Temporal variation in food resources determines onset of breeding in an Australian mistletoe specialist

Abstract

Temporal variation in the onset of breeding has been described for various species in a range of systems. Many of these studies have found a relationship between the timing of breeding and resource levels leading to a matching of life-history stages to resource abundance. However, most of this work has been conducted in northern hemisphere temperate zones – highly regular systems where temperature and other climatic factors have a predictable influence over food abundance. We present data gathered over two years on the timing of breeding in a nomadic mistletoe specialist, the Painted Honeyeater (Grantiella picta), relative to temporal variation in the abundance of its main food resource, fruit of the Grey Mistletoe (Amyema quandang), in an Australian semi-arid environment. Arrival and departure of the breeding population occurred either side of peak mistletoe fruiting in both years. Clutches were initiated on average on Day 66 of the breeding season (assigned as 1 October for both years) in 2004 (5 December) and Day 49 (18 November) during 2005, i.e. 17 days earlier in 2005. Abundance of mistletoe fruit peaked in January in both years but increased significantly earlier in 2005. Abundance of fruit was almost identical at the mean clutch initiation dates in both years, reaching comparable levels 19 days earlier in 2005. The timing of life-history stages followed the progression of fruiting phenology and was closely matched to resource levels despite marked differences in the temporal availability of fruit between years. Painted Honeyeaters appear similar to northern hemisphere passerines that use photoperiod to time their overall breeding season and then incorporate information from the local environment to fine-tune initiation of breeding. By cuing directly on the food resource, Painted Honeyeaters may avoid temporal mismatching in this highly unpredictable environment.