We explored adaptive factors affecting the preformative molt in the passerine family Cardinalidae, and concluded that the ancestor inhabited forest habitats and underwent a partial preformative molt that included wing coverts but not primaries. Later radiations within the family appeared to be characterized by transitions from forests toward more open habitats, and such transitions also correlated positively with increased preformative molt investment, plumage signaling, and flight. While previous studies had highlighted the role of time and energy constraints in the evolution of the preformative molt in passerines, we conclude that adaptation to the physical environment has had a greater influence than constraints on the evolution of this molt in Cardinalidae. Using molt data from 430 individuals from 41 of the 51 Cardinalidae species, we tested whether social and environmental factors (delayed plumage maturation and habitat openness), as well as that of physiological and time constraints (body mass, migration distance, and breeding latitude), have influenced the evolution of the preformative molt in this family. We predicted that these five factors could relate to the extent of the preformative molt in terms of energy investment, plumage signaling, and flight. We also examined whether or not the presence of an auxiliary preformative molt correlated to the extent of the preformative molt. We found a strong phylogenetic signal for the preformative molt in Cardinalidae due to shared ancestry, with habitat openness correlating significantly with increased molt extent. We also found a very strong relationship with the auxiliary preformative molt, indicating that both episodes form part of the early life molt strategy in this family. Evolutionary histories and the environments to which each taxonomic group has adapted can diverge across passerines, and we expect that future studies will further discover the nature and strength of the evolutionary drivers of preformative molt.
LAY SUMMARY
We reconstructed the evolution and investigated the factors that have influenced molt strategies during the early life of the songbird family Cardinalidae
This “preformative” molt, which has evolved to meet the needs of young songbirds at least during their first fall and winter, is highly variable; even birds of the same species frequently replace different wing feathers.
We hypothesized that this variation allows adapting to the particular environment into which bird species evolve. We explored the factors that correlate with this variation in Cardinalidae, a family distributed throughout the Americas with a wide range of ecological requirements.
Our results indicate that the ancestor of Cardinalidae was a forest-dwelling species that did not replace primaries (the longest flight feathers) during early life, but that transition from forest to open habitats during the evolution of Cardinalidae correlated with the replacement of primaries.
Since increased solar radiation causes feather degradation, we speculate that species that colonized open habitats increased preformative molt extent to cope with exposure to increasing radiation.
Our findings show an adaptive mechanism linking molt extent (especially replacement of primaries) to the physical environment in songbirds.
