Nestling growth rate and food consumption increases under experimentally prolonged day length in a New World Sparrow

When evaluating avian reproduction, life history theory examines the
trade-offs between parental effort, the number and size of offspring, and
the rate of nestling development. The growth rates and body sizes of
developing birds vary geographically and can diverge with both latitude
and migratory strategies. In terms of offspring size, growth rate can
deviate in nestlings of the same or similar species due
to the correlated influences of weather events,
predation pressure, food availability, number of nestmates, and parental
provisioning. Furthermore, a longer photoperiod for species nesting at
higher latitudes increases the duration over which a nestling can be fed
each day, and increased nestling provisioning has been positively
correlated with growth rate. Whether the amount of time in which a bird is
fed during development drives this variation in growth rate and morphology
is unknown. By removing supplemental environmental stressors (e.g., food
availability, weather, predation pressure) and standardizing feeding rate
and environment, we explored the influence of daily duration of nestling
provisioning on dark-eyed junco (Junco hyemalis) nestlings. We hand-reared
65 chicks of a sedentary junco subspecies (J. h. carolinensis) under both
their natural photoperiod and the longer photoperiod of a closely related
migratory subspecies (J. h. hyemalis) and compared growth rate, mass,
morphology, and the amount of food consumed. Average growth rate, fasted
mass, wing length, and total daily food consumption were all greater in
birds hand-reared under the longer, more northern photoperiod treatment.
These findings suggest that increased daily photoperiod at higher
latitudes may allow for greater total food provisioning and thus may play
a role in the ability of parents in compressed breeding seasons to produce
high-quality offspring. This points to a trade-off between provisioning
effort and nestling growth rate in lower latitude (shorter photoperiod)
populations and points to an important role of developmental plasticity on
growth rate and morphology.