Schaefer, Jim

Migratory fish can influence the rivers where they spawn by depositing nutrients and organic matter which increase primary and secondary production. Past research in the Laurentian Great Lakes has focused on individual tributaries, accordingly, the spatial extent of subsidies and how environmental factors influence subsidies are not clear. To determine which tributaries received subsidies, I compared stable carbon isotope values (δ13C) of resident stream fishes above and below 54 barriers in 37 tributaries. Subsidies were found in found across 43 of the barriers. The subsidy magnitude varied among the lakes, with Lake Superior having significantly larger subsidies. Correspondence analysis of environmental factors showed that large differences in δ13C were associated with steeper river channels on the Canadian Shield with little agricultural land-use. Migratory fish supply resource subsidies to rivers across the Great Lakes basin, though their magnitude is contextually dependent.

Author Keywords: barriers, Great Lakes, migratory fish, resident stream fish, resource subsidies, stable isotopes

I tracked summer movements and activity of snowshoe hares (Lepus americanus) in southwestern Yukon, Canada, during their population cycle (2015–2022) to assess the primary drivers of movement. Hares exhibited variable movement and activity during the cycle, exhibiting increased home range size and higher daily displacement during low population densities. Males exhibited more dramatic increases in their home ranges (>3-fold), and had greater and more variable movement rates and time spent travelling than females. The ratio of predators to hares was highest at low hare densities when hares were moving most, and seasonal activity of hares seemed unrelated to that of predators. Differences between sexes imply that reproductive activities likely were the main driver of hare movement variation rather than food availability. These findings reinforce that, even in highly variable environments, potential rewards associated with successful mate search and reproduction may outweigh the risks associated with reproductive behaviour.

Author Keywords: behaviour, boreal forest, GPS telemetry, home range, movement ecology, predation risk

Population cycles are characterized by predictable temporal oscillations in population size and are influenced by densities of both predators and prey. These oscillations are influenced by the predator functional response, i.e. the influence of prey density on predator kill rate. The Canada lynx (Lynx canadensis) is a predatory mammal with cyclic northern populations driven by snowshoe hare (Lepus americanus) density. Despite some understanding of the drivers of lynx cycles, we lack understanding of how lynx hunting behaviour, including kill site selection, is influenced by the spatio-temporal distribution of prey. These concepts are explored in chapter one of this thesis.

In chapter two, we (coauthors and I) built on work in Kluane region of the Yukon where lynx and hare populations have been tracked through several population cycles. Over six winters, we deployed GPS collars on >40 individual lynx, some of which were fitted with satellite transmitters, accelerometers, and audio recorders. We validated the use of these technologies for identifying hare kills with an accuracy of >87%. This validation is the foundation for chapter three of this dissertation.

In chapter three, we investigated the drivers of spatial variation in lynx kills. Using snow track transects through four winters of declining hare density, we developed a robust model of habitat-specific hare abundance over time. Using model predictions, in combination with lynx Utilization Distributions derived from GPS locations and related habitat associations, we determined the importance of hare abundance, lynx spatial use, and landscape characteristics such as vegetation density in determining patterns of lynx kills and space use. Lynx kill sites were most strongly predicted by lynx space use, followed by the relative abundance of hares, an index of tree cover density, and elevation. Lynx space use itself was not strongly predicted by hare relative abundance, but rather by a shift to the use of more open habitats when hares were abundant to higher use of denser habitats as hare populations declined; this apparently corresponded to temporal changes in hare distribution. This thesis helps to disentangle the drivers of spatio-temporal variation in predator foraging behaviour, with important implications for understanding predator-prey dynamics.

Author Keywords: animal behaviour, biologging, foraging, habitat selection, Lynx canadensis, predator-prey dynamics

Range expansion by the bobcat (Lynx rufus) may be contributing to range contraction by the Canada lynx (Lynx canadensis), but interactions between them are not well understood. To investigate the potential for competition, I conducted a literature review of hierarchical habitat selection by these two species. I determined that the lynx and the bobcat select different resources at the first and second orders, and that the fourth order is under-studied compared to higher orders. I therefore conducted a snow-tracking study of fine-scale habitat selection by lynx and bobcat in an area of sympatry in northern Ontario. I found that the two species selected similar resources at the fourth order, but appeared to be allopatric at the level of the home range. These results suggest that competition is unlikely to occur between lynx and bobcat, and other factors should be considered as more probable causes of the lynx range contraction.

Author Keywords: Bobcat, Canada lynx, Competition, Habitat selection, Scale, Snow tracking

Populations of grassland birds, including the Bobolink (Dolichonyx oryzivorus), are experiencing steep declines due to losses of breeding habitat, land use changes, and agricultural practices. Understanding the variables affecting reproductive success can aid conservation of grassland species. I investigated 1) whether artificial nest experiments accurately estimate the impacts of cattle on the daily survival rate of Bobolink nests and 2) which local, landscape, and temporal variables affect daily survival rate of Bobolink nests in Southern Ontario. I replicated an artificial nest experiment performed in 2012 and 2015 to compare the daily survival rate of artificial and natural nests at multiple stocking rates (number of cattle × days × ha-1). I also monitored Bobolink nests and modeled daily survival rate using local variables (e.g., stocking rate, field use, patch area), landscape variables (e.g., percent forest within 2, 5, and 10 km), and temporal variables (e.g., year, date of season). Results indicate that artificial nest experiments using clay shooting targets overestimated the impacts of stocking rate on the daily survival rate of Bobolink nests. With natural nests, region (confounded by year and field use), stocking rate, and date of season were the strongest predictors of daily survival rate; with stocking rate and date of season both having a negative effect. Management should focus on conserving pastures with low stocking rates (< 40 cattle × days × ha-1), late-cut hayfields, fallow fields, and other grasslands to protect breeding grounds for the Bobolink and other declining grassland bird species.

Author Keywords: Bobolink, Daily survival rate, landscape variables, local variables, Nest survival, temporal variables

Pastures and hayfields provide surrogate habitat for many declining grassland birds. Understanding agricultural land use dynamics and habitat quality can impact conservation of grassland species. I investigated 1) patterns of land use change in protected and unprotected sites in relationship to Bobolink occurrence in Carden, Ontario, Canada and 2) whether continuous grazing at lowmoderate cattle densities provided suitable breeding habitat, using both real and artificial nests. I replicated the 2001-2005 Ontario Breeding Bird Atlas to evaluate site habitat changes and Bobolink population trends. In continuously grazed pastures and late-cut hayfields, I monitored Bobolink abundance and reproductive success and modeled daily survival rate of nests using habitat management, vegetation structure, and prey availability. Results indicated that Bobolink have declined by -15.3% since 2001 in Carden; losses were explained almost entirely by changes from suitable breeding habitat (e.g. hayfields) to tilled land or by the colonization of shrubs. For pastures, stocking densities of ≤ 1Animal Units/ha did not negatively impact Bobolink. Year and caterpillar biomass, and vegetation height were the strongest predictors of nesting success in pastures and hayfields, respectively. Focus on the preservation of suitable habitat on the breeding grounds and management on small-scale beef farms can contribute to conservation action for this declining species.

Author Keywords: agricultural management, avian ecology, Bobolink, continuous grazing, grassland birds, nest success

Around the world, many populations of migratory shorebirds appear to be declining. Conservation strategies to reverse declining trends rely on, among other information, a firm understanding of breeding ground population dynamics. From 2010 to 2014, I studied a breeding population of Dunlin (Calidris alpina hudsonia) near Churchill, Manitoba using mark-recapture methods. I found that females were significantly larger than males. I subsequently developed an equation based on morphological features that successfully classified 87.1% of females and 92.6% of males, sexed using molecular techniques. Using program MARK, I quantified the annual apparent survival of adults (± SE) within the breeding population (0.82 ± 0.063 for males, 0.73 ± 0.12 for females). Transient adults made up a significant percentage of the female population (32%, P = 0.011), but non-significant in the male population (12%, P > 0.05). Re-sight rate was high for both sexes, and ranged from 0.86-0.90 per year. Sex, year, and nest initiation date were the factors that had the greatest influence on annual returns. There was no significant difference in mean inter-annual nest site distance between sexes (male: 82.01 ± 13.42 m, female: 208.38 ± 55.88 m, P > 0.05). The high survival estimates obtained in this study suggest that the breeding population is stable and may not be contributing to suspected population declines within the subspecies.

Author Keywords: demography, discriminant function analysis, mark-recapture, sexual size dimorphism, survival

Most grassland bird populations are in decline, so it is becoming increasingly important to understand how they use agricultural field types and form their communities. I performed point counts in cultural meadow, intensive agriculture, and non-intensive agriculture areas in 2011 and 2012. Generalized linear models were used to determine the habitat relationships of six focal species. I found that non-intensive agriculture was used most often and intensive agriculture was often avoided, but there were exceptions which indicate habitat use can be species-specific. I determined in which habitats competition was likely occurring and which species pairs were competing in 2011. In 2012, I experimentally tested these relationships by introducing artificial competitors onto sites. By comparing presence-absence data from 2011 to 2012, I found evidence of habitat-mediated interspecific and conspecific attraction involving Bobolink and Grasshopper Sparrow. This research contributes to the current understanding of grassland bird community ecology and conservation.

Author Keywords: agriculture, BACI, community ecology, habitat use, species at risk, species interactions