In order to determine the impact of lesser snow goose (Chen caerulescens caerulescens) herbivory on above and belowground nutrient dynamics, a grazing and nutrient addition experiment was conducted in two habitat types utilized by snow geese near Churchill, Manitoba. Forage plant nutrition, soil microbial biomass, and inorganic and organic soil nutrients were measured in relation to the timing of grazing, over two consecutive summers. Soil was collected from the rhizosphere to determine the influence of foliar herbivory on root-microbe interactions. Primary productivity in both habitats is co-limited by the availability of both nitrogen (N) and phosphorus (P). Aboveground defoliation either caused a reduction or no change in soil microbial biomass nutrients (carbon (C), N, or P). Defoliated shoots had higher N concentrations and did not show compensatory growth within the season. Root biomass was somewhat reduced with grazing, but higher whole plant N content suggests that grazing does not compromise N-uptake.

In order to determine the impact of lesser snow goose (Chen caerulescens caerulescens) herbivory on above and belowground nutrient dynamics, a grazing and nutrient addition experiment was conducted in two habitat types utilized by snow geese near Churchill, Manitoba. Forage plant nutrition, soil microbial biomass, and inorganic and organic soil nutrients were measured in relation to the timing of grazing, over two consecutive summers. Soil was collected from the rhizosphere to determine the influence of foliar herbivory on root-microbe interactions. Primary productivity in both habitats is co-limited by the availability of both nitrogen (N) and phosphorus (P). Aboveground defoliation either caused a reduction or no change in soil microbial biomass nutrients (carbon (C), N, or P). Defoliated shoots had higher N concentrations and did not show compensatory growth within the season. Root biomass was somewhat reduced with grazing, but higher whole plant N content suggests that grazing does not compromise N-uptake.

Anthropogenic perturbations to Arctic ecosystems have influenced large-scale climate processes, as well as finer-scale ecological relationships within and amongst populations of species. Life history theory predicts a trade-off between the temporal variation in a vital rate and its impact on population dynamics. Here, we examine the drivers of long-term variation in reproductive success in a sub-Arctic common eider (Somateria mollissima) colony, and evaluate the impacts of variation in reproductive success on eider population dynamics. In Chapter 2, we develop a suite of nest survival models to evaluate the effects of variation in predator abundance, the availability and spatial distribution of alternative prey, and breeding season climate on annual common eider nest success. Eider nest success declined across the 41 years of study, but was also highly variable across years. Annual variation in nest success was driven by a complex interaction between predators and alternative prey, as well as breeding season climate. Our results suggest that increased abundance of snow geese (alternative prey) may buffer annual fluctuations in arctic fox abundance, yet result in a long-term decline in eider nest success suggesting apparent competition via other predator species (e.g. gulls). The effect of breeding season climate was subtle compared to the influence of biotic factors and indicated that cold, wet conditions in early spring were correlated with decreased nest success, while warm, wet conditions in late spring increased eider nest success. In Chapter 3 we develop a stochastic population model to evaluate the relative effects of variation and covariation amongst multiple vital rates on population dynamics, and determine the impact of long-term changes in the abundance of alternative prey on eider population dynamics. Consistent with life history predictions, we found that proportional changes in adult survival have the largest impact on population dynamics, yet high variation in the vital rates underlying fertility contribute more to actual variation in population growth. The eventual exodus of alternative prey from the eider colony reduced the long-term growth rate, primarily through negative impacts on mean nest success.

Grain sorghum provides energy-rich seeds for waterfowl. I conducted experiments in 22 sorghum fields in Arkansas, Mississippi, and Louisiana during falls 2006 – 2007 to evaluate abundance of ratoon grain (i.e., second crop after harvest), waste grain, and natural seeds. I also conducted surveys of wintering waterfowl in flooded croplands and moist-soil wetlands to evaluate if ducks and geese differentially used habitats. Fertilized plots in 2007 produced >4 times more ratoon grain (x = 219.57 ± 39.65 [SE] kg/ha) than other treatments. Fertilized plots in southern regions of my study area produced ~5 times more ratoon grain (x = 262.93 ± 50.28 kg/ha) than others. Mallards and other ducks used moist-soil wetlands (x >65 ducks/ha) more than other habitats. I did not observe geese using flooded sorghum. I recommend not manipulating sorghum stubble after harvest, fertilizing, and flooding it after ratoon grain has matured, and integrating moist-soil wetlands into agricultural lands.

Increased growth of the mid-continent population of Lesser Snow Geese (LSGO) has led to the degradation of coastal salt marsh and sedge meadow habitats across Canadian Arctic and sub-Arctic ecosystems. It is believed that a human-induced trophic cascade caused by agricultural habitat modification along migratory routes and wintering grounds has contributed to the increase in LSGO numbers, which has resulted in the alteration of habitat quality and connectivity along northern breeding and stopover sites used by various avian species. This habitat degradation has been shown to decrease the presence and temporal persistence of ground-nesting passerine and shorebird species at a local level and may lead to decreases of Arctic / sub-Arctic breeding avian species across landscapes that LSGO utilize and degrade. In 1999, four paired study plots were established, and used in conjunction with a single study plot from 1976, in order to measure the composition of habitat parameters (barren ground extent; graminoid and shrub cover) and to estimate the number of avian nests found in these plots. Using this historical data along with our findings from 2010 and 2011, our main objectives were to: 1) document the change in the aforementioned habitat parameters over time; 2) estimate the local nesting occupancy rates of the common Savannah Sparrow (SAVS), a robust and adaptable ground nester; and 3) determine which habitat variables are indicative of the rates of change and occurrence of nesting by SAVS within the study plots. By using ANOVA, linear mixed effects, and multi-state occupancy models, results suggest that an increase in barren ground, decreases in shrub and graminoid cover, and a loss of connectivity between suitable nesting patches has led to a 10% (λ = 0.90) annual decline in the probability that SAVS nesting occurred across the study plots from 1999 to 2010. These model results may be used to estimate long-term trends in persistence of breeding SAVS and other similar ground-nesting avian species that share habitats with LSGO along Arctic and sub-Arctic ecosystems. (93 pages)