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.

Capture and handling

We captured female wild turkeys opportunistically in flocks ranging from three to >20 using rocket nets baited with corn from January–March 2014–2019. We aged each individual using the presence of barring on the 9^th and 10^th 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).

Group Definition

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).

Nest Monitoring

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).

Analysis of reproductive timing

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.