Incubation Temperature Affects Duckling Body Size and Food Consumption Despite No Effect on Associated Feeding Behaviors

Abstract

Synopsis Developmental conditions can have consequences for offspring fitness. For example, small changes (<1°C) in average avian incubation temperature have large effects on important post-hatch offspring phenotypes, including growth rate, thermoregulation, and behavior. Furthermore, average incubation temperatures differ among eggs within the same nest, to the extent (i.e., >1°C) that differences in offspring phenotypes within broods should result. A potential consequence of within-nest incubation temperature variation is inequality in behaviors that could cause differences in resource acquisition within broods. To investigate this, we incubated wood duck (Aix sponsa) eggs at one of two ecologically-relevant incubation temperatures (35°C or 36°C), formed mixed-incubation temperature broods after ducklings hatched, and conducted trials to measure duckling behaviors associated with acquisition of heat (one trial) or food (three trials). Contrary to our predictions, we found no effect of incubation temperature on duckling behaviors (e.g., time spent occupying heat source, frequency of feeding bouts). However, we found evidence that ducklings incubated at the higher temperature consumed more food during the 1-h feeding trials, and grew faster in body mass and structural size (culmen and tarsus) throughout the study, than those incubated at the lower temperature. Apparent food consumption during the trials was positively related to culmen length, suggesting that differences in food consumption may be driven by structural size. This could result in positive feedback, which would amplify size differences between offspring incubated at different temperatures. Thus, our study identifies incubation temperature as a mechanism by which fitness-related phenotypic differences can be generated and even amplified within avian broods.

Incubation temperature as a constraint on clutch size evolution

“…Although it is possible that some phenotypic differences could be adaptive responses to incubation temperature, it is likely that lower incubation temperatures produce suboptimal phenotypes (see Table S1). For example, wood ducks that are artificially incubated at lower temperatures are smaller (DuRant et al., 2010; Hope et al., 2020), and survival probability in the wild increases with duckling body mass (Sedinger et al., 2018). Wood ducks incubated at lower temperatures also have more difficulty exiting the nest (Hope et al., 2019), and failing to exit the nest is fatal.…”

Warmer incubation temperatures and later lay‐orders lead to shorter telomere lengths in wood duck (Aix sponsa) ducklings

“…We transported eggs to Virginia Tech at room temperature, weighed all eggs, and rotated unincubated eggs twice daily before beginning incubation. To stagger hatching, we held eggs for 5 days after their lay‐date (all eggs were held for the same number of days) before beginning incubation, which does not affect hatchability (Hope et al, 2018, 2020; Walls et al, 2011).…”