Dear colleagues,
Our study on the effects of conspecific scarring on all sex and age classes in
three divergent killer whale populations is now published open access in
Behavioral Ecology and Sociobiology at https://rdcu.be/eccmc
Citation: van Weelden, C., Tixier, P., Doniol-Valcroze, T., Guinet, C. &
Towers, J.R. (2025). Divergent killer whale populations exhibit similar
acquisition but different healing rates of conspecific scars. Behavioral
Ecology and Sociobiology 79: 39. https://doi.org/10.1007/s00265-025-03576-6
Abstract: Scars obtained from interactions with conspecifics may be caused by
both playful and aggressive activities, making them useful when studying
cetacean behaviour. This study investigates the effects of age and sex on
conspecific scar acquisition and healing in three genetically distinct
populations of killer whales (Orcinus orca) each with unique diets and social
structures. The sample consisted of 50 of the most commonly photo-identified
individuals from all sex and age classes in each of the Bigg’s, Northern
Resident, and Crozet killer whale populations. The number of new scars annually
acquired by an individual as well as how long it took them to disappear were
extracted from annual photo-identification images of these individuals taken
between the years of 2008 and 2021. Scar acquisition was analysed using a
generalized additive model while scar healing was assessed using Kaplan-Meier
survival curves. Results showed an inverse relationship between scar
acquisition and age, as well as an effect of sex with males being more scarred
than females amongst all age classes. No significant differences in scar
acquisition between populations was found. Scar re-pigmentation was faster in
Northern Residents compared to Crozet and Bigg’s individuals and varied amongst
age classes, with scars on calves and juveniles disappearing more quickly than
those on adults. These population- and age-based differences in healing may be
due to scar severity, while results around scar acquisition suggest that the
nature of physical interactions between sex and age classes in this species are
homogenous despite cultural and genetic differences that have evolved between
populations.
Significance Statement: In several species of odontocetes, including killer
whales, scars caused by the teeth of conspecifics are typically attributed to
social behaviours associated with reproductive competition. Previous research
has suggested that divergent but sympatric populations of killer whales each
with unique diets, social structures, and behaviours have frequencies of
scarring which differ amongst sex and age classes in each population. Using
more robust data we conclude that rates of scar acquisition between these same
populations and another non-sympatric population are remarkably similar when
compared between sex and age classes, but that one population exhibited
significantly different rates of healing. These results suggest that sexually
selected behaviours have not diverged as strongly as ecological adaptations
have in this species, but that scars are likely caused by mild to intense play
and aggression which are specific to population, sex, and age class.
Jared Towers
Executive Director
Bay Cetology
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