December was another quiet month for the choughs, and it seems, for now at least, their exploratory days are over. The birds rarely ventured further than half a kilometre from the aviary, apparently content probing for insects in the grazed fields near the aviary. The ten juveniles were at least a little more adventurous than the older six birds however, and for the first few weeks in December, could faithfully be found every morning, perched on the muddy cliffs at the mouth of Mourier Valley, digging furiously, doing what looked like some impressive excavation work!
Quite what the birds were finding there is unclear, but our pitfall trapping showed that there were still plenty of insects about, including rove beetles, ground beetles, minotaur beetles, earthworms and leatherjackets. Leatherjackets (crane fly larvae) are known to be a favourite food item for choughs, and this is certainly evident with our birds as they excitedly, and rather comically, chase each other when one chances upon the prized invertebrate prey.
Unsurprisingly December brought more downpours, fog, gale force winds and hail, but I am thrilled to say that the choughs have battled through, all in good health. We only had one morning of heavy frost, and interestingly, early that day the birds were nowhere to be seen in the usual grazed fields.
We eventually tracked the flock to Mourier Valley, and found them foraging amongst the dead stands of bracken. We hadn’t observed the birds foraging there before, but closer inspection revealed the soil was very soft, and presumably easier to probe for insects in than the harder ground of the grazed fields. Will, Jennifer and I also adapted to the windier, wetter weather and located several “good” gorse bushes to huddle beneath or, in Jennifer’s case, lie flat on her back underneath, just to have a bit of a break from the pounding, relentless wind!
December marked seven months of living free for the older birds, and three months for the juveniles. Faecal samples were submitted to the laboratory at Durrell as part of our continuous post-release health screening. The results were very encouraging and showed that the birds’ parasite load has decreased since their last screening in October. We also monitor their health by weighing them, and we now have a second set of scales so that when the weather allows we can weigh as many individuals as possible. Despite halving the quantity of dry mix and insects that we feed the choughs in October, regular weighing shows that the birds definitely aren’t suffering from lack of food, with several even putting on weight. This and their low levels of parasites, indicates the birds are clearly maintaining good body condition and are acclimatising well to their environment.
The older choughs developed a new habit this month; during feeds they would collect several mealworms or a “beakful” of dry mix and fly out of the aviary, disappearing out of sight to a nearby field. At first we wondered whether they were simply taking their food away from the group to eat it in peace, but careful observation revealed that although sometimes they were eating it, other times they were digging a hole and hiding the food in there. Choughs caching mealworms has previously been observed by Eric Bignal in his study of supplementary feeding wild choughs in Islay (report published in British Wildlife), and the birds there were seen marking their caches with different objects such as feathers, to aid finding them later. Although we feed our choughs twice a day, they don’t receive a huge amount and it is quickly consumed, so perhaps the adults are caching food so that they have access to it later in the day.
At the beginning of the month we started to notice several muddy patches scattered randomly across the sheep grazed fields. We quickly discovered the culprits- the choughs of course. They seem to have developed a penchant for tearing up the grass, and we’ve observed the group many times this month energetically flinging clumps of grass into the air, no doubt searching for soil invertebrates to feed on.
The adult female Mauve, finally gave up pursuing her previous partner Green this month, focussing her attention instead on the two-year-old male White. We monitor the location and activity of the birds hourly throughout the day, and White and Mauve are almost always found foraging close together, often separate from the rest of the group. During supplementary feeds the pair also feed from the same dish, and regular roost checks throughout the month revealed that rather than returning to the aviary with the rest of the group at sunset, they roost together in the quarry. Fingers crossed we may now have two potential breeding pairs to keep an eye on in 2015!
Regular visitors to Sorel will undoubtedly have noticed significantly fewer sheep out and about on the north coast towards the end of the month. Unfortunately several young sheep were taken ill and because it was not clear at first what the problem was, the flock was moved into the fenced-off aviary field for close monitoring and care by their shepherd Aaron Le Couteur (CS Conservation). Test results revealed the sheep had a gastro-intestinal problem, and, being a primitive breed, they have physiological differences so often respond differently to parasites compared to commercial sheep breeds. The flock has now been treated with a novel drug and are fortunately well on the road to recovery.
We sadly said goodbye to Will at the end of December, after four months on the project. He started volunteering one week after the juveniles were released and has been following their progress ever since, spending many hours radio tracking the birds across the island and observing their antics on the cliff tops at Sorel. Will has been a huge help both in the field and in developing our invertebrate monitoring project. We wish him every success as he moves to England to pursue a career in wildlife conservation. You can read his brilliant piece about his time on the project here