Welsh Journals

The Mammals of Sully Island PETER N. FERNS, B.Sc., PH.D. University College, Cardiff Introduction Since 1972, a regular winter live-trapping programme for small mammals has been carried out on Sully Island by undergraduates from the Zoology Department, University College, Cardiff. In some years, information has also been collected on the rabbit popula- tion. The trapping programme has now ended, and the object of this paper is to sum- marise the results obtained during the course of the eight years between 1972 and 1979. Sully Island is connected to the mainland during approximately half of the tidal cycle by a rocky causeway about 400 metres long. The island itself is about 110 metres wide from north to south, and 440 metres long. It has a total vegetated area of about 3.00 ha and is made up of Triassic marls and limestones resting non-formably on Carboniferous Limestone. The eastern half of the island is a 'Site of Special Scientific Interest' because of these geological features. A promontary fort of uncertain age occupies the eastern end and consists of three ramparts (shown as banks in Fig.l). This fort is a scheduled Ancient Monument. The ruins of a small building are situated on the northern side near the edge of the cliff. The island also has several features of ornithological interest (see Appendix) and is on the British Trust for Ornithology's Register of Ornithological Sites. The southern side of the island, together with the western and eastern ends, are bound- ed by cliffs, but the central area on the northern side is relatively flat and is flanked by a storm beach with an extensive zone of shingle below it. Vegetation One hundred and twenty eight species of flowering plants have been recorded on Sully Island and the vegetation falls into three distinct categories-grassland, scrub and marsh (Fig. 1). The island was at one time grazed regularly, though in 1843 a crop of oats was Fig. 1: Distribution of vegetation on Sully Island. The broken line running across the marsh indicates the southernmost limit of permanent standing water during average winter conditions