
Bulls 
Adult males, known as bulls, are divided into two classes: 
harem bulls and idle bulls. A harem bull is a bull guarding one or more 
cows on the breeding ground and is easily classified. A harem bull may 
remain continuously with his harem without water or food for a consider- 
able period. Bartholomew (1953) observed that the total period of harem 
duty for 16 bulls ranged from 18 to 41 days with a mean of 31 days. The 
longest recorded period is 59 days (Scheffer, 1950b) but some bulls 
undoubtedly remain longer. The idle-bull group includes (1) subadults 
not large enough to win a place on the breeding grounds, (2) senile 
animals whose worn teeth and lack of physical vigor deny them access to 
the breeding area, (3) exhausted bulls which have spent their strength 
on the rookeries and have retired to the hauling grounds. The idle bulls 
are vaguely defined, since the distinction between an idle bull and a 
large bachelor is a matter of personal opinion. For the purpose of 
tables and computations an arbitrary dividing line must be drawn between 
bulls and bachelors. The writers have followed tradition and drawn this 
line between the sixth and seventh years. The known facts concerning 
sexual maturity in the male are outlined in appendix B. 
Counts of bulls 
Harem-bull statistics obtained by direct count over a period 
of years (and from aerial photographs of Sivutch rookery in 1948) provide 
a valuable index of the size and growth of the herd. Each year since 
1905, Government officials in charge of the Pribilofs have conducted a 
harem-bull census (Sims, 1906). Before 1905, counts were made infrecuently. 
Table 2 shows the annual bull count since the cessation of pelagic sealing 
in 1911. The general manager now makes his count in mid-July, completing 
it in 8 to 10 days. On the basis of their proximity to cows, he classi- 
fies the bulls as harem or idle. After the early morming sealing drive 
from a hauling ground, the manager walks along the adjacent rookery where, 
from the ground and from elevated walkways, he counts the bulls holding 
harems (fig. 4). The count is probably accurate within 5 percent, since 
the harem bulls are a stable group and they stand out clearly above the 
smaller cows clustered around them. Simultaneously, the manager counts 
the idle bulls which are scattered near the fringes of the rookeries 
(fig. 5). Since some are patrolling the seaward margins of the rookeries 
and others have been driven with the bachelors to the killing field, the 
count of idle bulls is probably accurate within 20 percent only. Table 3 
gives a breakdown of the bull count by rookeries in recent years. Over a 
long period, 1926-51, the ratio between the number of harem bulls on St. 
Paul and those on St. George has remained quite constant; of the total 
number of harem bulls an average of about 82.9 percent occurred on St. 
Paul and 17.1 percent on St. George (table 4). Table 5 shows the trend of 
the buil count since 1911, fitted to a smooth curve. 
