Beluga Whale ( <scp> <i>Delphinapterus leucas</i> </scp> ) Behavior Towards a Dead Conspecific

How do animals react to dead or dying conspecifics? Do they comprehend death? Do they grieve? These are the fundamental questions asked in the field of comparative thanatology, which focuses on how animals respond to death (Anderson 2016; Gonçalves and Biro 2018). Thanatological behaviors, such as carrying, supporting, grooming, or nurturing a corpse, or exhibiting curious, aggressive, cannibalistic, or sexual behaviors towards a corpse (Monsó and Osuna-Mascaró 2021), have been observed in several mammal species, including African elephants (Loxodonta africana; Douglas-Hamilton et al. 2006), dingoes (Canis dingo; Appleby et al. 2013), hippos (Hippopotamus amphibius; Inman and Leggett 2020), giraffes (Giraffa camelopardalis; Bercovitch 2013), non-human primates (Yang et al. 2016; Cronin et al. 2011; Anderson 2018; Toyoda et al. 2024; Porter et al. 2019), and several species of cetaceans (Methion et al. 2023; Castro et al. 2022; Cockcroft and Sauer 1990; Shedd et al. 2021; Bearzi et al. 2018). In the field of marine mammalogy, epimeletic behavior, described as caring for, nurturing, or supporting sick, injured, or dead individuals, has been documented in at least 20 species of cetaceans (reviewed in Bearzi et al. 2018). Most observations of epimeletic behavior in cetaceans have involved one or more adults assisting a dead individual by keeping them afloat and commonly involve a deceased calf (Cockcroft and Sauer 1990; Bearzi et al. 2018; Methion et al. 2023; Castro et al. 2022). From an evolutionary standpoint, epimeletic behavior towards sick or injured conspecifics is an adaptive trait as it may increase the likelihood of survival for the sick or injured individual; however, epimeletic behavior towards a dead conspecific is often considered maladaptive (Bearzi et al. 2018), as caregiving cetaceans can spend hours to days providing aid to deceased individuals, foregoing foraging attempts and lagging behind their groups (Cheng et al. 2018; Pedrazzi et al. 2022; Shedd et al. 2021). Between July 1 and July 9, 2024, we conducted field work in Churchill, Manitoba, Canada (58.768410, −94.164963) to study and monitor beluga whales (Delphinapterus leucas) from the Western Hudson Bay (WHB) beluga population. The field program consisted of boat- and drone-based activities, including drone video and imagery collection, which were conducted from Cape Merry (58.785705, −94.201626). On July 2, 2024, at approximately 10:37 CST, a dead calf was spotted from the drone (DJI Mavic 3E) within the Churchill River estuary (58.783542, −94.206536), surrounded by several free-swimming belugas. The dead calf and surrounding belugas were recorded for ~4 min and 17 s before the depleted drone battery required us to land, and we were unable to relocate the calf after changing the batteries. We classified the calf as a neonate, as it was roughly 1/3 the size of an adult beluga and was lighter in color than other calves observed in the video (Michaud 2014). It is possible that the calf was stillborn or died shortly after birth; however, we could not determine the cause of death, as there were no signs of physical trauma. We observed a visible slick on the surface of the water where the dead calf was floating, and it is possible that the slick was cervical mucus, amniotic fluid, or afterbirth, indicative of a recent birth (e.g., Biancani et al. 2021). Alternatively, the slick could have been a byproduct of decomposition. In this study, we described our observations of the dead calf and the behaviors of the surrounding beluga whales. Caldwell and Caldwell (1966) categorized three behaviors exhibited by non-distressed individuals during epimeletic episodes that we used to assess the whales' behavior: standing-by, excitement, and supporting. Standing-by refers to individuals that approach and remain close to a distressed individual without providing assistance (we define “close” as being within 3 body lengths), while excitement refers to individuals aggressively circling an animal in distress or exhibiting aggressive behaviors towards apparent outside threats, without providing assistance to the animal in distress (Caldwell and Caldwell 1966). Supporting behavior refers to individuals that physically support the animal in distress by lifting and maintaining the individual at the surface (Caldwell and Caldwell 1966). To assess whether the behaviors of surrounding belugas towards the dead calf were epimeletic in nature, we used an ethogram based on published definitions of epimeletic behavior (Caldwell and Caldwell 1966; Table 1) and analyzed the drone footage in Behavioral Observation Research Interactive Software (BORIS; Friard and Gamba 2016). We documented 15 instances where belugas from outside of the video frame swam directly towards the dead calf, including 4 mother-calf pairs and 11 individuals. There were between 3 and 12 belugas within 3 body lengths of the dead calf throughout the entire recording (Figure 1) and up to 16 belugas were observed within a single video frame (Figure 2). We could not estimate the total time that each individual spent with the dead calf due to poor water clarity, glare from the sun, and our inability to identify individuals; however, the dead calf was surrounded by free-swimming belugas for the entire duration of the video. This type of behavior is indicative of standing-by defined by Caldwell and Caldwell (1966) and has been observed in several cetacean species during epimeletic events (Cartwright et al. 2025; Cheng et al. 2018; Pedrazzi et al. 2022; Castro et al. 2022). We did not observe any behaviors that could be classified as excitement, including aggressive or excited behaviors towards the dead calf or apparent outside threats (Caldwell and Caldwell 1966). We did observe belugas coming into contact with the dead calf on three separate occasions (Figure 3); however, each interaction was brief (~3 s) and we do not believe that these interactions could be classified as supporting behaviors. The lack of supporting behavior in this study is interesting, as many cases of cetacean epimeletic behavior involving a calf have documented supporting behaviors (Shedd et al. 2021; Castro et al. 2022; Methion et al. 2023). However, since our recording of the event was brief, we cannot rule out that supporting behaviors occurred before or after our encounter. It remains unclear how the surrounding whales detected the dead calf; however, multiple species are known to use distress calls to elicit help from conspecifics, including bats, deer, and cetaceans (e.g., Russ et al. 2004; Lingle and Riede 2014; Carter et al. 2015; Kuczaj et al. 2015; Cheng et al. 2018). In cetaceans, epimeletic behaviors are associated with increased vocalizations and changes in acoustic properties from both the animal in distress and surrounding individuals (Kuczaj et al. 2015; Cheng et al. 2018; Pedrazzi et al. 2022). These changes in vocalizations are thought to elicit aid from others and convey important information regarding the animal in distress (Cheng et al. 2018; Pedrazzi et al. 2022). In captive belugas, contact calls between mothers and their calves increased during the death of a calf, and a similar call was emitted by a wild female beluga carrying a dead calf in the St. Lawrence River (Vergara et al. 2010). These contact calls are thought to help maintain social cohesion and mother-calf recognition (Vergara et al. 2010). Given that belugas are a highly vocal species (Chmelnitsky and Ferguson 2012), it is possible that the belugas observed swimming directly towards the dead calf in this study were alerted by the calls of other attending whales. Since we did not observe any excitement or supporting behaviors, it is difficult to ascertain whether any of the behaviors observed were truly epimeletic in nature. Instead, the belugas seen swimming towards and around the dead calf could have been curious about the novel object in their habitat. Curiosity is often described as the impetus for exploring one's environment (Byrne 2013; Lilley et al. 2017) and is likely an adaptive trait, as the information gathered during these exploratory behaviors may be useful for adapting to and understanding one's environment in the future (Glickman and Sroges 1966; Byrne 2013). In captive cetacean studies, gaze duration, bubble trails, bubble bursts, and open mouths have been used as proxies for curiosity and exploratory behaviors (Lilley et al. 2017; Guarino et al. 2017), and although several belugas were observed gazing at the dead calf by circling it or investigating it from a vertical position, none of the other exploratory behaviors were observed. Belugas have been observed exhibiting epimeletic behavior towards conspecifics, different species, and inanimate objects (Smith and Sleno 1986). For example, a wild beluga was observed carrying an immobile neonate on its head, while several other belugas were observed carrying inanimate objects such as planks, nets, an amniotic sac and placenta, and a caribou (Rangifer tarandus) skeleton (Smith and Sleno 1986). It has been hypothesized that carrying inanimate objects may be a surrogate behavior in response to a mother losing its calf (Smith and Sleno 1986). This hypothesis is supported by observations of a captive beluga carrying her placenta for 10 h after her newborn calf had died and was removed from the pool (Kilborn 1994). Once her placenta was removed, the beluga was observed carrying a buoy with a rope attached to it, which was a novel behavior for this particular beluga (Kilborn 1994). Captive belugas in other aquaria have also been observed carrying inanimate objects following the death of their calves (Kilborn 1994). In this note, we assessed the behaviors of wild belugas towards a dead conspecific and identified one out of three defined epimeletic behaviors performed by up to 16 beluga whales: standing-by. Although epimeletic behavior towards a dead conspecific is often considered maladaptive, of the three epimeletic behaviors assessed here, standing-by is the least energetically demanding, allowing conspecifics to provide compassion while reducing negative consequences to themselves. Drone footage allowed for a unique perspective of beluga behaviors that would be difficult to assess from a boat, and although we could not determine whether the standing-by behavior was purely epimeletic or curiosity-driven, the behaviors described provide valuable insights into the thanatological and social behavior of free-swimming beluga whales. Justine M. Hudson: conceptualization, data curation, funding acquisition, investigation, methodology, visualization, writing – original draft, writing – review and editing. Cortney A. Watt: funding acquisition, project administration, supervision, writing – review and editing. The authors would like to thank Amanda Belanger for her assistance in the field. We would also like to thank the Churchill Northern Studies Centre and Bear Safe Security Services for their logistical help while in the field. Thanks also to two reviewers whose comments improved the final version of this paper. This research was conducted under Fisheries and Oceans Canada Animal Use Permit OPA-ACC-2024-12. Open Access funding provided by the Fisheries and Oceans Canada library. The authors declare no conflicts of interest. The data that support the findings of this study are available from the corresponding author upon reasonable request. Video S1: Drone video of belugas in Churchill, Manitoba, toward a dead conspecific. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

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