American Toad in Northern Virginia 
85 
We made a number of other assumptions in our skeletochron- 
ological analysis, and these assumptions weaken the precision and 
reliability of our age estimates. Procedurally, it is desirable to record 
MSG counts and measurements from the same region in the same bone. 
We used penultimate phalanges in most cases, and those phalanges 
derived from the second through fourth digits of the left or right hand. 
Using phalanges from different digits and occasionally the ultimate 
phalanx should not alter the number of visible MSGs, but it will 
increase the variation in MSG diameters. Further, the maximum 
diameter of the first MSG was selected in part on the basis of Hemelaar’s 
data (1985) on B. bufo, a different though similar-sized species of toad. 
Even though the preceding factors may have increased the variation of 
our MSG measurements, the range of diameters for each year class (Fig. 
1) is comparable to Hemelaar’s (1985: figures 2,3) data. Therefore we 
believe that the resulting age estimates are reasonably accurate, and if 
used as a unit rather than individually, they provide a reliable picture of 
the age structure of this American toad population. 
The only other age structure data for B. americanus derives from a 
population in central Illinois (Acker et al. 1986), nearly identical in 
latitude to Eakin Park. In the Illinois population, males 2-3 years old 
and females 3-4 years old were the most numerous age classes. This 
pattern does not match that of the Eakin Park population, although the 
age range is nearly identical for the two populations. The most striking 
difference between the two populations is the absence of 2-year-old 
females at Eakin Park and the presence of few 4-year-old and no 5-year- 
old males in Illinois. Although not wishing to overinterpret these data, 
they do suggest that the average lifespan for male American toads 
seldom exceeds 4 years. 
Size and age are not correlated in either the Illinois or the Eakin 
Park population. Both populations have females significantly larger 
than the males, although the Illinois females are smaller (65-84 mm 
SVL). The males of the two populations are approximately equal in size 
(Illinois, 55-75 mm SVL). 
The average size of Eakin Park ampletic males was nearly identical 
to the average for the entire male population. Indeed, the smallest male 
captured was in amplexus; thus, these data suggest that nonrandom 
mating by larger toads is not operating in the Eakin Park population. 
Although large male B. americanus have a mating advantage in some 
populations (e.g. Gatz 1981), this advantage is not evident or clear-cut 
in all populations (e.g. Kruse 1981, Wilbur et al. 1978). Our samples 
are, however, too small to evaluate nonrandom mating critically in the 
Eakin Park population. 
