John G. Bruggink

Proximate Cues for a Short-Distance Migratory Species : an Application of Survival Analysis

Abstract Investigation of bird migration has often highlighted the importance of external factors in determining timing of migration. However, little distinction has been made between short- and long-distance migrants and between local and flight birds (passage migrants) in describing migration chronology. In addition, measures of food abundance as a proximate factor influencing timing of migration are lacking in studies of migration chronology. To address the relationship between environmental variables and timing of migration, we quantified the relative importance of proximate external factors on migration chronology of local American woodcock (Scolopax minor), a short distance migrant, using event-time analysis methods (survival analysis). We captured 1,094 woodcock local to our study sites in Michigan, Minnesota, and Wisconsin (USA) during autumn 2002–2004 and documented 786 departure dates for these birds. Photoperiod appeared to provide an initial proximate cue for timing of departure. Moon phase was important in modifying timing of departure, which may serve as a navigational aid in piloting and possibly orientation. Local synoptic weather variables also contributed to timing of departure by changing the rate of departure from our study sites. We found no evidence that food availability influenced timing of woodcock departure. Our results suggest that woodcock use a conservative photoperiod-controlled strategy with proximate modifiers for timing of migration rather than relying on abundance of their primary food, earthworms. Managing harvest pressure on local birds by adjusting season lengths may be an effective management tool with consistent migration patterns from year to year based on photoperiod.

Where and How Wolves (Canis lupus) Kill Beavers (Castor canadensis)

Beavers (Castor canadensis) can be a significant prey item for wolves (Canis lupus) in boreal ecosystems due to their abundance and vulnerability on land. How wolves hunt beavers in these systems is largely unknown, however, because observing predation is challenging. We inferred how wolves hunt beavers by identifying kill sites using clusters of locations from GPS-collared wolves in Voyageurs National Park, Minnesota. We identified 22 sites where wolves from 4 different packs killed beavers. We classified these kill sites into 8 categories based on the beaver-habitat type near which each kill occurred. Seasonal variation existed in types of kill sites as 7 of 12 (58%) kills in the spring occurred at sites below dams and on shorelines, and 8 of 10 (80%) kills in the fall occurred near feeding trails and canals. From these kill sites we deduced that the typical hunting strategy has 3 components: 1) waiting near areas of high beaver use (e.g., feeding trails) until a beaver comes near shore or ashore, 2) using vegetation, the dam, or other habitat features for concealment, and 3) immediately attacking the beaver, or ambushing the beaver by cutting off access to water. By identifying kill sites and inferring hunting behavior we have provided the most complete description available of how and where wolves hunt and kill beavers.

Seasonal Variation in Assimilated Diets of American Beavers

Abstract American beavers (Castor canadensis) forage on various aquatic and terrestrial plant species. We used stable isotope analysis of carbon (C) and nitrogen (N) to estimate source contributions of seasonal assimilated beaver diets in Voyageurs National Park, Minnesota, from Apr. 2007 to Nov. 2008. Mean (±95% confidence interval) annual beaver diets were estimated as 45.5 ± 11.4% terrestrial and 55.5% aquatic vegetation (22.0 ± 14.5 emergent and 33.5 ± 7.9 floating leaf). Percentages of floating leaf and terrestrial vegetation were similar between winter and summer assimilated diets, but emergent vegetation increased 45% in summer. Although δ15N was 7% greater in summer, δ15N and δ13C were similar by age class and sex, as were assimilated percentages of emergent, floating leaf or terrestrial vegetation. Variation in total assimilated aquatic vegetation did not affect subadult and adult seasonal changes in body mass, tail thickness or tail area, but kit body condition was negatively related to total as...

Foraging location quality as a predictor of fidelity to a diurnal site for adult female American woodcock Scolopax minor

Abstract Quality of recently used foraging areas is likely an important predictor of fidelity to specific locations in the future. We monitored movement and habitat use of 58 adult female American woodcock Scolopax minor at three study areas in Minnesota, Wisconsin and Michigan, USA, during autumn 2002 and 2003, to assess the relationship between foraging habitat use decisions and environmental conditions at previously used foraging locations. We assessed whether habitat variables which related to food and weather were related to distance between locations on subsequent days of individual woodcock that choose diurnal foraging locations when they return from night-time roosting locations. We predicted that woodcock would return to foraging locations used on the previous day (i.e. shorter distances between daily foraging locations) when environmental conditions on the prior day were favourable. Woodcock generally made short (i.e. 48% < 50 m and 91% < 400 m) between-day movements, but also occasionally (∼ 7%) abandoned prior foraging areas. The primary determinants of woodcock movements during autumn (prior to migration) were low local food availability and potential for increased food availability elsewhere. The quality of foraging locations was an important predictor of future foraging habitat use for woodcock, consistent with the hypothesis that woodcock movement behaviour balances the risks associated with movement with the potential benefits of increased energy intake in new foraging areas.

Weekly Summer Diet of Gray Wolves (Canis lupus) in Northeastern Minnesota

Abstract Wolves (Canis lupus) are opportunistic predators and will capitalize on available abundant food sources. However, wolf diet has primarily been examined at monthly, seasonal, or annual scales, which can obscure short-term responses to available food. We examined weekly wolf diet from late June to early October by collecting scats from a single wolf pack in northeastern Minnesota. During our 15 wk study, nonungulate food types constituted 58% of diet biomass. Deer (Odocoileus virginianus) fawns were a major food item until mid-July after which berries (primarily Vaccinium and Rubus spp.) composed 56–83% of weekly diet biomass until mid-August. After mid-August, snowshoe hares (Lepus americanus) and adult deer were the primary prey. Weekly diet diversity approximately doubled from June to October as wolves began using several food types in similar proportions as the summer transitioned into fall. Recreational hunting of black bears (Ursus americanus) contributed to weekly wolf diet in the fall as wolves consumed foods from bear bait piles and from gut piles/carcasses of successfully harvested or fatally wounded bears. To our knowledge, we are the first to examine wolf diet via scat analysis at weekly intervals, which enabled us to provide a detailed description of diet plasticity of this wolf pack, as well as the rapidity with which wolves can respond to new available food sources.

Influence of spotted knapweed on diversity and abundance of small mammals in Grand Sable Dunes, Michigan, USA.

ABSTRACT: Spotted knapweed (Centaurea stoebe L. ssp. micranthos [Gugler] Hayek) is an exotic plant that displaces native vegetation leading to altered plant and animal communities. We compared small mammal abundance and diversity in areas with, and without, spotted knapweed in Grand Sable Dunes, Michigan, to determine whether presence of this plant affected the small mammal community. We live trapped small mammals in June and August 2003 in six plots in native dune vegetation and in six plots in areas with spotted knapweed and native dune vegetation. Mean number of captures per trap of mice in spotted knapweed plots ( = 0.50 ± 0.31) was nearly double that in native plot ( = 0.27 ± 0.19; F1,20 = 18.251, P < 0.001). Amount of total vegetative cover in spotted knapweed plots ( = 71 ± 12% SD) was almost twice that in native plots ( = 37 ± 11%). Mean number of captures per trap was positively related to percent cover (F1,20 = 5.239, P = 0.033). Mice are seed and insect predators, seed and spore dispersers, and serve as prey for numerous species. Thus, the positive response by mice to the spotted knapweed invasion may have caused additional changes to this community.

Effects of Forest Patch Characteristics on Small Mammal Species Composition, Grand Sable Dunes, Michigan

ABSTRACT: Species inventory is considered an important component of natural resource management in National Park System units. We trapped small mammals in forested patches in the Grand Sable Dunes, Pictured Rocks National Lakeshore, Michigan, during 2007 and 2009 to inventory species occurrences and test predictions of island biogeography theory in a terrestrial landscape. We captured 538 individuals representing nine small mammal species. Fewer species were present in isolated patches than those closer to the mainland or another patch (F1, 11 = 5.752, P = 0.035), as predicted. Contrary to predictions, there was no relationship between species richness and patch area, proportion of patch edge, or other isolation metrics. We documented range expansion of a southern species, the white-footed mouse (Peromyscus leucopus Rafinesque), into the Grand Sable Dunes. White-footed mice were more likely to be captured in less isolated patches (Omnibus &khgr;21 = 9.684, Nagelkerke R2 = 0.605, P = 0.002). Our results provide the first small mammal inventory for the Grand Sable Dunes and will serve as a baseline for future monitoring of small mammal species in this perched-dune system.

Female American black bears do not alter space use or movements to reduce infanticide risk

Infanticide occurs in a variety of animal species and infanticide risk has large implications for the evolution of behavior. Further, the sex hypothesis of sexual segregation predicts that for species in which infanticide occurs, females with dependent young will avoid males to reduce risk of sexually-selected infanticide. Infanticide risk-avoidance behavior has been studied primarily in social species, but also occurs in some solitary species. We used generalized linear mixed models to determine if space use and movements of female American black bears (Ursus americanus) during the breeding season were consistent with the sex hypothesis of sexual segregation in the Upper Peninsula of Michigan, USA. Space use and movements of female black bears (n = 16) were not consistent with avoidance behavior to reduce sexually-selected infanticide risk. Females with cubs occupied core areas (mean = 4.64 km2, standard error [SE] = 1.28) and home ranges (mean = 19.46 km2, SE = 5.10) of similar size to females without cubs (core area [mean = 4.11 km2, SE = 0.59]; home range [mean = 16.07 km2, SE = 2.26]), and those core areas and home ranges were not in areas with lesser relative probability of male use. Additionally, females with cubs did not reduce movements during times of day when male movements were greatest. As female bears do avoid potentially infanticidal males in populations with greater levels of infanticide, female black bears may exhibit variation in avoidance behavior based on the occurrence of infanticide.