9th International Deer Biology Congress

AUTHORS: Tanya M. Roerick, Department of Fish, Wildlife and Conservation Ecology, New Mexico State University, Las Cruces, NM; James W. Cain III*, U.S. Geological Survey, New Mexico Cooperative Fish and Wildlife Research Unit

ABSTRACT: Decades of fire suppression, logging, and overgrazing have altered the conditions of southwestern forests resulting in increased densities of small diameter trees and an overall increase in fuel loads. These increasing tree densities have been associated with decreases in biodiversity, reduced habitat quality, degraded foraging conditions for ungulates, and more frequent and severe wildfires. In response, land managers are increasingly implementing landscape-scale forest restoration treatments through the use of prescribed fire and forest thinning in an attempt to mitigate the risk of catastrophic wildfires and improve habitat conditions for a variety of wildlife species. Similar vegetation treatments are commonly implemented by wildlife managers specifically to improve habitat conditions for mule deer (Odocoileus hemionus). We monitored responses of female mule deer to forest restoration treatments and wildfires in northern New Mexico. Our specific objectives were to: 1) assess changes in abundance of key forage species; 2) estimate differences in forage quality; and 3) determine habitat selection patterns of mule deer in relation to recent wildfires, forest restoration treatments (including the time since treatments), and other habitat characteristics. Herbaceous forage biomass was greater in wildfire burned areas than prescribed burns, forest thinning, and untreated areas. Oak forage biomass was greater in wildfire burned areas compared to prescribed burns, forest thinning, and untreated areas. Thinned areas tended to have higher oak forage biomass than untreated areas. Mule deer selected for areas burned by prescribed fire and avoided wildfire burned and thinned areas less than 5 years old. Mule deer strongly selected for thinned areas >5 years old. At both the landscape and within home range scale, grasslands were avoided during all seasons, pinyon-juniper woodlands were selected for in winter, and oak vegetation and mixed conifer forests were selected during summer. Data collected during our study suggests mule deer benefit from recent prescribed burns and older forest thinning. The lack of selection for wildfire burned areas was unexpected given the differences in forage biomass observed. Knowledge of the short- and long-term effects of restoration treatments will provide managers with guidance for making informed decisions regarding implementation of vegetation treatments to benefit mule deer.

AUTHORS: Kirby D. Bristow, Mathew J. Clement, Larisa E. Harding* – Wildlife Research Branch, Arizona Game and Fish Department

ABSTRACT: Large wildfires in the western USA have increased in both frequency and intensity and may have significant impacts on wildlife use of habitats. The impacts of increased fire severity can be problematic and may not follow well known recovery trajectories. Responses of mule deer (Odocoileus hemionus) to habitat treatments designed to enhance shrub forage availability after two large, recent fires on the Kaibab Plateau in northern Arizona are not well documented. We examined location data from mule deer on the Kaibab plateau to determine the relative influence of wildfire severity, habitat treatments, and other environmental variables on winter habitat selection patterns. We used locations from 30 adult female mule deer fitted with global positioning system (GPS) collars to model probability of use as a function of habitat covariates using negative binomial regression. The best model describing habitat use by mule deer on the Kaibab plateau winter range included covariates describing the amount of treated area, fire severity, distance to developed water, snow depth, terrain ruggedness, vegetation height and solar radiation. Deer use increased in areas with lower average fire severity, reduced snow depths and closer to developed water sources. Similarly, lower terrain ruggedness and higher solar radiation were associated with increased deer use. This information may be important in designing landscape treatments to improve winter range habitat conditions for mule deer.

AUTHORS: Andrew R. Little, Daniel B. Warnell School of Forestry and Natural Resources, University of Georgia; Stephen L. Webb, Noble Research Institute, LLC; Brad S. Cohen, David B. Stone, Gino J. D’angelo, Karl V. Miller – Daniel B. Warnell School of Forestry and Natural Resources, University of Georgia

ABSTRACT: In cervids, male mate search strategies are influenced by the spatial distribution and reproductive synchrony of females [1]. Roving is a common strategy employed by males in cases where receptive females are distributed in unpredictable patches across a landscape. However, roving is energetically costly compared to other search strategies, suggesting males should incorporate spatial knowledge during their searching to maximize encounter probabilities with females [2]. For example, males may increase their encounter probability with mates when selecting for patches used by females [3].

To improve our understanding of how males may increase their likelihood of encountering receptive females, we examined changes in resource selection of 21 male and 11 female white- tailed deer (Odocoileus virginianus) during pre-breeding (13 September − 25 October) and breeding seasons (26 October − 27 November) in Harris County, Georgia, USA. Because sexual segregation is common among white-tailed deer populations, we hypothesized that males and females would be sexually segregated during pre-breeding [4]. We also hypothesized that males would align their resource selection with females during breeding season to increase their encounter probabilities.

We observed differential resource selection between sexes and seasons. During pre-breeding, females selected for agriculture and shrub-scrub vegetation types, while avoiding deciduous and evergreen forests, riparian, and developed areas. Interestingly, during pre-breeding, males selected for vegetation types that females avoided (e.g., deciduous and evergreen forests, and riparian areas), suggesting some level of sexual segregation prior to breeding season. During breeding season, females altered their resource selection from pre-breeding by selecting for deciduous forests and water sources (e.g., ponds, impoundments), while avoiding evergreen forests, shrub-scrub, riparian, and developed areas. As expected, males maintained selection of deciduous forests and riparian areas, but avoided vegetation types that females were no longer using such as agriculture and shrub-scrub.
Spatial mapping revealed an overall pattern of shifted resource selection for females between the pre-breeding and breeding periods; this also was evident for males (Figure 1). Spatial depiction of landscape use revealed that the two sexes utilized resources much differently during pre-breeding, a sign of sexual segregation. As expected, the areas predicted to receive the greatest use by females during the breeding season appeared to influence resource selection and the spatial distribution of males. Our research provides insight into how males alter behavior and spatial use of the landscape to match that of females during the breeding season, which should increase encounter probabilities with mates. Future analyses will examine how encounter probabilities may influence male movement behaviors.

AUTHORS: Stephen L. Webb, Noble Research Institute, LLC

ABSTRACT: Resource selection modeling has strong applications in conservation because resource selection is a fundamental ecological process shaping movement and distribution [1], and offers spatially explicit guidance for targeted management. As animals move across the landscape, they must make trade-offs associated with resource selection to meet needs of survival and reproduction, and for minimizing risk [2]. Fitness is influenced by resource-related decisions by individuals where each resource choice has costs and benefits associated with it. Therefore, individual variation (also referred to as heterogeneity) warrants further investigation in resource selection modeling and how it structures demographic performance such as survival.

Studies of Rocky Mountain elk (Cervus elaphus) and white-tailed deer (Odocoileus virginianus) will be presented to highlight the conceptual framework to study individual variation in resource selection and its applications for modeling demographic outcomes and functional responses, and improving conservation and management. The general approach included estimating resource selection functions (RSFs) and estimating Cox proportional hazards models to quantify risk of mortality as a function of covariates depicting landscape-level features. Spatial models of occurrence and risk are combined to provide a spatially-explicit assessment of the relationship between habitat and demographic performance, wherein low-performance habitat (e.g., sink habitat) was defined as high probability of occurrence coupled with high risk of mortality, and high-performance habitat (e.g., source habitat) was high probability of occurrence coupled with low risk of mortality. For white-tailed deer, fully random effects models are used to estimate conditional (i.e., representing an individual) and marginal (i.e., representing the population-level response) coefficient estimates from RSFs to study behavioral strategies that may influence survival or encounter probability of mates during rut.

Variability in the occurrence of elk was driven by selection for specific resource features as well as responses to human activity. Risk of mortality in elk was a function of human modification of the landscape with little variation explained by resource features. Proximity to industrial (i.e., oil and gas) development was associated with increased risk of mortality whereas proximity to residences and agricultural structures was associated with decreased risk. Individual-level results revealed added complexity – risk of mortality was associated with a consistent pattern of occurrence relative to industrial development, yet the association between risk and occurrence relative to structures (e.g., houses, barns, buildings) was highly variable and likely a function of disparate land-use practices [3]. Using individual elk RSF coefficients (i.e., conditional responses) revealed functional responses for human disturbance and security cover. Elk selected randomly for disturbed areas when level of disturbance was low, but elk showed stronger avoidance as disturbance increased. Elk also used greater security cover relative to its availability especially when exposed to human disturbance [4]. Results from white-tailed deer are forthcoming based on data from [5] and [6].

Prioritizing management based on occurrence without a connection to a demographic outcome risks poor performance because occurrence alone can be a misleading indicator of fitness. Therefore, management may be most effective when individual variation is considered and linked to demographic outcomes.