Gretchen F. Wagner, Szymon Marian Drobniak , Michael Griesser

Reproductive allocation varies greatly across species and is determined by their life-history and ecology. This variation is usually assessed as the number of eggs or propagules (hereafter: fecundity). However, in species with parental care, individuals face trade-offs that affect the allocation of resources among the stages of reproduction as well as to reproduction as a whole. Thus, it is critical to look beyond fecundity to understand the evolution of life-histories and how investment into different reproductive components interact with each other. Here we assessed the influence of species-specific traits and ecological factors on interspecific variation in reproductive performance at each nesting stage of 72 avian populations. Annual productivity was unrelated to annual fecundity. Annual fecundity correlated positively with a fast life-history pace, precociality and non-migratory habits, but these traits were unrelated to reproductive success. Rather, the breeding ecology of a species determined productivity at each stage of nesting, but did not influence fecundity. These results challenge prevailing theory and emphasize that conclusions of interspecific variation in fitness based on numbers of eggs may be equivocal. Moreover, parental decisions regarding reproductive allocation face diverse constraints at different stages of reproduction, influencing the evolution of reproductive tactics in species with parental care.