The influence of patterns of food abundance on the breeding seasons and clutch-sizes of Red Wattlebirds and Noisy Friarbirds

Abstract

Red Wattlebirds ('Anthochaera carunculata') typically lay two eggs and have a long breeding season, whereas Noisy Friarbirds ('Philemon corniculatus') usually have a clutch of three eggs and a short breeding season. We watched nests over five breeding seasons (1990, 1998-2001) near Armidale, in northern New South Wales, and recorded how frequently adults fed nestlings and removed faecal sacs. We also noted the type and size of food brought to the young. Friarbirds visited young significantly more frequently than Wattlebirds in 1990, but not in the other four years. Friarbirds also brought larger prey than Wattlebirds did, including cicadas, Christmas beetles ('Anoplognathus' spp.) and unidentified large insects. Wattlebirds fed their young a wide variety of insects as well as substantial amounts of manna. Cicadas and Christmas beetles are abundant from late November to late January, which coincides with the time when Friarbirds are feeding their nestlings and fledgelings. This suggests that the short breeding season and large clutch of Friarbirds is a result of the seasonal pattern of their food supply. Wattlebird parents took away fewer faecal sacs, and less frequently visited their young simultaneously than Friarbirds did. This is contrary to what would be expected if the small clutch and long breeding season of Wattlebirds was a result of high nest predation in that species relative to Friarbirds.