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International audience; The Mascarene Petrel Pseudobulweria aterrima is a critically endangered seabird endemic to Reunion Island, with an extremely small population suffering several threats. Fifteen polymorphic microsatellite loci were isolated from this species to analyse genetic diversity, estimate contemporary effective population size, search for evidence of a population bottleneck and see whether results support the hypothesis that life history traits could preserve allelic diversity in small populations. Results from 22 individuals found grounded as a consequence of light pollution highlight a surprisingly high genetic diversity, an absence of inbreeding, a contemporary effective population size estimated at approximately 1211 individuals and a probable bottleneck around 10 000 generations ago. Additional studies on genetic diversity and structure from a larger number of samples are thus required to evaluate the evolutionary potential of this critically endangered species.

We report the results of a study of light-induced mortality of petrels at Reunion Island which holds two endemic endangered species, Barau’s petrel ( Pterodroma baraui ) and Mascarene petrel ( Pseudobulweria aterrima ), together with an endemic non threatened subspecies of Audubon’s shearwater ( Puffinus lherminieri bailloni ). We collected 2348 birds attracted to lights between January 1996 and December 1999, among which 70% were Barau’s petrels and 29% were Audubon’s shearwaters. We found also three specimens of the very rare Mascarene petrel. Most grounded birds were fledglings (94%). Light-induced mortality was seasonal and linked with the breeding schedule of each species. At least 20–40% of the fledglings of Barau’s petrels produced annually are attracted by lights. Light-induced mortality is a recent perturbation at Reunion Island. Thus, the effects of this disturbance on the population dynamics of these long lived seabirds may be hard to detect at the present time, but they are likely to occur in the near future. Conservation actions are proposed to limit the light-induced mortality together with other actions and long-term studies focused on the most endangered species.

Although the genus Pseudobulweria was described in 1936 for the Fiji Petrel (Ps. macgillivrayi), its validity, phylogenetic relationships, and the number of constituent taxa it contains remain controversial. We tried to clarify these issues with 496 bp sequences from the mitochondrial cytochrome-b gene of 12 taxa representing three putative subspecies of Pseudobulweria, seven species in six other genera of the Procellariidae (fulmars, petrels, and shearwaters), and one species each from the Hydrobatidae (storm-petrels) and Pelecanoidi- dae (diving-petrels). We also include published sequences for two other petrels (Procellaria cinerea and Macronectes giganteus) and use Diomedea exulans and Pelecanus erythrorhynchos as outgroups. Based on the pronounced sequence divergence (5 to 5.5%) and separate phylo- genetic history from other genera that have been thought to be closely related to or have been synonymized with Pseudobulweria, we conclude that the genus is valid, and that the Mascarene Petrel (Pseudobulweria aterrima) and the Tahiti Petrel (Ps. rostrata) are distinct spe- cies. In trees constructed with maximum parsimony and maximum likelihood, Pseudobul- weria is the sister taxon to Puffinus and Calonectris, and these genera in turn are most closely related to Bulweria (and Procellaria in the maximum-parsimony tree). Pseudobulweria is not closely related to Pterodroma in either tree. Because Ps. r. trouessarti from New Caledonia, and Ps. r. rostrata from Polynesia differ by only 0.6%, these taxa do not deserve species status and should be regarded as valid subspecies. Received 7 October 1996, accepted 23 July 1997.