Breeding summer visitor, passage migrant, winter visitor
Mathew (1894) knew of colonies of 20-30 pairs which Lockley et al (1949) used as a datum to note a considerable subsequent increase in breeding numbers with 1000 pairs at Skomer and 800 pairs at Skokholm; they added that they bred at Caldey, St Margaret’s, Ramsey, Sheep Island and some mainland cliffs such as those at Pwll Deri.
Lesser Black-backed Gulls continued to increase and the Skomer colony had reached 3657 pairs by 1970 with 2500 at Skokholm. During this period Harris (1965) noted that they predominantly foraged on the agricultural mainland and mainly ate beetles. The population increased rapidly thereafter and numbered about 20,300 pairs by 1983, with 15500 at Skomer and 4557 at Skokholm. Studies showed that about 80% of their food consisted of small fish, mostly young blue whiting and poor cod (Todd 1986). Although birds continued to frequent agricultural land, and a few visited rubbish tips, the greatest proportion flew out to sea to the south-west to feed upon fish discards from the trawlers in the southern Celtic Deep, as far away as 80-100km. There has been a reduction in numbers since then, the Seabird Register survey of 1985-1987 finding 16560 pairs. Census results from Skomer illustrate how the population has changed.
The colonies at Skokholm and SKomer experienced large scale breeding failure in 1989 and 1990, and low productivity in 1991 and 1992, with eggs hatching but few young being reared. A shortage of fish seems to have been the cause, due to changes in fishing practice. The bulk of the population have now switched to foraging in mainland fields, and studies at the colonies show that they are bringing back insufficient food. They are also spending long periods away from the nest, which has led to increased predation of eggs and young by other adults. If fish remains unobtainable the population may dwindle to a level that can be sustained by food gleaned from agricultural sources. They visit all parts of Pembrokeshire to feed in the pastures, being particularly attracted to fields where slurry is being sprayed, which are being ploughed or which have just been cut for silage.
Most lesser black-backed gulls nest on the plateaux and slopes of the islands, with comparatively few on the cliffs, but a few use the roofs of buildings at the old Esso oil refinery at Herbrandston. Roof nesting was suspected in the past at Kensington hospital (St Bride’s) and at the former county cinema in Haverfordwest.
Many leave Pembrokeshire after breeding, ringing showing that they can reach Spain and Portugal by October, some penetrating to Morocco and the Canary islands during the course of the winter. Others pass through Pembrokeshire on spring and autumn passage. The bulk of the breeding birds return during March.
Rather few lesser black-backed gulls used to winter in Pembrokeshire, with 10-13 seen in 1937 (Lloyd’s diaries) and usually less than ten in a winter during the 1950s. Winter numbers had increased to about 1500 by 1971 and to 7000 by 1987, most roosting at Llysyfran reservoir. Whether these are local birds in unclear.
In most winters up to five birds of the Scandinavian races are identified between 16 November and 22 March, the majority seeming to fit the description of subspecies intermedius, which have darker mantles than the British race. A group of 30 of this subspecies seen at the Gann on 18 January 1987 was accompanied by a very convincing black-backed subspecies fuscus.
Fieldwork 1984-88 (based on 478 tetrads)
Red = breeding confirmed = 24
Orange = breeding probable = 1
Total tetrads in which registered = 25 (5.2%)
Donovan J.W. & Rees G.H (1994), Birds of Pembrokeshire
The means of field identification of the different races of LBbGs has developed beyond the assessment of the shades of the upperparts, prevalent during the 1990s. It would seem prudent therefore to discard past racial identifications in favour of more rigorous examination of future occurrences.
Graham Rees
Friday, October 25, 2013 at 9:32AM 
