Discussion
Our current understanding of social behavior in wild turkeys is based on
visual observations of interactions during the breeding season (Watts
and Stokes 1971, Healy 1992). We used high resolution movement data to
assess social behaviors coupled with timing of nest initiation to infer
social rank amongst females, and provide an alternative approach to
infer behaviors and evaluate reproductive synchrony in wild turkeys
(Bakner et al. 2019, Lohr et al. 2020). We found that female wild
turkeys had social organization within flocks, likely maintained by
social hierarchies that influence behaviors of individuals throughout
their lives (Watts and Stoke 1971, Healy 1992). Our findings offer
evidence that social dominance may influence timing of reproduction in
wild turkeys, and subsequently influence individual reproductive
success.
We found that female wild turkeys rarely left social groups prior to
initiation of their first nest attempts. Similarly, Badyaev et al.
(1996a ) observed that female wild turkeys in Arkansas typically
left their winter flocks at the same time regardless of physiological
factors or age. We also found that prior to the onset of nest
initiation, >80% of females within social groups
overlapped ranges, so clearly females within social groups spatially
constituted a single social unit (Brown 1975). Stable social groups have
been observed in multiple avian species, including female black grouse
(Lyrurus tetrix tetrix ) who frequently occupied the same
territory while foraging (Kruijt and Hogan 1967). Similarly, groups of
female greater prairie chickens (Tympanuchus cupido pinnatus )
exhibited social interactions during visits to leks (Robel and Ballard
1974) and female sage grouse (Centrocercus urophasianus )
maintained social hierarchies that influenced timing of reproduction
(Scott 1942).
We observed that timing of the onset of first nest initiation at the
population level (e.g., across our study site) was similar across years.
Researchers have noted similar observations previously, and attributed
synchronous nesting behaviors at the population level to the potential
that photoperiod most influences timing of reproduction (Healy 1992,
Migaud et al. 2006, Walton et al. 2011). We also noted that average
dates of first nest initiation for female wild turkeys on our site were
comparable to dates reported across populations throughout the
southeastern United States (Thogmartin and Johnson 1999, Palmer et al.
2013, Crawford et al. 2021). Conversely, within social groups we found
substantive temporal variation in timing of nest initiation within
years. Because social rank can dictate access to mates in species with
pronounced dominance hierarchies, the fact that asynchronous nesting
occurred within social groups on our study site was not surprising
(Robel and Ballard 1974, Foster 1981, Webster 1994). We also observed
that ~30% of successful initial first nests were
produced by ~4% of females in our population, females
we presumed to be dominant within their respective social groups. We
note that these initial first nests by default were successful early in
the nesting season, and previous works have noted the importance of
successful early nesting attempts in sustaining wild turkey populations
(Porter et al. 1983, Crawford et al. 2021). Contemporary literature has
detailed the ecological significance of having females be successful at
hatching clutches early in the nesting season for various species,
including willow ptarmigan (Lagopus lagopus ; Wilson et al. 2007)
and greater sandhill cranes (Antigone canadensis ; Ivey and Dugger
2008).
Within social groups, we expected 1–2 days to occur between each female
initiating their first nest attempt, based on observations of nesting
behaviors in captive wild turkeys detailed in Healy (1992). However, we
found that on average, 3–7 days elapsed between successive nest
attempts by individual females within a social group. We acknowledge
that we have no way of confirming that we captured the dominant female
within each social group, and recognize that we didn’t capture all
individuals in every social group we studied. However, we offer that
it’s reasonable to assume that dominance hierarchies existed within the
social groups we monitored, and that these hierarchies influenced timing
of nest initiation across females. Robel and Ballard (1974) noted that
disruption of subordinate female greater prairie chickens by dominant
females caused 2-3 day delays in copulation. Logically, disruption could
increase time between successive nest attempts across subordinate
females within a group, which may ultimately benefit dominant females if
copulation was delayed in subordinate females or if they were forced to
mate with inferior males (Foster 1981, Bro-Jørgensen 2002). However,
female disruption only offers a partial explanation for the delay
between successive nest attempts we observed. In lekking species,
females are constrained in mate choice, and disruption of copulations
between females and dominant males can occur via harassment from
low-ranking males, which also could delay nesting (Foster 1983, Trail
1985). Likewise, if females are forced to travel farther to find
suitable dominant males or return to breeding areas repeatedly to
copulate with those same males, onset of nesting could be delayed
(Alatalo et al. 1988).
Our findings suggest that larger social groups tended to exhibit more
synchronized nest initiation, that number of days nest attempts across
females declined as group size increased, and that more synchronized
nesting attempts within a social group (as determined by days between
nest attempts across females) resulted in greater probability of nest
success. Previous research has demonstrated that larger male coalitions
of wild turkeys attract more breeding opportunities through improved
mate attraction relative to smaller coalitions (Krakauer 2008), which
also has been observed in other species that use forms of leks (Jiguet
and Bretagnolle 2006, Ryder et al. 2009). Likewise, in various species
including wild turkeys, larger male coalitions are typically associated
with larger social groups of females, are socially dominant over smaller
coalitions, and would contain the highest ranked males within the
breeding population (Watts and Stokes 1971, Krakauer 2005, Bygott et al.
1979). Conversely, smaller groups of female wild turkeys are often
associated with pairs of subordinate males or singletons (Watts and
Stokes 1971). In species with pronounced social hierarchies, breeding
with dominant males confers females with fitness benefits such as
greater reproductive success (Wong and Candolin 2005, Majolo et al.
2012), offering a partial explanation for our observation that nest
success was greater in larger groups with improved nesting synchrony.
Lastly, in birds where females aggregate into social groups,
reproductive success in general may be positively associated with group
size (Burger 1979, Canestrari et al. 2008).
Previous works noted that female wild turkeys typically nested within
~4 km of their winter range (Vander Haegen 1988, Badyaev
and Faust 1996). Wild turkeys often shift ranges and exhibit temporal
variation in resource selection as winter flocks dissolve and females
move to breeding areas (Badyaev et al. 1996b , Miller and Conner
2007, Little et al. 2016). We found that females located first nest
attempts an average of 2,107 m from the centroid of their 21-day range
prior to nest initiation, a considerably shorter distance than reported
by Badyaev et al. (1996a ) specific to distances from nest sites
to center of winter ranges. We predicted that dominant females would
move shorter distances than subordinate females between the center of
their 21-day range and their initial nest location, but our findings did
not support this prediction. Likewise, we found that distances between
nest sites and the centroid of the 21-day range before nest initiation
failed to influence nest fate. This finding contradicts Badyaev et al.
(1996b ) who reported that females that traveled greater distances
between pre-nesting ranges and their eventual nest site had greater nest
success.
Our findings suggest that dominance hierarchies within social groups may
influence timing of nest initiation in female wild turkeys. Established
social bonds among individuals within social groups may be maintained
throughout multiple seasons (Brandl et al. 2019). Thus, individuals in
the same winter flocks are more likely to become members of social
groups prior to breeding (Riehl 2011, Watkins et al. 2022), and
subsequently reproduce in areas near other group members (Liu et al.
2013, Firth and Sheldon 2016). The genetic structure of social groups
can have important implications for fitness, as emerging evidence
suggests that females identify a cost to association with kin during the
early reproductive season (Watkins et al. 2022). We suggest future
research evaluating potential influences of sociality and dominance on
nest success also incorporate genetic data on individuals within social
groups, as sociality may also influence genetic variation, and therefore
may play an important role in reproductive success (Sugg et al. 1996).