Abstract
Parental provisioning behavior is a major determinant of offspring growth and survival, but high provisioning rates might come at the cost of increased predation threat. Parents should thus adjust provisioning activity according to current predation threat levels. Moreover, life-history theory predicts that response to predation threat should be correlated with investment in current reproduction. We experimentally manipulated perceived predation threat in free-living great tits (Parus major) by presenting parents with a nest predator model while monitoring different aspects of provisioning behavior and nestling begging. Experiments were conducted in 2 years differing greatly in ecological conditions, including food availability. We further quantified male territorial aggressiveness and male and female exploratory tendency. Parents adjusted provisioning according to current levels of threat in an apparently adaptive way. They delayed nest visits during periods of elevated perceived predation threat and subsequently compensated for lost feeding opportunities by increasing provisioning once the immediate threat had diminished. Nestling begging increased after elevated levels of predation threat, but returned to baseline levels by the end of the experiment, suggesting that parents had fully compensated for lost feeding opportunities. There was no evidence for a link between male exploration behavior or aggressiveness and provisioning behavior. In contrast, fast-exploring females provisioned at higher rates, but only in the year with poor environmental conditions, which might indicate a greater willingness to invest in current reproduction in general. Future work should assess whether these personality-related differences in delivery rates under harsher conditions came at a cost of reduced residual reproductive value.
Highlights
In altricial bird species, parental provisioning is crucial for offspring growth and survival (Naef-Daenzer and Keller 1999; Metcalfe and Monaghan 2001), but it might come at the cost of an increased threat of offspring and adult predation (Skutch 1949)
Most studies to date have focused on immediate parental responses towards an increased predation threat (e.g., Ghalambor and Martin 2001; Eggers et al 2005; Peluc et al 2008), but little is known about how parents adjust different aspects of their provisioning behavior following an increase in predation threat
We further explored how much of the observed parental responses were due to the short human disturbance at the nestbox, when placing or removing the models, because human presence itself might be perceived as a predation threat for both parents and offspring
Summary
Parental provisioning is crucial for offspring growth and survival (Naef-Daenzer and Keller 1999; Metcalfe and Monaghan 2001), but it might come at the cost of an increased threat of offspring and adult predation (Skutch 1949) This is because higher nest visitation rates and higher parental activity might increase the likelihood of attracting predators of either nestlings or parents (Skutch 1949; Martin et al 2000b). Monitoring visit rates while neglecting other aspects of provisioning behavior might not give a full understanding of parental adjustments and responses towards different levels of perceived predation threat This is because it is likely that parental responses involve changes in feeding rate, and changes in the size or the type of prey delivered to the nest (Wright et al 1998; Mathot et al 2017). This implies that nest visitation rates might not always be a good predictor of the actual amount of food, nutrients, and energy delivered to the nest (e.g., Bengtsson and Rydén 1983; Blondel et al 1991; Wright et al 1998; NaefDaenzer and Keller 1999; Grieco 2001)
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