234 
PACIFIC SCIENCE, Vol. XIII, July 1959 
Nonreproductive Social Behavior 
Monk seals appear to have no fixed social 
organization. Although aggregations of 2-3 
to as many as 36 were seen hauled out on 
Midway beaches, the animals paid little atten- 
tion to each other. Lone animals are fre- 
quently seen. At the end of the trails leading 
up into the Scaevola scrub, we seldom found 
more than one seal. When hauled out on 
sandspits or small islands in lagoons, it ap- 
pears that the aggregations result more from 
a desire to rest on a favorable spot than from 
a gregarious tendency. Hostility between in- 
dividuals was not observed except during 
sexual behavior. 
Several times, however, it was noted that 
the presence of one seal appeared to stimulate 
another to haul out near it. For example, we 
visited the western point of Eastern Island 
frequently and no seals were seen there. 
Shortly after two mothers chose this point on 
which to bear their pups, we observed two 
other seals haul out to sleep in their general 
vicinity. 
The Hawaiian monk seals are not thigmo- 
tactic as are northern elephant seals {Mirounga 
angustirostris) (Bartholomew, 1952) and most 
otariids. If a sleeping seal is touched, however 
lightly, it immediately awakens with a start. 
If the cause of its disturbance is another seal, 
it simply rolls or crawls a short distance and 
goes back to sleep. Monk seals were never 
observed lying in contact with one another. 
When seen in the water during the nonre- 
productive period, seals were generally alone. 
When two or more individuals were seen 
together, it appeared to be because of their 
proximity to a favorite sandspit. When groups 
were startled into the water, each seal went 
its own way and the group quickly dispersed. 
Only once, on November 29, 1956, did we 
observe adults, not sexually excited, swim- 
ming in close company. On this occasion, 
three seals were swimming about 40 yards 
offshore. One soon left and the other two 
rolled leisurely on their backs and frequently 
raised their heads to look at us. 
Reproductive Behavior 
Field observation of sexual behavior in the 
monk seal is hampered by lack of obvious 
sexual dimorphism. Adult males are darker 
than most females. Females usually appear 
larger and fatter than males. In many of the 
observations which we interpreted as sexual 
behavior, the sex of the animals was not veri- 
fied by observation of the external genitalia. 
Copulation was not observed; undoubtedly, 
as in most phocids, it takes place in the water. 
Seals which appeared to be pairs engaged in 
sexual behavior were observed on numerous 
occasions from March 5 to July 8. 
Several times we observed seals (appar- 
ently males) approach females with pups. In 
every case, the female displayed threat behav- 
ior and the approacher was repulsed. Solitary 
males swimming near beaches occupied by 
females with pups showed considerable inter- 
est while still some distance away. On April 
14, a male hauled out directly in front of a 
mother and pup, his head raised and appear- 
ing alert. He was quickly repulsed, whereupon 
he swam to another female and pup about 
100 yards down the beach. Although one of 
us was standing only a few feet away, he 
hauled out. Without raising her head, the 
female snorted and the male backed into the 
water, leaving the vicinity. 
The sense of smell may aid males searching 
for females. On April 17, we observed a male 
about 100 yards offshore suddenly stop, raise 
his head and gaze at a female directly up wind 
from him. Holding his head high above the 
water, he then swam rapidly and directly to- 
ward her, hauling out in front of her. The 
female reared, snorted, and threatened, to 
which the male responded in a similar way. 
Although open-mouthed sparring continued 
for several seconds at close quarters, the ani- 
mals did not bite each other. The male then 
backed hurriedly into the water, glancing sev- 
eral times at the female as he swam away. 
On April 2, when a female on the beach 
without a pup was approached by a male as 
