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Indices of Affiliation in Captive Orca Whales
M. Noonan, M. Conners, M. Viksjo, K. Pastwick, D. Gartz, L. Chalupka, J.
Portner & D. Perri.
Canisius College, Buffalo, New York & Marineland of Canada, Niagara
Falls, Ontario.
Presented at the Animal Behavior Society,
Carbondale, Illinois, July, 1998.
Introduction
Observers of wild cetaceans often utilize both
physical proximity and/or degree of behavioral synchronization as indices of affiliation
among individuals. That is, when assemblages of free ranging whales have been studied, a
heightened degree of attachment is inferred for animals which (a) characteristically
maintain short distances between themselves and/or
(b) characteristically rise to the surface and dive with near simultaneity (or show
other evidence of behavior synchrony).
In this project, we monitored both of these parameters in a group of four juvenile orca
whales in an effort to ascertain whether stable patterns of affiliation could be revealed
in the narrow confines of captivity.
Subjects
The group consisted of two females, Ne (5 years old) and
Ma (1.5 years), and two males, Kk (3 years) and Nv (1 year).
Procedures
The four whales were housed together in a oval shaped pool, 20 m long x 8 m wide x 4 m
deep. We observed them from 7 to 9 am, 3 days per week, for 8 months. Our observations
took place from 2 m high platforms adjacent to the pool, and we employed the
Observer™ computer program for data collection and analysis. During alternating 9
minute intervals, we either
(a) repeatedly assessed physical distance between each possible pair of whales
(utilizing instantaneous sampling at 30 second intervals), or (b) continuously recorded
the precise time of each breath taken by each whale. For inter-whale distance we
calculated the proportion of all observations for each possible pair of whales that they
were found within 2 meters of each other (i.e., within approximately one whale’s body
length). For breath synchrony, we calculated the proportion of breaths by either whale in
a pair that were followed within 5 seconds by a breath by the other whale in the pair. For
the present analysis, each type of data was combined within calendar months.
Results
Breath Synchrony:
- All combinations of whales showed greater breath synchrony than would be expected by
chance. For the average focal pair of whales, 29% of either whale’s breaths occurred
within five seconds of breaths by the other. (Since the whales averaged only one breath
per minute, one would expect a random breath by either whale in any given pair to be
followed within 5 seconds by a breath by the other to occur only 16% of the time.)
- There was relatively little variation on this measure. Pair averages ranged only between
0.26 and 0.32.
- This measure showed relatively little consistency from month to month.
Inter-Whale Distance:
- For each pair of whales, this measure showed marked consistency from month to month.
- Additionally, this measure showed considerable variation from pair to pair. The average
over 8 months ranged from 0.47 for Ne+Nv (close to what one would expect if the whales
were moving randomly in the pool) to 0.83 for Kk+Ma (indicating that on 83% of our samples
over the 8 months those two whales were found to be within one body length of each other).
Discussion
Assuming that our index of inter-whale distance reflects affiliation:
- We note that the whales tended most often to segregate into male-female pairs, and not
into same-sex or similar-age groupings. The most consistently close spacing was maintained
between the 3 year old male and the 1½ y.o. female (Kk+Ma), and other male-female
combinations also tended to show close spacing (Ne+Kk and Ma+Nv).
- It appears that during December and January there was a shift in the pattern of
affiliation in which the tightest pairing, Kk+Ma, tended to loosen somewhat and the Ne+Kk
and Ma+Nv pairs tended to strengthen. In the following months, the social pattern
re-approximated the original configuration.
Summary
During our observations, the young whales we studied were characteristically quite
active--very frequently changing position and spacing from moment to moment. Nevertheless,
it does appear that our assessment of average inter-whale distances revealed stable
patterns of social clustering.
Although all of our whales evidenced a degree of synchronization in the timing of their
breaths, pairwise analysis of breath synchrony appeared to be less useful as an index of
affiliation, at least on a month by month basis as we have utilized it here. We are
presently exploring the possibility that this index will be more useful when examining
variations in affiliation on a shorter time scale.
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