The treefrog’s deadline: a pond must last long enough

Listening was only the beginning

The Pinelands Commission established twenty long-term frog-calling stations in 1996 along the western Mullica watershed’s transition from forest to developed and farmed land. Its monitoring account identifies eighteen ponds used by Pine Barrens treefrogs. Calling surveys established a continuing record, while more intensive work investigated what happened after breeding. Pinelands Commission, long-term environmental monitoring.

Watching development against the water level

A 2010 report followed southern leopard frogs, spring peepers and Pine Barrens treefrogs in three old excavated ponds with hydrology resembling natural ponds. Researchers observed eggs, larvae and metamorphosis, then subtracted hypothetical water-depth reductions from measured records. They did not pump the ponds down as a field treatment. Kirkwood–Cohansey anuran-development report (2010).

Greater simulated reductions increasingly restricted development. Treefrogs had the greatest estimated vulnerability of the three species. The study also found different apparent thresholds when two years of development observations were compared with the longer water-level record, showing why a short interval can miss stressful years. Kirkwood–Cohansey anuran-development report (2010).

What the result does not establish

The authors cautioned that some developmental stages were absent from samples at particular ponds and that numbers were small in places. A breeding call is therefore not proof that young frogs successfully left the water. The important research story is the link between life-cycle timing and pond duration, with uncertainty retained rather than replaced by a single universal drying threshold. Kirkwood–Cohansey anuran-development report (2010).