Pink-footed shearwater (Puffinus creatopus) COSEWIC assessment and status report: chapter 7

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Population Sizes and Trends

There are currently no estimates of total population size for the Pink-footed Shearwater. However, there are crude estimates of the number of breeding pairs as derived from counts of the number of burrows in each colony.

Hodum and Wainstein (2003) estimated a minimum of 2,544 occupied burrows, or breeding pairs, on Santa Clara during the 2003 breeding season. While direct counts of the total number of burrows on Robinson Crusoe appear unfeasible (Hodum and Wainstein 2002), Hodum and Wainstein (2003) estimated between 1,325 to 2,626 occupied burrows from both full and partial censuses within three study colonies on the island. The authors note that this should not be considered an estimate of Pink-footed Shearwater population size on Robinson Crusoe as many areas with burrows have not been censused. Additionally, occupancy rates were based on those determined for Santa Clara, and were not measured directly for these burrows. Current estimates for Isla Mocha are some 25,000 burrows (Guicking 1999). Assuming that all those counted on Isla Mocha are active, the estimates from all islands combined could equate to a minimum total breeding population of 57, 738 – 60, 340 individuals.

While populations in the Juan Fernandez group appear to have been more or less stable over the past 15 years (Guicking 1999), populations are believed to have declined severely in the past, particularly those on Robinson Crusoe. These declines have been attributed primarily to coati depredation. However, although current numbers likely lie much below those prior to the introduction of coatis (Bourne et al. 1992, Guicking and Fiedler 2000), due to a lack of historic information on population sizes, or the extent of colonies, quantitative estimates of the population decline are non-existent (P. Hodum pers. comm. 2003).

Although there is no direct evidence, populations on Isla Mocha are believed to be declining, most likely due to the effects of chick harvesting (Guicking 1999). It is estimated that approximately 20% of the annual chick production is taken each year (Guicking 1999), although this is a very rough estimate (Guicking in litt.).