Arasan, have a taste disagreeable to the bird 
(Arasan is actually used as a bird repellent!). 
Elder (1964), working with the pigeon, reported 
parallel experience. 
Certain genetic factors that come together 
at fertilization are destined to be lethal to the 
embryo. Lethal genes in poultry and the curious 
phenocopies have been enumerated by Landauer 
(1954) and additional ones are being discovered 
each year, One would expect that natural se- 
lection would weed out these genes, or pheno- 
copies, from natural populations, but that they 
must exist is shown by the production of 
"sterile'' eggs by the dickcissel (Spiza amer- 
icana) (Long, 1963) and perocephaly in the 
common grackle (Quiscalus quiscula) and 
mockingbird (Mimus polyglottos) (Wetherbee, 
1958), 
The induction of lethal mutations by ionizing 
irradiation is well known and is a much more 
feasible (if also academic) approach to the use 
of gamma irradiation in vertebrate pest control 
than attempted radiation castration. 
The direct lethal radiosensitivity of avian 
embryos has been shown by Wetherbee et al. 
(ms.) to vary according to the embryonic age 
at exposure, A dose of 900 roentgens is lethal 
to 100 percent of quail embryos exposed at 1 to 
7 days of age. About 50 percent die if exposed 
at that same level at 7to 12 days of age whereas 
older embryos are much less sensitive. Pigeon 
eggs are a little more Sensitive at all stages 
of incubation. But irradiation exposure of eggs 
for direct kill is quite impractical when actually 
the same end could be achieved with ahammer! 
A slight improvement over the hammer was 
the use of emulsified oils, sprayed over the 
eggs of the herring gull in Maine and Massachu- 
setts by the U.S. Fish and Wildlife Service from 
1934 to 1953. This pioneer embryocidal pro- 
gram was a move in the right direction, but 
economical and sophisticated methods and tools 
had not been developed at that time. 
We have recently published a paper (Wether- 
bee et al., 1964) that reports the embryocidal 
activity of Sudan Black B in birds. Almost all 
fertile eggs laid by females fed an acute dose 
of Sudan Black B (as little as 500 mg. per 
kilogram body weight) failed to hatch. This dye 
was shown to have no deleterious effects on 
adult birds, in fact an LD-50 could noteven be 
demonstrated at extremely high levels, using 
both acute and chronic toxicity procedures. 
After a single dose of 500 mg. per kilogram, 
embryos in 93 percent of all eggs laid by 
20 female quail for the ensuing 10 days died 
(significantly different from the experimental 
control group). The compound wag found to be 
harmless to mice and to have no effect on the 
viability of mouse embryos. The dye is exerted 
transovarianly into the egg yolks of the imme- 
diate next 7 days' lay, after which time more 
dye must be ingested to maintain continued lay- 
ing of affected eggs. The likelihood of second- 
ary effects of Sudan Black B on predatory 
birds eating the dyed eggs is remote, as only 
a small fraction of the low dose ingested finds 
its way to the yolk; most passes outthe diges- 
tive tract. Males are not affected. Field tests 
made by R. P. Coppinger at the Massachu- 
setts unit indicated that this inexpensive com- 
pound was acceptable to herring gulls and met 
all our expectations as an embryocide, based 
on our experience in the laboratory. 
SUMMARY 
Most conflicts between man and vertebrates 
are directly avoidable. When the problem is 
not avoidable, local changes in the habitat re- 
sult in diminished pressure from the nuisance, 
Removing the ecological requirements in short 
supply of the problem species is generally 
superior to introducing ecological intoler- 
ances, Under extraordinary conditions actual 
reduction of the vertebrate's population over 
its entire range can probably be achieved 
through newly developed birth-control tech- 
niques. Three types of chemosterilants are 
available: Male sterilants, female sterilants, 
and embryocides. The compounds of greatest 
practical utility at this time are (1) Sperma- 
tocide, T.E.M., (2) spermatocidal alkane sul- 
fonic esters, (3) estrogen, D.E.S. (for certain 
mammals), (4) antiestrogen, U-11, 555A, 
(5) odcide, SC-12937, and (6) embryocide, 
Sudan Black B. 
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