Radar Surveys for Audubon’s Shearwater on Saba, Netherlands Antilles

Audubon’s Shearwater (Puffinus lherminieri), known locally as Wedrego on Saba and St. Eustatius, is a medium-sized seabird species that feeds at sea and nests on islands throughout the Caribbean and worldwide. The species is known to nest on Saba, however estimates vary widely on the island population. The shearwaters are active on-island at night when they fly in off the sea to their nests which consist of burrows or natural cavities. Globally and in the Caribbean, Audubon Shearwater populations are threatened by introduced predators such as cats, rats, and goats.

Researchers have traditionally noted the extreme limitations of using conventional aural and visual methods when surveying species such as shearwaters that visit breeding areas only at night. Work on individual vocalization patterns has been developed for other species (Fernandez and Delnevo 2009), and on-going efforts are being pursued for Wedrego. These techniques are being developed, and tested for future use. However, currently, and in general, population estimates for this species can be fraught with uncertainty, variable accuracy, and broad statistical and biological confidence limits.

Marine radar has proven effective as an observation tool, to obtain accurate, reliable counts of species, their daily timing and pattern of movements, that are otherwise difficult or impossible to observe directly, such as the Marbled Murrelet (Day and Cooper 1995), and the Black-capped Petrel (Brown 2012; Brown 2013). These studies demonstrated that radar is an effective observation and monitoring tool that far extends researchers’ ability to observe and monitor nocturnal seabirds, and enables accurate, consistent counts.

Little is known regarding the species on Saba, including how many individuals are present on the island, probable nesting areas, and flight paths the species use between at-sea foraging areas and on-island nest areas. Without a basic understanding of these parameters it is difficult to identify and prioritize conservation actions.

Herein, we describe a pilot study that used marine radar on Saba from 11-17 December 2014 to survey for Audubon’s Shearwaters.