Discussion
Previous literature detailing how weather influences gobbling activity
has reported contradictory results (Scott and Boeker 1972, Bevill 1973,
Kienzler et al. 1996, Miller 1997, Palumbo et al. 2019), leading to
uncertainty in the relative contribution of weather variables to daily
fluctuations in gobbling activity. We used the most comprehensive
dataset currently available on wild turkey gobbling activity, coupled
with local weather metrics, to evaluate relationships between gobbling
activity and weather. Collectively, our findings suggest weather
variables can influence daily gobbling activity and are at least
partially responsible for oscillations in gobbling activity throughout
the spring reproductive season.
Gobbling is a behavior males use to attract females and ensure
reproductive opportunities (Buchholz 1997). However, gobbling increases
predation risk as predators are attracted to calls, so males must
balance increasing predation risk with attracting mates (Tuttle and Ryan
1981, Burk 1982, Jennions et al. 1997). In birds, weather conditions can
also increase predation risk, therefore males may adopt varying calling
strategies in response to weather conditions (Carr and Lima 2010, Digby
et al. 2014). We found rain had the greatest influence on gobbling
activity, as has been shown in earlier works (Bevil 1973, Kienzeler et
al. 1996). During rain events, calling males may be more vulnerable to
predation as their hearing and vision, which they rely on for detecting
predators, are compromised (Healy 1992, Candolin and Voigt 1998, Hedrick
2000). Furthermore, during rain events sound attenuation is increased,
making it harder for the gobble to be heard by other individuals
(Lengagne and Slater 2002). Alternatively, rain may simply reduce the
ability of the ARU to detect gobbles, although we detected 21,180
gobbles during rain events and literature on other bird species reported
that rain negatively influenced calling (Staicer et al. 1996, Bruni et
al. 2014, Digby et al. 2014).We posit that the influence of rain on
gobbling activity recorded by ARUs is likely a combination of detection
and ecology, but when reporting gobbling chronology should be
considered.
Increases in animal activity and calling have previously been associated
with increases in barometric pressure across multiple species (Oseen and
Wassersug 2002, Wellendorf et al. 2004, Pellegrino et al. 2013,
Zagvazdina et al. 2015). Changing barometric pressure is a well-known
predictor of storm fronts, with barometric pressure falling as inclement
weather approaches and rising as the storm system dissipates (Saucier
2003, Breuner et al. 2013). Miller et al. (1997) found no relationship
between gobbling and barometric pressure, but we observed an increase in
barometric pressure from one day to the next resulted in increased
gobbling activity. Given changes in barometric pressure and its
relationship to inclement weather such as rain, we conclude that this
relationship is best explained by turkeys gobbling more in weather
conditions not associated with storm systems.
Extant literature has noted a significant relationship between decreased
calling and higher temperature in various birds that use auditory
courtship behaviors (Hansen and Guthery 2001, Gudka et al. 2019).
Vocalization and thermal relationships are likely related to overheating
and higher metabolic rates that can occur with increased ambient
temperatures, especially for endotherms who use energetically costly
courtship behaviors (Dillon et al. 2010, Silva et al. 2015). We observed
a similar relationship between higher temperatures and gobbling activity
but note that previous studies at southern latitudes reported no
relationship between temperature and gobbling activity (Miller et al.
1997, Palumbo et al. 2019), whereas at more northern latitudes studies
have reported positive relationships between gobbling and temperature
(Kienzler et al. 1996). One could speculate that this relationship could
be related to the removal of males causing drops in gobbling later in
the sampling period when temperatures are warmer. However, given that we
had 5 years of data on an un-hunted site where gobbling continued until
the end of the sampling period (Figure 2), we suspect that this is not
the case. Wild turkeys at southern latitudes may reduce gobbling at
higher temperatures, but we offer that the pattern may not be similar at
northern latitudes.
Sound attenuation increases at greater wind speeds, and previous studies
have demonstrated wind can negatively influence calling frequency and
the ability to hear calls in multiple species (Lengagne 1999, Lengagne
and Slater 2002, Yip et al. 2017). We observed that greater wind speeds
had a negative effect on daily gobbling, consistent with previous
studies (Bevill 1973, Kienzler et al. 1996, Miller et al. 1997). The
ability for either human observers or ARUs to detect gobbling as wind
speeds increase may be diminished (Kienzler et al. 1996). Alternatively,
during high wind speeds birds may change behaviors as perceived risk
increases, as individuals have increased difficulty detecting predators
due to confusion with moving vegetation (Boyko et al. 2004, Carr and
Lima 2010). We suspect males may be less inclined to gobble as wind
speeds increase because the desired outcome from calling may be limited
by the ability of receptive females to hear the call, and because
predation risk may increase.
Wakefield et al. (2020) used the same modeling approach that we used,
focused on describing the influences of female reproduction (laying or
incubating) and cumulative removal of males on daily gobbling activity.
Wakefield et al. (2020) found the proportion of females in reproduction
positively influenced gobbling activity, but the impact of male removal
at the same time had a greater negative impact on gobbling activity. We
also recognize other variables not measured in our or previous studies
may be contributing to variation in daily gobbling, such as varying
levels of testosterone in males, interactions/encounters with females,
and population vital rates such as male age structure (Miller et al.
1997, Chamberlain et al. 2018, Wakefield et al. 2020).
As gobbling activity is positively correlated with hunter satisfaction
and linked to reproduction, it is often a key determinant used by state
agencies when considering regulatory frameworks (Bevill 1975, Hoffman
1990, Little et al. 2001, Casalena et al. 2011, Isabelle et al. 2015).
Given our results, we suggest that when describing gobbling activity,
managers should account for how weather patterns may influence gobbling
chronology. Weather variables should be coupled with site specific
reproductive timing and harvest data to fully understand gobbling
chronology on a given site. We recommend future studies investigate the
relationship between daily gobbling activity, weather, and reproductive
phenology of females in an un-hunted population and populations
subjected to varying hunting seasons and harvest rates.