Alastair Franke

The influence of weather and lemmings on spatiotemporal variation in the abundance of multiple avian guilds in the arctic.

Climate change is occurring more rapidly in the Arctic than other places in the world, which is likely to alter the distribution and abundance of migratory birds breeding there. A warming climate can provide benefits to birds by decreasing spring snow cover, but increases in the frequency of summer rainstorms, another product of climate change, may reduce foraging opportunities for insectivorous birds. Cyclic lemming populations in the Arctic also influence bird abundance because Arctic foxes begin consuming bird eggs when lemmings decline. The complex interaction between summer temperature, precipitation, and the lemming cycle hinder our ability to predict how Arctic-breeding birds will respond to climate change. The main objective of this study was to investigate the relationship between annual variation in weather, spring snow cover, lemming abundance and spatiotemporal variation in the abundance of multiple avian guilds in a tundra ecosystem in central Nunavut, Canada: songbirds, shorebirds, gulls, loons, and geese. We spatially stratified our study area based on vegetation productivity, terrain ruggedness, and freshwater abundance, and conducted distance sampling to estimate strata-specific densities of each guild during the summers of 2010–2012. We also monitored temperature, rainfall, spring snow cover, and lemming abundance each year. Spatial variation in bird abundance matched what was expected based on previous ecological knowledge, but weather and lemming abundance also significantly influenced the abundance of some guilds. In particular, songbirds were less abundant during the cool, wet summer with moderate snow cover, and shorebirds and gulls declined with lemming abundance. The abundance of geese did not vary over time, possibly because benefits created by moderate spring snow cover were offset by increased fox predation when lemmings were scarce. Our study provides an example of a simple way to monitor the correlation between weather, spring snow cover, lemming abundance, and spatiotemporal variations in Arctic-breeding birds.

Landscape heterogeneity drives intra‐population niche variation and reproduction in an arctic top predator

While intra-population variability in resource use is ubiquitous, little is known of how this measure of niche diversity varies in space and its role in population dynamics. Here we examined how heterogeneous breeding environments can structure intra-population niche variation in both resource use and reproductive output. We investigated intra-population niche variation in the Arctic tundra ecosystem, studying peregrine falcon (Falco peregrinus tundrius, White) breeding within a terrestrial-marine gradient near Rankin Inlet, Nunavut, Canada. Using stable isotope analysis, we found that intra-population niches varied at the individual level; we examined within-nest and among-nest variation, though only the latter varied along the terrestrial-marine gradient (i.e., increased among-nest variability among birds nesting within the marine environment, indicating higher degree of specialization). Terrestrial prey species (small herbivores and insectivores) were consumed by virtually all falcons. Falcons nesting within the marine environment made use of marine prey (sea birds), but depended heavily on terrestrial prey (up to 90% of the diet). Using 28-years of peregrine falcon nesting data, we found a positive relationship between the proportion of terrestrial habitat surrounding nest sites and annual nestling production, but no relationship with the likelihood of successfully rearing at least one nestling reaching 25 days old. Annually, successful inland breeders raised 0.47 more young on average compared to offshore breeders, which yields potential fitness consequences for this long-living species. The analyses of niche and reproductive success suggest a potential breeding cost for accessing distant terrestrial prey, perhaps due to additional traveling costs, for those individuals with marine nest site locations. Our study indicates how landscape heterogeneity can generate proximate (niche variation) and ultimate (reproduction) consequences on a population of generalist predator. We also show that within-individual and among-individual variation are not mutually exclusive, but can simultaneously arise and structure intra-population niche variation.

Estimating nestling diet with cameras: quantifying uncertainty from unidentified food items

Cameras at nest sites are becoming a common means for quantifying nestling diet, but there are two problems associated with this method: food items delivered to nestlings often cannot be identified, and quantification of error around diet estimates for individual nests is problematic. We present a novel method of incorporating unidentified food items into diet estimates and quantifying error around these estimates for individual nests. In our method, unidentified food items are accounted for by considering all of the possible ways in which they could be allocated among previously defined food categories (possible outcomes). We then calculate the probability of each possible outcome by assuming the probability that an unidentified food item belongs to any given category is equal to the proportion of identified items from that category. All possible outcomes, along with the probability of each, represent a probability space. We allocate the unidentified food items to each category according to the most probable outcome in the probability space when estimating the contribution of each food category to nestling diets. Confidence intervals around diet estimates for each food category are estimated by simulating many samples from this probability space and using kernel density estimation. We demonstrate the implementation of our method with data from motion-sensitive cameras monitoring Arctic peregrine falcon Falco peregrinus tundrius nests in Nunavut, Canada.

Estimating Economic Carrying Capacity for an Ungulate Guild in Western Canada

Elk Island National Park in western Canada provides an ideal case study for an economic carrying capacity es- timate because it supports high density of four species of ungulates (11/km 2 ), lacks large predators, and is enclosed by a 2.1-meter mesh fence. This high density of ungulates has created persistent management challenges by altering vegetation structure and community composition. Using linear programming, we explored optimal allocation of forage resources for bison (Bison bison bison), moose (Alces andersoni), wapiti (Cervus elaphus manitobensis) and deer (Odocoileus virgini- anus and O. hemionus) to maximize ungulate biomass and numbers, when constrained by use of the major forage classes and minimum viable populations (MVP) of those ungulate species that do not cross the boundary fence (bison and wapiti). Maximum numbers of animals were achieved by a stocking combination dominated by deer and bison, whereas maximum biomass was attained when bison and moose were abundant but deer were absent. Wapiti remained at MVP during all so- lutions. Optimal solutions consistent with current ungulate densities were associated with 7 to 11% forage removal. This is less than normally assumed for sustainable forage use, and may reflect the need to account for other biotic and abiotic losses to forage in carrying capacity models for which ungulate densities can be constrained by availability of a preferred forage class (e.g., grass) as well as forage quality. This research extends the conventional animal-unit concept to multi- species systems and provides templates based on forage biomass allocation for resource managers facing similar problems of joint stocking in different environments.

Stable isotope mixing models fail to estimate the diet of an avian predator

ABSTRACT Predation can shape community structure, so understanding the diet of predators is an important aspect of ecology. Stable isotope analysis using Bayesian mixing models is a potentially powerful method of estimating diet, but results are often ambiguous. A commonly cited advantage of Bayesian mixing models is the ability to include informative priors, which can improve precision and accuracy of mixing model results. However, factors such as a large number of potential prey and high amounts of variation and correlation among isotopic signatures of prey can lead to imprecise estimate of diet when Bayesian mixing models are used. In this study, we tested the efficacy of using Bayesian mixing models for stable isotopes to estimate the diet of Arctic Peregrine Falcon (Falco peregrinus tundrius) nestlings in Nunavut, Canada, consuming a diversity of terrestrial and marine prey. In addition to stable isotopes, we also estimated diet composition by monitoring peregrine nests with motion-sensitive cameras. Stable isotope analysis was conducted using blood plasma samples collected weekly from nestlings and tissue samples from all prey groups they consumed. Uninformed mixing models, based on stable isotopes alone, had wide credible intervals around diet estimates, which indicated lemmings (Lemmus trimucronatus and Dicrostonyx groenlandicus) were the main contributor to diets. In contrast, diet estimated with motion-sensitive cameras had high precision and indicated that insectivorous birds were the dominant prey consumed. When informative priors from motion-sensitive camera data were included in Bayesian mixing models, resulting diet estimates had narrow credible intervals and generally reflected the priors. We conclude that with our data stable isotope analysis alone is inaccurate for monitoring the diet of Arctic Peregrine Falcons, but motion-sensitive cameras at nest sites provide a viable alternative method.

Precipitation and ectoparasitism reduce reproductive success in an arctic-nesting top-predator

Indirect impacts of climate change, mediated by new species interactions (including pathogens or parasites) will likely be key drivers of biodiversity reorganization. In addition, direct effects of extreme weather events remain understudied. Simultaneous investigation of the significance of ectoparasites on host populations and extreme weather events is lacking, especially in the Arctic. Here we document the consequences of recent black fly outbreaks and extreme precipitation events on the reproductive output of an arctic top predator, the peregrine falcon (Falco peregrinus tundrius) nesting at the northern range limit of ornithophilic black flies in Nunavut, Canada. Overall, black fly outbreaks and heavy rain reduced annual nestling survival by up to 30% and 50% respectively. High mortality caused by ectoparasites followed record-breaking spring snow precipitation, which likely increased stream discharge and nutrient runoff, two key parameters involved in growth and survival of black fly larvae. Using the RCP4.5 intermediate climate scenario run under the Canadian Global Climate Model, we anticipate a northward expansion of black fly distribution in Arctic regions. Our case study demonstrates that, in the context of climate change, extreme weather events can have substantial direct and indirect effects on reproductive output of an arctic top-predator population.

Nesting habitat selection and distribution of an avian top predator in the Canadian Arctic

Detecting and planning for ecosystem changes from climate and land-use alteration is limited by uncertainty about the current distribution of many species. This is exacerbated in remote areas like the Arctic, where the impacts of climate change are the strongest and where industrial exploration and development are expanding. Using remotely-sensed environmental information and known nest sites, we estimated the breeding distribution and habitat selection of the peregrine falcon ( Falco peregrinus ) throughout most of Nunavut, a massive northern Canadian territory (〉1.8 M km 2 ) encompassing ∼15% of the world’s tundra biome. Our results show that peregrine falcons selected features of prior known importance such as rugged topography, but also sites with higher than average summer temperatures, more productive land classes, lower mean elevations, and lower mean summer precipitation. Our model identifies several areas of high relative probability of peregrine occurrence, some of which were unrec...

Long-term phenological shifts in migration and breeding-area residency in eastern North American raptors

ABSTRACT Climate change can affect the distribution, abundance, and phenology of organisms globally. Variations in the timing of passage during autumn and spring migration can have consequences at individual and population levels. We assessed whether global climatic indexes and increasing air temperature over a 28 yr period were concurrent with shifts in the autumn migration phenology of 16 eastern North American raptor species. We used count data from 7 eastern North American raptor-migration watch sites and examined whether key species-specific traits such as migration strategy (complete vs. partial and trans-equatorial vs. not), diet specialization, body mass, flight strategy (soaring vs. flapping), and latitude of the northern limit of breeding distribution were associated with a shift in the timing of autumn migration. Our results suggest an overall delay across species in autumn migration passage date of ∼1 day decade−1, which coincided with an increase in temperature across eastern North America. This shift in average autumn passage date was more pronounced in short-distance migrants (+1.03 days decade−1); no shift was detected in trans-equatorial migrants. Although we did not detect clear links between annual climatic indexes and the other life-history traits studied, the results nonetheless indicate that the autumn migration phenology of eastern North American raptors may be delayed by ongoing climate change. However, the amplitude of these effects varies on a species-by-species basis. Our results—combined with new evidence of an earlier passage during spring migration for the same species in the same area—suggest that, since 1985, most raptors spent ∼2 additional days decade−1 north of our studys migration sites. Such an increase in time spent at northern latitudes in a large number of terrestrial avian predators over a wide geographic area may have profound impacts on population and ecosystem dynamics. Unraveling such impacts will require linking interspecific and intraspecific variations in phenological adjustments to ongoing climate change.

Body condition and reproductive phenology

In avian species nesting in environments characterized by a short breeding season, late or delayed breeders usually experience lower reproductive success compared to early breeders (Meijer et al. 1990, Drent 2006, Legagneux et al. 2016). For example, reduced clutch size (Perrins 1970, reviewed by Meijer et al. 1990) and decreased nestling or fledgling survival (Daan et al. 1988, reviewed by Drent 2006) in late breeders is well documented. In Arctic environments where the breeding season is particularly short, reproductive phenology strongly influences reproductive success (Lepage et al. 2000, Descamps et al. 2011, Anctil et al. 2014). Further, reproduction is an energetically demanding period of the annual cycle, especially for females that must assume the costs of egg formation (Williams 2005, Nager 2006, Vézina and Salvante 2010). During the pre-laying period, female birds face a trade-off between the advantages of early reproduction (higher reproductive success) and the costs associated with early reproduction at a time when ambient temperature is still low (e.g., allocating sufficient energy to self-maintenance rather than reproduction; Drent and Daan 1980, Rowe et al. 1994). Individuals that balance the allocation of energy between self-maintenance and reproduction during this critical lifehistory stage are expected to achieve greater success (Stearns 1992), for CHAPTER 12