Nol, Erica

Long-term avian population declines, particularly for the avian insectivore guild, are a conservation concern. With widespread and continuing population trends, climate change and its negative effects on avian food resources is a plausible cross-species driver. My goal was to evaluate whether bottom-up trophic effects of climate change could be influencing avian populations. I used a space-for-time approach to assess the influence of snowpack and soil moisture variability on arthropods and subsequent effects on nest survival. In the 2010 and 2011 growing seasons, I sampled arthropods, soil moisture (soil volumetric water content; VWC), snowpack (snow water equivalent; SWE), forest floor depth (L, F, H layers) and soil texture in conifer plantations and mixed deciduous forest in Southern Ontario's Ganaraska Forest (~4, 400 ha). I used additive linear mixed effects models to assess the responses of arthropod groups' (e.g., order or class) relative biomass (g/day) and abundance (count/day) to those variables. Influences for each arthropod group's biomass and abundance were typically in the same direction. Maximum annual SWE significantly positively influenced most arthropod groups and annual relative difference in VWC positively influenced one quarter. In mixed directions, forest type influenced half of the groups and soil texture and forest floor depth each affected less than one quarter. I then used structural equation models to evaluate relationships between SWE, VWC, the biomass of three arthropod functional guilds, and logistic-exposure model calculated daily nest survival rates for American Robin (Turdus migratorius), Eastern Wood-Pewee (Contopus virens), Least Flycatcher (Empidonax minimus), Ovenbird (Seiurus aurocapilla), and Red-eyed Vireo (Vireo olivaceus). Arthropod guilds included diet-based food, predaceous arthropods and soil-dwelling bioindicators. SWE significantly positively influenced food biomass in all five models and negatively influenced predaceous arthropods in three models. Soil moisture had a mix of positive, negative, and null effects. Eastern Wood-Pewee and Red-eyed Vireo nest survival positively related to food and negatively related to predaceous arthropod biomass. American Robin, Least Flycatcher and Ovenbird nest survival did not appear to be related to arthropod biomasses. Through bottom-up relationships, predicted climate change-induced reductions in snowpack may cause food resource declines and negatively affect some forest breeding bird populations.

Author Keywords: Arthropod biomass, Bottom-up, Forest birds, Nest survival, Path analysis, Precipitation

Northern flying squirrels (NFS) are mycophagous specialists (fungi-dominated diet) thatmay be displaced with southern flying squirrel (SFS) range expansion, thereby limiting fungal dispersal in forest communities. To understand the implications of squirrel species turnover on mycophagy, we investigated the home ranges of both flying squirrel species who are living in stable sympatry. We found no significant difference in home range sizes and identified spatial overlap between the two species. Through habitat selection ratios we found SFS were strongly selecting for deciduous-dominated habitats more than NFS. Lastly, we conducted microscopy on flying squirrel scat and found NFS were eating more fungi than SFS. We conclude that the squirrels are sharing the same habitat landscape but are finding ways to partition the habitat accordingly to allow for sympatry. SFS may contribute to the spore-dispersal cycle similarly to their northern counterpart through moderate fungus consumption and large home range sizes.

Author Keywords: diet, flying squirrels, Glaucomys, home range, mycophagy, sympatry

Understanding threats to declining species at multiple stages of their annual cycle is important for determining the cause of their declines and conserving their populations. To assess potential responses to changing habitat and predators under climate change, I compared the nest site characteristics, responses to human intruders, and migratory patterns between Short-billed Dowitchers and Stilt Sandpipers breeding in Churchill, MB. I conducted behavioural observations and habitat surveys and deployed radio transmitters on birds during incubation. Short-billed Dowitcher nests had higher concealment and adults were more aggressive than Stilt Sandpipers. Short-billed Dowitchers took an eastern migratory route and stopped in the southeast US, whereas Stilt Sandpipers migrated west. Short-billed Dowitchers displayed relatively high connectivity during migration with nearly 1/3 of confirmed stopovers occurring at a single site in Georgia. These findings highlight the importance of considering varying antipredator defense and migration strategies in the face of climate change.

Author Keywords: Central Flyway, incubation, Midcontinent, migratory connectivity, Motus, nest concealment

Migration, space use, and phenology play key roles in shaping avian populations and are therefore critical for conservation. My thesis examines the migration strategies and non-breeding spatial requirements of Virginia's beach-nesting American Oystercatchers (Haematopus palliatus), as well as the nesting phenology of mid-Atlantic American Oystercatchers and Piping Plovers (Charadrius melodus). I assessed migratory decisions using field-readable bands and GPS transmitters, finding that ~90% of Virginia's beach-nesting American Oystercatchers migrate out-of-state during the non-breeding season, though tested hypotheses did not strongly predict migration patterns. I then estimated home range sizes of American Oystercatchers during the non-breeding season, revealing high individual variation (12.1-201.6 km²) and a potential trend toward larger home ranges in males. Finally, I analyzed clutch initiation timing of American Oystercatchers and Piping Plovers in response to climate change, finding that American Oystercatchers advanced timing of breeding by 10.7 days between 2005-2022, while Piping Plovers showed no significant shift.

Author Keywords: behavioural ecology, climate change, home-range, migration, movement ecology, phenology

Diversity of flowers in flowering plants is understood to facilitate mating success, and yet understanding the relationships between plant sexual diversity and mating patterns remains a challenge. In this thesis, I used Sagittaria latifolia, an aquatic plant with unique sexual systems, to investigate relationships between plant sexual diversity, mating patterns, and reproductive success and to understand their evolutionary consequences. First, I measured the magnitude of sexual selection in a dioecious and a monoecious population of S. latifolia, while accounting for size variation. I showed that sexual selection does operate in natural populations of plants. Estimates of sexual selection were similar in both populations, possibly due to the temporal separation of female and male flowering in hermaphroditic S. latifolia, enabling individuals to act temporarily as unisexuals. Second, I examined how seasonal differences in sex allocation and flowering time can affect male mating opportunities, and the effect on reproductive success in hermaphroditic S. latifolia. I found that shifting allocations to be more male-biased with earlier flowering increased male mating opportunities. However, greater mating opportunities did not equate to higher rates of siring, indicating that factors other than temporal overlap contribute to male reproductive success. Finally, I determined the factors affecting mating and reproductive success of males and male-function hermaphrodites, distinguishing between the predictable effects of plant-level traits and population-level features, and unpredictable effects of stochastic factors. Across both populations, we found that plant-level traits had a greater impact on mating and reproductive success than population-level features. Nevertheless, these effects were frequently masked by stochastic factors. Furthermore, unexplained variation in mating and reproductive success may stem from additional plant traits affecting post-pollination gametophyte-sporophyte interactions. My findings indicate that while sexual selection does operate in natural populations of S. latifolia as expected under Bateman's principles, temporal overlap in flowering, plant traits and population features did not explain patterns of male mating or reproductive success, suggesting that post-pollination factors may be influencing mating outcomes.

Author Keywords: Phenology, Plant mating, Plant reproduction, Sagittaria latifolia, Sex allocation, Sexual selection

Arctic breeding shorebirds are often considered alternate or secondary prey to avian and terrestrial predators that primarily feed on cyclic populations of rodents. Predation risk can strongly influence habitat selection; however, there is limited understanding of how nest placement by shorebirds and subsequent risk of nest predation are affected by spatiotemporal patterns involving the indirect effects of alternate prey on predator activity. I examined nest fates of Whimbrel (Numenius phaeopus) and Dunlin (Calidris alpina) at the southernmost edge of their breeding ranges at Polar Bear Provincial Park, Ontario, using field surveys including direct observations, camera monitors and thermal probes. I used resource selection functions (RSFs) to compare used and available habitat features near shorebird nests. I assessed whether shorebird nest predation was affected by spatial patterns in avian predator activity, habitat, and small mammal alternate prey and annual variation in cyclic small mammal abundance. RSFs confirmed strong habitat selection for graminoid fen habitats with avoidance of tundra heath, presumably to avoid terrestrial predators that may use them as travel corridors. Shorebird nest predation was not affected by the spatial variation in avian predator activity. However, Dunlin nest predation risk was affected by spatial variation in small mammal abundance. Further, the effect was strongest in years consistent with peaks in the small mammal population cycle. These findings highlight the important effects of spatiotemporal variation of alternate prey densities on Arctic-Subarctic food webs, providing insights on the complex relationships affecting shorebird nest success.

Author Keywords: apparent competetion, Dunlin, Empirical Bayesian Kriging, Shorebird, Subarctic, Whimbrel

The Lesser Yellowlegs (Tringa flavipes) is a steeply declining shorebird that breeds across boreal North America. I studied nest survival in Anchorage, Alaska, USA and Churchill, Manitoba, Canada and nest site selection factors in Churchill. Nests were monitored at each site and daily nest survival rates (DSR) were calculated based on a maximum likelihood approach. Overall nest survival was ~63% for Anchorage (lcl–ucl = 0.450–0.773, n=49) and ~28% (lcl–ucl = 0.113–0.481, n=26) for Churchill. Earlier initiation dates, warmer mid-incubation temperatures and lower temperature variability during nesting were linked with higher DSR. I tested nest site selection at territorial and microhabitat scales using multiple logistic regression to compare nest sites with random points. Lesser Yellowlegs selected territories further from water and, at the microhabitat scale, taller shrubs. Projected climate-related shifts in weather and habitat will likely present both benefits and challenges to Lesser Yellowlegs.

Keywords: Lesser Yellowlegs, Tringa flavipes, shorebird, nest survival, nest success, nesting habitat, breeding habitat, boreal, sub-arctic, climate change, Anchorage, Alaska, Churchill, Manitoba

Author Keywords: boreal, breeding habitat, Lesser Yellowlegs, nest survival, shorebird, Tringa flavipes

I used 31 years of Semipalmated Plover (Charadrius semipalmatus) population data to assess the effects of vital rates on a local breeding population of plovers in Churchill, Manitoba, Canada. I used three similar Bayesian Integrated Population Models (IPMs), with the last a coupled IPM population viability analysis (PVA) approach to predict the impact of changing spring temperatures on future population size. I estimated adult and juvenile apparent survival, fecundity, immigration rate, and yearly population size estimates, and I found that population growth rate was most highly correlated with immigration and adult apparent survival. Moreover, I found that the population remained relatively stationary with a slight decline in recent years. I also found a significant positive effect of spring average daily minimum temperature on juvenile apparent survival. I used this effect to inform my PVA and to evaluate the risk of quasi-extinction for 20 years after the end of the study. I found a low quasi-extinction risk and a greater probability of the population increasing in the next twenty years when informed by predicted spring temperatures from global climate models. My findings suggest some resilience of this species to one effect of climate change and emphasize the importance of continued monitoring to assess if declines in this species will change as multiple threats to their existence in the sub-arctic progress.

Author Keywords: Bayesian, Climate change, Integrated population model, Population dynamics, Population viability, Semipalmated Plover

Climate change affects birds' reproductive ecology by altering breeding timing, distribution, and habitat suitability. Snowmelt patterns complicate these changes affecting habitat availability and suitability for birds and their arthropod prey. Snow varies as a function of both large-scale climate patterns and local-scale topography. I used elevational gradients as a proxy for local- scale snow impacts, investigating how elevation affects arthropod abundance, and nest placement, initiation, fate, and habitat for Lapland Longspur (Calcarius lapponicus) and Semipalmated Sandpiper (Calidris pusilla) north of Baker Lake, Nunavut. I found and monitored nests over multiple breeding seasons and used pitfall traps and conducted vegetation surveys. Results show that elevation significantly affects arthropod biomass and nest placement, but not nest initiation or success. Both species preferentially nested at lower elevations with higher arthropod biomass. Thus, birds in the central Arctic choose nesting sites at lower elevations with better food availability rather than higher elevations with earlier snowmelt.

Author Keywords: Arctic, arthropod biomass, Lapland Longspur, nest site selection, nest success, Semipalmated Sandpiper

Many species of shorebirds depend on stopover sites to rest and refuel during their long-distance migrations. To determine how shorebirds use migratory stopover sites, we tracked three species of shorebirds at two stopover sites in British Columbia, Canada from 2018-2021 during northward and southward migration using automated telemetry. Western Sandpipers (Calidris mauri) stayed longer at the Fraser River Estuary (4-8 days) compared to Tofino (2-6 days). We assessed habitat use of Sanderlings (Calidris alba), Semipalmated Plovers (Charadrius semipalmatus), and Western Sandpipers between beaches and mudflat at the Tofino stopover site. Time spent at the beach and mudflat habitats varied by species, tidal period, time of day, migration period, and human disturbance. This study shows that different stopover sites, and habitats within stopover sites, offer a unique set of characteristics used by birds exhibiting varying migration strategies, highlighting the importance of conserving a diversity of migration stopover locations and habitats.

Author Keywords: habitat use, human disturbance, length of stay, migration, shorebird, stopover site