The timing of when diamondback terrapins nest within a nesting season is variable and has been shown to be influenced by environmental factors (e.g. timing of tides). In a previous study on the nesting behavior of terrapins on Wallops Island we observed terrapins nesting more often on cloudy days compared to days with little to no cloud cover. We proposed that terrapins may be doing this to avoid high temperatures or to reduce risk of desiccation. To study this observation further we collected nesting diamondback terrapins during the 2018 nesting season (June 1- July 4th) on Wallops Island, VA. Upon capture, we collected a single blood sample from the cervical sinus which we used to measure plasma osmolarity. We predicted that terrapins that nested on overcast days or days with high cloud cover would be more likely to have a greater plasma osmolarity than those found on sunny days due to being under greater osmotic stress.
Results/Conclusions
We collected a total of 76 blood samples (28 sunny, 25 partly cloudy, and 23 on mostly cloudy days) from nesting terrapins. We found that blood samples collected from terrapins that nested on mostly cloudy days had significantly lower plasma osmolarity (309.98 ± 7.67 mOsm) than those collected on sunny (323.55 ± 10.59 mOsm) and partly cloudy (322.25 ± 13.89 mOsm) days (P<0.001). These data are contrary to our original suspicions that terrapins with greater plasma osmolarity (greater osmotic stress) would prefer to nest on days with more cloud cover. Therefore it is likely that other factors which may correlate with blood osmolarity are the primary factors in determining when diamondback terrapins initiate nesting activity.