Macro- and microhabitat predictors of nest success and hatchling survival in eastern box turtles (Terrapene carolina carolina) and spotted turtles (Clemmys guttata) in oak savanna landscapes
Characteristics of nest sites of eastern box turtles (Terrapene carolina carolina) and spotted turtles (Clemmys guttata) in northwestern Ohio and southern Michigan in 2018-2019. Nest sites were located by radio-tracking gravid female turtles to nest sites, nests were monitored until hatchling emergence (HatchDate), and radio-transmitters were attached to hatchlings, which were then monitored via radio-telemetry to determine whether they survived to enter overwintering. Macrohabitat data were collected for the land cover patch within 10 m of the nest site and included distance to nearest road (m) and distance to nearest habitat edge (m). Microhabitat data were recorded within 1 m of the nest site and included date of nest construction (DayOfYear), % shade cover over the nest (Shade), and total depth of the nest cavity (Depth; mm). Macrohabitat and microhabitat variables were used as predictors in separate models of nest success and juvenile (i.e., hatchling) survival to overwintering for each species. Alternate nests were caged to prevent predation by mammals (Caged). We also recorded female plastron length (mm), number of eggs (ClutchSize), number of surviving hatchlings (AliveHatchlings), and whether the nest was depredated (Predated). In the “SWGTurtles” file, for each nest, NestSuccess was assigned as 1 if any live hatchlings were recovered from the nest. NestSuccess was 0 if no live hatchlings were recovered and there was evidence of predation or egg mortality as described above. In the “SWGHatchlings” file, hatchlings that were either found dead or whose transmitters were recovered with damage consistent with a predator attack were assigned a survival value (i.e., PresumedSurv) of 0. Hatchlings that were known to have entered hibernation were assigned a PresumedSurv of 1. Hatchlings for which we lost the radio signal more than three days from predicted transmitter battery expiration (TransmExpiry) were assumed to have been depredated (i.e., the transmitter was either broken or carried out of signal range by a predator) and were assigned PresumedSurv of 0. The final group of hatchlings were those whose radio signals were lost within three days of predicted transmitter battery expiration. For these hatchlings, if transmitter expiration (EndDate) occurred after 1 October (the date at which most surviving hatchlings had reached the location at which they subsequently overwintered), we presumed the hatchling had survived to enter hibernation and assigned a PresumedSurv of 1. If transmitter expiration occurred before 1 October for hatchlings in this group, we assigned the hatchling an “unknown fate” and excluded it from analysis (data for this group not included in the manuscript and not shown here)..