EFFECTS OF THE 1982-83 EL NINO EVENT ON 2 ENDEMIC LANDBIRDS ON THE SNARES ISLANDS, NEW-ZEALAND

The major El Nino/Southem Oscillation event of 1982-83 disrupted weather patterns at the Snares Islands in the New Zealand subantarctic. There was an abnormal preponderance of westerly and south-westerly winds, rainfall was 3.6 times greater than the mean for the succeeding four summers and temperatures were significantly cooler than three of the four subsequent summers. Compared with four succeeding years, the few Snares Island Snipe Coenocorypha aucklandica huegeli that bred in 1982-83 did so 24 days later on average, breeding was successful in significantly fewer territories (20% c.f. 46-84%) and 3.1 times fewer young per territory left nests (0.4 c.f. 0.91-1.90). Adult mortality measured by density in the winter following the El Nino was 2.5 times greater than the mean for the 1984 to 1987 winters. High adult mortality and low recruitment of juveniles following the 1982-83 season resulted in a low density of snipe in the study area in 1983-84. Only one Black Tit Petroica macrocephala dannefaerdi nest was found in 1982-83. The first Black Tit fledglings seen in 1982-83 were a full month later than the mean date for three subsequent years. Widespread reproductive failure and delayed breeding by Snares Island Snipe and Black Tit in 1982-83 and high mortality of adult Snares Island Snipe during the 1983 winter were probably caused by a reduction in their invertebrate food supply. © 1990 CSIRO. All Rights Reserved.