DOI: 10.5061/dryad.fbg79cp10
title: Reproductive asynchrony within social groups of female eastern wild turkeys

description: Coordination in timing of reproduction is driven by multiple ecological
 and sociobiological processes for a wide array of species. Eastern wild
 turkeys (Meleagris gallopavo silvestris) use a male dominance polygynous
 mating system, where males communicate with females via elaborate
 courtship displays and vocalizations at display sites. Most females prefer
 to mate with dominant males, therefore asynchronous breeding and nesting
 may occur which can disproportionately influence individual fitness within
 breeding groups. For female wild turkeys, there are reproductive
 advantages associated with earlier nesting. As such, we evaluated
 reproductive synchrony within and between groups of GPS-tagged female
 eastern wild turkeys based on timing of nest initiation. We examined 30
 social groups with an average of 7 females per group (range 2-15) during
 2014-2019 in west central Louisiana. We found that the estimated number of
 days between first nest initiation across females within groups varied
 between 3-7 days across years, although we expected 1-2 days to occur
 between successive nesting attempts of females within groups based on
 observations of captive wild turkeys in the extant literature. The number
 of days between successive nest attempts across females within groups was
 lower for successful than failed attempts, and nests with an average of
 2.8 days between initiation of another nest were more likely to hatch. Our
 findings suggest that asynchronous reproduction may influence reproductive
 success in female wild turkeys.
description: <em><strong>Capture and
 handling</strong></em> We captured female
 wild turkeys opportunistically in flocks ranging from three to &gt;20
 using rocket nets baited with corn from January–March 2014–2019. We aged
 each individual using the presence of barring on the
 9<sup>th</sup> and 10<sup>th</sup> primaries
 (Pelham and Dickson 1992). We fitted all females with a uniquely
 identifiable aluminum rivet tarsal band and GPS/VHF transmitter (89g;
 Biotrack Limited, Wareham, Dorset, UK; Guthrie et al. 2011). Transmitters
 were attached backpack style using marine grade shock cord (3mm), which
 typically degraded after several years and fell off the birds if they were
 not recovered dead. We programmed GPS units to collect data at 1-hour
 intervals (Cohen et al. 2018) between 05:00 to 20:00 daily with one
 location at night (23:59:58) to identify roosts until the battery died or
 the unit was recovered. We immediately released individuals at the capture
 location following processing. Capture, handling, and marking procedures
 were approved by the Louisiana State University Agricultural Center Animal
 Care and Use Committee (Permits A2015-07 and A2018-13). We monitored
 live-dead status daily during the reproductive season using handheld Yagi
 antennas and Biotracker receivers (Biotrack Ltd., Wareham, Dorset, UK). We
 downloaded GPS locations once per week via a VHF/UHF handheld command unit
 receiver (Biotrack Ltd., Wareham, Dorset, UK).
 <em><strong>Group
 Definition</strong></em> Wild turkeys flock
 together in groups of adult males, juvenile males, or females. We assumed
 that females within a specific area had access to the same resources and
 presumably the same preferred males. Based on estimates of daily movements
 by females (Conley et al. 2016, Bakner et al. 2019), we considered
 individuals captured within 2 km of each other to use the same area as
 these individuals appeared to regularly interact, and at further
 distances, the probability of overlap with other flocks was low (0.02;
 Niedzielski and Bowman 2016, Schofield 2019). To further ensure we
 accurately defined groups, we used a dynamic Brownian Bridge movement
 model (dBBMM) to create 99% utilization distributions (UDs) for each
 individual (Byrne et al. 2014) for the 21 days before the first female in
 each group laid the first egg at an eventual nest site. We chose a 21-day
 period because we were interested in overlap in space use during the time
 immediately preceding initiation of the first nest in the group (Watts and
 Stokes 1971). We calculated all UDs in program R version 3.2.5 (R Core
 Development Team 2020) using package move (Kranstauber and Smolla 2013).
 We used a window and margin size equal to 21 and 9 respectively, and a
 location error of 10 m (Byrne et al. 2014).  Individuals that share space
 may constitute a single social unit (Brown 1975), therefore we calculated
 the percentage of female UDs that intersected at least one other female’s
 unique UD within a defined group during the 21-day period to quantify
 shared space use (Kernohan et al. 2001). If a female’s UD intersected any
 other female’s UD within their group, we considered those females to share
 space and to likely have access to the same resources. We also assumed
 that females with overlapping UDs are likely to mate with the same
 dominant males, as females often move in loose groups on display sites
 (Höglund et al. 1990, Watts and Stokes 1971).
 <em><strong>Nest
 Monitoring</strong></em> We determined
 locations of each nesting attempt for each female when an individual’s
 locations became concentrated around a single point for several days
 (Guthrie et al. 2011, Conley et al. 2015, Yeldell et al. 2017, Wood et al.
 2019). We defined the first date of nest incubation as the first day we
 recorded the nightly roost location at the nest site, indicating the
 female continued incubation during the night (Bakner et al. 2019). To
 determine the first date of egg laying (hereafter nest initiation), we
 evaluated GPS locations to determine when a female initially visited the
 nest site as female wild turkeys do not visit their nest site until they
 lay their first egg (Conley et al. 2016, Collier et al. 2019). We
 monitored each nesting attempt following Bakner et al. (2019) and after
 nest termination, located nest sites using VHF telemetry and GPS data to
 confirm the nest location and determine nest fate. We considered a nest to
 have been depredated or abandoned if the female left the nest ≤25 days
 into incubation, or if only intact eggs, no eggs, or egg fragments were
 found at the nest bowl. We considered a nest successful if ≥1 live poult
 hatched, and was confirmed visually during subsequent brood surveys
 following methods outlined in Chamberlain et al. (2020).
 We scaled the initiation date of the first nest attempt to group,
 where the date of the first nest initiation was noted as day 1. We
 delineated subsequent nest attempts based on the number of days after the
 first nest was initiated. We subtracted the initiation day of the second
 nest from the initiation day of the first nest, and then subtracted the
 initiation day of the third nest from the initiation day of the second
 nest, and so on for each first nest attempt within each group. We then
 calculated the mean number of days between each nest initiation attempt
 within each group. We speculated that groups with more individuals would
 have more days between subsequent nest attempts compared to smaller
 groups. Presumably, larger groups would contain more females competing to
 copulate with dominant males (Orbach et al. 2015), whereas smaller groups
 would have less competition and thus be able to copulate in a shorter
 temporal window, resulting in a narrower time window during which nests
 were initiated by females in that group (Dewsbury 1982, Foster 1983, Avery
 1984, Trail 1985, Gratson et al. 1991, Möller 1992).
 <em><strong>Analysis of reproductive
 timing</strong></em> Female wild turkeys
 that attempt reproduction earlier within a season are expected to have
 greater annual reproductive success compared to later breeding individuals
 (Crawford et al. 2021, Keever et al. 2022). Females can presumably select
 nest sites that could confer fitness advantages through improved nest
 success (Sӕther 1990, Martin 1995a, Martin 1995b, Crawford et al. 2021,
 Keever et al. 2022), compared to females that nest later and may be forced
 to nest in suboptimal parts of their ranges or travel farther distances to
 find suitable nest sites (Badyaev et al. 1996, Schaap et al. 2005). To
 test the prediction that females that initiated nests earlier would travel
 shorter distances within their ranges prior to onset of nest initiation,
 we used the distance between a female’s nest location and the centroid of
 the UD range of the 21-day period before the first nest of each group was
 initiated as our metric. We measured the distance between the centroid of
 each female’s 99% UD range to each of her nest attempts in ArcGIS 10.6
 (Environmental Systems Research Institute, Inc., Redlands, California,
 USA). To locate the centroids of each 99% UD, we calculated the x and y
 centroid of each UD in the attribute table. We then created a line between
 each nest attempt and the centroid and calculated the distance between
 each nest attempt and the centroid within the 99% UD. To test for
 differences in mean distance traveled for females with successful versus
 failed nests, we used an independent 2-group t-test with an α=0.05 in R (R
 Core Team 2020).  Likewise, we used a binomial generalized linear model
 (GLM) in R (R Core Team 2020) to estimate nest success as a function of
 first nest initiation date. We then used a Poisson GLM to estimate the
 rate (in days) at which females initiated their first and second nesting
 attempts as a function of group size and year.  Finally, we used linear
 regression to evaluate the effect of group size on the number of days
 between nesting attempts within groups.