Larus argentatus – GWYLAN Y PENWAIG – Breeding resident and winter visitor
|Breeding possible||excluded from total|
|No of tetrads occupied||66 (of 478)|
|Percentage of tetrads||13.8%|
Mathew (1894) commented on an increase in the number of breeding herring gulls in the wake of the sea birds preservation act of 1869. Lockley et al (1949) traced a continued increase, despite large scale collection of gulls eggs; for example, about 3000 eggs were taken in one season at Skokholm, from a colony of 1000 pairs.
Limitations were put upon the collection of eggs at Skokholm and Skomer and the harvesting of eggs generally declined throughout the county as social conditions changed. Herring gulls accelerated their rate of increase, a process aided by the abundance of food at local refuse dumps. In 1969 Operation Seafarer recorded 11740 pairs breeding in Pembrokeshire, including 1350 pairs on Skokholm and 2200 pairs at Skomer. Most nest on the cliffs of the mainland and islands but roof nesting has been noted at Tenby and the Esso refinery at Herbrandston and suspected elsewhere.
Herring Gulls began to decrease in the lat 1970s, coinciding with the introduction of black plastic bags for refuse collection. In warm conditions these bags make good incubators for the bacterium Clostridium botulinum which is thought to have poisoned the gulls feeding on the rubbish tips. By the time the Seabird register survey of 1985-87 was conducted the breeding population had shrunk to 4062 pairs, with 613 pairs at Skomer, and 321 at Skokholm. Changes in rubbish tip operations are coming into force which will make harmful food less accessible to gulls, and this may reverse the decline.
Herring gulls are not confined to scavenging on rubbish tips, but feed widely across the fields of the county, where earthworms form an important part of their diet. They also feed around the rocky shores and the estuaries and pick up fish offal at Milford Docks, though fewer catches are landed there than in the past.
Although generally regarded as sedentary, many of our herring gulls disperse from the breeding grounds in the winter, certainly as far as the upper Bristol Channel. Juveniles can venture further, with recoveries from North Wales, Ireland, France, Holland and Poland, as well as of an Irish-bred bird visiting Pembrokeshire.
Small numbers of Scandinavian birds of the subspecies argentatus were detected in the winters of 1985 to 1987, with records occurring between 11 December and 22 February.