Predator-prey interactions in Arctic Peregrine Falcons

  • Author / Creator
    Hawkshaw, Kevin
  • Species interactions are thought to underlie the stability of ecosystems, and nowhere is studying such interactions more important than the rapidly changing Arctic. The foraging behaviour of generalist consumers is influenced by the abundance of multiple resources, and generalists are thought to confer stability to resource populations. Surprisingly, explicit treatment of the diverse prey communities that many predators encounter in nature has been relatively rare, with most studies confined to predator-prey pairs. My thesis investigates the relationships between predator and multiple
    prey in an Arctic ecosystem on the western coast of Hudson Bay from 2015-17, using Peregrine Falcons (Falco peregrinus) as a model species.

    First, I set out to quantify prey abundance on the landscape using distance sampling for avian species and Arctic ground squirrels (Urocitellus parryii ), and a combination of burrow counts and snap trapping for microtine rodents (lemmings and
    voles). Results of snap trapping indicated 2015 was a year of low microtine abundance, while abundance was highest in 2016 and slightly less high in 2017. Burrow counts and
    distance sampling data were analyzed using density surface modelling according to six habitat covariates, and results indicated that freshwater, productive vegetation, and low elevation were the most consistent predictors of avian abundance across species and groups. Terrain ruggedness positively influenced abundance for Arctic ground squirrels and microtine rodents, while Arctic ground squirrels specifically were more abundant at low elevation, in areas with little freshwater, and in areas with productive vegetation. Conversely, microtine burrow counts were higher in areas with freshwater that were far from the coast.

    Second, I analyzed the abundance of the most common prey types for Peregrine Falcons in relation to distance from falcon nests to evaluate evidence for a “landscape of fear” that structured prey distribution. I found songbird and goose abundance to be positively related to distance from falcon nests, and in the case of songbirds, this relationship was present even during falcon incubation, when prey consumption is relatively low. This I argue, likely indicated avoidance of breeding Peregrine Falcons when songbirds arrived in the study area and established territories. Goose
    abundance was only lower near falcon nests in late summer, when vulnerable goslings entered the population. Unexpectedly, duck abundance was negatively influenced by
    distance from falcon nests in late summer, which I argue was likely due to similar nesting habitat selection between Peregrine Falcons and Common Eiders (Somateria
    mollissima), which were the dominant duck species detected in surveys.

    Finally, I used distribution maps constructed using the aforementioned density surface models to fit a complex multispecies functional response model utilizing nearly 11,000 prey deliveries recorded by remote cameras placed at Peregrine Falcon nests. Considering uncertainty in prey identification, camera failures, and prey abundance estimates, the resulting model demonstrated negative impacts of microtine rodent (lemming and vole) abundance and food supplementation (from a concurrent experiment) on the consumption of other prey. This indicated a potential short-term mutualism between prey types as falcon diet shifted with the microtine rodent cycle, adding to a large body of literature demonstrating the indirect effects of microtine rodents on other Arctic fauna. Model predictions indicated a wide range
    of biomass consumption across nests. Predictions with a random effect of nest site-year combination differed substantially from those without, indicating potentially
    strong individual differences in foraging between breeding pairs in this population. Predicted biomass consumption was most strongly related to the abundance of small birds (songbirds and shorebirds), indicating Peregrine Falcon nestlings may face an energy shortage at nests with low local small bird abundance. Surprisingly, biomass consumption by nestlings was generally unrelated to experimental food supplementation, providing context for a previous study demonstrating higher nestling survival at supplemented nests. Overall, my thesis provides insight into how Peregrine Falcons, as apex predators of the Arctic, provision their offspring and mediate indirect interactions among prey, and is a rare investigation of predator functional responses in a multi-prey context.

  • Subjects / Keywords
  • Graduation date
    Fall 2021
  • Type of Item
  • Degree
    Doctor of Philosophy
  • DOI
  • License
    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.