Abstract from: Wildlife Society Bulletin 28(4):895-901 (Winter 2000)

USING EGG-MASS COUNTS TO MONITOR WOOD FROG POPUALTIONS


William B. Crouch, Department of Natural Resources Science, University of Rhode Island, Kingston, RI 02881, USA

Peter W. C. Paton, Department of Natural Resources Science, University of Rhode Island, Kingston, RI  02881, USA

Abstract: Calling surveys are used to monitor trends in frog populations for most North American species. However, wood frogs (Rana sylvatica), one of the most abundant species in New England, may not be detectable using calling surveys at breeding ponds.  We assessed efficacy of using egg mass counts to monitor wood frog populations in southern Rhode Island from 1997 to 1999.  We completely encircled 8 breeding ponds with drift fence arrays to quantify adult wood frog population size and then censused egg masses.  Egg mass counts were very correlated with number of females (r = 0.97, P < 0.001) and males (r = 0.95, P < 0.001), and accounted for approximately 92% of females captured by drift fence arrays. Counts of egg masses at the same breeding ponds by 2 observers varied by 12%.  Based on studies of egg deposition chronology, breeding ponds should be surveyed over a 3-week period to ensure that all egg masses are censused. In smaller breeding ponds with <100 egg masses, 16% of egg masses may be deposited at sites away from the communal aggregation.  Therefore, the entire breeding pond should be searched to ensure all egg masses are counted.  Egg mass surveys are more cost effective than drift fence arrays and provide more information than calling surveys.  We suggest that egg mass counts may be an effective means to monitor wood frog populations, as it is a relatively accurate and precise survey technique.

 

The research areas were completely surrounded by driftnet fencing and ex-large coffee cans (pitfall traps) were placed in the ground to capture migrating animals.