Influence of weather on gobbling activity of male wild turkeys
PATRICK H. WIGHTMAN,11Email: pw78598@uga.eduWarnell School of Forestry and Natural Resources, University of Georgia, Athens, GA 30602, USA
JAMES A. MARTIN, Warnell School of Forestry and Natural Resources, University of Georgia, Athens, GA 30602, USA
JOHN C. KILGO, USDA Forest Service, Southern Research Station, P.O. Box 700, New Ellenton, SC 29809, USA
EMILY RUSHTON, Georgia Department of Natural Resources – Wildlife Resources Division, Social Circle, GA 30025, USA
BRET A. COLLIER, School of Renewable Natural Resources, Louisiana State University Agricultural Center, Baton Rouge, LA 70803, USA
MICHAEL J. CHAMBERLAIN, Warnell School of Forestry and Natural Resources, University of Georgia, Athens, GA 30602, USA
Abstract Gobbling activity of Eastern wild turkeys (Meleagris gallopavo silvestris ; hereafter, turkeys) has been widely studied, focusing on drivers of daily variation. Weather variables are widely believed to influence gobbling activity, but results across studies are contradictory and often equivocal, leading to uncertainty in the relative contribution of weather variables to daily fluctuations in gobbling activity. Previous works relied on road-based auditory surveys to collect gobbling data which limits data consistency, duration, and quantity due to logistical difficulties associated with human observers and restricted sampling frames. Development of new methods using autonomous recording units (ARUs) allows researchers to collect continuous data in more locations for longer periods of time, providing the opportunity to delve into factors influencing daily gobbling activity. We used ARUs from 1 March to 31 May to detail gobbling activity across multiple study sites in the southeastern United States during 2014 – 2018. We used state-space modeling to investigate the effects of weather variables on daily gobbling activity. Our findings suggest rainfall, greater wind speeds, and greater temperatures negatively affected gobbling activity, whereas increasing barometric pressure positively affected gobbling activity. Therefore, when using daily gobbling activity to make inferences relative to gobbling chronology, reproductive phenology, and hunting season frameworks stakeholders should recognize and consider the potential influences of extended periods of inclement weather.
Key words acoustic monitoring, gobbling, Meleagris gallopavo, Convolutional Neural Network, weather, wild turkey.
Male birds often rely on visual and auditory courtship behaviors to portray reproductive fitness to females, attract mates, and maintain social and dominance hierarchies (Williams 1984, Omland 1996, Buchholz 1997, Mateos 1999, Cornec et al. 2017). Frequency of courtship behaviors, such as vocalizations by males, change in response to conspecifics along with anthropogenic and environmental influences (Staicer et al. 1996, Berg et al. 2005, Slabbekoorn and Ripmeester 2008). Ecological theories such as the adaptive acoustic hypothesis and risk reward theory suggest birds adopt different vocalization strategies depending on environmental conditions to maximize the effectiveness and costs associated with calling (Orians 1969, Zanette et al. 2006, Lima 2009, Luther 2009).
The wild turkey (Meleagris gallopavo ) is a non-migratory upland game bird indigenous to North America whose mating strategy is a form of polygamy similar to exploded lekking (Krakauer 2008). Turkeys use a polygynous-promiscuous mating system, where females choose males who are competing for mating opportunities via visual displaying (e.g., strutting) and auditory vocalizations (e.g., gobbling, drumming; Healy 1992). Turkeys gobble to secure mates by attracting females, maintain territories, and compete with other males (Bailey and Rinnel 1967, Bevill 1973, Healy 1992). Gobbling activity is believed to be influenced by a variety of factors, such as time of day, timing of female reproductive activities, conspecifics, hunting, weather, predation risk, age structure, and testosterone levels (Kienzler et al. 1996, Miller et al. 1997, Chamberlain et al. 2018, Wightman et al. 2019, Wakefield et al. 2020). Wildlife managers and agencies are interested in understanding factors influencing gobbling activity, as it is the primary determinant of hunter satisfaction and is likely linked to reproductive success (Casalena 2011, Schroeder 2014, Isabelle 2015, Chamberlain et al. 2020).
Historical research relied on roadside surveys to describe gobbling activity, but results from previous studies contained notable discrepancies in regards to drivers of variation in gobbling activity. For example, early studies reported both positive and negative effects of nesting phenology, weather, and hunting pressure on gobbling activity (Bevill 1975, Kienzler et al. 1996, Miller et al. 1997, Lehman et al. 2005, Palumbo et al. 2019). However, no definitive relationship between any of the aforementioned variables and gobbling activity was established, likely due to a lack of uniformity in data collection, coupled with logistical difficulties in obtaining high quality, detailed, spatially-explicit gobbling data. Furthermore, roadside surveys were generally not conducted during inclement weather, and can be additionally biased by observer error, sample design, and manpower limitations (Miller et al. 1997, Lehman et al. 2005, Palumbo et al. 2019).
Development and use of autonomous recording units (ARU; Rempel et al. 2005, Mennill et al. 2012, Colbert et al. 2015) offer researchers the ability to thoroughly detail gobbling activity. With advancement of ARU technology, recent studies have elucidated how factors such as time of day, nesting phenology/female receptivity and hunting influence gobbling activity using spatially and temporally robust datasets (Chamberlain et al. 2018, Wightman et al. 2019, Wakefield et al. 2020). In general, gobbling activity was highest 30 minutes prior to sunrise until 150 minutes post sunrise (hereafter; daily gobbling activity) and fluctuated considerably from one morning to the next (Wightman et al. 2019). Additional work has indicated that female nesting phenology was positively related to gobbling activity, with onset of reproductive activities resulting in an initial peak of gobbling (Chamberlain et al. 2018, Wakefield et al. 2020). Furthermore, contemporary literature has noted hunting activity may have a greater negative influence on gobbling activity than the positive effect of nesting phenology (Wightman et al. 2019, Wakefield et al. 2020). However, there is no existing literature using ARUs to investigate the relative influences of weather variation on gobbling activity. Thus, research is needed to evaluate how weather may influence gobbling activity. We hypothesized that morning weather conditions would influence gobbling activity; therefore, our objectives were to evaluate potential relationships between gobbling activity of male Eastern wild turkeys (Meleagris gallopavo silvestris ) and a suite of weather variables across multiple study sites in the southeastern United States.