Executive Summary

Together with the Pennsylvania Game Commission, we developed an integrated population model (IPM) to estimate harvest rate, survival probability, and abundance for turkey in three wildlife management units in Pennsylvania that are managed for fall turkey hunting and three WMU groups managed in during the spring season. Overall, we found that, across all WMUs we see an increase in turkey abundance over time. Male juvenile and adult abundance was consistently greater than both female adult and juveniles per sq. mile of their respective WMU.

WMU groups were established too… the groups consisted of…

For adult females, density per sq. mile of turkeys increased from 0.8 to 1.5 in WMU 3D, 2.9 - 0.1 in 4D, and 22 - 36 in 2D. For adult males, 6.8 - 20.4 in group 2, 1.1 - 2.1 in group 6, 1.8 - 4.2 in group 7.

Previous versions of the IPM, which were conducted in a spreadsheet model, assumed male juvenile harvest rates and female adult harvest rates were the same. The issue here is that this can overestimate female survival. In this model, we found that harvest rates for females ranged between 0.1 - 0.4, and the known-fate model we implemented found that survival for adult and juvenile females averaged about 0.6 in 2D, 0.56 in 3D, and 0.78 in 4D, showing that survival is lower than previously estimated.

Background

The eastern wild turkey (hereafter, turkey) are a widespread and abundant game species that inhabit various landscapes in eastern North America. Turkeys experience annual fluctuations in reproduction and survival because of their fast-paced life history. Habitat quality, weather conditions, hunting pressure, disease, and predation collectively shape the demographic processes of wild turkeys Mcghee et al. (2008).

Despite the extensive research conducted on turkeys over the past 50 years and the subsequent large body of literature, there are still knowledge gaps regarding demographic rates and life history strategies for this species. A review conducted by suggests that our understanding of turkey demographics and the impact of factors such as habitat quality and quantity, predator abundance, and changes in hunting pressure on vital rates is incomplete. Research has found that survival and reproduction of adult, second-year females are among the most influential vital rates influencing wild turkey population growth, and the degree of control managers have on these vital rates depends on the abiotic or biotic conditions that limit them, making them system and context-specific .

In Pennsylvania, turkeys are an important game species, and the state consistently leads the country in both the spring and fall turkey harvests, as well as the number of turkey hunters . Pennsylvania is also one of the few states to offer a spring male season and a fall either-sex season. Fall hunting seasons for either sex of turkeys result in predominantly female and young-of-the-year being harvested. Females are more susceptible to harvest because brood flocks persist into the fall, and a common hunting strategy of breaking up flocks and recalling individuals is the most successful. Therefore, the fall harvest has the potential to effect population abundance because it can be an additive source of mortality for females .

To help inform management on wild turkey populations in Pennsylvania, we developed an age- and stage-structured Bayesian IPM to monitor population trends using data from three wildlife management units (WMUs, Figure 1). The study areas, WMU 2D, 3D, 4D, and 5C were each chosen to be representative of the diversity seen across the state of Pennsylvania.

Study area WMUs

Figure 1. Wildlife Management Units in Pennsylvania. Dark grey units indicate areas of hen telemetry efforts.

Figure 1. Wildlife Management Units in Pennsylvania. Dark grey units indicate areas of hen telemetry efforts.

Study Area 1 (WMU 5C - Southeast and Northeast Regions)

WMU 5C represents a mix of urban, suburban, and large agricultural land use. The study area has the lowest turkey population densities among the regions considered. Its average spring harvest densities from 2018 to 2020 were recorded at 0.32 birds per square mile. Additionally, the hunter density is relatively low at 2.2 hunters per square mile, and a poult-to-hen ratio of 1.9 poults per hen. Hunter success rate is 15%. This WMU is closed to Fall turkey hunting, and therefore not included in this analysis.

Study Area 2 (WMU 2D - Northwest and Southwest Regions)

WMU 2D represents one of the most diverse Pennsylvania landscapes with a high interspersion of habitats suitable for wild turkeys. This area boasts one of the highest turkey population densities. The average spring harvest density from 2018 to 2020 is 1.38 birds per square mile. The hunter density is 4.7 hunters per square mile, a hunter success rate of 26%, and a poult-to-hen ratio at 2.9 poults per hen.

Study Area 3 (WMU 3D - Northeast Region)

WMU 3D comprises vast expanses of publicly owned wooded landscapes surrounded by human development. The study area has semi-low turkey population densities and a spring harvest density of 0.50 birds per square mile from 2018 to 2020. The hunter density is 3.3 hunters per square mile, and the hunter success rate is 14%. The poult-to-hen ratio in this area is 2.4 poults per hen.

Study Area 4 (WMU 4D - Northcentral and Southcentral Regions)

WMU 4D features large expanses of publicly owned wooded landscapes bordered by extensive agriculture. This study area exhibits a medium-level turkey population density and records an average spring harvest density of 0.68 birds per square mile from 2018 to 2020. The hunter density is 4.0 hunters per square mile, with a hunter success rate of 16% and a poult-to-hen ratio above average at 3.0 poults per hen.

Population model

The population model framework will use multiple data sets, game take surveys to inform the harvest rate, survival, and abundance of male turkeys in our population model. For females, we relied on telemetry data to determine survival rate, prior information to determine the harvest rate, and subsequent abundance. Recruitment was calculated based on poult-to-hen ratios obtained through summer site surveys (Figure 2). Our population dynamics models consider sex and age class and operate annually. We incorporate hunting season timing for each sex and life history category (adult, juvenile) on a yearly basis. For males, the model year starts in May, while for females, it begins in November to align with their hunting season.

Figure 2. Data and population model structure for estimating survival, harvest rates, survival, and recruitment.

Figure 2. Data and population model structure for estimating survival, harvest rates, survival, and recruitment.

Results

Harvest rates for each sex and age class

Harvest rates for adult males varied from 0.16 to 0.35 among all wmus, with credible intervals of 0.14 to 0.43 (Figure 3). Juvenile males had a range of 0.031 to 0.1 across all wmus, with credible intervals of 0.035 to 0.142 (Figure 3). We made the assumption that adult and juvenile female harvest rates were equal. For females, harvest rates were lower than those for males, ranging from 0.007 to 0.017 with credible intervals of 0.008 to 0.054 (Figure 3).

Survival probability for each sex and age class

The survival probability for adult males ranges from 0.4 to 0.735, while for juvenile males it ranges from 0.712 to 0.914 (see Figure 4).

Using the data for females, we were able to estimate survival for each management unit. However, we were unable to estimate survival across years. For adult females, the survival rates ranged from 0.288 to 0.601, while for juveniles the rates ranged from 0.286 to 0.598 (Figure 5).

Recruitment of poults into the population

Abundance for each sex and age class

To calculate abundance, we divided the reported number of birds harvested by the estimated harvest rate for each sex and age class. Figure 7 shows the abundance over time for all combinations of sex and age class.

Tables

Harvest rates with 95% confidence intervals for each sex/age class across WMUs over four years.
Sex/Age Class WMU Year Median 2.5% CI 97.5% CI
male adult 2D 2019 0.233 0.189 0.276
2020 0.241 0.197 0.286
2021 0.210 0.174 0.250
2022 0.254 0.209 0.309
3D 2019 0.257 0.208 0.306
2020 0.265 0.216 0.316
2021 0.236 0.195 0.282
2022 0.278 0.229 0.338
4D 2019 0.248 0.201 0.292
2020 0.256 0.209 0.302
2021 0.226 0.187 0.268
2022 0.268 0.223 0.324
male juvenile 2D 2019 0.059 0.048 0.068
2020 0.062 0.052 0.072
2021 0.050 0.042 0.059
2022 0.068 0.057 0.083
3D 2019 0.069 0.055 0.083
2020 0.073 0.059 0.087
2021 0.060 0.050 0.071
2022 0.080 0.067 0.098
4D 2019 0.065 0.052 0.076
2020 0.068 0.056 0.080
2021 0.056 0.047 0.066
2022 0.075 0.063 0.092
female juvenile 2D 2019 0.050 0.031 0.085
2020 0.011 0.009 0.014
2021 0.031 0.024 0.039
2022 0.016 0.013 0.021
3D 2019 0.005 0.004 0.007
2020 0.015 0.010 0.021
2021 0.011 0.007 0.016
2022 0.014 0.009 0.020
4D 2019 0.017 0.012 0.024
2020 0.018 0.013 0.024
2021 0.015 0.011 0.021
2022 0.025 0.019 0.033
female adult 2D 2019 0.039 0.028 0.052
2020 0.022 0.017 0.029
2021 0.011 0.009 0.014
2022 0.012 0.009 0.016
3D 2019 0.022 0.016 0.031
2020 0.012 0.008 0.017
2021 0.007 0.004 0.011
2022 0.008 0.005 0.013
4D 2019 0.072 0.052 0.097
2020 0.012 0.008 0.017
2021 0.009 0.006 0.012
2022 0.010 0.007 0.014
Survival probabilities with 95% confidence intervals for each sex/age class across WMUs over four years.
Sex/Age Class WMU Year Median 2.5% CI 97.5% CI
male adult 2D 2019 0.436 0.361 0.485
2020 0.415 0.333 0.470
2021 0.487 0.419 0.536
2022 0.372 0.287 0.459
3D 2019 0.375 0.303 0.428
2020 0.355 0.278 0.412
2021 0.423 0.358 0.476
2022 0.315 0.239 0.398
4D 2019 0.399 0.328 0.449
2020 0.379 0.302 0.434
2021 0.449 0.386 0.500
2022 0.337 0.258 0.424
male juvenile 2D 2019 0.727 0.580 0.817
2020 0.707 0.556 0.808
2021 0.762 0.620 0.852
2022 0.655 0.488 0.810
3D 2019 0.675 0.517 0.774
2020 0.653 0.494 0.765
2021 0.716 0.560 0.818
2022 0.599 0.426 0.768
4D 2019 0.697 0.544 0.792
2020 0.675 0.521 0.783
2021 0.734 0.585 0.833
2022 0.620 0.449 0.786
Survival probabilities with 95% confidence intervals for each sex/age class across WMUs.
Sex/Age Class WMU Median 2.5% CI 97.5% CI
female adult 0.568 0.482 0.633 1
0.483 0.647 2
0.560 0.477 0.657 3
female juvenile 0.563 0.493 0.622 1
0.569 0.494 0.643 2
0.558 0.477 0.649 3
Density of turkeys per square mile with 95% confidence intervals for each sex/age class across WMUs over four years
Sex/Age Class WMU WMU area (m^2) Year Density 2.5% CI 97.5% CI
female adult 2D 2486.7 2019 1.5 1.1 2.1
2020 2.2 1.8 2.7
2021 4.5 3.7 5.3
2022 3.7 2.8 4.6
2023 4.2 3.0 5.5
3D 2102.6 2019 0.3 0.2 0.5
2020 1.3 1.0 1.7
2021 1.4 1.1 1.7
2022 1.4 1.1 1.8
2023 1.4 1.0 1.9
4D 2742.9 2019 0.4 0.3 0.5
2020 1.6 1.3 2.0
2021 1.8 1.4 2.2
2022 1.9 1.4 2.5
2023 1.9 1.3 2.8
female juvenile 2D 2486.7 2019 2.3 1.4 3.7
2020 5.8 5.0 7.0
2021 2.1 1.8 2.6
2022 3.7 3.0 4.4
2023 3.9 2.9 4.9
3D 2102.6 2019 2.0 1.5 2.7
2020 1.1 0.9 1.4
2021 1.1 1.0 1.4
2022 1.0 0.8 1.3
2023 1.3 1.0 1.7
4D 2742.9 2019 2.5 1.8 3.4
2020 1.6 1.3 2.0
2021 1.6 1.4 1.9
2022 1.6 1.2 1.9
2023 2.1 1.5 2.7
male adult 2D 2486.7 2019 4.9 4.1 6.0
2020 4.3 3.6 5.3
2021 5.9 4.9 7.1
2022 4.5 3.7 5.5
2023 4.0 3.0 5.6
3D 2102.6 2019 1.6 1.3 2.0
2020 1.2 1.0 1.5
2021 1.1 0.9 1.4
2022 1.3 1.0 1.6
2023 1.0 0.7 1.4
4D 2742.9 2019 2.3 1.9 2.8
2020 1.8 1.6 2.3
2021 1.7 1.5 2.1
2022 2.0 1.6 2.4
2023 1.6 1.2 2.3
male juvenile 2D 2486.7 2019 3.2 2.7 3.9
2020 5.8 5.0 7.0
2021 2.1 1.8 2.6
2022 3.7 3.0 4.4
2023 3.9 2.9 4.9
3D 2102.6 2019 0.9 0.8 1.2
2020 1.1 0.9 1.4
2021 1.1 1.0 1.4
2022 1.0 0.8 1.3
2023 1.3 1.0 1.7
4D 2742.9 2019 1.4 1.1 1.7
2020 1.6 1.4 2.0
2021 1.6 1.4 1.9
2022 1.5 1.2 1.9
2023 2.1 1.5 2.7

References

Haegen, W. Matthew Vander, Wendell E. Dodge, and Mark W. Sayre. 1988. “Factors Affecting Productivity in a Northern Wild Turkey Population.” The Journal of Wildlife Management 52 (1): 127–33. https://doi.org/10.2307/3801072.
Mcghee, Jay D., Jim Berkson, David E. Steffen, and Gary W. Norman. 2008. “Density-Dependent Harvest Modeling for the Eastern Wild Turkey.” The Journal of Wildlife Management 72 (1): 196–203. https://doi.org/10.2193/2006-484.
Vangilder, Larry D., and Eric W. Kurzejeski. 1995. “Population Ecology of the Eastern Wild Turkey in Northern Missouri.” Wildlife Monographs, no. 130: 3–50. https://www.jstor.org/stable/3830761.