Dwayne R. Etter

Survival and Movements of White-Tailed Deer in Suburban Chicago, Illinois

Management of high-density suburban deer populations requires knowledge of survival and movement to predict population trends. However, natural and human-induced influences on survival and movement of suburban deer are poorly understood. Therefore, we marked 208 (60 bucks, 148 does) white-tailed deer (Odocoileus virginianus) from forest preserves in Chicago, Illinois, USA (1994-1998). Seasonal and annual survivorship was >0.80 for 114 does and 13 bucks. Deer-auto collisions produced the highest mortality rates, 0.10 (95% CI 0.06 to 0.14) and 0.17 (95% CI 0.0 to 0.37). Spring dispersal for does was 7% (3 of 41) for fawns and 6% (5 of 83) for yearlings and adults; and for bucks it was 50% (8 of 16) for fawns and 7% (2 of 30) for yearlings and adults. All dispersals were <9 km, except for I parous doe that moved 33.9 km. Doe home ranges averaged 51 (95% CI 40.5 to 61.5), 26 (95% CI 22.0 to 30.0), and 32 (95% CI 19.6 to 44.4) ha for winter-spring, summer, and fall, respectively. A priori, we developed a set of 10 logistic regression models for suburban doe survival relative to home range size and traffic exposure indices. Using Akaikes Information Criterion (AIC), the best models included covariates reflecting home range size and traffic exposure. Inference across a ≥90% confidence set of survival models indicated substantial spatial heterogeneity in mortality risk for suburban does. High survival and philopatry by suburban deer apparently contribute to their overabundance in metropolitan areas.

Noninvasive Estimation of Black Bear Abundance Incorporating Genotyping Errors and Harvested Bear

Abstract Estimating black bear (Ursus americanus) population size is a difficult but important requirement when justifying harvest quotas and managing populations. Advancements in genetic techniques provide a means to identify individual bears using DNA contained in tissue and hair samples, thereby permitting estimates of population abundance based on established mark–capture–recapture methodology. We expand on previous noninvasive population-estimation work by geographically extending sampling areas (36,848 km2) to include the entire Northern Lower Peninsula (NLP) of Michigan, USA. We selected sampling locations randomly within biologically relevant bear habitat and used barbed wire hair snares to collect hair samples. Unlike previous noninvasive studies, we used tissue samples from harvested bears as an additional sampling occasion to increase recapture probabilities. We developed subsampling protocols to account for both spatial and temporal variance in sample distribution and variation in sample quality using recently published quality control protocols using 5 microsatellite loci. We quantified genotyping errors using samples from harvested bears and estimated abundance using statistical models that accounted for genotyping error. We estimated the population of yearling and adult black bears in the NLP to be 1,882 bears (95% CI = 1,389–2,551 bears). The derived population estimate with a 15% coefficient of variation was used by wildlife managers to examine the sustainability of harvest over a large geographic area.

Effort and the Functional Response of Deer Hunters

Managers of overabundant deer have failed to incorporate relevant predator-prey theory into management research. In particular, understanding the functional response of deer hunters (deer encountered/time) to declining deer density is important because functional responses determine relative effort (time/deer encountered) required to harvest a deer and may, in turn, influence hunter perceptions of deer density and costs associated with deer removal. We used information-theoretic techniques and nonlinear regression to reanalyze data from controlled hunts in Illinois, Michigan, Wisconsin, and Ontario. Alternate models include killing rates or sighting rates as Type 1 (linear), Type 2 (hyperbolic), or Type 3 (sigmoidal) functions of deer density. Akaikes information criteria suggested that optimal models for most data sets were Type 1, although this may have been a artifact of small sample sizes. Nonetheless, effort curves derived from fitted functional responses indicated that relative effort accelerates as deer density declines. Accelerating effort requirements on the part of deer hunters likely hinders agency efforts to reduce overabundant deer populations and may be a source of hunter perceptions of unrealistically reduced deer herds. If general, this relation-ship (1) may determine what levels of harvest/removal are realistic, (2) is a potential source of bias in population estimation, and (3) may contribute to hunter distrust of agency efforts to reduce population size.

White-tailed Deer Dispersal Behavior in an Agricultural Environment

ABSTRACT Dispersal behavior was examined for 119 male and 102 female white-tailed deer (Odocoileus virginianus) fawns marked in central and northern Illinois. Fawn movement behavior was recorded for 35 single, 78 pair and 10 triplet litters that survived intact beyond family breakup in late spring. Males (65%) dispersed at a higher rate than females (39%). Females dispersed Apr.–Jul., while males dispersed Apr.–Jul. and Sep.–Nov. The dams and siblings movements most affected fawn movement behavior with most fawns of dispersing/migrating females and siblings leaving their natal range. As yearling-adult densities and forest cover increased on our study areas, female fawn dispersals decreased. Habitat scarcity in spring coupled with high fawn survival into the spring months promoted higher than expected female dispersal behavior. Distance traveled to a new range did not differ among study areas, years or month of dispersal for either sex. Single fawns were as likely to disperse as fawns from pairs or triplets. Control of high density deer populations will be more difficult where female dispersal is prevalent, as in the agriculturally dominated Midwest landscape.

Noninvasive Hair Sampling and Genetic Tagging of Co-Distributed Fishers and American Martens

Abstract Estimation of abundance is important for assessing population responses to management actions. Accurate abundance estimates are particularly critical for monitoring temporal variation following reintroductions when the management goal is to attain population sizes capable of sustaining harvest. Numerous reintroductions have taken place in the Great Lakes region of North America, including efforts to restore extirpated fishers (Martes pennanti) and American martens (M. americana). We used a DNA-based noninvasive hair-snaring method based on one trap design and trapping -grid configuration, and evaluated capture–mark–recapture (CMR) analytical approaches to simultaneously estimate population size for co-distributed fishers and American martens in a 671-km2 area of the Ottawa National Forest in the western Upper Peninsula of Michigan, USA. We included harvest as a final recapture period to increase probability of recapture and to evaluate potential violations of geographic closure assumptions. We used microsatellite markers to identify target species, eliminate congener species, and provide individual identity for estimation of abundance. Population estimates for fishers and martens on the study area ranged from 35 to 60 and 8 to 28, respectively. Estimators incorporating harvest data resulted in up to a 40% increase in abundance estimates relative to estimators without harvest. We considered population estimates not including harvest data the most appropriate for the study due to timing of sampling and environmental factors, but inclusion of harvested individuals was shown to be useful as a means to detect violations of the assumption of geographic closure. We suggest improvements on future CMR sampling designs for larger landscape scales of relevance to management through incorporation of habitat or historical harvest data. Noninvasive genetic methods that simultaneously estimate the numerical abundance of co-distributed species can greatly decrease assessment costs relative to traditional methods, and increase resulting demographic and ecological information.

American black bear habitat selection in northern Lower Peninsula, Michigan, USA, using discrete-choice modeling

Abstract Since 1990, increases in American black bear (Ursus americanus) population and distribution in the Lower Peninsula of Michigan, USA, have led to positive trends in black bear harvests, sightings, and nuisance reports. Policy makers and wildlife managers can prepare for the difficult task of managing future bear–human interactions by using resource selection models to assess bear habitat selection and predict future bear range expansion. We modeled habitat selection by black bears in the northern Lower Peninsula of Michigan using 6 environmental variables based on radiotelemetry locations from 1991–2000 for 20 males and 35 females. We developed Bayesian random effects discrete-choice models for males and females separately to estimate probability of bear selection of grid cells at 3 spatial resolutions (1 km2, 4 km2, 9 km2). These models weight individual bears and their relocations, allowing inference about both individual and population-level selection characteristics. We assessed goodness-of-fit of individual models using a Bayesian P value that estimated deviance between a simulated dataset and the observed dataset. Models for males at the 9-km2 resolution and for females at 4-km2 resolution fit our data better than others; both indicated that locations of bears were negatively associated with water, small and medium roads, mean patch size, patch size coefficient of variation, edge density, developed land-use, and non-forested wetlands, and positively associated with Shannons diversity index, aspen (Populus spp.), and forested wetlands. Furthermore, the variability in selection by individual female bears for non-forested wetland and individual male bears for agriculture was large relative to the variability in selection of other land-use or land-cover types. Male bears had more heterogeneity with respect to selection of land-use or land-cover types than female bears. There were significant correlations between male bear age and their respective selection parameter estimates for small roads, medium roads, and developed land-use. Running Bayesian random effects discrete-choice models at multiple resolutions accounted for variability due to unequal sample sizes and bear behavior, and demonstrate the utility of the Bayesian framework for bear management purposes.

Sex Affects Age Determination and Wear of Molariform Teeth in White-Tailed Deer

Field estimation of the ages of adult white-tailed deer (Odocoileus virginianus) and other ungulates often requires assessment of the degree to which molariform teeth wear over time. This widely used technlque is applied without regard to the sex of the animal being aged, but sex-based differences in ungulate life history traits such as diet, habitat use, and foraging behavior may affect tooth wear patterns differently for males and females. We examined sex-specific differences in tooth wear and morphology for adult (>1.5 yrs old) deer collected in northeastern Illinois (1993-97). We randomly sampled 100 mandibles from adult deer (50 M:50 F), stratified by cementum annuli year classes 2-7, to obtain 29 measurements of width, height, length, and visible dentine on premolars 2 and 4, and molars 1 and 3. Principle components (PC) analysis indicated that 61% of the overall sample variation was explained by PCs 1-3. Analysis using MANOVAs suggested effects (P < 0.05) due to sex and age when component scores from PCs 1-3 were used as dependent variables. Teeth from male deer were wider and tended to show more visible dentine (wear) on occlusal surfaces. Age class estimates of 10 experienced observers indicated substantial observer variation in the wear-replacement aging technique A repeated measures ANOVA indicated that sex effects in the wear-replacement aging technique become significant when the effects of observer variation are controlled. Stage-based projection models based on sex-specific age ratios of white-tailed deer had different growth rates and adult sex ratios when corrected for a sex bias in wear-replacement aging, indicating that common population analysis methods are sensitive to a sex-based bias. Managers should use caution when comparing adult age ratios derived from tooth wear because of potential sex biases in tooth wear patterns.

Application of large-scale parentage analysis for investigating natal dispersal in highly vagile vertebrates: a case study of American black bears (Ursus americanus).

Understanding the factors that affect dispersal is a fundamental question in ecology and conservation biology, particularly as populations are faced with increasing anthropogenic impacts. Here we collected georeferenced genetic samples (n = 2,540) from three generations of black bears (Ursus americanus) harvested in a large (47,739 km2), geographically isolated population and used parentage analysis to identify mother-offspring dyads (n = 337). We quantified the effects of sex, age, habitat type and suitability, and local harvest density at the natal and settlement sites on the probability of natal dispersal, and on dispersal distances. Dispersal was male-biased (76% of males dispersed) but a small proportion (21%) of females also dispersed, and female dispersal distances (mean ± SE  =  48.9±7.7 km) were comparable to male dispersal distances (59.0±3.2 km). Dispersal probabilities and dispersal distances were greatest for bears in areas with high habitat suitability and low harvest density. The inverse relationship between dispersal and harvest density in black bears suggests that 1) intensive harvest promotes restricted dispersal, or 2) high black bear population density decreases the propensity to disperse. Multigenerational genetic data collected over large landscape scales can be a powerful means of characterizing dispersal patterns and causal associations with demographic and landscape features in wild populations of elusive and wide-ranging species.

Factors affecting harvests of fishers and American martens in northern michigan

ABSTRACT Harvest data (e.g., number of animals harvested, trapper effort) are an important source of information for state wildlife agencies to manage harvested furbearers. These data provide evidence to support adapting harvest regulations when necessary. Setting appropriate harvest regulations for fishers (Martes pennanti) and American martens (Martes americana) is critical, as these species often exist at low densities, are sensitive to timber-management practices and trapper-harvest, and experience some level of interspecific predation and competition in sympatric populations. We estimated effects of management (e.g., number of fishers or martens harvested per trapper per season [harvest limit], season length) and extrinsic (e.g., weather, pelt prices) factors on regulated harvests of fishers and martens in the Upper Peninsula of Michigan during 1996–2007. We used generalized linear mixed models in an information-theoretic approach (quasi-likelihood adjusted Akaike Information Criterion [QAIC]) to discern which factors most strongly influenced fisher and marten harvests. For harvest of fishers, the 3 QAIC-best models included harvest limit, season length, and number of trappers, suggesting that regulatory changes within the ranges tested may be implemented to influence harvest. The QAIC-best model (harvest limit) contained 26% of the weight of evidence, and using an independent subset of data, showed no difference between model predictions and harvest data. In contrast, harvest of martens was not strongly influenced by any factors we tested. Possible reasons for a lack of measurable effects while modeling harvest of martens include a low harvest limit (i.e., 1 marten) or incidental harvest of martens by fisher or bobcat (Lynx rufus) trappers. Knowledge of influences on harvest will lead to informed decision-making when managers are setting harvest regulations, particularly for low-density furbearers.

Migration Behavior among Female White-Tailed Deer in Central and Northern Illinois

ABSTRACT Thirty-nine female white-tailed deer (Odocoileus virginianus) were migrators from three study areas in central and northern Illinois, 1980–1993. Migrants averaged 21.5%, 9.4% and 14.6% of marked females known alive each year on the east-central, west-central and northern study areas, respectively. Females migrated to a summer range between late Feb. and early Jul. and to the winter range between late Sep. and early Jan. Spring migration distances averaged between 7.3 and 15.9 km from the winter range. Female fawns of migrating mothers were more likely to disperse or migrate than were fawns of sedentary mothers. Migrating females survived as long as sedentary females and significantly better than females that dispersed, but fawn recruitment was lower for migrating females compared with sedentary females. Winter severity did not affect return behavior from a summer range. Hunter harassment on the summer range initiated migration back to the winter range in 59% of 22 monitored migrations for 14 radio marked females. Prevailing winds from the winter or summer range appeared to help locate these ranges for 10 of 19 spring migrations for 16 females and three of seven fall migrations for four females. Migration behavior allows females to more fully utilize the fragmented landscapes of the agricultural Midwest. Migration behavior among females appears to result from resource competition among females including parturition sites where female densities are high and available habitats are scarce.