Delaware Deer Harvest & Research
By: Dr. Jacob M. Haus, Dr. Jacob L. Bowman, Joe Rogerson
Over the past several years, the University of Delaware has worked in cooperation with Division of Fish & Wildlife on a large-scale deer research project in Sussex County. Some of the main objectives for this study have been to understand how deer are using the landscape and how those behaviors might influence their survival. Much of the study is still ongoing, however the portion of the project involving adult bucks concluded earlier this year.
From late 2013 until 2017, researchers trapped deer on both public and private lands throughout Sussex County. Deer were captured a number of different ways, but the primary method was with rocket nets. We baited net sites with corn and used night vision goggles to monitor deer activity. When a buck approached the corn pile, a biologist would trigger a series of rockets that shot a net over the back of the deer and we would quickly sedate and blindfold them. All button bucks (6-9 month olds) received a lightweight collar with elastic that expanded as their necks grew larger over the coming year. We deployed more advanced GPS collars on older bucks that recorded a location every hour during the hunting season. Both types of collars were equipped with a sensor that could detect when an animal had not moved for more than 8-hours, indicating a potential mortality, and the collar would send out a notification to the research team. We could then locate the deer and determine a cause of death. In total, we collared and monitored 72 yearling bucks (1-2 year olds) and 33 adult bucks (3 years old or older).
Just over half of the juvenile bucks we collared left their home range as yearlings to establish a new adult range, a behavior biologist call dispersal. Young males disperse much more frequently than females do, a behavior that deer have evolved to avoid inbreeding during the fall. Some bucks dispersed as far as 15 miles but shorter distance dispersals were much more common, with an average distance of 4 miles. Overall, 60% of yearling bucks lived to see their second birthday. For those that were killed, 80% were harvested and the rest were either hit by cars or died of natural causes such as hemorrhagic disease (EHD). We identified a few factors that contributed to the probability a yearling buck would survive. First, if they used habitat farther from edges (such as a field/forest edge) they were more likely to survive, probably because hunters often prefer to set their stands in these areas. The strongest predictor however, was whether a yearling buck used public land during the hunting season. For bucks that never set foot on public land, three out of four survived into the spring, whereas only one out of four bucks that used public land survived. Yearling survival rates around 70% on private land is comparable to some of the best managed areas of the country; however survival rates below 30% on public land result in a younger age structure on these areas.
The annual survival probability for adult bucks was 39%, lower than that of yearling bucks, which suggests hunters in southern Delaware often selected to pass yearling bucks for an opportunity to harvest an older male. The good news for public land hunters is that the adult bucks they hunt are just as likely to survive as their private land counterparts, we found that the difference between harvest rate on public and private land disappeared in bucks more than 2 years old. We also observed a lot of variation in the habitat selection among older bucks; each deer had its own individual tendencies. A few generalities held true for most of the adult population though, such as an avoidance of edge habitat and a selection for forested wetlands. The avoidance of edge habitat is interesting considering the impact such areas had on yearling buck survival. Bucks even increased their avoidance of edge habitat as they grew older. This may be a learned behavior, or it may be that bucks with a tendency to avoid these risky areas simply live longer. Either way, for a better chance at seeing or harvesting an older age buck, hunters may want to consider leaving the field edges and heading deeper into the woods.
The University of Delaware is also nearing the end on a multiyear study of adult doe movement and fawn survival. Several deer from both projects are still carrying ear tags and radio collars. Hunters who encounter tagged or collared deer are encouraged to treat them exactly as they would have if the collar were not present. Selectively targeting or passing collared deer will bias survival estimates and negatively affect the results of the studies. If you harvest or find a deer with a collar or ear tags, please call (302) 831-4621 to report the animal to University of Delaware researchers. We greatly appreciate the many landowners who allowed us access to their property to capture and track deer. This project would not have been possible without their generous support. This research was funded by the Delaware Division of Fish and Wildlife through a grant from the Wildlife and Sport Fish Restoration Program (Pittman-Robertson Act), University of Delaware, and the McIntire-Stennis grant from the U.S. Department of Agriculture.