In temperate zone species, timing of the breeding season is determined by the minimum photoperiod or "critical day length" and the development of photorefractoriness. The integration of environmental cues like food, temperature, rainfall, and behavioural interactions determines the breeding window. However, there are a number of examples for breeding activities outside this time window. Here we investigated the possible mechanisms for early seasonal breeding activities in a population of wild canaries (Serinus canaria) that inhabits an isolated island within the Madeiran archipelago. In December 1999, breeding activities were observed six weeks before the usual onset of the breeding season on the island, which can be related to unusual heavy rainfall during the two previous months. Moreover, testosterone (T) levels of the birds were significantly higher as during the same time in previous years and showed no difference to the T levels found in the breeding season. Thus, birds do not rely on the cues given by the photoperiod alone, but react independently of day-length to favourable environmental conditions, like water availability. Therefore, the individuals of this wild canary population can be considered as seasonal opportunistic breeders. © 2003 Elsevier Science (USA). All rights reserved.