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)
