Double-observer approach to estimating egg mass abundance of vernal pool breeding amphibians

Wetlands Ecology and Management
By: , and 



Interest in seasonally flooded pools, and the status of associated amphibian populations, has initiated programs in the northeastern United States to document and monitor these habitats. Counting egg masses is an effective way to determine the population size of pool-breeding amphibians, such as wood frogs (Rana sylvatica) and spotted salamanders (Ambystoma maculatum). However, bias is associated with counts if egg masses are missed. Counts unadjusted for the proportion missed (i.e., without adjustment for detection probability) could lead to false assessments of population trends. We used a dependent double-observer method in 2002–2003 to estimate numbers of wood frog and spotted salamander egg masses at seasonal forest pools in 13 National Wildlife Refuges, 1 National Park, 1 National Seashore, and 1 State Park in the northeastern United States. We calculated detection probabilities for egg masses and examined whether detection probabilities varied by species, observers, pools, and in relation to pool characteristics (pool area, pool maximum depth, within-pool vegetation). For the 2 years, model selection indicated that no consistent set of variables explained the variation in data sets from individual Refuges and Parks. Because our results indicated that egg mass detection probabilities vary spatially and temporally, we conclude that it is essential to use estimation procedures, such as double-observer methods with egg mass surveys, to determine population sizes and trends of these species.

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Publication type Article
Publication Subtype Journal Article
Title Double-observer approach to estimating egg mass abundance of vernal pool breeding amphibians
Series title Wetlands Ecology and Management
DOI 10.1007/s11273-004-7524-7
Volume 13
Issue 3
Year Published 2005
Language English
Publisher Springer
Contributing office(s) Patuxent Wildlife Research Center
Description 16 p.
First page 305
Last page 320
Country United States
State Maine, Maryland, Massachusetts, New Hampshire, New Jersey, New York, Pennsylvania, Vermont, West Virginia
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