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Brood Surveys and Hunter Observations Used to Predict Gobbling Activity of Wild Turkeys in
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Mississippi
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Matthew D. Palumbo,* Francisco J. Vilella, Bronson K. Strickland, Guiming Wang, Dave
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Godwin
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M.D. Palumbo, B.K. Strickland, G. Wang
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Department of Wildlife, Fisheries, and Aquaculture, Mississippi State University, Mississippi
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State, MS 39762
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Present address of M.D. Palumbo: Westchester County Airport, 14 Loop Road Building 10,
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White Plains, New York 106704
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Francisco J. Vilella
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USGS Cooperative Research Unit, Department of Wildlife, Fisheries, and Aquaculture,
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Mississippi State University, Mississippi State, MS 39762
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Dave Godwin
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Mississippi Department of Wildlife, Fisheries, and Parks, 1505 Eastover Drive, Jackson, MS
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39211
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*
Corresponding author: Plums526@aol.com
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Disclaimer: “This draft manuscript is distributed solely for the purposes of scientific peer
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review. Its content is deliberative and predecisional, so it must not be disclosed or released by
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reviewers. Because the manuscript has not yet been approved for publication by the U.S.
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Geological Survey (USGS), it does not represent any official USGS finding or policy”.
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Abstract
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The Mississippi Department of Wildlife, Fisheries, and Parks utilize data from turkey hunter
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observations and brood surveys from across the state to manage wild turkey (Meleagris
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gallopavo) populations. Since 1996, the Mississippi Department of Wildlife, Fisheries, and
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Parks’ (MDWFP) personnel and cooperating wildlife managers have collected gobbling, jake
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observation, and brood survey data to better forecast poult recruitment and hunting quality. Our
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objective of this study was to evaluate if MDWFP’s survey data can be used as a viable predictor
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of gobbling activity and hunt quality. We used three mixed models to investigate the relationship
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between number of gobblers heard per hour of hunting (expected hunt quality) and the number of
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jakes observed per hour of hunting one year prior (model 1), the number of gobblers heard per
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hour of hunting and the total number poults per total hens observed 2 years prior (model 2), and
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the number of jakes seen per hour of hunting one year prior and the total number of poults per
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hens 2 years prior (model 3) from 1996 to 2008 among 5 wild turkey management regions
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encompassing the state. We incorporated year and region as random effects to account for spatial
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and temporal variation. We found that model 1 (P = 0.001) and model 3 (P <0.001) displayed
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significant relationships. We recommend managers incorporate hunter observations of jakes seen
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per hour of hunting the previous year as an indicator of statewide gobbling activity, rather than
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the brood survey data. Gobbling activity is influenced by a multitude of factors and further
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research is warranted to determine statewide relationships.
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Introduction
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Many states index wildlife population abundance by collecting harvest data or use data
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gathered during hunting seasons to estimate harvest, number of hunters, and days of hunting
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(Strickland et al. 1994). However, many of these estimates vary greatly, making yearly and
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regional comparisons difficult (Connelly et. al. 2005). Thus, wildlife agencies also rely upon
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observations from field personnel to index wildlife populations. For some states, recruitment
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estimates for wild turkey (Meleagris gallopavo) are indexed through brood surveys conducted by
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volunteers on “routine duties” during summer (Shultz and McDowell 1957; Wunz and Shope
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1980).
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The Mississippi Department of Wildlife, Fisheries and Parks (MDWFP) uses a
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combination of hunter harvest data and field observations to index wild turkey populations
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throughout the state. Harvest data collected through a Spring Gobbler Hunting Survey (SGHS)
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are used to index harvest rates, population size, age structure and gobbling activity on a yearly
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basis across the state. Additionally, data collected during brood surveys conducted by the
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MDWFP, Mississippi Forestry Commission, U.S. Forest Service, U.S. Army Corps of Engineers,
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and Weyerhaeuser Company are used to index reproduction and estimate productivity of wild
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turkey populations statewide. The MDWFP uses a combination of data from the SGHS and
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brood survey to predict the age structure and population levels that spring hunters can expect.
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The MDWFP also attempts to predict gobbling activity based on the brood survey of two years
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prior and jakes seen one year prior from the SGHS, which is used to categorize expected hunt
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quality. On average, adult gobblers gobble more than sub-adults (Bevill 1973; Hoffman 1990)
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and male two and three year age classes are dominant over older sibling groups (Watts 1968).
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This dominance can be displayed through increased gobbling (Bevill 1973). Thus, the MDWFP
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assumes that the two year old age class of gobblers is the most vocal age group of male turkeys
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(D. Godwin, A. Butler, and J. Koloski, MDWFP, unpublished report). However, gobbling
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activity has been reported to be extremely variable and influenced by a variety of factors
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(Hoffman 1990; Lint et al. 1995; Kienzler 1996; Miller et al. 1997a; Miller et al. 1997b)
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Since 1996, MDWFP and cooperating personnel have recorded number of gobblers heard
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per hour of hunting, number of jakes seen per hour of hunting, and number of poults per hen
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from five turkey management regions in Mississippi. Our objective was to determine if a
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relationship exists between counts of jakes observed and poults per hen and subsequent gobbling
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activity. A relationship among these counts would make predictions of gobbling activity more
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reliable and strengthen current strategies for turkey harvest recommendations.
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Methods
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In the SGHS, individual hunters voluntarily report throughout the spring season (typically
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mid-March to 1 May) location of hunt (i.e., whether the hunt was on private or public land); date;
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start and end time of hunting; county of hunt; number of gobblers heard; number of gobbles
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heard; number of gobblers, jakes, hens and unknowns seen; time a gobbler was harvested; and
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beard and spur lengths (D. Godwin, A. Butler, and J. Koloski, Mississippi Department of
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Wildlife, Fisheries and Parks, unpublished report). From June to August while conducting daily
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activities, brood survey participants record number of poults, hens with and without poults,
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gobblers, and “unknown” (age and gender not discernible) observed, as well as location (county
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and/or wildlife management area).
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We calculated mean number of gobblers heard per hour of hunting, mean number of
jakes observed per hour of hunting, and total poults per total hens observed for each turkey
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management region 1996-2008. The five turkey management regions were delineated by
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differences in physiography and location of logistical support (Figure 1).
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We estimated the mean number of gobblers heard per hour of hunting as a conservative
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index of gobbling activity (Gobbling Activity Index, GAI) since the propensity to gobble may
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differ among birds. We assumed that number of jakes seen per hour of hunting would be an
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adequate index of recruitment of one-year-old gobblers to the two-year age class, when gobblers
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are assumed to be most vocal (Jake Recruitment Index, JRI). Total number of poults per total
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hens (Nest Success Index, NSI) was used as an index of fecundity and recruitment (Glidden
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1977; Seiss 1989). Previous research at the Tallahalla Wildlife Management Area (TWMA) in
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Mississippi found a high correlation (r = 0.82) between number of successful nests two years
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prior and number of gobblers heard the current year (Miller et al. 1997b). Therefore, we assumed
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that NSI from 2 years prior would index abundance of two-year-old gobblers.
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We tested 3 separate mixed models to determine the relationships among NSI, JRI and
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GAI from 1996 – 2008 using the SAS 9.2 software package (SAS Institute, Cary North Carolina,
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USA). We used the mean count of GAI, JRI, and NSI for each region and year for analysis and
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did not have NSI data for 1996. In model one we compared JRI to NSI to determine if poult
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recruitment was a reliable predictor of jakes observed while hunting the following year. In
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model two we compared GAI to JRI to determine if the mean number of jakes observed while
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hunting was a reliable predictor of gobbling activity the subsequent year. Finally, with model
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three we compared GAI to NSI to determine if poult recruitment was a reliable predictor of
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gobbling activity two years later. We used year and region as random effects to account for
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annual and regional variation in turkey counts and used the Kenward-Rodgers degrees of
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freedom adjustment for models with multiple random effects (Littell et al. 2006). From each
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model we output parameter estimates and associated errors for use predictive models.
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Additionally, to gauge model fit we compared the predicted values from our mixed models to the
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observed values for JRI in model one and GAI in models two and three using Pearson’s
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correlation coefficient. We acknowledge this is not a true correlation between the response and
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explanatory variables, but we provide this correlation statistic as a simple measure of model fit to
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augment the F- and P-values for each model.
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Results
All three models demonstrated relationships between current and prior turkey counts. In
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model one, JRI was related to NSI one year prior (n = 60, F = 16.39, P < 0.001) with a
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correlation of r = 0.65 between observed and predicted JRI counts. In model two, GAI was
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related to JRI one year prior (n = 65, F = 11.46, P = 0.001) with a correlation of r = 0.91 between
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observed and predicted GAI counts. Finally, in model three, GAI was related to NSI two years
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prior (n = 60, F = 3.52, P = 0.067) with a correlation of r = 0.91 between observed and predicted
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GAI counts (Table 1.)
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Discussion
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Previous research has focused on monitoring broods to index population parameters, such
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as productivity (Speak et al. 1969; Gardner et al. 1972; Glidden 1977; Speake1980; Bartush et al.
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1985). Miller et al. (1997b) attempted to correlate an estimate of productivity (i.e., nest success)
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to breeding behavior (i.e., gobbling activity) for wild turkeys. Miller et al. (1997b) detected a
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significant correlation between nest success two years prior to number of gobblers heard, but not
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to number of calls heard. They hypothesized the proportion of two-year-old birds in the
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population could be indexed by nest success two years previous and can contribute to the
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potential of hearing an individual turkey gobble. We attempted to test this hypothesis at the
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regional scale and did not detect the same relationship. But, we did determine the JRI used to
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track the proportion of juvenile male turkeys in a population that will potentially be recruited to
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the two year old age class was as suitable index of gobblers heard during a hunting season.
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The Miller et al. (1997b) research was performed on TWMA in central Mississippi and nest
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success was determined from radio-monitored hens from 1984 -1995 from Palmer et al. (1993)
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and Miller et al. (1995). Palmer et al (1993) and Miller et al. (1997b) indexed nest success from
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daily monitoring hens until they were found in the same location for 2 consecutive days,
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whereupon the hens were considered to have initiated nesting. During incubation hens were
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located twice daily to determine hatching date, nest destruction or desertion, or hen mortality. As
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soon as incubation stopped researchers approached the nest to determine fate (Palmer et al. 1993
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and Miller et al. 1995). These hens and their nests where intensely monitored (Palmer et al. 1993
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and Miller et al. 1995) compared to the brood survey that the MDWFP can efficiently conduct.
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The NSI of total poults per total hens seen 2 years prior, which is gathered from staff while they
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are conducting routine duties throughout the state, is not as accurate. And therefore we
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recommend not using the NSI as an indicator of expected hunt quality (i.e., gobbling activity) at
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the regional level.
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But the NSI was significantly correlated to the JSI which indicates that it can track population
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size of wild turkeys at the statewide level. Furthermore, the JSI was also significantly correlated
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to the GAI which indicates that the JSI, a surrogate for the gobbler population one year prior, is
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an indicator of gobbling activity. But previous research by Lint et al. (1995) at TWMA reported
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that gobblers heard per day was not related (P= 0.14) to estimates of gobbler population size but
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was strongly correlated to harvest and harvest per effort.
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Our statewide analysis resulted in different correlations than were documented at a single
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management area, TWMA. The TWMA studies were at one research site where turkeys
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observed, monitored, and hunted could be considered of one population. Therefore estimates of
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these metrics are more consistent over years. Through the SGHS hunters may be visiting several
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different areas and essentially recording data from several different populations. We attempted to
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address the lack of spatial congruence by incorporating region and year as random effects, which
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resulted in detecting significant statewide correlations.
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The SGHS is useful to track long-term trends in wild turkey populations across the state.
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But the amount of spatial variation between sources of data such as gobbling activity, brood
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surveys, and jake encounters, likely can result in poor models to explain gobbling activity.
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Standardization of brood, jake, and gobbling call count surveys should be warranted to decrease
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this variation. The ability of observers to detect and identify birds has been recognized as a
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source of variation in many studies trying to detect birds (Diefenbach et al. 2003), therefore,
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unbiased observers (i.e. not hunters) that are consistently assigned to specific surveys may
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reduce variation. Additionally, attempting to predict a behavioral response that is influenced by
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such a variety of factors may consistently result in a high level of inaccuracy. The indices we
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investigated can be used to predict regional gobbling activity with consideration that there is a
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large amount of variation associated with this mating behavior. Therefore, we recommend
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further research into potential sources of variation (i.e., observers, habitat, hunter effort and
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success, brood survey effort, weather, population dynamics) at regional levels, so that more
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accurate relationships can be determined.
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Acknowledgements
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We greatly appreciate the efforts of Mississippi’s sportsmen and the various natural
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resource agencies that have gathered wild turkey observations. We thank S. L. Edwards, R. S.
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Seiss, A. Butler, J. Koloski for their support. Funding for this project was provided by the
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Mississippi Department of Wildlife, Fisheries, and Parks through project W-48-56, Study 58 of
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the Federal Aid in Wildlife Restoration Program. Any use of trade, firm, or product names is for
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descriptive purposes only and does not imply endorsement by the U.S. Government.
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Tables
Table 1.
Three mixed models with year and region as random effects to determine the relationship among gobblers heard per
hour of hunting, mean number of jakes seen per hour of hunting one year prior and the total poults per total hens seen 2
years prior from 1996 – 2008 across all 5 of Mississippi Department of Wildlife, Fisheries, and Parks wild turkey
management regions.
Model
Response
variable
Explanatory
variable
Intercept
estimate
SE
Slope
estimate
SE
Num
df
Den df
Fvalue
Pvalue
2
GAIa
JRIb
0.563
0.063
0.483
0.143
1
53.4
11.46
0.001
3
GAI
NSIc
0.609
0.066
1
JRI
NSI
0.098
0.028
a. Mean number of gobblers hear per hour of hunting.
0.029
0.051
0.016
0.013
1
1
47.8
57.9
3.52
16.39
0.067
<0.001
b. Mean number of jakes seen per hour of hunting one year prior.
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c. Total poults per total hens observed 2 years prior.
Figure Captions
Figure 1.
The Mississippi Department of Wildlife, Fisheries, and Parks wild turkey
management regions from 1996 - 2008.
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