CHARACTERIZATION
OF BEHAVIOR
OF HUMPBACK WHALES
IN HAWAIIAN WATERS
James D. Darling
2001
West Coast Whale
Research Foundation
206 - 2199 Broadway
Vancouver, B.C. V6K
2F1
and
Whale Trust
300 Paani Place
Paia, Maui HI 96779
www.whaletrust.org
Report for:
Hawaiian Islands Humpback Whale
National Marine
Sanctuary
Division of Aquatic
Resources
Department of Land and
Natural Resources
1151 Punchbowl Street,
Room 330
Honolulu, Hawaii 96813
EXECUTIVE SUMMARY (Full
report)
Humpback whales make annual
migrations to winter assembly areas in subtropical and tropical waters
to mate and, after a year gestation, give birth. The main Hawaiian
Islands are the largest such assembly area in North Pacific. Since the
late 1970s humpback whale research in Hawaii has been at the forefront
of the investigation of reproductive behavior patterns of this
species. This report reviews available information and summarizes our
current understanding of the behavior of humpback whales in Hawaii.
Humpback behavior patterns in
Hawaii represent a continuum of reproductive activities that begin on
late season feeding grounds and occur throughout the migration. In
Hawaii, whales are found around all the main islands, with
concentrations on shallow banks within the Four Island Group, Penguin
Banks and to a lesser degree off the Kona coast and Kauai. It is
apparent whales circulate freely throughout the islands, although
questions remain as to if differential use of specific locations
occurs. Cows with newborn calves are more likely to be found in
shallow, inshore waters than the general population.
Humpback whale abundance peaks in
February-March, but whales are common from December through May and
seen as early as September and as late as June. The arrival and
departure of whales is segregated to some degree by age, sex and
reproductive condition, with strong suggestions that, with the
exceptions of some males, many whales are present for short periods
relative to a five-six month long season.
Female reproductive cycles govern
much of the humpback whale behavior in Hawaii. Humpback whales give
birth on the average every two-three years, although postpartum estrus
is common with annual birth occurring in some portion of the
population. The sexual cycle peaks during the three-five winter
months, with peak ovulation in January-February. Females are
seasonally polyestrus, undergoing several cycles if pregnancy does not
occur. Peak ovulation period coincides with most behavioral activity
in Hawaii including the peak of singing, male competitive and
aggressive behavior, and transience of individuals among groups. With
a 50:50 sex ratio, and the average birth rate two-three years, many
more mature males than fertilizable females are present in any one
breeding season, leading to increased competition among males.
It is generally agreed that
humpbacks follow a polygynous or promiscuous mating system. The former
implies that males monopolize females in some way; in the latter they
do not. Mating system hypotheses include dominance polygyny where
males develop and maintain, through display and fighting, a hierarchy
for access to females; and lek polygyny where males assemble and
advertise to females through song. A further emerging hypothesis
proposes formation of male coalitions and cooperation to access
females. All these hypotheses require further testing.
Most male behavior patterns,
interactions and associations are short-lived, lasting only minutes to
hours, with the animals apparently orienting to any female in estrus.
Earlier studies emphasized male antagonism and avoidance of each
other; more recent studies report non-agonistic male-male
interactions. Male behavior patterns include singing; interaction with
singers, at times forming all male pairs, trios or larger groups; and
escorting or guarding females, defending or challenging the escort
position with a variety of agonistic behavior including displays,
sounds and physical clashes that may result in bloody wounds. There
are some suggestions of cooperative and even care-giving behavior
amongst some males.
Female behavior patterns are set in
two contexts: mating or birth and newborn care. Some portion of
females undergoes postpartum ovulation and are involved in both
activities in one season. Little is known about female mating
strategies and behavior; however, this likely includes maximizing
contact with males, minimizing contact and potential competition with
females, and accomplishing mating in as short time as possible for
energetic considerations. Female behavior may include acceptance of
the male escort, leading or being chased by multiple competitive
males, and mating. Female-female associations are rare on the breeding
grounds. A typical behavior flow begins with a female-male pair in
apparent calm union; this pair joined by other males often leading to
competitive groups; and eventually the group breaking up leaving a
pair again, which may or may not include the original male. Female
behavior may influence the selection of a mate through encouraging
competition and accepting/rejecting copulation. It has been proposed
that females select males based on song but there is no evidence to
support this hypothesis.
Female humpbacks in Hawaii are
involved in birth, nursing and protection of young. These cows with
newborn often occupy shallow, inshore waters presumed to separate them
from mating activity and harassment of males, more turbulent offshore
conditions, and predators. Birth has not been observed, although
circumstantial evidence indicates it peaks at the time of year whales
are in Hawaii. With sightings as early as December, cows with newborn
peak in numbers in February-March, and are usually the last groups
seen in May and June. Cow/calf pairs usually maintain an active
separation from each other. Cows with calves apparently travel and
circulate through the region like other whales. Travel is the most
cow/calf common behavior. When resting the cow often lies in a
horizontal position at 30-70 feet below the surface with calf under
her head or body. The calf surfaces every five to six minutes,
circles, and dives back towards the cow, with the cow surfacing every
10-20 minutes. Suckling occurs when cow/calf is either stationary or
traveling. Play is a common activity with the calf mimicking most
adult actions and postures. Some sounds by the calf and between cow
and calf have been documented, but relative to males they are quiet.
It has been proposed that the single male escort is accepted by the
cow as it may offer indirect protection from groups of males.
Juveniles, ranging from yearlings
to four to five years old, make up a portion of the Hawaiian humpback
population; little is known of their behavior patterns. They are found
on the periphery of adult groups, in association with adult males
including involvement in apparent sexual activity, in juvenile pairs,
and alone. One observation reports a sub-adult attempting to feed in
Hawaii.
We may have a greater understanding
of humpback whale reproductive behavior than other whales; however,
overall, our knowledge is still young and dynamic with many aspects at
the hypothetical stage and others barely described. Streams of
important investigation include the relationship of habitat and
behavior, male and female reproductive strategies, and factors that
affect birth and newborn success.
Humpback
Vocalization Video
