Developmental changes in the resting strategies of killer whale mothers and their calves in managed care from birth to 36 months

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The development of cetacean sleep has not been explored fully. Questions such as whether cetacean mothers regulate their offspring’s resting behaviour and do resting behaviours change over the course of cetacean development remain unanswered. To address these questions, an investigation of the resting strategies and activity levels for four killer whale (Orcinus orca) calves and their mothers in managed care during free-swim conditions was conducted during the first three years of life. A series of interrelated hypotheses were assessed using three independent sets of archived data (24 h behaviour records, video recordings, and instantaneous sampling) collected from two facilities. Together, the results indicated that mothers adjusted their activity levels based on their calves’ current level of development. Floating, often a preferred resting behaviour, was rarely observed during the first post-parturition month for any of the mother–calf pairs. Rather, the mother–calf pairs tended to display fast-moving mother–calf swims with frequent trajectory changes as the calf gained swimming proficiency. Although floating occurred more frequently over time for all pairs, all four killer whale mother–calf pairs displayed a preference for a slower-paced pattern swim (i.e., swim-rest). Calves preferred to rest with their mothers over resting with others or independently. The similarities in resting strategies displayed by the killer whale mother–calf pairs housed in independent facilities without temporal overlap emphasizes the conserved nature and development of these strategies in a precocial cetacean species with extended maternal care.



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  • Changes in activity level swims from 1 month pre-parturition to 1 month post-parturition using 24 h behavioural observation instantaneous sampling data from Facility A. The graph represents the estimated mean percent of time the killer whale mother spent at each activity level 1 month before birth as compared to the estimated mean percent of time the killer whale mother–calf pair spent at each activity level during the first month after the birth of the calf.

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  • Changes in activity level swims according to time of day (AM vs PM) for the pregnant female killer whale 1 month pre-parturition (a) and for the killer whale mother–calf pair 1 month post-parturition (b) at Facility A. The y-axis indicates the mean percent of time the mother (a) or the mother–calf pair (b) spent swimming at each activity level.

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  • Mean percent of time the killer whale mother–calf pair at Facility A spent swimming at each activity level over the first 7 weeks post-parturition.

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  • Developmental changes for mother–calf and independent calf swims at Facility A at 6 month intervals from 1 month until 36 months post-parturition. (a) Mean percent of time the calf spent swimming with her mother at each activity level. (b) Mean percent of time the calf spent swimming independently at each activity level.

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  • Developmental changes in estimated mean percent of time 3 killer whale calves at Facility B spent swimming at each activity level at 6 month intervals from 1 month until 36 months post-parturition.

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  • Estimated mean percent of time 3 killer whale calves at Facility B spent swimming at each activity level every month for the first year of life.

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