Population trends, breeding success and predation rates of Hutton's shearwater (Puffinus huttoni) : a 20 year assessment

Monitoring of breeding success in 2006/07 and 2007/08, and visits in Dec 2007 to assess levels of stoat predation and burrow densities were undertaken in order to assess the status of Hutton's shearwaters ( Puffinus huttoni ) at the 2 remaining breeding colonies. Long-term (20 year) estimates of burrow density within the Kowhai Valley show a consistent increase in burrow density within this colony. Along with the discovery of a new area of burrowed ground, these results suggest the population of Hutton's shearwater has increased in this colony over the last 20 years. Burrow density data for Shearwater Stream are less robust, but does not appear to show a decline. Measures of predation rates in the Kowhai colony show no major differences in the numbers of adult shearwaters found on transects in comparison with the late 1990s and the recovery of shearwater carcasses from burrows in 2 recent seasons also does not differ from the late 1990s. Burrow occupancy levels in both colonies in 2006/07 are similar to the 1990s. In contrast, breeding success in both the Kowhai Valley and Shearwater Stream were very low in the 2006/07 and 2007/08 breeding seasons. Due to the lack of evidence suggesting an increase in stoat predation, these low values of breeding success are hypothesised to be a result of poor at-sea feeding conditions. The apparently consistent lower breeding success at the Shearwater Stream colony (and lack of evidence for alternative local environmental impacts such as heavy snowfall or rain events within this colony) may well be a consequence of stoats, due to the differential impact of stoats at this small colony (8,000 breeding pairs) in comparison to the far larger Kowhai Valley colony (106,000 pairs). Continued annual monitoring within both colonies and a programme of stoat trapping within the Shearwater Stream colony are recommended in order to better