Data for: Passive and active parental food allocation in a songbird

Parent-offspring conflict over food allocation can be modeled using two
theoretical frameworks: passive (scramble competition) and active choice
(signaling) resolution models. However, differentiating between these
models empirically can be challenging. One possibility involves
investigating details of decision-making by feeding parents. Different
nestling traits, related to competitive prowess or signalling cryptic
condition, may interact additively or non-additively as predictors of
parental feeding responses. To explore this, we experimentally created
even-sized, small broods of pied flycatchers and manipulated nestling
cryptic quality, independently of size, by vitamin E supplementation. We
explored how interactions between nestling cryptic condition, size,
signals, and spatial location predicted food allocation and prey-testing
by parents. Parents created the potential for spatial scramble competition
between nestlings by feeding from and to a narrow range of nest locations.
Heavier supplemented nestlings grew faster and were more likely to access
profitable nest locations. However, the most profitable locations were not
more contested, and nestling turnover did not vary in relation to spatial
predictability or food supply. Postural begging was only predicted by
nestling hunger and body mass, but parents did not favor heavier
nestlings. This suggests that size-mediated and spatial competition in
experimental broods was mild. Pied flycatcher fathers allocated food in
response to nestling position and begging order, while mothers seemingly
followed an active choice mechanism involving assessment of more complex
traits, including postural intensity interacting with order, position, and
treatment, and perhaps other stimuli when performing prey-testings.
Differences in time constraints may underlie sex differences in food
allocation rules.