The recent spate of dead birds reported along the Irish east coast was a cause of much concern both to BirdWatch
Ireland staff and to the public in general. Obviously the initial worry was that toxic pollution or a contagious
disease might have been the cause, but the National Parks and Wildlife Service were able very quickly to rule
these out The cause of death was confirmed as starvation, and all of the dead birds recovered were found to
have been in an emaciated condition. Interestingly, many were also heavily infested with nematode parasites,
which would likely have placed an additional burden on the birds' nutritional reserves. Such parasites are
extremely common in many wild birds and tend not to cause them too many problems, but in cases where a bird
is already weak and lacking in food they could perhaps be the Final straw.
Despite the fact that various different species (Cormorants, Manx Shearwaters, Shags, Razorbills, etc.) were
reported both to us and to the media as being found dead, with the exception of a Great crested Grebe found
at Poolbeg all of the birds in fact turned out to be juvenile Guillemots. We would normally expect to receive
reports of some dead young Guillemots and other auks at this time of year, as mortality of youngsters immediately
after the breeding season can be quite high, though numbers reported this year do seem higher than normal.
I suspect that
the reason that the newspapers and other media initially chose to focus on the story may have been because
they were mindful of a possible avian 'flu connection and so paid more attention to reports of dead birds
than would normally have been the case. Though no-one can be fully certain, I suspect that the deaths were
likely due to a combination of factors that affected the birds. It is certainly true that most Guillemots at
Irish colonies did begin to nest somewhat later than average this year, though it is not possible to say whether
or not global warming played a role in this. I don't think it would be correct to say that the birds are confused
as to the time of year or that the temperature is affecting their thinking in this regard: in very (perhaps overly)
simple terms, if the climate were warmer we might expect the birds to attempt to breed earlier rather than later.
Breeding can be delayed due to a number of factors, such as storms and other rough weather in areas between the
wintering grounds and breeding colonies, meaning that the bulk of the birds are reluctant to travel. Also, poor
feeding for the adults during the winter may mean that they need to spend longer building up their energy
reserves in late spring/early summer before they are ready to go through the rigours of raising chicks. Of
course, some of these factors themselves could conceivably have been caused or contributed to by global
warming, but it is too early to be certain.
Other seabirds breeding in the Irish Sea, such as various tern
species, Cormorants, etc., bred at the normal or average time this summer, and did not seem to be affected
by food shortages at all. Many of these species, particularly the terns, rely on the same general
prey (sand eels) as the Guillemots, and they seemed to cope just fine. In fact, Guillemots can catch prey at
a far greater depth than then terns can, which means that when food is scarce the Guillemots and other auks
usually tend to fare better than the terns. Also, there is no evidence that the breeding itself went badly
at the Irish auk colonies once it had commenced, and the adult birds certainly seemed to raise their chicks
as normal, which would lead us to believe that there was still plenty of food available for them throughout
the summer.
I think that the key factor here is that all of the dead Guillemots were juveniles. These leave their nests
and fend for themselves before they are able to fly (though they are able to swim and dive extremely well),
which means that they need their prey to be relatively close by. Normally this is not a problem in mid-summer,
and by the time September comes the youngsters are more mobile and better able to follow the fish shoals.
However, if the young birds were a few weeks behind in terms of their development, they would still not
have been able to fly properly and, if the fish moved significantly, may not have been able to fly with
the older birds to follow them. Young terns, which don't leave their colonies until they can fly, did not
suffer any problems, and seem to have been able to feed just fine on the sand eels. The increased incidence
of nematode parasitism amongst many of the young Guillemots may have made an otherwise survivable situation
more deadly; the reasons for this increase in parasites is not yet known, but natural fluctuations are
very common and do not themselves necessarily give cause for concern.
