Intra- and intergenerational costs of handicapping in the Saffron Finch (Sicalis flaveola), a thraupid with delayed plumage maturation

Life history theory posits negative trade-offs between current reproduction and survival and between current and future reproduction. We tested if the Saffron Finch (Sicalis flaveola), a sexually dichromatic thraupid with age-related plumage coloration, conforms to the expectations under this theory. Previous studies in nest-box systems have shown that both drab young males and bright-yellow older males provide similar parental care and achieve comparable reproductive success. We experimentally handicapped females and males from both age classes by clipping of three primary remiges to manipulate their parental care efforts. We compared mating pairs conformed by handicapped males of both age classes paired with non-handicapped females, handicapped females paired with either handicapped or non-handicapped males of both age classes, against control pairs (non-handicapped individuals). We assessed weight changes, feeding rates, brooding bout duration, nest temperature, and return rates for both adults and nestlings, as well as growth rate, asymptotic weight, time spent at the nest, and fledgling success. Contrary to expectations, none of the experimental individuals adjusted their feeding rates. However, we observed intra- and intergenerational costs for handicapped females mated to second-year males, including shorter brooding bouts, greater weight loss, slower offspring growth, and lighter fledglings. Thus, in our study system, lower-quality females paired with second-year males may be maximizing reproductive success under less-than-ideal circumstances.