Fortune telling seabirds: sooty shearwaters (Puffinus griseus) predict shifts in Pacific climate

Abstract

Indices calculated from “muttonbirding” diaries collected by the Rakiura Māori of New Zealand were correlated with future values of the Southern Oscillation Index (SOI), and the Pacific Decadal Oscillation (PDO) from 1957 to 2010. Spearman correlations showed that La Nina events tended to occur after those harvest seasons with relatively high success and chick size, whereas El Nino events tended to occur after harvest seasons with relatively low success and chick size. Generalized boosted regression models show that chick size alone is able to predict shifts in SOI from 0 to 12 months after the harvest. A model that included chick size, 2-year average PDO (prior to the harvest), and one year averages of SOI (prior to the harvest), was able to predict shifts in SOI 13–20 months after the harvest. It is likely that sooty shearwater adults (and therefore chick size and quantity) are being affected by oceanographic conditions that are also precursors to shifts in SOI, and that there is a complex interaction between PDO prior to the harvest, the harvest indices and SOI. The location and timing of adult birds at the time they are provisioning chicks could lead to potential mechanisms and requires further study.