Using activity densities as an alternative approach to measuring ungulate giving-up densities in the presence of non-target species

Giving-up densities (GUDs) are a frequently used technique that ascertains the value of a forager’s patch use by measuring foraging harvest rate. However, it is not always feasible to measure GUDs due to issues such as non-target species accessing the food items and experimental designs not meeting all of the assumptions of GUDs. Under such circumstances, measuring activity densities can be a valuable alternative approach that can still address many of the same ecological questions as GUDs. Our objective was to design a feeder that enables the accurate measurement of ungulate habitat preference and space use by measuring activity densities and excluding non-target species from data collection. We conducted two experiments to measure the efficacy of our feeder design. The first measured the activity densities of white-tailed deer ( Odocoileus virginianus ) in three habitat types (forest, old-field, and ecotone). We then used trail cameras to monitor the frequency at which non-target species accessed our modified feeder design compared to a traditional feeding bin used in GUD experiments. We found that our feeders were able to discern habitat preference, and that white-tailed deer preferred to use the old-field habitat over the forest. From the camera-trap experiment, we found that non-target species foraged 173 times from feeding trays and zero times from our feeder design during asynchronous 5-day sampling periods. Additionally, our feeder design can be tailored to other ungulate species and provides a method that can quantify resource use and preference via measuring activity densities, while removing non-target species from data collection. Significance statement Giving-up densities (GUDs) are a powerful behavioral indicator of foraging preference. Studies that measure GUDs frequently address the foraging behavior of individuals relative to habitat preference, predation risk, and other costs that can influence the fitness of a forager. However, many studies that measure GUDs deal with the issue of non-target species gaining access to the food source which can alter the results of a study and, in some cases, make results impossible to attain. The feeder design that we use for this experiment is suitable for measuring activity densities in place of GUDs for ungulate species and restricts access to non-target species that could alter the results of an experiment. Our approach provides a method for research that is related to foraging behavior and landscape