Introduction

A relatively new addition to the breed-ing avifauna of North America, the Manx Shearwater has the most northerly breeding range of any shearwater. It gained fame as the subject in the first demonstration of long-range homing in birds: a remarkable 5,150-kilometer journey from Boston, MA, to its Welsh nesting colony in 12.5 days (Matthews 1953). Although this burrowing nocturnal nesting species breeds locally in Canada and perhaps in the United States, its primary breeding range lies in Iceland, the Faeroe Islands, Great Britain, Ireland, France, and possibly the Azores, Madeira, and the Canary Islands.

The Manx is probably the best-known shearwater, its breeding biology having been studied in the northeastern Atlantic Ocean since the 1920s. Fieldwork by R. M. Lockley, M. P. Harris, C. M. Perrins, M. de L. Brooke, and others laid a sturdy foundation for its life history. Brooke’s 1990 monograph is an excellent summary of this work. Studies of the Manx Shearwater, facilitated greatly by the long period of banding, provided empirical support for one of population biology’s fundamental tenets: lowered post-fledging survival is associated with lower weights and/or lower fat reserves at fledging (Perrins et al. 1973).

Despite these comprehensive treatments, the status of the Manx Shearwater’s small and recently established population in North America is not well known. Like most procellariiforms, its pelagic ecology during migration and winter remain little studied. The Manx is the nominate member of a complex taxon that consists of at least 8 forms, many or all often regarded as separate species. Strong natal philopatry has tended to isolate these shearwaters, leading to intriguing divergence in several behavioral and ecological habits, including migratory pattern, foraging habitat, and diving proficiency.