ORIENTATION OF FRESHWATER HATCHLING BLANDING'S (EMYDOIDEA BLANDINGII) AND SNAPPING TURTLES (CHELYDRA SERPENTINA) DISPERSING FROM EXPERIMENTAL NESTS IN AGRICULTURAL FIELDS

Tilled crop fields and natural nesting areas of many freshwater turtles have common characteristics that attract nesting females, but as some crops mature, their canopies block access to natural environmental cues used by hatchlings during orientation and dispersal from nests. we examined orientation of 417 naive and 232 experienced hatchling Blanding's turtles (Emydoidea blandingii) and snapping turtles (Chelydra serpentina) during dispersal from experimental nests in three 60-m square arenas located in soybean and corn fields or by tracking re-located experienced hatchlings in a corn field at weaver dunes, Minnesota, USA. for both species, orientation patterns of nave hatchlings in crop fields were primarily random (indicating no environmental cues were available) and secondarily bimodal in both directions of crop row alignment (a dispersal pattern consistent with following paths of least resistance). in contrast to nave individuals, dispersal patterns of natural-experienced hatchling Blanding's turtles were non-random, not in the direction of crop row alignment, and in the directions they had been moving prior to being released in crop fields. hatchling Blanding's and snapping turtles with 45-150 minutes dispersal experience at different times of day in a prairie arena were able to disperse directionally when re-released in a corn plot, a result that supports rapid development of a compass for maintaining headings when targets are not visible. morning-and afternoon-experienced hatchling Blanding's turtles dispersed in different directions in a corn plot and in a different direction or pattern (random versus directional) from their previous dispersal in the prairie arena. the results of our study indicate that mature crop canopies that block access to natural environmental cues used for dispersal from nests pose more substantial orientation problems for naive hatchlings than for experienced hatchlings that are able to use a compass to maintain dispersal headings when environmental cues are not available.