Breeding cues in a wetland-dependent Australian passerine of the seasonally wet-dry tropics



The Capricorn yellow chat Epthianura crocea macgregori (Aves: Meliphagidae) occurs in the seasonal wet-dry tropics. This region, although coastal, is typified by highly variable annual rainfall. The Capricorn yellow chat breeds in wetlands, predominantly in the summer–autumn period, but has the capacity to breed in response to out-of-season rainfall events, consistent with an opportunistically breeding species. Most studies of breeding cues in passerines have been on species centred on temperate climates with predictable rainfall season, arid biomes with a highly variable rainfall quantity and season, and the relatively non-seasonal wet tropics. This study was focused on a species that occurs in an intermediate situation with a highly variable but summer dominant rainfall season. It aimed to identify which proximal cues are used by birds in such environments to prepare for breeding. Monthly observations at a breeding ground over a 45-month period were regressed against environmental and climatic variables. There was a significant positive relationship of chat abundance with average minimum monthly air temperature and the extent of inundation. Invertebrate food availability was also sampled. Cross-correlation with prior monthly rainfall showed that abundance of insects (Diptera, Hemiptera and Lepidoptera) and semi-aquatic invertebrates peaked 1–2 months following large rainfall events, coinciding with peaks in presence of dependent young of Capricorn yellow chats. Thus, the Capricorn yellow chat matches the model for arid-adapted birds in which seasonal cues (e.g. increasing day-length or temperature) in spring lead to breeding preparedness, but breeding only occurs in response to proximal factors such as rainfall. However, the Capricorn yellow chat differs in that breeding is delayed until rainfall is sufficient to inundate its wetland habitat and stimulate the production of food resources associated with the low vegetation and muddy margins of the temporarily flooded pools and channels; suggesting that inundation may be the most important breeding cue.