Parents are expected to exhibit intermediate levels of investment in parental care that reflect the trade-off between current versus future reproduction. Providing parents with supplemental food may allow for increased care to the current brood (additive model), re-allocation of parental effort to other behaviours such as self-maintenance (substitution model) or may provide parents with a buffer against provisioning shortfalls (insurance model). We investigated the impact of parental food supplementation on provisioning behaviour and breeding success in Arctic-breeding peregrine falcons (Falco peregrinus tundrius) over five successive breeding seasons (2013-2017). We found that supplemental feeding had no impact on mean provisioning rates, yet resulted in increased nestling survival probability, increased nestling body mass, and decreased variance in nestling body mass and provisioning rates. These results are consistent with parents adopting a hybrid of the additive and substitution models. We suggest that food supplementation enables increased investment in other forms of parental care (e.g., nest defence, brooding) without altering mean provisioning rates. The lack of observed effects on mean provisioning rates, coupled with increased survival and body mass of offspring, suggests a potential reallocation of parental effort. The findings contribute to understanding the responses of peregrine falcons to food supplementation, highlighting the need for future studies to explore broader environmental contexts and potential long-term effects on parental survival and future reproduction.

Funding provided by: Natural Sciences and Engineering Research CouncilROR ID: https://ror.org/01h531d29Award Number: #RGPIN-2018-04358 Funding provided by: Northern Research Supplement *Crossref Funder Registry ID: Award Number: NRS-2018-517979 Funding provided by: University of AlbertaROR ID: https://ror.org/0160cpw27Award Number: Funding provided by: MitacsROR ID: https://ror.org/00cjrc276Award Number: #IT18033 Funding provided by: Government of NunavutROR ID: https://ror.org/03wf6h922Award Number: SC180029 Funding provided by: Nunavut General Monitoring Program *Crossref Funder Registry ID: Award Number: EC73_2019-20 Funding provided by: Nunavut Arctic CollegeCrossref Funder Registry ID: http://dx.doi.org/10.13039/501100021105Award Number: Funding provided by: Agnico Eagle Mines*Crossref Funder Registry ID: Award Number: Funding provided by: Government of NunavutROR ID: https://ror.org/03wf6h922Award Number: SC180030 Funding provided by: Government of NunavutROR ID: https://ror.org/03wf6h922Award Number: SC190039 Funding provided by: Government of NunavutROR ID: https://ror.org/03wf6h922Award Number: SC190042

For full methodological details, please refer to the full manuscript. In brief: Parents at 52 nest sites were provided with supplemental food (quail) every 5 days (weather permitting) across the 5 study years; 75 nests were included as controls and were visited at the same regularity but not food-supplemented. Nest cameras were placed at nests included in the study, and photos were processed after the field season to extract data used to calculate inter-visit intervals (IVIs). Nestlings were also weighed during regular nest visits and were banded during the final nest visit. Data was analysed using Bayesian mixed-effect models using the 'brms' package in the R statistical environment (version 4.2.0).