et al. (ms.). It would seem that whole-body 
irradiation sufficient to cause irreversible 
sterility is too near the lethal level in verte- 
brates. Radionuclide ingestion might well be 
used against spermatogenesis, but the prob- 
lems of environmental contamination are prob- 
ably insuperable. High-energy microwave 
(radar) failed to sterilize birds or eggs under 
field conditions (Wetherbee, progress reports, 
1959-64), 
Spermatocidal drugs and chemosterilants 
offer the greatest potential threat to male 
fecundity. The numbers of compounds tested in 
human birth-control research are legion; those 
that have been tested in wildlife species and 
found practical are few. Jackson et al. (1961) 
orally administered a number of simple alkane 
sulfonic esters to rats and reported extraor- 
dinary results. Cumulative doses produced 
predictable periods of reversible sterility 
according to dose rate. No effects on libido 
were noted nor any toxic side effects. DavidE. 
Davis (1959) found that triethylenemelamine 
(T,E.M.) inhibited testicular recrudescence in 
starlings, with the testis becoming merely an 
interstitial organ, A limited field test on red- 
winged blackbirds (Agelaius phoeniceus) with 
this cytocide indicated a probable causal reduc- 
tion in fecundity (Vandenbergh and Davis, 1962), 
While T.E.M., on the basis of Davis's work, 
presently has the highest candidacy for opera- 
tional use against male birds (in spite of nega- 
tive findings that we have experienced when the 
compound is used on sexually active male 
birds), Enheptin (2-amino, 5-nitrothiazole) 
also has potential for special purposes. This 
compound tested at the Massachusetts unit has 
no effect on rats but has differential potencies 
among bird species. 
Antifecundity in the Female 
Although some species of vertebrates are, 
at least theoretically, monogamous, most are 
polygamous. Biological economy places more 
value on the ovum than on the spermatozoan 
in either instance, and our search for repro- 
ductive inhibitors in vertebrates has focused 
on the female with that good justification. 
Somes (1962) and Consuegra (1962) at the 
Massachusetts unit have reviewed the physio- 
logical inhibition of odgenesis and ovum sus- 
107 

tentation in birds. Mammalian antifecundity 
research, which of course includes the human 
species, has a ponderous literature and is 
bustling with activity. No pretense is made here 
of relating the findings of that science to wild- 
life management. However, Balser (1964) and 
Linhart and Enders (1964) have studied the 
management of mammalian predator popula- 
tions (coyotes, Canis latrans, and red foxes, 
Vulpes fulva) with antifecundity agents. 
Balser's work at the Denver laboratory of the 
U.S. Bureau of Sport Fisheries and Wildlife 
is focused on upsetting the normal endocrine 
balance by oral administration of baits con- 
taining diethylstilbestrol (D.E.S.). His field 
tests indicated that 80 percent of the female 
coyotes taken off a treated area were repro- 
ductively inhibited (this is probably 100 per- 
cent of those that took bait) and 100 percent 
of those taken off a reference area showed 
no inhibition, 
Induced sterility in game and pan fishhas so 
far been a failure and no practical method 
has been devised, although with the every-day 
discovery of new antifecundity compounds it 
may be premature for aquatic biologists to be 
pessimistic, - 
We have found that the expensive progesta- 
tional 19-nor steroids that currently enjoy 
wide usage in human birth control also have 
physiological potency in birds but of extremely 
short duration, The various androgens and 
estrogens bring about their classical effects, 
but are soon swept away by the hormonaltides 
of the normal organism in its natural environ- 
ment, The antiestrogen U-11, 555A, a diphenyl- 
indene derivative, made by the Upjohn Com- 
pany, inhibits oviposition for several days in 
laboratory-held quail (C. coturnix) (McEvoy 
and Wentworth, ms.). This and related com- 
pounds, except for frank estrogenic agents, 
were the most potent oral mammalian anti- 
fertility agents reported up to 1963 (Duncan 
and Lyster, 1963), 
Various dietary deficiencies and feed addi- 
tives accidentally or purposefully included in 
poultry rations have been shown to depress 
the production of eggs. As we have already 
mentioned for males, dietary deficiencies are 
impossible to maintain in wild populations. 
Treatment of blackhead disease in poultry 
with sulfanilamide yields solf-shelled eggs 
that cannot hatch (Hinshaw and McNeil, 1943). 

