The Effect of Human Predation, Rats and Goats on Small Colonies of Wedge-Tailed Shearwaters (Puffinus pacificus) in Southwest Madagascar
Three islands: Betsiboko, Jamanjaky Be and Jamanjaky Roa, off the coast of Morombe in Southwest Madagascar were visited in November 2005 to verify the existence and evaluate the health of wedge-tailed shearwater (Puffinus pacificus) colonies that were described by Otto Appert in the 1960’s (Hawkins (a) 2005; Hawkins (b) 2005). These three islands experience varying degrees of human use, ranging from low: light human predation on shearwater chicks, to high: the presence of domestic animals, collecting fuelwood on the island and more intensive harvesting of chicks. Interviews were conducted with the local Vezo (fishing) people to quantify the human predation on the shearwater chicks. Vegetation maps were drawn and observations on human presence and general state of the islands were made to determine the degree of use, outside of predation, each island experienced. Active, inactive and unknown burrows were found using transects and used to make a comparison of the burrow composition to determine whether the differences in human use correlated to a significant difference in the breeding population of shearwaters. The island with the highest degree of human use (Bestiboko) was found to have a significantly different burrow composition than the other two islands (Jamanjaky Be and Jamanjaky Roa). Using the mean burrow densities from the transect data, the population of each colony was estimated as well (Betsiboko-8 breeding pairs, Jamanjaky Roa-62 breeding pairs and Jamanjaky Be-128 breeding pairs). Although human predation appeared to have decreased the size of all of the colonies over time, it was found that indirect anthropogenic effects, the introduction of rats and goats, had a more discernible impact on the population of breeding shearwaters. While the conditions these three colonies experience are unique to Southwest Madagascar, the conclusion that rats contributed significantly to the decline in the population of the wedge-tailed shearwaters on Betsiboko can be applied to other populations of burrow-nesting seabirds (Thiebault 1995; Blight et al. 1999).
Will, Alexis P., "The Effect of Human Predation, Rats and Goats on Small Colonies of Wedge-Tailed Shearwaters (Puffinus pacificus) in Southwest Madagascar" (2005). Independent Study Project (ISP) Collection. 408.
Madagascar: Ecology and Conservation