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Data from: Parental control: Ecology drives plasticity in parental response to offspring signals

Caro, Shana123; Velasco, Adara42; van Mastrigt, Tjomme52; van Oers, Kees5; Griffin, Ashleigh S.6; West, Stuart A.6; Hinde, Camilla A.2

Research facility: Netherlands Institute of Ecology
Published Jun 12, 2025 on Dryad. https://doi.org/10.5061/dryad.18931zd87

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Abstract

Bird species differ in their parent-offspring interactions, and these differences may be caused by environmental variation. When food is plentiful, the chicks that are begging the most are fed the most. When food is scarce, bird species instead feed the largest offspring. While this variation could be due to parents responding to signalling differently based on food availability, it could equally be due to offspring adjusting their behaviour, to variation in information availability, or to confounding factors not related to the environment. We tested between these competing explanations experimentally, by manipulating food availability in a population of wild great tits, Parus major, while standardising offspring size and behaviour by creating mixed cross-fostered broods just before filming. To simulate variation in ecological conditions, we experimentally manipulated food availability in an alternating pattern: half of the broods received supplemental food (mealworms and waxworms) in a feeding tray given to parents, while the other half experienced natural conditions. We wanted all parents to be exposed to equivalent information from their broods during filming, so that we could rule out the possibility that offspring are driving any differences in parental provisioning preferences. We therefore standardized brood size and offspring supplementation history across all broods immediately before filming on day 8. We measured chick body size by weighing chicks during the cross-fostering, and measured begging intensity from our videos. We painted all chicks with a dot of red, non-toxic acrylic paint on the head just before filming, so that we could individually identify chicks in the videos. All videos were coded by the same observer, blind to the experimental treatment and to chick weight ranks. The order in which the observer coded the videos was random concerning whether parents were supplemented and unsupplemented. Adult identity was determined by the difference in crown feather glossiness of males and females. This isolated the effect of parental strategies while holding offspring begging and size constant across treatments, but with sufficient variation within broods to generate usable information for parents. We found that when food was more plentiful, parents were: (1) more likely to preferentially feed the chicks that were begging the most; and (2) less likely to preferentially feed larger chicks. Overall, our results suggest that parents have more control over food distribution than suggested by scramble competition models, and that they flexibly adjust how they respond to both offspring signals and cues of offspring quality in response to food availability. Consequently, depending upon environmental conditions, parental plasticity and predictably different signalling systems are favoured.