The Gregarious Guillemots

Well time has flown by since my last post! It was a very busy spring season with all attention focused on the spectacular cliffs covered in myriads of seabirds. Studying the guillemots and razorbills breeding success dominated my time in May and June and gave me a really privileged insight into the trials and tribulations of their lives. I witnessed a huge range of behaviours in the guillemots. As they nest in such dense colonies there are lots of interactions between individual birds.

Guillemots form strong pair-bonds, which are maintained from year to year, most birds breed for the first time at 5 years old. In the dense colonies pairs have a ‘nest’, and in most cases return to the same location each year, which they defend as a territory. Guillemots defend the smallest known nest-area territory of any bird, about 0.05m². This includes the nest-site and an adjacent area where the off-duty (not incubating) bird of the pair can rest. They will have several neighbours most of which are less than 5cm away. Their territory is used for courtship, mating and raising their young. Before incubation begins the colony will roost at sea overnight, returning to their nests each morning, they will do this for varying periods of times from an hour to all-day, but the amount of time spent on the cliffs increases as the season progresses. So in April, on some days the whole colony would be on the cliffs and then the next day there wouldn’t be any birds. They also were more likely to be present on the cliffs for longer when the weather was calm.

Before the eggs were laid I would see a lot of allopreening (figure 1) between mates, this is when the bird preens the head and neck of its mate. Often you could see the feathers of the recipient were raised and when being preened on the chin and throat they would raise their heads vertically. To me this looked as though the recipient was enjoying the experience. The pair would also bow frequently and pairs would do this together regularly before allopreening. It is thought that bowing indicates the pair’s ownership of their territory. If one of the pair had been in a confrontation they would return to their mate and perform a mutual fencing display, where they clash bills together. This seemed to suggest that they ‘had each other’s backs’ and was a way of providing comfort and support to the bird involved in the confrontation.

 

Figure 1 Allopreening

It is when the pairs are re-establishing their sites that the most aggression occurs. If the bird feels threatened, for example, if another bird is intruding of its territory, then it will assume the alert-posture (figure 2), whereby it stands upright, extends its neck and raises its wings. Often alert-bowing will follow, where the neck moves rapidly down in an arc and then up again. The rival will respond by assuming the alert-posture as well and rebuffing the attack by pointing and stabbing its beak at its opponent. If the aggression escalates then the birds stand on their tip-toes and lift their wings higher, they can then start jabbing and grappling their beaks. However full blown fights like this weren’t common and aggression was more regularly meet with appeasement behaviour. This behaviour is well-develop to aid high-density nesting and most antagonistic interactions compromise one bird threatening and the other would display an appeasement behaviour after first retaliating briefly. Appeasement behaviours include side-preening (figure 3), turning-away and stretching-away (figure 4).

Figure 2 Alert-posture

Figure 3 Side-preening

Figure 4 Turning-away (left) and stretching-away (right)

Guillemots do not build a nest; the egg is laid directly onto the ledge. An interesting adaption to what might seem a perilous situation is it that the eggs are heavily taped at one end (figure 5); this means an egg will roll in tight circles rather than off the edge of the ledge. Both parents take it in turns to incubate the egg for up to 24 hours at a time. The egg rest on the bird’s feet and is then tucked tightly under the bird as they sit on it, there it rests against a brood-patch. This is an area of skin without feathers and is well-supplied with blood-vessels at the surface; it is an adaption many birds have to increase heat transfer to their egg(s). This also means the egg is completely out of sight to predators, such as the herring gulls. The off-duty mate roosts at sea along with immature birds, leaving just the incubating birds on the cliffs at night. In the morning and evening the number of birds on the cliffs increases as the birds change-over. The change-over is a ritualised and careful manoeuvre; the off-duty bird first approaches the incubating bird and bows its head. Sometimes the incubating bird appeared to ignore this action so its mate would preen it until it agreed to move. This agreement was demonstrated by mutual head-bowing and then both birds would shield the egg by raising their wings as the change-over happened. This would happen quickly and the raising of wings is clearly an anti-predator adaption as this is when the egg is most exposed.

Figure 5 Eggs

For my study I was trying to record the contents of the ‘nest’ and as you can imagine this was quite difficult as the egg is completely hidden under the incubating bird. Therefore a bird which is sat down could be either incubating or just sitting down. This meant I would wait to see if the bird would lift its breast so I could see whether or not it had an egg. Clearly this is something the birds do as infrequently as possible to protect their egg for predators.  If the incubating birds mate was present or if it was preening itself, there was a good chance that I would be able to sneak a peek. I also noticed that on many occasions, the first time I would see an egg at a nest both birds would be present and they both appeared very interested by the appearance of their egg.

More often than not, the incubating birds were asleep on the cliffs; they would be faced towards the cliff with their breast against the rock. Their heads were hunched into their bodies and their bills with either raised slightly or tucked into their wing. Often I could see them slowly blinking and they looked like someone who was very tired struggling to keep their eyes open. When the bird was like this I would record that they were incubating and move to the next bird, as they seemed to be able the sleep for hours.  

Once the birds were incubating their eggs the colony seemed a lot calmer. I regularly saw the off-duty mate preen the back of the incubating bird. Close physical contact with their incubating neighbours was tolerated and I actually witnessed birds preening the backs of incubating neighbours.

Once the eggs began hatching the dynamic of the colony changed again. I began seeing birds landing with fish in their beaks. Frequently, these birds would return to ‘nests’ where a chick was not present. On further reading it is likely that these birds had lost their eggs. If the bird was at the nest by itself it would just hold the fish, sometimes bowing its beak to its feet as if attempting to feed a chick. If its mate was present they would exchange the fish at their feet. This behaviour often led to aggression as other birds would try to steal the fish.

Again another clue for me that an egg had hatched was the presence of both parents at the nest and intense interest. Once the chick has hatched it continues to be brooded against the brood-patch for a few days. Which means a bird can still appear to be incubating even once the chick has hatched. The incubating birds did however seem to like preening the heads of their chicks. Also the off-duty mate would appear with a single fish for the chick and the feeding of the chick happened in much the same way as the change-over, where both parent would raise their wings to shield the chick. It was during these moments that I could record the contents of the ‘nest’.

It is after about 4 days that the chick becomes too big to the brooded against the brood-patch and is instead brooded under the wing. At this point it was much easier for me to see if a bird had a chick or not. Once the chick reaches 9-10 days old it is able to thermoregulate and does not need to be brooded, although the chick will remain under its parent’s wing to protect it from predators for the majority of the time. However when the coast is clear they will emerge from their parents wings and go for a wander round to their neighbours. This is when fights seemed to break out between neighbouring birds; as parents tied to protect their wandering chick.

Sadly but inevitably as the season progressed more and more birds lost their eggs and chicks to predation. So I more frequently saw birds bringing in food for ‘phantom chicks’. This ‘phantom chick’ phenomenon was also apparent in another behaviour; footlocking. This is when a bird bends forward so the bill touches the ground, and they then nibble their feet or pick up and drop small stones by their feet. It looked as if the bird was going to preen its chick and then realised there wasn’t one there. Furthermore, when chicks were lost the female would stay at the nest site for days still incubating their ‘phantom chick’. I really felt sorry for these birds that had invested so much into rearing a chick and now would have to wait until next year to try again.

Later in the season younger non-breeding birds also increasing begin to visit the breeding ledges. This combined with birds that had failed and wandering chicks, not forgetting preying gulls, made for a hectic colony. Then as soon as they arrived they began to leave.

The chicks start to ‘jump’ at around two weeks old. They are called jumplings rather than fledglings as they leave the nest before they can fly, and jump into the sea. This happens on calm evening before dusk and with a colony here of over 30,000 birds they jump in quite quick succession. I would certainly recommend having a picnic on the top of the cliffs around the summer solstice to witness this amazing spectacle. Chicks are seen wandering around, preening frantically and flapping their tiny underdeveloped wings. They then move to the edge of the cliff with their father, bowing to each other as they go and being pecked by the other birds they have to squeeze past. Once at the edge they bow more and more frequently until the chick jumps! They normally fall straight down with their wings and large feet outspread and will land on their bellies. If they’re lucky they will hit the water but many bounce of rocks as the fall and may have to jump a few more times before the reaching the sea. There they are reunited with their father and swim out to sea, he will care for the chicks for up to another 12 weeks. The mother stays at the nest site for up to three weeks after the chick has fledged.

And that is the amazing breeding season of a Guillemot, there’s certainly a lot to it and I feel very lucky to seen all those varied and wonderful moments. After completing my work in the morning to monitor the breeding success of the guillemots and the razorbills and I was able to ‘pop-up’ and talk to some of you up on the cliffs. As I sure many of you know we had a pair of Kestrels nesting on the cliffs this year, very well camouflaged but in plain view and close enough to be able to observe them with ease. This was one of the things I most enjoyed sharing with visitors. As they were so well camouflaged most people were unaware of their presence but once pointed out they couldn’t believe how close they were. I know it was for me, and I think it was for many others, the best view of kestrels they have ever had.  We had four young kestrels fledge from that nest and we see them soaring overhead on the reserve regularly. What a spring!


Written by Charlotte (assistant ranger)