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INDICES OF AFFILIATION DURING REUNION OF FAMILY MEMBERS IN CAPTIVE ORCA WHALES
M. Noonan, L. Chalupka, M. Conners, K. Pastwick, M. Viksjo & D. Perri
Canisius College, Buffalo, NY 14208 & Marineland of Canada
Presented at the Animal Behavior Society, Lewisburg, PA, June, 1999.
Introduction
In the wild, killer whales live in family groups whose membership
remains stable over long periods of time. It is widely assumed that the recognition of
whales by each other, both as individuals and as family members, plays a large role in
maintaining these groups. The means by which these bonds are established, and the duration
over which they can be maintained during periods of separation, have yet to be explored.
This study took place at Marineland of Canada in Niagara Falls,
Ontario. For husbandry reasons, two juvenile orcas were housed separately from their
mothers over a two-year period. The goal of this project was to access the degree to which
mother-offspring recognition occurred upon the reunion of these separated family members.
Methods
During the first week following their reintroductions, the whales were
observed between 7 and 9 am on 5-6 days of the week. Four indices of affiliation were used
to access mother-offspring recognition:
Motion Synchronization
Over repeated 30-second sample intervals, each whales’ speed was gauged on a
five-point scale. Whales whose speeds were similar were classified as synchronized at that
moment.
Inter-Whale Distance
For each 30-second sample interval, the distance between each pair of
whales was estimated. Whales that were within 2 meters of each other were
classified as together at that moment.
Reciprocal Touching
Continuous observations were made to record each time one whale touched another whale.
For each pair of whales we tabulated the number of touches.
Breath Synchronization
During continuous observation periods, we recorded the time that each whale took a
breath. For each pair of whales, if the breath by one occurred within five seconds by the
breath of another, they were considered synchronous at that moment.
Results
Motion Synchronization
As a general rule, the two young whales were not usually found to be in
synchrony with the adult females. Of the 2,098 samples recorded, the mothers and calves
were observed as being identical in swimming speed on only 534 occasions (25%). More
importantly, chi square analysis of the frequency with which the two calves were
synchronized with each adult showed no greater synchrony for mother-offspring pairs than
for the opposite combinations (X2 = 0.278, ns; X2 = 0.083, ns).
Inter-Whale Distance
Similarly, the distances maintained among the whales also did not
reveal evidence of recognition. For each reunion, the frequency with which the two calves
were and were not within two meters of the adult was no greater for the mother-offspring
pairs than for the unrelated calf-adult combinations (X2 = 0.012, ns; X2
= 2.902, ns).
Reciprocal Touching
The amount of touching between pairs of whales also did not indicate
signs of mother-offspring recognition. In one reunion, although we recorded 406 instances
of touches involving the three focal whales, not a single one of these touches occurred
between either calf and the adult female. In the second reunion, 70% of all touches did
occur in adult-calf combinations and the chi square analysis yielded a highly significant
difference between the two calves (X2 = 99.1, p < .001). However, this was
attributable entirely to a single brief episode of close contact that occurred only on the
third day of observation and it took place between the adult female and the unrelated
calf.
Breath Synchronization
Here too, there was no sign of greater affiliation between
mother-offspring pairs than for the unrelated pairs. Of the 590 breaths we recorded for
the focal whales, only 106 (18%) were recorded as synchronous between the calves and the
adult female, and there were no significant differences between the two calves on this
measure.
Conclusions
While the reunion of these whales was generally characterized by
amicability, there was no evidence to suggest that either mother-offspring pair showed
signs of recognition.
In the wild, orca pod members often come into and out of association
with each other and the separation times often last for days without any detriment to the
long term group cohesion. In fact, different pods of related individuals have been
observed separating over periods of months and then reuniting with apparent recognition.
These field observations notwithstanding, our present findings suggest that the mechanisms
that underlie maternal-offspring bonds in orcas cannot endure two-year separations.
Perhaps the maternal-infant bond requires a longer continuous period at its onset, or
perhaps two years is too long a period of separation even for a well established bond. It
is also possible that because the period in question spanned a time over which the
offspring were undergoing a great deal of growth and behavioral development, they were
"unrecognizable" by the time of re-union in a way that might not be true for two
separated adults.
In the wild, pods of whales are believed to have unique family calls.
Our research team is currently investigating the degree to which the calls of the mother
and offspring whales in this study differed after their 2-year separation. It is hoped
that future work, such as this, will allow us to conclude more about the maintenance of
the social bonds in whales.
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