What We're Learning About Turkeys
By Drs. Angela Holland and Jacob Bowman
The University of Delaware and the Delaware Division of Fish and Wildlife recently collaborated on a research project monitoring survival and movement of male wild turkeys throughout the state of Delaware. We trapped turkeys for three years and used GPS backpack transmitters to follow turkey movement throughout the year but collected extra data during the spring and the hunting season. While our primary project goal was to understand what factors affected male turkey survival, we were also able to look at how much birds move and changes in body measurements.
We were able to monitor turkey movement throughout the year but focused particularly on the spring season (April 1 - June 30) since this timeframe overlaps with both the breeding season and the hunting season. We used hourly locations to estimate turkey home ranges and determine how much they were moving. We then looked at overlap of home ranges with the amount of forest and public land. Across all years and for both juveniles and adults home ranges were on average 2 mi2 with juveniles having more variable (sometimes much larger and sometimes much smaller) home ranges. Movement rates were also fairly consistent between years and ages. Male turkeys typically moved about 200 yards each hour during non-roost hours. More than half of an individual’s home range was comprised of forested land for juveniles and adults during all three years of the study. As we expected, turkeys use a mixture of landcover types, relying slightly more, at least spatially, on forested areas. Not quite 20% of harvest records occurred on public land in Delaware in recent years and there was a similar rate of harvest on public land in our turkey sample. Interestingly, turkey home ranges overlapped with public land at about the same rate with, on average across ages and years, 18% of home ranges consisting of public land. This value however varied greatly by individual. Some individuals in both age classes in every year maintained a home range exclusively on private property, while others had over 90% of their home range on public land. Hunters utilizing private or public land have opportunities to harvest turkeys and perhaps even the same bird as it moves across the landscape.
Once we had an understanding of how turkeys were moving, we could determine if their land cover preferences or movement rates affected their survival. In short, they do! Turkeys moving more each hour on average were more likely to die during the spring season than turkeys that did not move as much. However, the amount of forest or public land within the turkey’s home range did not affect survival. We were able to confirm that harvest was the primary source of mortality for the male turkey population in Delaware, but other sources of mortality occurred. Mortality due to natural events such as predation (foxes, raptors, owls) or disease was the next leading cause of mortality after harvest and juveniles were more susceptible to natural mortality events. Other, but very rare, sources of mortality included vehicle collisions and illegal harvest (harvest outside of the hunting season). Survival rates for adult and juvenile turkeys in Delaware are similar to populations throughout the Mid-Atlantic region.
One advantage of capturing individuals as juveniles was that we had known age turkeys in our study group. With known age individuals we were able to compare changes in body measurements such as weight, beard length, and spur length at different ages based on data collected at harvest and comparing it to data collected during capture. Turkey weight increased from the juvenile year to the adult stage but remained fairly consistent as birds aged, so older birds did not weigh more. But, as expected, beard length and spur length both increased with age. Due to the length of the study, we did not have a large sample size for known age 3- and 4-year-old birds, but as bands are returned this data set will grow. We also noticed that weights of adult birds at time of harvest generally decreased over the harvest season. Most likely condition of adult males decreases over the course of the breeding season which overlaps with the hunting season, resulting in harvest of lower weight birds later in the season. So, if you have the option to hunt earlier in the season take it for the possibility of a slightly better condition bird.
Research on survival of game species is one way we can better understand how harvest and hunting pressure affects dynamics of managed populations. But to get the most accurate representation of what is happening in a wild population, our tagged and monitored individuals should not get any special treatment or attention. In other words, purposely avoiding or harvesting a turkey in the study can sway the results. For example, in the first year of this study juvenile survival was lower than adult survival and the primary cause of juvenile mortality was harvest. This was an unexpected and highly unusual result for male turkeys in a population that is primarily limited by harvest since hunters typically harvest adult birds (about 80% of harvest records). Upon closer inspection we noticed that all of the juvenile mortality events due to harvest that year occurred within closely associated flocks in the same general area. It’s possible that this was a coincidence, alternatively, birds in this flock were harvested regardless of age because they were known to be banded. We do our best to make sure our study individuals are representative of the population and our research techniques do not affect their behavior or chances of survival, but we need the cooperation of the hunters.
We are incredibly appreciative of the public support for this project over the years. From reporting harvest of tagged individuals to allowing access to private property, this project would not have been possible without the cooperation of hunters and landowners. Learning more about our state’s game species is a more successful endeavor when we all work together!