Experimental Assessment of the Impact of Agricultural Machinery on Wood Turtles (Glyptemys insculpta)

The wood turtle (Glyptemys insculpta) is a threatened species that uses agricultural fields, in part, to nest, bask, and feed. This use of anthropogenic habitats has resulted in the injury and death of individuals during crop harvest. Turtles have been exposed to hay harvests for over a century but the increased use of rotary disc mowers may have increased mortality rates to unsustainable levels. Mitigation measures have focused on raising blade height to minimize contact with turtles but these measures are based on the dimensions of the largest turtles and the effects of agricultural machinery on subadults, juveniles, and hatchlings have not been quantified. We sought to quantify how different agricultural machinery affects wood turtles at multiple life stages through experimental trials using 2 mower types. Cantaloupe (Cucumis melo) halves were used as turtle proxies to avoid actual harm to turtles. We found that rotary disc mowers resulted in a significantly greater injury to adult (i.e., female, male, and subadult) and young (i.e., juvenile and hatchling age class) proxies at low grass heights (10-20 cm) compared with sickle cutter bar mowers. Young proxies were found to be essentially unaffected by the sickle mower at all grass heights, but they were highly affected by the rotary disc mower at grass heights from 10 to 18 cm. If blade heights were to be raised to reduce the risk to wood turtles, a minimum blade height of 17 cm would be needed to obtain > 50% of adults remaining undamaged during harvest and a minimum height of 15 cm would be needed for young turtles.