Pink-footed shearwater (Puffinus creatopus) COSEWIC assessment and status report: chapter 6
Very little information exists on the biology of the Pink-footed Shearwater. The species is a colonial breeder, nesting in burrows generally in the forest. They normally return to land under the cover of darkness. During the non-breeding season a large proportion of the population undertakes a lengthy trans-equatorial migration, spending the northern summer and fall off the coasts of the United States and Canada.
The Pink-footed Shearwater breeds during the austral summer (Murphy 1936 in Guicking et al. 2001), with birds returning to the colonies during November and December (Harrison 1983). The laying of the single egg (Guicking 1999) occurs in December and January (Harrison 1983). Eggs hatch from the end of January to the beginning of February (Hodum and Wainstein 2002, 2003), and fledging takes place in May (Guicking et al. 2001). Incubation is likely shared by both parents. At hatching, one parent stays with the chick during its first days (Guicking and Fiedler 2000, Hodum and Wainstein 2002). Chicks are then left unattended, and adults are almost never found in the burrows during the day after this initial, brief brooding period, returning only at night to feed their young (Guicking 1999, Hodum and Wainstein 2002). Hodum and Wainstein (2002, 2003) estimated a hatching rate of 85% for burrows monitored on Santa Clara during the 2002 breeding season, and 78% for 2003. For successfully hatched chicks, 88% survived to day 36-46 during the 2002 season (Hodum and Wainstein 2002). For the 2003 season, and for those chicks hatched by 12 February, Hodum and Wainstein (2003) report a chick survival rate to March 21 of 88%. Exact fledging dates, and survival until fledging have not been investigated; however, the authors report an overall breeding success rate, including unhatched eggs, of 69% for 2003 (Hodum and Wainstein 2003).
There is some evidence of extended foraging trips of up to one or even two weeks for breeding birds on Isla Mocha (Guicking et al. 2001). While the authors discuss the possibility that those prolonged absences were the result of the stress of capture, handling and tagging, similar investigations on Santa Clara provide an alternative explanation. While monitoring of individual burrows and data from satellite tagged breeders at this site indicated foraging trips of 2-4 days duration during the 2002 breeding season (Hodum and Wainstein 2002), information from these techniques during the 2003 season indicated extended foraging trips of 2-18 days (Hodum and Wainstein 2003). This suggests considerable interannual differences in foraging behaviour. This research is ongoing.
As in all shearwater species, large numbers of non-breeders (including young, prospecting birds, adults that skipped breeding that year and failed breeders of the current year) are present in the colony during the breeding season. Toward the end of the season, these individuals leave the colony before the breeders, with fledglings the last to leave (Guicking et al. 2001). Breeding biology appears to be similar between Isla Mocha and colonies in the Juan Fernandez group (Guicking and Fiedler 2000). The degree of immigration, if it occurs, between the colonies is unknown.
For the Pink-footed Shearwater in general, there is no information on sex ratio, age at first breeding, proportion of breeders in the population, individual frequency of breeding or annual breeding success.
There is currently no information available on adult, sub-adult or juvenile survival rates. The causes of natural mortality are unknown.
Results from the Juan Fernandez group indicate that male Pink-footed Shearwaters are significantly larger than females. There is also evidence that breeding birds from Juan Fernandez are larger than those at Isla Mocha. As the former constitutes an oceanic environment, as opposed to the coastal ecosystem of Isla Mocha, the difference in morphometrics could indicate differing environmental adaptations (Guicking and Fiedler 2000).
Following breeding, birds from Isla Mocha move north along the western coasts of South America towards North America. It is unknown whether the entire population migrates. In addition, it is unclear if the populations from Juan Fernandez engage in the same trans-equatorial migration (Schlatter 2002).
The migration is largely indicated by the increasing presence of Pink-footed Shearwaters along the continental shelf from the Gulf of California to British Columbia, during the months of April and into November each year. Individuals have been recorded as far north as the Gulf of Alaska, and a few remain in North America during the boreal winter months (Harrison 1983). Peak numbers tend to occur in each region in September/October (Wahl 1975, Ainley 1976, Guzman and Myres 1983, Briggs et al. 1987, Vermeer et al. 1989, Hatler et al. 1978, Tershy et al. 1993). From late October numbers begin to decrease as birds move back towards Chile.
While very little is known of the species occurrence in Central America during migration, they likely move rapidly through this area. Off Costa Rica, Pink-footed Shearwaters are known to occur regularly from May-June and again from September-October (Stiles and Skutch 1989).
Nutrition and interspecific interactions
The Pink-footed Shearwater employs a number of different feeding techniques, from surface feeding, to surface plunging in pursuit of prey (Ainley and Sanger 1979, Prince and Morgan 1987, Ribic and Ainley 1988/1989). Sardine and anchovies are believed to be the main prey of breeding birds in Chile (Guicking et al. 2001), as well as that of birds over-wintering off the coast of Chile and Peru (Ainley 1976). Baltz and Morejohn (1977 in Gould 1996) found a high proportion of squid in the stomachs of five birds collected off Monterey Bay, California. This suggests a shift in diet from breeding to non-breeding distributions. Fish are also considered important, and crustaceans a minor component of the diet (Ainley and Sanger 1979, Prince and Morgan 1987).
The Pink-footed Shearwater can be either solitary or gregarious and often associates with other shearwaters throughout its range, especially Sooty and Buller’s Shearwaters (Yocom 1947, Wahl 1975, Briggs et al. 1987, Guicking et al. 2001).
Pink-footed Shearwaters are ship-attracted (K. Morgan pers. comm. 2003) and as a result large numbers are often reported around fishing vessels (Martin and Myres 1969, Wahl 1975, Wahl and Tweit 2000).
Rafting behaviour has been noted off the Juan Fernandez colonies (Guicking and Fiedler 2000). Similarly, rafts of Pink-footed Shearwaters are often noted within the species’ wintering range (K. Morgan pers. comm. 2003). This likely increases the risk of mortality from either chronic or catastrophic oiling events.
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