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Don Lewis, Massachusetts Audubon Society,
Fox Island Wildlife Management Area

Hobson’s Choice — 4 June 2001

South Lieutenant Island presents diamondback terrapins with a Hobson’s choice: marginal nesting sites surrounded by the best developmental habitat in Wellfleet Bay.  Except for a single isolated sandy face where predation rates soar to over 90%, the south side of the island is ringed by a narrow strip, sometimes only inches wide, of soil and mixed vegetation between the high tide wrack line and a dense bearberry groundcover.  Turtles can opt for the more appealing dirt roads and driveways, but at the risk of encountering a host of predators, wild and mechanical, en route upland.  And the trek back to the nursery marsh for hatchlings would be doubly dangerous.

Two nests, indicated by red turtles on the orthographic map above, illustrate this dilemma.  Only 50 feet apart, these turtles choose equally borderline nesting locations.  The one on the left found a small scratch of soil (top center of photo) beneath a beach plum bush; the one of the right picked a location (dark spot 2/3s up & center right) sprinkled with grass and weeds.


Although riddled with roots, the left nest still yielded 14 live and emerged hatchlings.  The other, though, was invaded by vegetation which penetrated the eggs and killed the pipped hatchlings.  The only difference I could detect was that the soil in the first, productive nest felt moist to the touch; the second was bone dry — even after a soaking rain and fog.

Despite these hurdles, the overwhelming advantage of its abutting pristine marsh has made Lieutenant Island the most productive terrapin hatchery in Wellfleet Bay.