As might be expected, the numbers washing up on particular coasts vary somewhat from year to year, not just to changing mortality rates in the near shore waters but also on wind directions prevailing in the weeks prior to the count. This year there are already indications that the numbers of Razorbills and Guillemots are going to be higher than normal. The weather is the likely cause, with gales reducing food availability and extra stress while trying to avoid being carried too far down wind. Often in such wrecks the birds are found with flight muscles wasted away as well as having burned up their fat reserves. For the two auks (Razorbill and Guillemot) there are records going back to the 19th century of occasional early autumn wrecks as well as mid winter ones. In the Irish Sea auk wreck of 1969, the primary cause of fatal stress was shown to be problems during the post-breeding moult. After breeding these auks become flightless for at least six weeks while growing a new set of flight feathers. Other species vulnerable to winter wrecks round the British Isles have been Kittiwake (Cardigan Bay, Feb 1959) and Shag.
If early indications from personal observations are borne out by the full survey it seems likely that the species most affected in the waters from which birds have drifted to Anglesey this time is Razorbill. Taking estimates of breeding populations in the British Isles as a rough approximation of expected ratios if Guillemots and Razorbills were equally vulnerable, the expected ratio in body count would be 5 Guillemot to 1 Razorbill. From just the small and statistically inadequate sample I have seen so far the ratio here is reversed. It will be interesting to see if this is borne out when more data is available.
While the number of birds involved may be relatively large, past indications are that this sort of winter mortality will not have much effect on the auk breeding populations in the longer term. Both Razorbill and Guillemot are quite long lived, they do not breed until several years old and there tends to be a pool of non-breeders waiting to take places on the better ledges.
This article posted by Ivor Rees.