A look inside the net: freshwater turtles assort with conspecifics in feeding aggregations

Abstract

Historically, non-avian reptiles were assumed to be non-social - yet recent studies show diverse social behaviours in squamates, crocodilians, and turtles. Here, we investigate social structure within feeding aggregations of three freshwater turtle species caught in baited traps in a coastal marsh over 12 years. In 488 instances in which traps contained turtles, 45% contained multiple individuals, and these aggregations were strongly positively assorted by species. Midland painted turtles (Chrysemys picta marginata) and Blanding's turtles (Emydoidea blandingii) were captured with conspecifics more often than expected in non-social null models. Snapping turtles (Chelydra serpentina), the largest species in this study, were captured with conspecifics at a frequency similar to that predicted by null models, and were avoided by heterospecifics. This suggests that species differences play a role in how feeding aggregations are structured, with painted and Blanding's turtles driving strong positive species assortment while avoiding snapping turtles around food sources. We did not detect significant intraspecific sex assortment in any of the three species, nor did turtle body size strongly affect the probability of aggregating with conspecifics at the perceived food source in the traps. Our study illustrates how long-term monitoring data can be used to investigate social structure in wild populations, an approach that may be valuable for species of conservation concern.