Yearly and seasonal variation of breeding parameters in a declining multi-brooded passerine, the Tree Sparrow

species. Single-brooded species are adapted to time breeding so that their nestlings are in the nest when food is most plentiful (Lack 1954). In contrast, species that breed more than once per season seem to opt for a different tactic, by maximizing the number of annual broods. In this regard, Lack (1954) suggested that multi-brooded species should lay as soon as conditions permit. This notion was refined by Crick et al. (1993) who argued that multi-brooded species should start laying before the optimal clutch size is largest. Following this reasoning, there should be an increase followed by a decrease in clutch size through the season (Crick et al. 1993). Thus, multi-brooded species seem to opt for a ‘quantity over quality’ strategy. That is, seasonal productivity of multi-brooded species not only depends on the productivity of each breeding attempt, but also on the number of broods that parents can raise (Crick et al. 1993, Soler et al. 1995, Weggler 2006). It is clear, therefore, that single and multiple breeders differ in their strategies for maximizing fitness (Stearns 1992). Concerning multiple breeders, they must decide how to allocate their reproductive investment between successive breeding attempts (e.g. Robinson et al. 2010). This aspect is interesting because it allows us to obtain valuable information for discerning general (annual) trends on the basis of the outcome of each of Yearly and seasonal variation of breeding parameters in a declining multi-brooded passerine, the Tree Sparrow