A large winter turkey flock of mostly hens at one of the bait sites at Stephen A. Forbes State Recreation Area. Image from an INHS Wild Turkey Research Project Trail Camera.
Tracking Wild Turkey Hens in Illinois
Aside from being potential indicators of ecosystem health, wild turkeys are an economically important game species. Accordingly, considerable research attention has focused on understanding broad-scale habitat associations of turkeys and estimating demographic parameters. Forests or woodlands with mature trees are known to provide habitat that is preferred by turkeys for parts of their annual cycle, but turkeys have extensive and seasonally variable home ranges (e.g., <1 to 32 km2).
The importance of different habitat components is likely seasonally dependent. For example, food availability and safety from predators are important year-round, but quality nesting and brood-rearing habitat are critical during spring and summer. Aspects of vegetation structure and composition, including understory density, are known to influence nest-site selection and reproductive success. However, despite the numerous links between vegetation structure and aspects of wild turkey habitat use and demography, information on turkey responses to forest management promoting oaks and hickories, particularly prescribed fire, has been generally lacking.
To continue adding to our understanding of wild turkey ecology, behavior, and their response to forest management activities, we have focused on studying hen turkeys in western, central, and south-central Illinois. Research locations include privately-owned sites in Pike County, and on public lands in Shelby (Hidden Springs State Forest and U.S. Army Corp of Engineers Lake Shelbyville), Fayette (Ramsey Lake State Recreation Area), and Marion (Stephen A. Forbes State Recreation Area) counties.
Our primary objectives have been to 1) obtain data to document hen turkey nest-site selection and nesting success, 2) to assess what factors (e.g., landscape composition, vegetation structure, black fly abundance, and weather) have the most influence on whether a turkey nest survives to hatch, and 3) to determine what effects, if any, prescribed fire in forests has on hen turkey habitat use during the nesting and brood-rearing parts of the year (i.e., spring and summer).
We captured turkeys using air-powered cannon nets (i.e., Netblasters) at sites baited with cracked corn during winter (mid-January – March) each year. Each captured bird was banded with an aluminum rivet leg band. Age (1 year old vs. >1 year old) of each captured individual was determined by evaluating the shape, wear, and barring on the ninth and tenth primaries (i.e., wing feathers).
Every captured hen was fitted with a PinPoint micro-GPS transmitter (Lotek Wireless Inc., Ontario, Canada). We released all birds at the capture site immediately after processing. Transmitters were programmed to record several (8-27) locations during daylight hours and one location at midnight every day. Each micro-GPS unit was also equipped with a dual axis activity sensor which records forward-backward (x-axis) and left-right (y-axis) movements and allowed us to infer activities such as incubation/loafing, running, and flushing/flying.
Each micro-GPS-marked bird was relocated every week during the breeding season and bi-weekly during the non-breeding season by using receivers connected to hand-held or truck-mounted antennas. Transmitters lasted up to a year if hens survived that long. Importantly, remote download of the stored location and activity data on transmitters permitted us to collect the data without disturbing nesting hens or influencing turkey movements—we could download their data from up to 500 meters away.
Some of the interesting findings so far based on data collected from 2015 to 2022:
- Hen turkeys are particularly vulnerable to predation during the lead up to nesting and during incubation phase of the nesting period. Each year 5 to 25 percent of hens die during this period, but they remain relatively safe the rest of the year.
- Each year, most nesting attempts fail to make it to the poult stage (i.e., fail to hatch). We have monitored 166 nesting attempts of radioed hens prior to 2023 and of that total 29 (17 percent) successfully hatched, 129 (78 percent) failed, and 8 (5 percent) had an unknown fate. These success rates are similar to those found in other published studies and appear adequate to maintain turkey populations in the areas where we are studying them (based on winter flock sizes and hunter harvest data).
- Most nesting failures occur during incubation (eggs and/or hens preyed upon), but several nests also fail during egg laying (eggs abandoned or preyed upon). Based on visitation to baited camera traps, suspected nest predators include raccoons, opossums, coyotes, foxes, and bobcats. Most hens attempt a second nest if their first of the year fails—one tagged hen made four nesting attempts during one breeding season.
- Nesting success/failure is poorly predicted by landscape metrics (e.g., amount of the landscape that is forested, distance to forest edge), black fly abundances, weather factors, temporal factors (i.e., early- vs. late-season), or vegetation cover metrics. Hens tend to place their nests on the ground in places where the vegetation height in the 50-100 cm range (think knee- to waist-high on yourself) is not too sparse and not too dense. There is a higher tendency for nests in the densest cover to fail.
- Hens spend some hours, separate from laying eggs, sitting on nests for up to 6 days before round-the-clock incubation begins. During the ~26-28 days of incubation, hens take recesses (to defecate, eat and move a bit) for an average of less than an hour each day, and tend to take them during afternoons.
- Pyrodiversity, here represented by having forest management units that vary in time-since-burn and burn frequency, provided hens in our study areas with a mosaic of managed habitat. Non-burned areas within managed forests proved to be an important habitat component for hens during reproduction (they often nested there). Among burned forest management units, during the egg-laying, incubation and post-hatch periods hens used (relative to habitat availability) those units that had had one or two full growing seasons since the last prescribed fire more than freshly burned units or units having had three or more growing seasons since the last prescribed fire.
This research would not have been possible without the tireless efforts of Dr. Christine Parker and Morgan Meador, who were graduate students and led the research and field work over the years, and several enthusiastic seasonal field technicians.
This research was funded with federal pass-through money from the Illinois Department of Natural Resources (specifically from the Federal Aid in Wildlife Restoration Act).
Dr. Jeff Hoover is an Avian Ecologist with the Illinois Natural History Survey, Prairie Research Institute, University of Illinois. Jeff has been studying forest songbirds since 1990 in upland and bottomland forests in Appalachia and The Midwest, and wild turkeys since 2015 in Illinois.