Ile aux Oiseaux, a small barrier island on the south-westen fringe of the Saloum Delta, Senegal, grows at a rate of about 100 in's per year in south-easten direction. It hosts an impressive breeding population of royal tens (Sterna maxima), caspian terns (Sterna caspia), slender-billed gulls (Larus genei) and grey-headed gulls (Larus cirrocephalus). All these are ground-breeding birds, and very vulnerable to predation and human disturbance. The Saloum Delta National Park's administration is trying to set up an effective protection against intruders. Ideally the expected breeding areas should be picketed off before the breeding season's start. In order to determine beforehand which areas are to be declared off-limits one should know which criteria the birds use for selecting the breeding sites. From 1998 till 2003 I undertook detailed annual surveys of the island's topography, its vegetation and the location of breeding colonies. The colonial species, i.e. royal terns, caspian terns and slender-billed gulls consistently showed preference for the vicinity of new beach crests, either on bare sand or where the vegetation was still low. Some colonies however are found inland, be it on former beach crests or on former beaches. Grey-headed gulls instead breed in a scattered fashion on low vegetation, mostly sea purslane (Sesuvium portulacastrum). Breeding sites are located exclusively on the island's most dynamic parts, its northern and southern extremes, in areas where little or no pioneer vegetation is to be found.
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