For many animal taxa, nutritional condition (i.e., fat levels) is a balance of food intake that increases condition versus energy outputs (i.e., cost of reproduction) that diminish condition. While nutritional condition gradients are common in nature, relatively little is known about how nutritional condition influences behavior. Current management practices in Wyoming offer a rare opportunity to evaluate the influence of nutritional condition on the behavioral strategies of a large, free-ranging population of elk (Cervus elaphus). The Wyoming Game and Fish Department (WGFD) operates 22 winter feedgrounds for population and disease management.
There are many native winter ranges nearby that also support elk, resulting in two groups that differ in their nutritional condition. Our study views supplemental feeding as a landscape-scale experiment that manipulates the nutritional condition of elk. Feedground populations with consistent, reliable winter food supplies should show less inter-annual variability in body condition and come out of winter with higher body-fat levels than non-fed elk. It is unknown whether fed elk make different cost-benefit tradeoffs or employ different strategies than non-fed elk outside of winter owing to difference in winter fat losses.
The objectives of this study are to evaluate differences between fed and non-fed elk in regards to 1) migration patterns, 2) foraging, 3) summer habitat selection, and 4) landscape-level distribution. In addition, parturition area delineation, interchange between fed and non-fed elk, and brucellosis seroprevalence will be characterized. This work is being conducted collaboratively by investigators from our research group, WGFD, and the US Geological Survey, and will make use of existing fine-scale movement monitoring (70 GPS collars on feedground elk). Female elk that are on native winter range (n=35) were captured in January 2010 and fitted with GPS collars that will record location data every hour for two years. To quantify the difference in body condition between fed and non-fed elk, 20 elk will be recaptured from each group in March 2011 and their body-fat levels will be estimated through ultrasound measurements. To test for differences between groups in migratory behavior, we will examine timing, pattern, and rate of travel for spring and fall migrations. To evaluate carry-over effects on foraging, we are locating collared individuals on summer range and conducting behavioral observations to estimate time budgets. To evaluate summer habitat selection, we will develop resource selection functions for individual elk and then compare groups of fed and non-fed elk. We are also interested in whether any behavioral differences scale up to influence landscape distribution of elk, which we are evaluating using stable isotope analysis. Stable isotope values are influenced by diet and physiology, and disparities between fed and non-fed elk should be reflected in distinct isotopic signatures in tissues such as fur, hoof, and tooth cementum.
Understanding the influence of body-condition on elk behavioral ecology throughout the year will provide insight into the generality of behavior-condition relationships and movement and distribution data that are crucial to effective conservation and management.
Initial stable isotope analysis from hair samples of elk during initial capture failed to show detectable differences with regards to isotope ratios. To determine if our hair location sampling was incorrect due to false assumptions regarding timing and rate of hair growth, we initiated a collaborative effort with Dr. Kreeger and his staff at the WGFD Sybille Wildlife Research Center to measure both hair and hoof growth rates using six captive elk. This portion of the project was initiated in December 2010 with the dyeing of a patch of hair on the elk’s back with Nyanzol D and filing a grooved notch into one digit 10 mm below the coronary corium. These six elk will be brought in through squeeze chutes at the facility once a month for one year in order to determine both annual and seasonal growth rates. Digits will be renotched each month and total digit length will be recorded. To our knowledge this has never been done on elk before. We will then use this knowledge to acurately determine the correct location on hair and hooves to sample for growth that would have occurred while the elk was on a feedground in winter.
Fall elk hunter harvest sample collection was very successful with the collaboration of WGFD staff from the Jackson, Pinedale and Laramie regions. From the Pinedale and Jackson regions, samples were solicited from elk hunters at check stations in all hunt areas containing or adjacent to feedgrounds. Check stations in the Laramie region were prioritized based on what WGFD biologists felt would be good oportunities to sample elk that never feed on agricultural fields (this would help to serve as a base for non-fed elk). Samples from 129 different elk were collected, including one hoof, one tooth and a pinch of hair. Sampling location and isotope analysis will wait until elk hoof and hair growth rate can be determined from the captive elk at Sybille.