Welsh Journals

References British Trust for Ornithology. 1983. Common Bird Census Instructions and Guidelines on Analysis. BTO. R. Bamford, Felin y Cwm, Eglwysfach, Machynlleth, Powys. Gull-Puffin interaction on the Island of Skokholm, west Wales R. H. Bradshaw Puffins are capable of carrying a number of small fish held in their bills back to their burrows. These fish are then fed to the young. Fish dangling from the bill of a Puffin tempt other birds. As a result some birds have developed the strategy of attacking fish-carrying Puffins and 'stealing' their catch. These attackers are known as kleptoparasites, the most common being the Arctic and Great Skuas (Stercorarius parasiticus and S. skua) and Herring and Lesser Black-backed Gulls (Larus argentatus and L. fuscus). Warmen et al (1983) observed two Razorbills (Alca torda) on Skokholm, possibly a pair, sitting on the sea. These birds saw a Puffin carrying fish, whereupon they chased it up to 1-5 km, and continued to chase other Puffins even after all other Razorbills had left the area. These two Razorbills also attacked Puffins on the sea. Gulls, however, do not do this but attack Puffins when landing (or coming in to land) at a colony. Gulls do not normally attack Puffins in flight as they can easily be outpaced. This short paper is concerned with the kleptoparasitic relationship between the Puffin (Fratercula arctica) and the Lesser Black-backed Gull (Larus fuscus). The Study Area and Methods The work was carried out over a four-day period during July 1985 at Crab Bay on the Island of Skokholm, west Wales. A permanent hide was present in the bay. Harris (1984) describes Skokholm as 106 hectares in extent and bounded by cliffs of Old Red Sandstone 15-30 m high. The middle of the island is covered with bracken but at the edge the vegetation is stunted due to extremes of wind, salt spray and grazing by multitudinous rabbits. The Flegg, J.J. & Glue, D. 1980. Field Guide No3, Nestboxes. BTO. Palmer, C.E. 1973. Titmice in Woodlands. Forest Record, 89. Forestry Commission. Puffins are restricted to a narrow band along the cliff edge and the majority nest in earthy burrows. From observations at the hide two hypotheses are suggested as strategies adopted by Puffins to avoid kleptoparasitic attack. The 'compact grouping' hypothesis. Puffins arrive at the colony, circle for a period of time gaining in number (forming a 'wheel') and then land together in compact groups within close proximity of each other. This, it is suggested, is designed to confuse the gull by 'swamping' it. The 'spray' hypothesis. Puffins arrive at the colony circle in a wheel but land in different areas of the colony in synchrony to distract and confuse the gull (a 'spray'). Thus both hypotheses predict that landing of Puffins should be 'clumped' in time. This was tested by counting the number of Puffins landing in 240 minute intervals and testing statistically to ascertain whether the landing pattern was significantly different from a random sample. If the Puffins were not landing in synchronous groups then the hypothesis could be rejected (and no test would be needed to find the actual position of landing). To investigate the spatial aspect of the first hypothesis, the colony was divided into eight areas by means of coloured markers. Over a four-hour period the area in which a particular Puffin landed was recorded. An 8 X 8 preceeding/following matrix was constructed. The data groups were pooled and chi-squared analysis was carried out in an attempt to prove this hypothesis. Also, counts were made at selected 15 minute intervals from 09.45 hrs until 20.00 hrs of the