Investigating Intrapopulation Variation in Activity Budgets and Reproductive Parameters Among Socially Distinct Communities of Dolphins

Amy J Lockley

Animals must make continual decisions about how to allocate their time and energy into activities vital for survival and reproduction. Coexistence among species, and conspecifics, can be facilitated when individuals reduce competition by using different resources or habitats, resulting in niche partitioning. While intrapopulation variation has been investigated for dolphins, little is known about how distinct social groups differ in their activity budgets, and what, if any, effects this may have on their reproduction. The objective of this study was to compare activity budgets and reproductive parameters of two socially and spatially distinct communities of Indo-Pacific bottlenose dolphins (Tursiops aduncus) in Mandurah, Western Australia. One community (Community A) is resident to the Peel-Harvey Estuary, and the second community (Community B) resides in coastal waters and shows high site fidelity to one of the two entrances to the estuary, Dawesville Channel. It is hypothesised that the dolphins’ activity budgets will vary seasonally and between the social communities, which if niche partitioning theory holds true, means reproductive output will be relatively similar. Behavioural photo-identification surveys (n = 934) to investigate seasonal variation in behaviour were conducted in 2016 and 2017. Surveys were also conducted in austral autumn 2025 (n = 140), along with group focal follows (n = 50.4 hours). Focal follow data were used to estimate activity budgets and quantify behavioural transitions probabilities with a Markov chain. The activity budgets derived from focal follows of the two communities differed significantly (p < 0.001), with travel and rest comprising the largest proportions of the activity budget for Community A and B, respectively. Transition probabilities and steady states obtained from the Markov model further supported these behavioural differences. The results support other studies reporting seasonal variation in dolphin behaviour and provides new insight into intrapopulation variation in behavioural patterns for a social species. With the data available, it is believed that behavioural variations between the two communities are unlikely to be influencing reproductive output, as it did not differ between the communities. The communities varied in their reproductive success, however hypotheses for this, such as differing threat profiles, must be explored further. Altogether, this new understanding of intrapopulation variation in behaviour and reproduction can be applied to develop targeted and effective management strategies to ensure population viability.

Investigating Intrapopulation Variation in Activity Budgets and Reproductive Parameters Among Socially Distinct Communities of Dolphins

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