The site comprises the smaller of the two islands of the Glorieuses Archipelago, which lie in the north of the Mozambique Channel, almost equidistant from Mayotte, Aldabra and Madagascar, but 180 km west of the northernmost tip of the latter. The larger island, Grande Glorieuse, is highly degraded and of little ornithological interest. Ile du Lys is a low (up to 15 m) coral islet 10 km north-east of Grande Glorieuse. The two are connected by sandbanks that are exposed at low tide. The vegetation is patchy evergreen bushland and thicket covering around 30% of the islet.
See Box for key species. Ile du Lys supports a very large colony of Sterna fuscata, in addition to a small population (around 100 pairs in 1994) of nesting Anous stolidus. No landbirds occur. In 1996, Grande Glorieuse held seven landbird species, with no endemic species or subspecies. In the past, eight additional seabird species bred there.
Non-bird biodiversity: The islet is a nesting site for the sea-turtle Chelonia mydas (EN).
BirdLife International (2018) Important Bird Areas factsheet: Glorieuses Islands. Downloaded from http://www.birdlife.org on 19/07/2018.