86 
Heather J. Kalb and George R. Zug 
The Eakin Park breeding population is fairly mobile. It is not tied 
tightly to a single site, but has shifted between four major open-water 
areas during the 6 years of observations. Perhaps this is typical of 
American toad populations; however, we have been unable to find 
comparable data in the literature. 
Breeding activity in B. americanus was associated with the first 
warm rain in late March or early April. The controlling factor seemed 
to be water temperature. Males did not call if the water temperature fell 
below 11°C, and cold fronts following a spring rain stopped chorus 
activity. 
ACKNOWLEDGMENTS.— We wish to thank H. Wimer for the 
histological preparations and J. Mitchell and C. Pague for reviewing the 
manuscript. We also thank Mr. Gilman C. Aldridge and the Fairfax 
County Park Authority for permission (permit SC-37) to study the 
toads in Eakin Park. 
LITERATURE CITED 
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experimentaux sur la signification des marques de croissance squelettiques 
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Accepted 30 August 1989 
