Data from: Plan ahead, or wing it? How storm-petrel parents adjust food delivery to young chicks

Parents must decide how to allocate energy gained from foraging between
self and offspring. Storm-petrels (Procellariiformes: Hydrobatidae) are
pelagic seabirds that travel hundreds of kilometers across multiple days
before returning to the nesting burrow to feed a dependent chick. Parents
return to the nest with food stored in the proventriculus, a portion of
which is regurgitated to their offspring. As the chick grows, provisioning
demands increase. However, it is unknown whether parents meet this
increasing demand by (1) altering their foraging strategies to acquire
more food or (2) allocating a greater proportion of their intake to the
chick. We designed, validated, and implemented a new technology—the Burrow
Scale Monitor—to measure Leach’s storm-petrels (Hydrobates leucorhous) as
they entered and exited the nesting burrow. We monitored breeding adults
over the first 30 days of chick rearing to determine whether storm-petrel
parents adjust their foraging intake to the age of the chick or simply
adjust energy allocation at the nest. Food delivery increased with chick
age, but this increase was driven to a much greater extent by parents
delivering a greater proportion of their body mass as food (i.e., a shift
in parental allocation) rather than by adults adjusting their foraging
strategy to match chick age. Only by measuring adult body mass on arrival
and exit at the nesting burrow could we understand how parents adapt their
provisioning strategy to the increasing demands of the growing
chick.