Received: 18 January 2022 | Revised: 16 December 2022 | Accepted: 1 January 2023 DOI: 10.1002/wsb.1429 R E S E A R C H A R T I C L E Factors influencing survival of female eastern wild turkeys in northeastern South Dakota Reina M. Tyl 1 | Christopher T. Rota 1 | Chadwick P. Lehman 2 1 Division of Forestry and Natural Resources, West Virginia University, PO Box 6125, Morgantown, West Virginia 26506, USA 2 South Dakota Game, Fish and Parks, 13329 US Highway 16A, Custer, South Dakota 57730, USA Correspondence Reina M. Tyl, Pennsylvania Game Commission, Bureau of Wildlife Management, 2001 Elmerton Ave., Harrisburg, Pennsylvania, 17110, USA. Email: rtyl@pa.gov Funding information South Dakota Game, Fish and Parks, Grant/Award Numbers: Grant W ‐ 75 ‐ R, Federal Aid Study 7564; National Wild Turkey Federation, Grant/Award Number: NWTF Project No: 2.1.2017; USDA National Institute of Food and Agriculture, McIntire Stennis Project, Grant/Award Number: WVA00124 Abstract Population growth can be sensitive to changes in survival rates for many avian species. Understanding sources of mortality, and how to mitigate negative effects on survival, can give managers insight into factors contributing to population change. Harvest trends of eastern wild turkeys ( Meleagris gallopavo silvestris ) in northeastern South Dakota suggest a decline in abundance. We investigated factors influencing survival of wild turkeys to identify potential factors contribut- ing to the decline. We monitored 122 female wild turkeys using VHF radio transmitters from February 2017 to April 2019. Annual survival was 0.52 (95% CI = 0.33 – 0.64) for juvenile and 0.49 (95% CI = 0.23 – 0.63) for adult females, respectively. Daily survival probability was significantly lower during the spring (log ‐ odds ratio [LOR] = − 0.9; 95% CI = − 1.5 – − 0.2) and while a juvenile female was incubating (LOR = − 0.67; 95% CI = − 1.23 – − 0.09) but not while an adult female was incubating (LOR = − 0.35; 95% CI = − 0.92 – 0.24). Mammalian predation was the leading cause of mortality, and female wild turkeys were most vulnerable to predation during the spring while engaging in nesting and rearing of young broods. Wild turkeys were at risk for additional sources of mortality while incubating nests that were not contributors to mortality during other periods of the year, as deaths caused by haying equipment — the second greatest cause of mortality — only occurred while a female was incubating. Reducing female mortality due to haying, by delaying cutting, installing flushing Wildlife Society Bulletin 2023;47:e1429. wileyonlinelibrary.com/journal/wsb | 1 of 16 https://doi.org/10.1002/wsb.1429 This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. © 2023 The Authors. Wildlife Society Bulletin published by Wiley Periodicals LLC on behalf of The Wildlife Society. bars on haying equipment, or increasing availability of suitable nesting cover types to reduce the probability of nesting in hayfields, could improve female survival. Annual survival during our study was about 16 – 29% lower than survival estimates from northeastern South Dakota during the 1990s, suggesting that reduced female survival could be contributing to the apparent decline in wild turkey abundance. K E Y W O R D S cause ‐ specific mortality, eastern wild turkey, Meleagris gallopavo silvestris , South Dakota, survival Eastern wild turkey ( Meleagris gallopavo silvestris ; hereafter wild turkey) are an important game species in North America. After being extirpated from much of their historic range, wild turkey populations have been restored throughout North America (Williams 1981). However, recent declines in wild turkey harvests (Tapley et al. 2011, Byrne et al. 2015, Casalena et al. 2015, Eriksen et al. 2015, Chamberlain et al. 2022), a commonly used index for wild turkey abundance, have led to renewed concerns from wildlife managers, hunters, and other stakeholders about factors influencing post ‐ restoration wild turkey population dynamics. Demographic models projecting population growth can be used to understand how sensitive population growth is to changes in survival and reproduction, identify potential causes of apparent declines in abundance, and inform management actions (Alpizar ‐ Jara et al. 2001, Pollentier et al. 2014 a , Lehman et al. 2022). Past demographic modeling efforts have identified female survival (Suchy et al. 1983, Alpizar ‐ Jara et al. 2001), reproductive parameters (i.e., nest success and poult survival; Roberts et al. 1995, Pollentier et al. 2014 a ), or both female survival and reproductive parameters (Vangilder and Kurzejeski 1995, Roberts and Porter 1996, Rolley et al. 1998) as having the greatest effect on wild turkey population growth. Although a recent study of wild turkey demography in nearby Wisconsin found population growth was most sensitive to changes in nest and poult survival (Pollentier et al. 2014 a ), during times of poor recruitment the impact of female survival on population growth may increase (Rolley et al. 1998). Given recent declines in wild turkey productivity (Byrne et al. 2015, Casalena et al. 2015), identifying factors limiting female survival is an important step toward determining possible drivers of population change. Predation is the leading cause of female wild turkey mortality throughout their range (Shields and Flake 2006, Moore et al. 2010, Pollentier et al. 2014 b , Little et al. 2016, Byrne and Chamberlain 2018). Additionally, while female harvest is typically not permitted during the spring (except for bearded females), fall harvest of females in Iowa during the 1990s negatively impacted annual survival (Little et al. 1990). However, more recent investigations into harvest rates have determined that, due to declining fall harvests (Chamberlain et al. 2022), current fall harvest rates of female wild turkeys may be low enough to have a negligible impact on survival (Pollentier et al. 2014 b , Buckley et al. 2022). Other sources of mortality include haying equipment (Leif 2001, Shields and Flake 2006, Pollentier et al. 2014 b ), disease (Palmer et al. 1993 a , Leif 2001, Pollentier et al. 2014 b ), severe winter weather (Lehman et al. 2001, Pollentier et al. 2014 b ), and vehicle collisions (Kurzejeski et al. 1987, Shields and Flake 2006, Moore et al. 2010, Pollentier et al. 2014 b , Little et al. 2016). Female wild turkey survival often varies seasonally. Many studies reported lowest survival during the spring and summer as females are especially vulnerable to predators while solitarily engaging in reproductive activities (i.e., incubating nests and caring for preflight offspring; Kurzejeski et al. 1987, Roberts et al. 1995, Wright et al. 1996, Lehman et al. 2001, Pollentier et al. 2014 b ). Additionally, several studies reported an inverse relationship between precipitation and nest success (Roberts et al. 1995, Lowery et al. 2001, Lehman et al. 2008) and 2 of 16 | TYL ET AL 23285540, 2023, 2, Downloaded from https://wildlife.onlinelibrary.wiley.com/doi/10.1002/wsb.1429, Wiley Online Library on [29/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License hypothesized that spring precipitation may improve the efficiency at which mammalian predators detect incubating females due to moisture ‐ facilitated olfaction (Storaas 1988, Palmer et al. 1993 b ). Other studies have found survival is lowest during severe winters, as persistent, deep snow cover can decrease foraging efficiency and make movement energetically expensive (Austin and DeGraff 1975, Porter 1977, Porter 1978, Healy 1992) at a time when wild turkeys need to augment their food intake to meet increased thermoregulatory demands (Haroldson et al. 1998). We evaluated annual survival of wild turkeys in northeastern South Dakota. Recent data suggest reduced abundance in the region, as reported harvests declined from a high of 5,809 males in 2010 to 2,482 males in 2016 (Huxoll 2016). Since survival of female wild turkeys can influence population growth (Suchy et al. 1983, Vangilder and Kurzejeski 1995, Rolley et al. 1998, Alpizar ‐ Jara et al. 2001), understanding mortality sources and factors that influence female survival is necessary to identify and mitigate causes of the apparent decline. Our objectives were to (1) estimate annual survival for adult and juvenile age classes, (2) determine effects of age class and environmental variables on daily survival probability, and (3) determine leading causes of mortality for female wild turkeys in northeastern South Dakota. STUDY AREA Our study was conducted in Codington, Deuel, Grant, and Roberts counties in northeastern South Dakota, USA. The study area is split between the Minnesota River ‐ Red River Lowland physiographic region, characterized by nearly ‐ level topography dominated by cultivated crops (i.e., row crops) and the Coteau des Prairies physiographic region, characterized by gently undulating to hilly relief dominated by rangeland (Flint 1955, Miller et al. 1979, Johnson et al. 1995). Elevations ranged from over 600 m above mean sea level on top of the Coteau to about 300 m above sea level in the Lowland (Miller et al. 1979). Most of the study area consisted of private and tribal lands (7,158 km 2 and 375 km 2 , respectively) with state (e.g., Game Production Areas; 66 km 2 ) and federal (e.g., Waterfowl Production Areas; 59 km 2 ) lands scattered throughout. Agricultural land uses dominate the study area, with about 93% of available land (i.e., excluding wetlands and open water) consisting of cultivated croplands, tallgrass prairie rangelands, and hayfields (Dewitz 2019). Common grasses include warm ‐ season grasses such as big bluestem ( Andropogon gerardii ), little bluestem ( Schizachyrium scoparium ), Indiangrass ( Sorghastrum nutans ), switchgrass ( Panicum virgatum ), and sideoats grama ( Bouteloua curtipendula ; Johnson and Larson 2007). Common cool ‐ season grasses include smooth brome ( Bromus inermis ), Kentucky bluegrass ( Poa pratensis ), western wheatgrass ( Pascopyrum smithii ), and green needlegrass ( Stipa viridula ; Johnson and Larson 2007). Numerous forbs and patches of western snowberry ( Symphoricarpos occidentalis ) are scattered throughout the rangelands (Johnson and Larson 2007). Forested areas along the east ‐ facing breaks where the Coteau descends into the Lowlands are dominated by bur oak ( Quercus macrocarpa ) on the drier slopes (Leatherberry et al. 2000). More mesic areas are dominated by elm ‐ ash ( Fraxinus spp.; Ulmus spp.) forests (Leatherberry et al. 2000) that are intermixed with trembling aspen ( Populus tremuloides ), box elder ( Acer negundo ), eastern cottonwood ( Populus deltoides ), and sugar maple ( Acer saccharum ; Knupp Moore and Flake 1994). Northeastern South Dakota is in a humid continental climate region, with mean annual precipitation of 57 cm and mean annual temperature of 6.5°C across the study area (Menne et al. 2012). About 60% of the total annual precipitation occurs during the nesting and brood ‐ rearing periods (April through August; Menne et al. 2012). Average annual snowfall for the region is 108.6 cm, and, on average, there are over 40 days of at least 13 cm of snow on the ground, but the number of snow ‐ covered days can vary greatly from year to year (Menne et al. 2012). Snow can accumulate up to half a meter in depth during winter months (Menne et al. 2012); however, snow depth is often variable across the study area as wind creates deep snowdrifts as well as wind ‐ swept areas. EASTERN WILD TURKEY FEMALE SURVIVAL | 3 of 16 23285540, 2023, 2, Downloaded from https://wildlife.onlinelibrary.wiley.com/doi/10.1002/wsb.1429, Wiley Online Library on [29/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License There were several open wild turkey hunting seasons during our study. During the Spring Prairie Turkey season, a limited number of hunters were permitted to harvest one male wild turkey using an approved firearm or archery equipment. During the Spring Archery Turkey season, an unlimited number of hunters were permitted to harvest one male wild turkey using archery equipment. Because South Dakota defines a male wild turkey as a wild turkey with a visible beard or spurs, bearded females within our study area were at risk of legal harvest during the spring seasons. Additionally, during the Fall Turkey season, a limited number of hunters were permitted to harvest one wild turkey of either sex within a hunting unit that covered a portion of Roberts County (Figure 1). F I G U R E 1 Map of the extent of the wild turkey hunting seasons in Codington, Deuel, Grant, and Roberts Counties in northeastern South Dakota, USA, during 2017 and 2018. 4 of 16 | TYL ET AL 23285540, 2023, 2, Downloaded from https://wildlife.onlinelibrary.wiley.com/doi/10.1002/wsb.1429, Wiley Online Library on [29/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License METHO DS Capture and radio ‐ telemetry Between 1 January and 31 March in 2017 and 2018, we captured wild turkeys using rocket nets (Thompson and Delong 1967, Wunz 1984, Delahunt et al. 2011). Following capture, we aged female wild turkeys as adult or juvenile based on presence or absence of barring on the 9th and 10th primary feathers (Williams 1961) and weighed each bird. We secured 80 g, very high frequency (VHF) radio transmitters (Advanced Telemetry Systems, Isanti, MN, USA) using a shock cord harness and backpack mount. Transmitters were <3% of the females' body weight to reduce the risk of the transmitter interfering with survival and reproduction (Fair et al. 2010). Transmitters were equipped with an activity signal, a nonmoving (loafing) signal that is activated instantaneously whenever the female is not in motion, and mortality signal set to activate after 8 hours of inactivity. We monitored radiomarked wild turkeys 6 days per week during spring and summer (1 April – 31 July) and monthly for the remainder of the year (1 August – 31 March). We determined onset of incubation by listening for nonmoving signals from VHF transmitters. We assumed females classified as juveniles when captured transitioned to adults on April 1 the year following their initial capture (Lehman et al. 2001). Cause ‐ specific mortality We investigated mortality signals as soon as possible upon initial detection. Due to frequent monitoring of radiomarked females during spring and summer, most mortality events were investigated within 24 hours after detecting a mortality signal. Incubation behavior has been known to occasionally activate the mortality signal. Therefore, we delayed investigation of mortality signals from females thought to be incubating until after the projected hatch date or until the location of the signal moved away from the suspected nest location (Shields and Flake 2006). Due to monthly monitoring of females by aircraft (i.e., aerial telemetry) during the fall and winter (Yarnall et al. 2020), it was possible for several weeks to have passed between the mortality event and detection of the mortality signal. However, once a mortality signal was detected, the mortality was investigated within 72 hours. We classified mortality events as mammalian predation, avian predation, haying equipment, vehicle collision, legal harvest, disease, or unknown. Necropsy of carcasses, evidence at the kill site, and transmitter condition were used to determine causes of death. Death was attributed to predation when examination of carcasses revealed hemorrhaging accompanied by puncture wounds (Lehman et al. 2007). Evidence such as tracks, feces, fur, carcass caching, and bite marks on the transmitter identified the mortality as mammalian predation. Sharp puncture wounds accompanied by removal of the head and neck region from the carcass, as well as presence of raptor feathers at the kill site, were characteristic of avian predation events (Miller and Leopold 1992, Thogmartin and Schaeffer 2000, Lehman et al. 2007). Death was attributed to haying equipment if the female was known to be incubating, the mortality event was detected immediately after haying of the vegetation around the nest, and there were signs of bodily injury at the nest. Death was attributed to a vehicle collision if the carcass was located adjacent to or on a roadway and signs of blunt force trauma were present on the carcass. If a whole carcass was located and there were no signs of emaciation, hemorrhaging, or other trauma, then the carcass was examined for diseases at the Animal Disease Research and Diagnostic Laboratory at South Dakota State University. We were conservative when assigning causes of mortality, and therefore, classified the cause as unknown if no cause of death could be assigned or if several weeks could have elapsed between the mortality event and assessment of cause of death due to monthly monitoring of radiomarked females during fall and winter. EASTERN WILD TURKEY FEMALE SURVIVAL | 5 of 16 23285540, 2023, 2, Downloaded from https://wildlife.onlinelibrary.wiley.com/doi/10.1002/wsb.1429, Wiley Online Library on [29/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License Environmental covariate estimation We sought to determine how rain and snow influenced female survival. To do this, we retrospectively acquired daily rain accumulation (mm; hereafter precipitation) and number of consecutive days with >3 cm of snow on the ground (hereafter consecutive snow ‐ covered days) data from the National Climactic Data Center's archive of weather data via Climate Data Online (CDO; Menne et al. 2012). Consecutive snow ‐ covered days only included days with at least 3 cm of snow on the ground because snow less than 3 cm in depth was not accurately detectable by the weather station (i.e., we assumed zero snow cover when there was <3 cm standing snow). Covariate data were downloaded from one weather station in Milbank, South Dakota (Lat Long = 45.2266 − 96.6233; Elevation = 384.1 m), whose period of record covered 100% of the duration of our study. While environmental covariates may vary over the study area due to changes in microclimate, we assumed information gathered from the weather station was representative of conditions observed each day. Modeling survival probability We assumed survival of individual i during day t was a Bernoulli random variable: y Bernoulli y p ~ ( ) it i t it ( − 1) where y it = 1 if an individual i survived day t , y it = 0 if an individual i was dead during day t , and where p it represented daily survival probability (Royle and Dorazio 2008). We further assumed a logit ‐ linear model for daily survival probability which we model as a function of age class (adult or juvenile), biological year (defined 1 April to 31 March the following calendar year), season (winter = 1 January to 31 March; spring = 1 April to 30 June; summer = 1 July to 30 September; or fall = 1 October to 31 December), incubating or not incubating, an interaction between age and incubation status, precipitation, and consecutive snow ‐ covered days. We accounted for repeated observations on individual females by fitting a random coefficients mixed ‐ effects model, where a unique identifier for each individual female wild turkey was the grouping variable (Hobbs and Hooten 2015). We assumed each coefficient j associated with wild turkey i was a Gaussian random variable: β Gaussian μ τ ~ ( , ) ji j j where μ j and τ j represented the population ‐ level mean and variance, respectively, of coefficient j We used informative prior distributions based on published estimates of female wild turkey survival rates for the intercept parameter and for the slope coefficient describing the difference in log odds daily survival between adult and juvenile wild turkeys (Tyl et al. 2020). We describe our procedure for deriving informative prior distributions in Appendix 1. Based upon previous studies of established populations (Table 1), we assumed a Gaussian ( x ̅ = 6.56, SD = 0.40) prior distribution for the population ‐ level mean intercept parameter, and a Gaussian ( x ̅ = − 0.09, SD = 1.01) prior distribution for the population ‐ level difference in log odds between adult and juvenile wild turkey survival. Given the lack of prior information on other variables, we assumed logistic (location = 0, scale = 1) prior distributions for population ‐ level means and uniform (minimum = 0, maximum = 10) prior distributions for population ‐ level standard deviations of remaining slope coefficients. We fit each model with JAGS version 4.3.0 (Plummer 2003) via the jagsUI version 1.4.9 interface (Kellner 2018) in program R version 3.5.1 (R Core Team 2018). We ran 3 chains for each model using trace plots to determine an adequate burn ‐ in period and subsequently ran models until we achieved reasonable convergence ( R ̂ ≤ 1.1 ; Gelman et al. 2013). We concluded that slope coefficients were different from 0 if 95% credible intervals (CI) did not overlap 0. 6 of 16 | TYL ET AL 23285540, 2023, 2, Downloaded from https://wildlife.onlinelibrary.wiley.com/doi/10.1002/wsb.1429, Wiley Online Library on [29/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License T A B L E 1 Comparison of estimates of female eastern wild turkey ( Meleagris gallopavo silvestris ) annual survival probability obtained from northeastern South Dakota from 2017 to 2019 with previously published estimates. Published estimates are organized into 3 categories — established, newly translocated, and other regions. Established and newly translocated studies occurred within the Midwest, United States region; other region studies occurred outside of the Midwest region. Newly translocated studies assessed survival probability immediately following a translocation event. Published estimates are distinguished by age class (adult or juvenile) when possible or reported as combined if the authors did not distinguish estimates by age class. Ranges of estimates represent variation in annual survival probability. Standard errors of published point estimates are presented in parentheses when reported by the authors. Population Status Age Class Adult Juvenile Combined Reference Established 0.49 (0.10) 0.52 (0.08) ‐ This Study ‐ ‐ 0.435 (0.073) Kurzejeski et al. 1987 0.576 – 0.639 0.434 – 0.644 ‐ Little et al. 1990 ‐ ‐ 0.445 – 0.693 Vangilder and Kurzejeski 1995 ‐ ‐ 0.527 (0.048) Wright et al. 1996 0.594 (0.056) – 0.759 (0.059) 0.526 (0.094) – 0.950 (0.042) ‐ Hubbard et al. 1999 ‐ ‐ 0.755 (0.113) – 0.800 (0.135) Humberg et al. 2009 0.607 0.404 ‐ Pollentier et al. 2014 b Recently Translocated ‐ ‐ 0.777 (0.057) Leif 2001 ‐ ‐ 0.721 (0.004) Lehman et al. 2001 ‐ ‐ 0.676 (0.023) Shields and Flake 2006 ‐ ‐ 0.219 (0.070) – 0.273 (0.066) Kane et al. 2007 ‐ ‐ 0.45 – 0.55 Switzer and Tucker 2009 0.194 (0.071) – 0.798 (0.081) 0.188 (0.098) – 0.725 (0.141) ‐ Parent et al. 2011 Other Regions ‐ ‐ 0.499 (0.026) – 0.810 (0.015) Palmer et al. 1993 a 0.495 (0.045) 0.502 (0.065) ‐ Roberts et al. 1995 ‐ ‐ 0.308 – 0.399 Chamberlain et al. 1996 ‐ ‐ 0.514 (0.033) – 0.560 (0.098) Vangilder 1996 0.56 (0.06) – 0.64 (0.04) 0.44 (0.06) – 0.61 (0.06) ‐ Pack et al. 1999 0.224 – 0.770 ‐ ‐ Miller et al. 1998 (Continues) EASTERN WILD TURKEY FEMALE SURVIVAL | 7 of 16 23285540, 2023, 2, Downloaded from https://wildlife.onlinelibrary.wiley.com/doi/10.1002/wsb.1429, Wiley Online Library on [29/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License We report survival probability at the annual, seasonal, and incubation period scale. We calculated annual survival probability by raising daily survival probability to the 365 th power. We calculated seasonal survival probability at 90 ‐ day intervals, which is the approximate length of a season. To allow clear comparison of differences in survival between spring and other seasons, we assumed female turkeys were not incubating during all seasonal survival calculations. We calculated survival probability across a complete incubation period by assuming it would take 28 days to incubate a successful clutch (Tyl et al. 2020). Note, however, that because adults are more likely to renest than juveniles (Tyl et al. 2020), adults could have spent, on average, more days incubating than juveniles. We therefore also estimated survival over the age class specific mean incubation periods observed during our study. R E S U L T S We captured and radiomarked 43 adult and 37 juvenile female wild turkeys during the winter of 2017, and we radiomarked an additional 42 juvenile females during the winter of 2018 to maintain a sample that was relatively balanced across age classes. Sixteen juveniles radiomarked during year 1 transitioned to the adult age class for year 2; 23 adults radiomarked during year 1 were alive at the beginning of year 2. Survival probabilities were estimated from a total of 122 individual female wild turkeys and were comprised of 776 daily intervals from February 16, 2017 through April 2, 2019. In total, our data set included 41,572 days where an individual wild turkey was at risk of death. Eight females (3 adults and 5 juveniles) were right censored from the survival analysis. Four individuals (2 adults and 2 juveniles) were right censored due to transmitter failure; 4 (1 adult and 3 juveniles) were right censored because their mortality was presumed to be a direct result of being captured and radiomarked. Daily survival probability was significantly lower during the spring (LOR = − 0.9; 95% CI = − 1.5 – − 0.2) and while a juvenile female was incubating (LOR = − 0.67; 95% CI = − 1.23 – − 0.09) but not while an adult female was incubating (LOR = − 0.35; 95% CI = − 0.92 – 0.24; Tables 2 and 3). Survival probability did not vary by year and was not affected by precipitation or consecutive snow ‐ covered days (Table 2). Annual survival probability for adults was 0.49 (95% CI = 0.23 – 0.63) and did not differ from juveniles (0.52; 95% CI = 0.33 – 0.64; Tables 1 and 2). Over a 28 ‐ day period, cumulative survival of non ‐ incubating adults was 0.96 (95% CI = 0.93 – 0.99) while survival of incubating adults was 0.92 (95% CI = 0.83 – 0.98), and survival of non ‐ incubating juveniles was 0.97 (95% CI = 0.94 – 0.99) while survival of incubating juveniles was 0.88 (95% CI = 0.75 – 0.96). There was not a significant difference between cumulative survival probabilities for non ‐ incubating and incubating adults (difference in surviving the interval = 0.04; 95% CI = − 0.02 – 0.13); however, cumulative survival was greater for non ‐ incubating juveniles relative to incubating juveniles while incubating (difference in surviving the interval = 0.09; 95% T A B L E 1 (Continued) Population Status Age Class Adult Juvenile Combined Reference ‐ ‐ 0.665 Wilson et al. 2005 0.478 (0.069) – 0.644 (0.064) 0.133 (0.034) – 0.277 (0.075) ‐ Casalena et al. 2007 ‐ ‐ 0.74 (0.02) Moore et al. 2010 ‐ ‐ 0.535 (0.062) – 0.835 (0.030) Reynolds and Swanson 2010 ‐ ‐ 0.55 Little et al. 2016 0.58 ‐ ‐ Byrne and Chamberlain 2018 8 of 16 | TYL ET AL 23285540, 2023, 2, Downloaded from https://wildlife.onlinelibrary.wiley.com/doi/10.1002/wsb.1429, Wiley Online Library on [29/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License CI = 0.01 – 0.22). On average, adult females spent more time incubating (24.24 days; 95% CI = 21.62 – 26.81) than juvenile females (17.90 days; 95% CI = 15.16 – 20.41). Survival of adult females over the 24 ‐ day adult mean incubation period (0.93; 95% CI = 0.85 – 0.98) did not differ from survival of juvenile females over the 18 ‐ day juvenile mean incubation period (0.92; 95% CI = 0.83 – 0.98). We observed 69 mortality events (37 adults and 32 juveniles). Predation was the leading cause of death ( n = 43), and over half of all mortality events were attributed to mammalian predation ( n = 38, 55%). Mortality due to agricultural haying equipment while incubating was the second ‐ greatest cause of mortality ( n = 7, 10%). Other T A B L E 2 Population ‐ level mean log ‐ odds ratio (LOR), lower 95% credible interval (CI) level, and upper 95% CI level for each covariate and interaction used to model daily survival probability of female eastern wild turkeys ( Meleagris gallopavo silvestris ) from February 2017 to April 2019 in northeastern South Dakota, USA. Covariate LOR Lower CI Level Upper CI Level (Intercept) 7.054 6.448 7.639 Female age class: Adult a 0.054 − 0.348 0.436 Study year: 2017 – 2018 a − 0.004 − 0.554 0.593 Study year: 2018 – 2019 a 0.303 − 0.313 0.972 Season: Spring a − 0.869 − 1.534 − 0.233 Season: Summer a 0.059 − 0.763 0.934 Season: Fall a 0.202 − 0.649 1.147 Incubating a − 0.513 − 0.910 − 0.102 Precipitation 0.412 − 0.031 1.023 Consecutive snow ‐ covered Days 0.400 − 0.427 1.680 Age × Incubation 0.159 − 0.237 0.555 Derived Variables b Adult incubation − 0.354 − 0.917 0.245 Juvenile incubation − 0.672 − 1.225 − 0.091 a Categorical variables were coded using sum ‐ to ‐ zero constraints. For each factor (female age class, study year, season, incubating), the coefficient for the omitted factor level equals − 1 × the sum of the factor levels reported on this table. b Derived variables — adult incubation and juvenile incubation — represent the combined age class specific effects of the incubating covariate and the age × incubation interaction. Adult incubation is derived by incubating + age × incubation; juvenile incubation is derived by incubating − age × incubation. T A B L E 3 Estimated probability (with lower and upper 95% credible interval [CI] levels) a female eastern wild turkey ( Meleagris gallopavo silvestris ) in northeastern South Dakota, USA, survives a standardized 90 ‐ day interval across all seasons. Probabilities are calculated from population ‐ level means presented in Table 2 and do not account for individual variation in survival probability. Season Survival probability (90 days) Lower CI Level Upper CI Level Spring 0.89 0.81 0.95 Summer 0.95 0.89 0.98 Fall 0.95 0.90 0.99 Winter 0.97 0.92 0.99 EASTERN WILD TURKEY FEMALE SURVIVAL | 9 of 16 23285540, 2023, 2, Downloaded from https://wildlife.onlinelibrary.wiley.com/doi/10.1002/wsb.1429, Wiley Online Library on [29/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License causes of death included disease (i.e., visceral gout, Coccidiosis), legal harvest (bearded females only), and vehicle collisions. A cause of death could not be confidently assigned to 11 mortality events. We did not find any evidence of legal or illegal harvest ‐ related mortality during the fall (Table 4). D I S C U S S I O N While our estimates of annual female survival probability were comparable to estimates from similar studies conducted in the 1990s (Kurzejeski et al. 1987, Little et al. 1990, Vangilder and Kurzejeski 1995, Wright et al. 1996, Hubbard et al. 1999), our estimates were lower than estimates of female survival from more recent studies of established wild turkey populations in Indiana (Humberg et al. 2009), Louisiana (Wilson et al. 2005), and South Carolina (Moore et al. 2010). Additionally, our estimates were lower than previous estimates of female survival from recently translocated, growing populations of wild turkeys in South Dakota (Lehman et al. 2001, Leif 2001), including an estimate from the same study area about 2 decades earlier (Shields and Flake 2006). Given that wild turkey population growth is sensitive to changes in female survival (Suchy et al. 1983, Vangilder and Kurzejeski 1995, Roberts and Porter 1996, Rolley et al. 1998, Alpizar ‐ Jara et al. 2001) and female survival in northeastern South Dakota has declined since the 1990s, reduced female survival could be contributing to the apparent population decline. Daily survival probability decreased during the spring season, independent of whether a female was incubating. Female wild turkeys may exhibit lower daily survival during the spring due to increased vulnerability to predation while shifting from winter to spring home ranges (Vangilder and Kurzejeski 1995) and while engaging in egg laying prior to initiating incubation, as females remove themselves from the safety of the flock, and therefore, are at increased risk of predation (Gill 2007). Incubating a clutch also increases female vulnerability to predation due to spending nearly all their time alone and on the ground (Vander Haegen et al. 1988, Roberts et al. 1995, Wright et al. 1996, Lehman et al. 2001, Pollentier et al. 2014 b ). Furthermore, females are at risk of additional mortality sources (i.e., haying equipment) while incubating that they are not susceptible to during other periods. Females spent only 2,509 days incubating out of 41,572 days where at least one female was at risk of mortality. However, even though incubation days accounted for only a small portion (6%) of all days at least one female was at risk of mortality, 25% of all mortality events occurred during incubation. Incubation proved to be a particularly risky activity for juvenile females, as daily survival T A B L E 4 Causes of mortality for female eastern wild turkeys ( Meleagris gallopavo silvestris ) in northeastern South Dakota, USA, during each season (winter = 1 Jan to 31 Mar; spring = 1 Apr to 30 Jun; summer = 1 Jul to 30 Sep; or fall = 1 Oct to 31 Dec) from February 2017 to April 2019. Cause of Death Winter Spring Summer Fall Total Percentage Incubating Mammalian predation 8 24 6 ‐ 38 55% 8 Haying equipment ‐ 7 ‐ ‐ 7 10% 7 Avian predation 2 2 1 ‐ 5 7% 1 Disease a ‐ 4 ‐ ‐ 4 6% ‐ Legal harvest ‐ 2 ‐ ‐ 2 3% ‐ Vehicle collision ‐ 2 ‐ ‐ 2 3% 1 Unknown 4 2 ‐ 5 11 16% ‐ Total 14 43 7 5 69 ‐ 17 a Disease was determined to be the ultimate cause of mortality. Two deaths resulted from visceral gout; 2 deaths resulted from intestinal impactions caused by Coccidiosis. 10 of 16 | TYL ET AL 23285540, 2023, 2, Downloaded from https://wildlife.onlinelibrary.wiley.com/doi/10.1002/wsb.1429, Wiley Online Library on [29/05/2024]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons License probability of juveniles decreased during incubation. However, because adult females spent more time incubating than juveniles, on average, the effect of incubation on survival probability was ultimately similar for both age classes. Increasing agricultural intensity within the study area may be facilitating elevated levels of haying ‐ related mortality. Wimberly et al. (2017) reported substantial conversion of grasslands to croplands in eastern South Dakota between 2004 and 2014, with most of the conversion happening on Conservation Reserve Program (CRP) grasslands. The loss of grasslands in eastern South Dakota mirrors overall trends in CRP enrollment in South Dakota, which has declined from a high of 1.8 million acres in 1995 to 1.1 million acres in 2018 (United States Department of Agriculture 2021). Decreased availability of suitable nesting cover due to widespread grassland conversion may result in a greater proportion of wild turkeys using unsuitable nesting cover, such as hayfields, increasing the frequency of haying ‐ related mortality events. Predation was the leading cause of mortality, which has been repeatedly found during investigations of female wild turkey cause ‐ specific mortality (Hubbard et al. 1999, Lehman et al. 2001, Shields and Flake 2006, Humberg et al. 2009, Pollentier et al. 2014 b ). Aside from predator control, which is not uniformly effective at meaningful scales (Miller and Leopold 1992), there is little managers can do to directly impact predation rates. However, it is worth noting that important wild turkey predators such as coyotes are known to select agricultural landscapes (Gosselink et al. 2003, Hinton et al. 2015). Increased agricultural intensity could therefore have indirect impacts on wild turkey demography via changes in predator populations. While we cannot directly attribute apparent regional declines in wild turkey abundance to agricultural intensification or loss of CRP grasslands, it is worth noting that abundance of grassland birds has been reported to be positively associated with the number of acres enrolled in CRP (Haroldson et al. 2006). Therefore, studies designed to quantify the effects of CRP loss on the population dynamics of wild turkey and other grassland birds could put the impact of recent agricultural intensification into greater focus. Harvest mortality during our study was limited to spring and accounted for only a small portion of all mortality events. Because spring wild turkey hunting occurs during the reproductive period, hunting regulations are designed to limit harvest of female wild turkeys. Only male wild turkeys or wild turkeys with a visible beard (allowing for the legal take of bearded females) are permitted to be harvested during the spring season in many states, including South Dakota. The proportion of individuals removed from a population during hunting seasons can be directly influenced through season structure changes. However, because hunter harvest accounted for only 3% of all mortality events, more conservative hunting regulations (i.e., prohibiting spring harvest of bearded females) are unlikely to have a strong impact on female survival. We found no strong influence of weather on wild turkey survival. While there is evidence that extended periods of deep snow and cold temperatures have deleterious effects on wild turkey survival (Austin and DeGraff 1975, Wunz and Hayden 1975), we did not observe any winter ‐ related causes of mortality, such as starving or freezing to death. Total snow accumulation (2018 = 72.1 cm; 2019 = 135.8 cm) and total number of days with snow depth greater than 15 cm (2018 = 10 days; 2019 = 71 days) during the winters (i.e., 1 Jan to 31 Mar) captured by our study may not have been severe enough to impact survival probability. Since mammalian predators use olfactory cues to locate prey (Storaas 1988), and wet conditions enhance growth of scent ‐ causing bacteria (Syrotuck 2000), we expected that female survival would be negatively affected by precipitation (in the form of rainfall), especially while incubating (Lehman et al. 2008). Since the spring seasons observed during our study were, on average, drier than normal (Tyl et al. 2020), it is possible that there was not enough opportunity for precipitation ‐ facilitated predation events to occur to negatively affect female survival. M A N A G E M E N T I M P L I C A TI O N S Regardless of trends in agricultural intensification and CRP enrollment, wild turkeys will continue to nest in hayfields in highly agricultural landscapes. In such landscapes, where haying equipment may be a leading contrib