80 
Heather J. Kalb and George R. Zug 
were able to estimate the ages of some marked individuals. In this 
report, we summarize our skeletochronological analyses and natural 
history observations. 
MATERIALS AND METHODS 
Each spring from 1983 through 1988, the toads breeding in Eakin 
Park (Fairfax Co., Va.) have been censused. In 1983-85, the toads were 
captured, measured, weighed, and individually marked. The toads were 
marked uniquely by removing the distal two phalanges using the 1-2-4-7 
coding technique (Ferner 1979). The toe tips were immediately preserved 
in 10% buffered formalin and 3-12 months later prepared histologically 
(see Zug and Rand 1987). The first digit (1 and 10) of the hand was not 
used because injury to the “thumb” could have affected the reproductive 
activities of the males. The numbers of individuals marked were: 1983, 
19; 1984, 40; 1985, 13. In subsequent years, all toads were counted and 
their location and behavior were noted. 
Two age estimates can be derived from the histological slides: (1) 
the number of periosteal layers observed, complete and incomplete, and 
(2) the sum of the number of complete layers observed and the estimated 
number of layers partially and completely resorbed. The estimate of 
resorbed layers is based on Hemelaar’s (1985: figures 2,3) graphic 
technique for the estimation of periosteal growth in B. bufo. Bufo 
americanus and B. bufo are equivalent-sized species; therefore, they are 
assumed to have similar growth rates. The use of Hemelaar’s technique 
and the potential difficulties with the assumptions are discussed in later 
sections. 
Each toad’s snout-vent length was measured with dial calipers to 
the nearest 0.1 mm (though measuring a live, struggling toad is, at best, 
accurate to 1.0 mm). Weights were taken on Pesola spring scales to the 
nearest 1 g. Air and water temperatures were recorded with a Muller and 
Weber quick reading cloacal thermometer to the nearest 0.2° C. 
Histological sections were examined independently by the two 
authors. Heather Kalb (HK) reviewed all the slides; selected the best 
section of the phalanx for each individual; and measured the diameters 
of the central marrow cavity, the endosteal ring, and each periosteal 
layer (Mark of Skeletal Growth, MSG) as delineated by a LAG (Line of 
Arrested Growth), across the dorsoventral axis of the phalanx. Because 
all toads were caught in early spring and had not begun a new growth 
cycle, the outside diameter of the phalanx represents the last LAG. The 
number of measured MSGs equals the total number of incomplete and 
complete periosteal layers present in each phalanx. George Zug (GZ) 
counted the total number of MSGs on the sections identified by HK, 
