All islands in the Houtman Abrolhos were searched for seabird breeding colonies during the last week of November and first week of December 1991 (Easter Group), 1992 (Wallabi Group) and 1993 (Pelsaert Group). The number of pairs in colonies located was counted or estimated, large colonies being estimated by point or quadrat sampling. Nineteen species. totalling over 1.6 million pairs, were recorded breeding on 122 islands, islets and rocks. The Houtman Abrolhos are particularly important for the conservation of Wedge-tailed Shearwaters (1 117 800 pairs on 12 islands), Little Shearwater (30 500 pairs on 26 islands), Roseate Tern (3 450 pairs on 20 islands). Sooty Tern (260 000 pairs on nine islands), Fairy Tern (480 pairs on 14 islands), Common Noddy (132 000 pairs on one island) and Lesser Noddy (48 800 pairs on three islands). These are the first comprehensive data on the numbers of breeding seabirds in the archipelago. Future regular counts or accurate estimates will enable trends to be documented and allow evaluation of the effects of environmental and human-induced changes, such as changes in sea temperatures and sea level, increased fishing effort and increased human visitation.

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