Minimally invasive physiological correlates of social behaviour in belugas (Delphinapterus leucas) under human care

Abstract

Simultaneous observations of reproductive physiology and behaviour were conducted on a group of two male and two female belugas under professionally managed care for one year to explore potential mating strategies. Weekly blow sampling for progesterone in females was used to define the breeding season by detecting three oestrous cycles in one female. Twice weekly blow sampling for testosterone and twice monthly testes measurements via ultrasonography were used to detect reproductive seasonality in both males. Female–male association frequency varied longitudinally, with 70% of all interactions occurring during the 16-week breeding season. Male–male associations did not vary seasonally. Male display behaviours towards the female occurred 14.8 times more frequently during the breeding season (0.164 ± 0.188 behaviours/min) than outside of the breeding season (0.011 ± 0.042 behaviours/min). The cycling female responded variably to male display behaviours by altering swim speed or body orientation towards the male. Although this small sample size limits broad conclusions, the frequent display behaviours, low copulation rate and lack of serious male–male aggression are consistent with predictions for pre-copulatory female mate choice developed from the current knowledge of beluga reproductive physiology. These observations, which are not feasible for wild belugas, provide important management considerations because reduced opportunities for mate choice could limit the reproductive rate, especially in small populations.

Cetacean Sociality, Reproduction, and Conservation

“…One possible mechanism is that human disturbance disrupts social behaviors that improve mating success, because beluga whales are facultative induced ovulators (Steinman et al 2012). A recent aquarium study monitoring hormone levels and behavior showed that hormone levels in a captive female rose only after two males had initiated reproductive displays for three weeks, with ovulation following several weeks later (Richard et al 2021). Breeding beluga whales in most North American aquaria has been difficult (Steinman et al 2012); an exception is a facility that had 54 beluga whales in in two pools, 1 which may have allowed for more social interactions.…”

“…Shown here are an adult whale (white; front-most whale), two young adults or subadults (light gray), and a young calf (small, dark gray). Beluga whales are facultative induced ovulators and while mating is difficult to observe in the wild, courtship in captive settings apparently follows ritualized sequences and it is possible that male mating displays help to induce ovulation(Steinman et al 2012;Richard et al 2021). Disturbance and disruption of beluga whale behavior and social structure may be a contributing factor to the lack of recovery by this and other beluga whale populations.…”

Synergy between behavioural research on beluga whales (Delphinapterus leucas) conducted in zoological and wild settings

“…Partial understanding of developmental time course Glabicky et al 2010;Lilley et al 2020;Richard et al 2021 Sequence of courtship behaviours?…”

Belugas (Delphinapterus leucas) create facial displays during social interactions by changing the shape of their melons

“…One exception is the melon shake, in which the actor vigorously shakes the head in dorsal/ventral plane, causing apparently passive yet marked extension and compression of the melon. Richard et al ( 2021 ) quantified the occurrence of this behavior and found that it was primarily performed by males toward a female recipient in conjunction with courtship behavior. These seemingly context-specific observations suggest a social function for melon shapes in belugas, analogous to facial expressions or displays, instead of a purely acoustic function.…”

“…For example, Aychet et al ( 2021 ) used the occurrence of specific behaviors performed by red-capped mangabeys ( Cercocebus torquatus ) to characterize behavioral contexts such as playful, affiliative, or agonistic interactions that included facial displays to demonstrate context dependent performance of several displays. Similarly, detailed observations of belugas in aquaria, where the animals can be observed underwater and from close proximity, have identified behavioral indicators of various contexts, including courtship (male toward female genital presents during ovarian cycling, Richard et al 2021 ), socio-sexual behavior (male-male genital presents, Hill et al 2015b ; Richard et al 2021 ), agonistic behavior (biting; Hill et al 2015b ), and affiliative behavior (group swimming, Hill et al 2015b ; Richard et al 2021 ). While establishing the goals of a communication signal in nonhuman animals is challenging, context specific use of melon shapes would support their communicative function.…”