Provisioning challenge: self-consumption versus nestling provisioning, an experimental study

A way of untangling the trade-off between investment in current offspring versus self-maintenance and future reproductive success is to determine how both parents allocate food between themselves and their offspring according to food availability. The hoopoe, Upupa epops, is an excellent model to test hypotheses about these decisions, since it is a central-place forager, a short-lived species and it reproduces successfully in captivity. We created different conditions of food availability (abundant/scarce) at two stages of the nestling period and provided different prey qualities in terms of digestibility and/or size. We hypothesized that parents would prioritize current offspring over their own maintenance. We predicted that (1) parents would offer their nestlings larger/more digestible prey, while they would eat smaller/less digestible prey and (2) when food was scarce, parents would not reduce the amount offered to nestlings. We found that both parents delivered high-quality prey to their nestlings at both stages and ate prey of lower digestibility in the early stage and smaller prey in the late stage. These results support the expectations for central-place foragers, as adults delivered the best prey to nestlings. When food availability was limited, parents at both nestling stages did not reduce the amount of consumed biomass. Despite nestlings receiving similar biomass in both treatments at the early stage, they experienced a reduction in biomass at the late stage when food was scarce. Therefore, hoopoes did not follow the typical strategy of a short-lived species, probably due to energy constraints related to a larger home range and prolonged nestling periods. In addition, females showed a more flexible response than males to changes in food availability, especially at the end of the breeding period. These sex-dependent responses could be related to different parental care investment at this stage when males take care of fledglings until independence and females are preparing for a second clutch.