ALES Graduate Seminar – Kevin Hawkshaw

Date(s) - 02/06/2021
1:00 pm - 2:00 pm

A graduate exam seminar is a presentation of the student’s final research project for their degree.  This is an ALES PhD Final Exam Seminar by Kevin Hawkshaw.  This seminar is open to the general public to attend.

Zoom Link:

Thesis Topic: Predator-prey interactions in Arctic Peregrine Falcons

PhD with Dr. A. Lee Foote

Seminar Abstract: 

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 was 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 on survey.

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. Taking into account uncertainty in prey identification, camera failures, and prey abundance estimates, the resulting model demonstrated negative impacts of microtine rodent abundance and food supplementation (from a concurrent experiment) on the consumption of other prey. This indicated a short term mutualism between prey types as falcon diet shifts with the microtine rodent cycle, adding to a large body of literature demonstrating the indirect effects of microtine rodents on other Arctic fauna. In combination with a model for meal size and estimates of prey mass, model predictions indicated a wide range of biomass consumption across nests in the study area. Predictions with random effects 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 food supplementation, providing context to previous study demonstrating higher nestling survival at supplemented nests. Overall, my thesis is a rare investigation of predator functional responses in a multi-prey context, providing insight into how Peregrine Falcons, as apex predators of the Arctic, provision their offspring and mediate indirect interactions among prey.