Eric L. Ludwig | Dr. Jacob L. Bowman | Matt DiBona
The turkey is typically a topic in the fall around Thanksgiving but Delaware like many states has a native population of turkeys. Though it seems hard to imagine now, the wild turkey disappeared from Delaware in the late 1800s from overhunting and habitat destruction. After nearly a century of absence, the Delaware Division of Fish and Wildlife with the assistance of the National Wildlife Turkey Federation began a restoration program in 1984. Thirty-four wild birds from Pennsylvania, Vermont and New Jersey were released into Sussex County, Delaware. In the following years, additional birds were released and others were captured and transferred to parts of the state where there was enough suitable habitat. The turkey population increased quickly, and by 1991 turkeys were abundant enough to establish a hunting season. Since then, Delaware’s turkey population has continued to increase and expand to nearly all parts of the state and turkey hunting continues to grow in popularity. And while the return of wild turkeys to Delaware remains one of our state’s great conservation success stories, researchers from the University of Delaware and DNREC Division of Fish and Wildlife are taking a closer look at the status of our turkey population to make sure these birds are here to stay.
To provide better information for management of wild turkeys, the Division of Fish and Wildlife recently teamed up with the University of Delaware to study wild turkeys. This research focused on estimating hen survival, poult survival (a poult is the name for young turkeys), nest success, and nest characteristics. Hens and the number of poults that they produce are the most important factors for maintaining sustainable populations of wild turkeys. Why? Because hens assume all the risk for hatching and raising the next generation of turkeys. Following breeding, females will begin searching for a suitable area to nest on the ground and begin laying eggs. For 28 days she will spend nearly all her time incubating those eggs, only leaving the nest briefly to find food and water. During this energetically stressful time, she and her nest are under constant threat of predation from foxes, owls, raccoons, snakes, etc. Similarly, a severe rain storm may leave a nest underwater or otherwise cause a hen to abandon a nest. All of which means: not all nests will hatch. If a nest is lost early enough in the nesting season, the hen may attempt to renest. Even if the nest and eggs do survive to hatch, poults are especially vulnerable to predation and weather conditions during their first weeks of life. If a poult is fortunate enough to survive its first two weeks of life, its chances of fledging and entering into the fall population increase dramatically. Therefore, by focusing our study on hen reproduction we were able to identify factors that are potentially limiting the production of turkeys in Delaware.
In January 2010, we started a two year study by trapping and placing backpack transmitters on female wild turkeys in Sussex County, Delaware. Backpack transmitters are fastened to the bird safely with two elastic cords under each wing which allows the transmitter to sit on the back of the bird. The transmitters produce a radio frequency that can be detected up to a mile away, which permitted researchers to determine where the birds are at any given time. Our research was focused around Redden State Forest which is located near Georgetown, Delaware. We trapped 104 birds in two years and placed radio transmitters on 76 hens. Each captured turkey received a unique, numbered leg band that includes information for people to contact the Division of Fish and Wildlife should they harvest a banded bird or otherwise find one dead. The hens were tracked throughout the year and were monitored during the nesting season to determine nest success and nest characteristics. We used the transmitter to locate nests and monitored them for hatching success, clutch size, and predation. We documented predation impacting both hen survival (predators ate the hen which resulted in loss of the nest) and nest success (predators ate the eggs which resulted in the loss of the nest). Foxes and owls were the only predator we documented killing adult hens and raccoons and foxes were implicated in removing eggs from turkey nests.
We located 68 nests during our study. Hens nested between April and June, with most nests started during the first week of May. Most of our nests hatched during the first week of June but hatching occurred from late-May through mid-June. Nests had an average of eight eggs per nest which is lower than in other states where the average is usually 10-14 eggs per nest. We observed nesting success rates of 19-32%, which is very low compared to other surrounding states. Although these measures were lower than other states, our poult survival was 34-52%, which was greater than other states. But is it surprising that a lot of nests failed? Not necessarily. To compensate for nest failure, turkeys (like many other species) have evolved a reproductive strategy that includes producing a lot of eggs in each nest. Such a strategy ensures that even though her nest may fail in a given year, in those years when she does hatch a successful nest, she produces many poults. And even though nest success seems to be lower for Delaware turkeys compared to other states, our higher poult survival estimates may help to offset this loss and still allow for a sufficient number of birds to be recruited into the population.
A key factor in understanding the sustainability of most populations is adult female survival. We documented a hen survival rate of 47-68%. The low end of this range was lower than surrounding states but the upper end was greater than surrounding states. In 2010, we had two major blizzards which might account for the 47% survival rate that year. These storm events left most of our study area covered with snow that rendered much of the turkey’s winter food supply (acorns, seeds, and grains) temporarily unavailable. If hens were unable to maintain sufficient body reserves going in the nesting season they may have been more vulnerable to predation. Most of the deaths that we recorded in both years resulted from predation, which was primarily from fox but also some from owls. We also observed some turkey deaths caused by vehicles and illegal harvest but these numbers were very low. Most of the mortalities occurred between April and June.
Some of our results for wild turkeys in Delaware are concerning because they are lower than estimates for similar research conducted on eastern wild turkeys in other states. At the same time, we observed more year to year variation in hen survival, poult survival, and nest success than we expected. Is this because there is that much annual variation in the population dynamics of wild turkey or is this an artifact of having two very different years in terms of weather conditions, predator pressure, etc.? Fortunately, because we still have 27 hens with transmitters alive in the wild, we plan to continue this project for another nesting season (spring 2012). An additional year will help clarify what factors are influencing turkey populations in Delaware as well as refine the precision of estimates of nest success and hen survival during the nesting season. Ultimately, the results of this research can be used by wildlife biologists to develop strategies to better manage this valuable wildlife resource. Delaware’s turkey population is a great reintroduction success story. The population has grown rapidly for the past 28 years, and now with our recent research, biologist can manage the turkey populations for many years to come.
Originally printed in Outdoor Delaware magazine. For more information about this magazine or to subscribe visit: http://www.dnrec.delaware.gov
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