“Higher nest predation favors rapid fledging at the cost of plumage quality in nestling birds”
Lea M. Callan, Frank A. La Sorte, Thomas E. Martin, and Vanya G. Rohwer (May 2019)
Trade offs of rapid development are expressed in body feathers of birds
Developing too quickly often forces organisms to compromise the quality of traits they grow. But which traits should express these compromises in quality the most? Some traits must be used for the entire life cycle (bones, organs, immune systems) while other traits can be repaired or replaced later in life (feathers, exoskeletons, fur). These differences in the duration that traits are used suggest that when rapid development forces organisms to compromise trait quality, traits used for short periods of time should suffer the greatest losses in quality compared to traits used for life.
The authors explore this idea using body feathers that young birds grow while in the nest. For many species, these feathers are replaced shortly after leaving the nest, making them a short-lived trait. Species that grow and develop quickly show the greatest losses in nestling feather quality compared to species that develop more slowly. By contrast, adult survival probability across species shows no relationship with development speed. These contrasting findings between the quality of short-term traits like nestling feathers and long term traits like those important for adult survival, suggests that when organisms must develop rapidly, they compromise the quality of traits that can be repaired or replaced later in life.
High predation risk can favor rapid offspring development at the expense of offspring quality. Impacts of rapid development on phenotypic quality should be most readily expressed in traits that minimize fitness costs. We hypothesize that ephemeral traits that are replaced or repaired after a short period of life might express trade-offs in quality as a result of rapid development more strongly than traits used throughout life. We explored this idea for plumage quality in nestling body feathers, an ephemeral trait. We found a strong trade-off whereby nestlings that spend less time in the nest produced lower quality plumage with less dense barbs relative to adults across 123 temperate and tropical species. For a subset of these species (n=67), we found that variation in the risk of nest predation explained additional variation in plumage quality beyond development time. Ultimately, the fitness costs of a poor quality ephemeral trait, like nestling body feathers, may be outweighed by the fitness benefits of shorter development times that reduce predation risk. At the same time, reduced resource allocation to traits with small fitness costs, like ephemeral traits, may ameliorate resource constraints from rapid development on traits with larger fitness impacts.