Examining the role of trade-offs between current and future reproduction in shaping provisioning decisions in birds
Creators: McKinnon, Rebekah A
Publisher: name: University of Alberta Library
Year: 2024

<p>Life-history theory and parental investment theory provide the theoretical framework for understanding the adaptive strategies employed by organisms to optimize reproductive success in dynamic environments. Avian species are a valuable model for testing these theories due to their diverse life-history strategies, readily observable behaviours, and amenability for manipulations of clutch/brood size. This thesis investigates the trade-offs associated with parental investment in current versus future reproduction, as well as the adaptive adjustments made by parents in response to changing environmental conditions, focusing specifically on Arctic-breeding Peregrine falcons (Falco peregrinus tundrius). The first objective of this thesis was to assess evidence for trade-offs between investment in current versus future reproduction in birds. To do this, we conducted a systematic review and meta-analysis of 52 studies, focusing on studies that included experimental manipulations of brood size and its impact on parental provisioning behaviours. The meta-analysis revealed strong support for the existence of trade-offs, with parents adjusting their provisioning efforts in response to changes in brood size. The systematic review also highlighted gaps in the published literature, including a lack of studies testing life-history trade-offs in longer-lived avian species, including raptors. The second major objective was to investigate evidence for adaptive adjustments in parental care in Peregrine falcons, which contributes to filling the gaps identified in the systematic review. This was achieved through two separate long-term studies; one observational and one experimental. The observational study relied on provisioning data collected over 7 breeding seasons and revealed that Peregrine falcons adaptively adjust their provisioning behaviour in response to natural variation in brood demand, with higher provisioning rates observed as nestling demand increases, both via increased nestling number and increased nestling age. We also show that variance in provisioning increases with increasing nestling demand, which is consistent with predictions from variance-sensitive provisioning theory. However, given the observational nature of the study, alternative explanations are also possible, and further work is required to allow stronger inference about the precise mechanism(s) underlying the observed shifts in variance. The experimental study involved providing food supplementation at Peregrine nests over 5 breeding seasons to evaluate how supplemental food would affect parental decisions with respect to allocation to current reproduction. We found no evidence that parents provided with supplemental food had higher provisioning rates to their offspring. However, despite the lack of effect on provisioning rates, there was strong support for a positive association between supplemental food and offspring survival probability and fledging body mass. Taken together, these results suggest that parents reallocated time/energy that was saved as a result of receiving supplemental food towards brooding or nest defence rather than towards provisioning. Overall, this research contributes to a better understanding of avian parental care strategies and their implications for reproductive success. The findings highlight the importance of adaptive adjustments in parental care behaviours in response to changing environmental conditions, particularly food availability. Future studies should continue to explore a broader range of parental care behaviours and incorporate detailed observations over multiple breeding seasons to further elucidate the mechanisms underlying parental investment decisions in birds, especially in longer-lived species like Peregrine falcons.</p>