this point if the birds were in the aviary they were already fed, settled, and hopefully asleep and oblivious to the keepers. Hatches were reopened the next day and the timing brought forward by 30-60 minutes each day. So eventually the birds were being released at 8am then locked in again at 9pm.
It meant that the team faced a long day spending the last hour before roost accounting for all six birds, then lurking in gorse bushes or hedgerows while waiting until sunset. On a couple of occasions the radio signals indicated that all six were at the aviary, but due to fading light and roost boxes it wasn’t obvious to see exactly where they were. We would not know until sunrise. Twice we found a bird had spent the night in the external roost box on the side of the aviary.
On one or two occasions Mauve would roost in the quarry whilst her partner chose to roost in the aviary with the others. She would reappear at the aviary in the morning for breakfast.
By the end of May the birds had clearly settled into a routine and were adapting well to life outside the aviary. The hatches were finally left open so the birds could come and go as they pleased.
Radio-tracking sessions started to blur into feeding sessions as the birds quickly learnt what time of day to expect staff to be at the aviary. At the first visit at 7:30am you might find them probing the ground by the edge of the cliff path, but as soon as they catch site of you or hear the gate opening they take to the air calling and fly to the aviary. It would also happen during the day, providing they were hungry enough. This time of year there are plenty of insects around to keep them occupied. As well as other distractions/attractions (depending on your view) at Sorel this time of year.
Dispersal range of released choughs
With the exception of the missing birds, the released choughs have not ranged far from their release site. We know choughs can fly far if they feel the need to. Yet during the breeding season they tend to stick within a few hundred metres of their nest site. Our choughs are not exactly in a normal situation though. What is more they are entering into an environment with no other choughs for guidance (or competition) and a habitat that still needs improving.
Last year they quickly turned the quarry into their second home and would venture no further. In fact they didn’t really spend much time elsewhere except the aviary. The only ground they touched in between was Sorel Point.
In April it looked like it was going to be much the same. As the group cohesion outside the aviary strengthened and the birds became more confident it quickly changed. By May they were foraging the grazed land next to the aviary. Probing for insects in amongst the flock of sheep.
After a week or so of exploring this area they decided to take it up a gear. During the phase of releases when hatches were opened around 10:30 and closed at sunset the group spent a few days visiting Crabbé.
Like clockwork they would fly west when the hatches opened. At first just circling the valley before heading to 2km west then soon straight to their destination. By the time the radio-trackers had jumped in the car and driven round the group would be back at Sorel.
We pre-empted them one day by splitting up and stationing one person at Crabbé before the hatches opened. Sure enough they flew over and continued over the shooting range out of site. Very quickly they returned, flew around Île Agois, then back to the aviary. They did this three times within 60 minutes and never landed at Crabbé.
These were exploratory flights which obviously told them they were better off staying at Sorel as they soon stopped going. This could be for very several reasons. Firstly the raven chicks had just fledged. They don’t pose a threat to the choughs but the parents definitely didn’t want the extra company in ‘their’ air space. A more likely threat would come from the nearby peregrine parents with their newly hatched, hungry chicks. Gunshot from inside Crabbé’s shooting range didn’t scare the choughs but guaranteed they weren’t going to land on the sand bank and grassy areas. The big drawback would be current habitat. A lot of agricultural fields, bracken and other overgrown vegetation are not what the choughs are looking for. There is a small area of short grass around the cliff path approach, but at the time of the chough visits there were hikers and farm vehicles that would deter a first time chough visitor from landing.
What is interesting is their lack of desire to explore the Devil’s Hole side of the valley where the sheep roam. They can see the land from the aviary, but as far as the team know the birds have never touched down over there. Maybe in time when they deplete their insect supply at Sorel.
The choughs also seem to avoid exploring the rocky cliffs on foot and the lower grazed areas that slope down into the sea. Again this might be something that comes with time. For now they seem happy around the aviary. Free board and lodgings. Why look anywhere else?
Training finally pays off
When people hear about how the releases have ‘skewed’ off plan they are quick to assume that the behavioural training has not worked. A bird is a bird; it will do its own thing. In some respects this is true. They haven’t always returned to the aviary when the whistle was blown for dinner but it may not be because they don’t know what the whistle means. There are many reasons why they don’t return and each bird has its own reason.
Evidence that the training has worked came to light once the birds gained confidence and started settling into a routine of returning to the aviary at night.
The choughs are now frequently flying up from the surrounding cliff top when they hear the whistle and heading straight to the aviary. They then land on the target boards where the keeper has left the food. If the food is left inside the aviary they can be cautious and wait patiently on the netting above until the keeper has left. They feel less restricted when the food is left outside and can fly within inches of the keeper’s head following them from target to target.
This has also meant we can continue to record body weights when they land on the scales in just the same ways as when they were locked in the aviary.
An interesting indirect pay-off of the training this year has been evident when they have encountered peregrines. The peregrine nesting season has probably meant there have been fewer interactions with the choughs compared to August and September last year. When a peregrine has flown along the cliff path the choughs take to the air and return to the aviary. They have obviously learnt to associate the aviary not just with food but with safe shelter.
The odd feather seemed to be appearing here and there on the ground at the release site. With all six accounted for and looking happy and healthy it could only really mean one thing. They’d started moulting. A couple of weeks later than last year but nevertheless the countdown had begun. By next month it is likely they will have moulted their tail feathers and dropped their radio transmitters.
UFO sightings over Jersey
We had a report of an unidentified flying object at Mont Orgueil Castle on the 6th. Chris Durbano a site guardian for the castle emailed Birds On The Edge to say he spent Saturday watching what he thought to be a chough feeding around the grounds of the castle. The bird disappeared as the numbers of visitors picked up during the day, but reappeared at closing time. Chris was able to take a photo clearly showing a chough stood on the ramparts of the castle. We suspect from the rings that it was Arthur our breeding male that escaped from the wildlife park on 30th April.
We visited the castle as soon as we read the message, but with the sighting being three days previous he (Arthur) had had a chance to move on. A few days after, we received a call about a chough sighted in a garden at Les Platons. The description of the bird and its behaviour makes it likely that it was indeed a chough. The team were in the area within thirty minutes of the sighting, but there was no site or sound of a chough.
It is more than likely that after being in Gorey, Arthur made his way round the coastline looking for suitable feeding grounds and a safe roost spot. It would be ideal if he made it all the way round to Sorel or back inland to the Wildlife Park. This has yet to happen and we can only hope that he finds sufficient resources to continue his journey.
A plea was made to the Jersey public and colleagues on the neighbouring islands and France were alerted to Arthur’s escape and the missing released pair (see report here). We received a handful of reports none of which resulted in finding them. We are still asking the public to report sightings of choughs via email or by phoning Durrell directly. As more and more choughs are released we will become even more reliant on the help of the public. It might be a small island but the choughs have one advantage over us….they can fly!
Landscaping at the aviary
A big thank you to Johnnie McLaughlin, Ecoscape, and Sally Dalman and the National Trust for volunteering to cut the grass and weeds around the aviary. The hedgerows are once again overgrown with bracken and weeds. It has created a haven for rodents especially rats and has been creeping closer to the aviary. Something has been having a go at the aviary netting and we need to deter them. The short grass should also create a better environment for insects, especially ants, which the choughs love to eat.