Monday, 31 March 2014

Razorbills in the 2014 Seabird Wreck

In a post here on 19th February attention was drawn to the major Seabird Wreck happening on the Welsh coast due to the persistent series of winter storms. The annual RSPB Beached Bird monitoring survey seemed likely to record numbers of bird bodies in orders of magnitude greater than typically found in recent decades. Also noted were early indications that disproportionate numbers of Razorbills were among the casualties in Wales. This indeed has turned out to be the case in North Wales with many more Razorbills being found than Guillemots, in spite of  having a breeding population only a fifth the size. Just a few Puffins were found here in contrast to the thousands found on the French coast, an event which inevitably attracted most of the news headlines about this seabird wreck.

Razorbill showing bill with white line and two grooves
beyond it of an adult
The enlarged and colourful beak of the Puffin in the breeding season will be familiar to all. Razorbills also have beaks that change to a lesser extent seasonally and grooves develop on the sides of the bill as the birds mature. Much of the work to clarify the sequence of bill development in Razorbills was done in the 1980s by eminent Welsh ornithologist, Peter Hope Jones. Careful examination of ringed birds of known age or breeding status as well as post-mortems on large numbers of birds killed in some major oil pollution incidents, enabled Peter to show that the characteristic vertical white line on the bill did not form until the bird’s second summer. In Britain Razorbills have only one white line, but a very small proportion of mature birds at some Norwegian colonies, as well as a few of those examined from fishery by-catches off Newfoundland had double white lines. Like many long-lived seabirds, Razorbills take several years to reach sexual maturity. Normally this is age 4, by which time most have the obvious white line and two other bill grooves beyond it. For simplicity this is referred to as W + 2, but some birds seen at the breeding colonies are W +1. The change in bill size and ornament occurs in late winter, so some February casualties may be expected with partly formed second grooves (W + 1.5).

During the seabird wreck of February 2014 I looked sufficiently closely at over 50 of the Razorbills washed up in Anglesey to have seen if they had white lines on their bills. As all did, none would have been first or second winter birds. This fits with ringing recovery data from British and Irish colonies, showing the young birds mainly disperse further to the south than the adults. Moreover, on fine winter mornings adult Guillemots and Razorbills sometimes come ashore at the breeding colonies for just a few hours. To do this it must be assumed that they would have been at sea within a few hours flying time of the colonies.
Peter Hope Jones surveying for Razorbills
and Guillemots accompanied by dependant
young in the Irish Sea, August 1981

As information on bill grooves might be of further interest in determining which segments of the Razorbill population succumbed off different parts of NE Atlantic coasts, photos were taken showing the bills of 25 birds on Anglesey beaches. Of these, 14 had the white line plus two grooves (W+2). Five more would be classified as W + 1.5 and five had W + 1. Only one bird was W + 0.5 and was thus probably over age 2 but still immature.

Whether In a few weeks time it may or may not be possible to detect if there are fewer Razorbills ashore in any of the South Irish Sea colonies remains to be seen. Guillemots stand on open ledges where sample sections of whole colonies can be monitored to determine breeding success.  This is somewhat more difficult with Razorbills as most lay in crevices or partly hidden under boulders, so estimates of productivity variability are less reliable in this species. Individual long-lived seabirds are known to sometimes skip a year in attempting to breed. Whether more Razorbills will enter this breeding season in poor condition and skip a year is possible and worth looking out for. The proportion of adult Razorbills accompanied by chicks at sea during the immediate post-breeding period in July-August might be an alternative indicator of productivity. The chicks leave the cliffs when half grown and are looked after at sea for about another 6+ weeks by one parent. At sea each small juvenile stays close to the parent, while making frequent high pitched contact calls. Experience from seabird at sea surveys in the 1980s showed that Ad+juv couples are relatively easy to distinguish. They were not scattered thinly all over the whole Irish Sea, but the young had been shepherded to a few favourable areas. Would this be another way to gather supporting evidence for relative breeding success?

This blogpost was written by Ivor Rees, a regular contributor to the Natur Cymru magazine.

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