UNIVERSITY PARK, Pa. — What level of fall wild turkey harvest by hunters causes population declines? That’s what researchers in Penn State’s College of Agricultural Sciences are learning midway through a five-year study of the birds.
The research, supported by the Pennsylvania Game Commission, U.S. Geological Survey, the National Wild Turkey Federation (NWTF) and the Pennsylvania Chapter NWTF, is estimating harvest rates of hen turkeys and assessing the importance of fall hunting-season length in managing turkey populations.
The fall harvest, during which hunters can take birds of either sex, is the easiest way to manipulate turkey population trends. If fewer hens are killed in the fall, then it is expected that more hens survive to reproduce the next spring.
“Hen harvest rates have ranged from 2 percent to 9 percent of the estimated hen population for the 2010, 2011 and 2012 hunting seasons,” said lead researcher Duane Diefenbach, adjunct professor of wildlife ecology and leader of the Pennsylvania Cooperative Fish and Wildlife Research Unit at Penn State.
“This is good news, because previous research has indicated that fall harvest rates of hens should be kept below 10 percent to prevent population declines. However, this study will provide data to see whether this ’10 percent rule’ really applies to Pennsylvania.”Previous research in Missouri actually measured the fall harvests of both males and females, but because so few males are taken by hunters in the fall season, the 10 percent level has been a rule of thumb used by biologists when managing fall harvests of hens.”
Two study areas
Each year of the ongoing Pennsylvania study, at least 200 female wild turkeys are trapped by researchers using rocket nets in each of two study areas during the fall and winter. All turkeys are fitted with aluminum leg bands, one on each leg. Leg bands on the females offer a reward and are stamped with a toll-free telephone number to report the band number.
About 60 hens each year also are equipped with a satellite radio-transmitter attached as a backpack that remains on the birds for life. “Transmittered” hens allow for estimates of how many birds survive to the fall hunting season. As hunters harvest reward-banded and transmittered birds, researchers can estimate the proportion of birds that are harvested — the harvest rate for hen turkeys.
Harvest-rate study. Now in the third year of the hen harvest-rate study, the Pennsylvania Game Commission this fall flipped the length of turkey hunting seasons in the two study areas. For the season that opens Nov. 2, the southern study area (Game Commission wildlife management units 2C, 2E, 4A, 4B and 4D) increases from two to three weeks, and the northern area (units 2F, 2G and 2H) decreases from three weeks to two weeks.
Researchers estimate female wild turkey harvest and survival rates by age class and fall season length, Diefenbach noted. Then they will determine how one-week changes to fall season length affect harvest rates of hens. This experimental manipulation of season length will strengthen the conclusions of the study and confirm whether the preliminary findings are consistent.
The research includes a survey, which is mailed to 10,000 Pennsylvania hunters with a postage-paid return envelope after each fall turkey season. Questions focus on hunting participation, success and satisfaction with fall turkey hunting, and reasons why hunters did or didn’t hunt — all to determine hunter recruitment and youth participation.
The Game Commission will use the information generated by the study to provide the longest possible fall turkey-hunting seasons without overharvesting hen wild turkeys.
Diefenbach has been surprised by one aspect of the research. Judging by banded male turkeys from a previous study, few gobblers are taken by hunters in the fall.
“We don’t have enough data to estimate specific harvest rates, but very few birds from the several thousand we banded for the gobbler study a few years ago were ever reported in the fall season,” he said.
Future population sizes
This shows how the fall harvest really can affect future population sizes, according to Mary Jo Casalena, the Pennsylvania Game Commission’s turkey biologist, who is collaborating on the research.
“Females comprise the majority of the harvest because they are with the brood flocks, which are easier to call in than adult males that roam by themselves or in small groups during fall,” she explained.
“Longer fall seasons translate to higher hen harvests. Harvesting too high a proportion of females in the fall can spell trouble next breeding season because it’s the females that incubate the eggs and raise the young.”