INTRODUCTION 
Several raptors including the bald eagle, golden eagle (Aquila 
chrysaetos), barn owl, and screech owl (Otus asia), and herons, such as the 
black-crowned night heron and Louisiana heron (Hydranassa tricolor), lack 
external sexual dimorphism both in the immature and mature state. Because 
these species occupy a terminal position in the food chain, and because some 
are particularly susceptible to the effects of environmental pollutants, they 
are currently being employed in experimental studies at the Patuxent Wildlife 
Research Center. It was necessary to develop a rapid and technically simple 
procedure to sex large numbers of these birds in order to form breeding pairs, 
and to gain a meaningful interpretation of subsequent experimental results. 
This preliminary report describes a method for the determination of sex by 
chromatographic separation of steroid hormones from the plasma, and identifi- 
cation of the components as products derived from either males or females. 
PROCEDURES 
Extraction and Concentration of Steroid Hormones 
Heparinized syringes were used to draw blood from the heart, the alar 
vein, or the jugular vein, depending on the size of the bird. The plasma was 
separated and processed immediately, or the plasma frozen until used. Plasma 
was extracted three times with an equal volume of absolute chloroform plus 
one-twentieth volume of 1.0 N sodium hydroxide (Bush, 1961). Extracts were 
pooled in 10 ml Snyder tubes and taken down under nitrogen at 45°C to 100 ul. 
Preparation of Chromatographic Columns 
Except for minor differences outlined below, methods for slurry prepara- 
tion, packing and developing of columns, and charring were essentially those 
outlined in the operator's manual supplied with a Centri-Chrom apparatus! (see 
also Ribi, et al. 1970). Eighty ml of a solution of ethyl acetate:cyclohexane 
(1:1 by volume) were added to 3 g of prepackaged silica adsorbent containing 
6 percent water, then stoppered and stirred vigorously until homogeneous. 
Four ml of the silica slurry were added to 3 x 65 mm glass columns and packed 
for 7 min by centrifugation at 1500 G. 
1 Ivan Sorvall, Inc., Newtown, Conn. 
