On 12 August 2021, a long-finned pilot whale calf was recorded in the company of three individual killer whales west of the Snæfellsnes Peninsula, West Iceland ( Table 1 ). The observation period for this encounter lasted 21 min, and no other cetaceans were detected in the area throughout the observation. The body condition of all the three killer whales was considered “normal” (mesomorphic), and the individuals were identified as adult females SN0092 “Dragonfly” and SN0540 “Sædís” and adult male SN0089 “Zale”. This group, henceforth also referred to as the 92s, has been documented feeding on Atlantic herring and has been observed on a total of 21 occasions between 2012 and 2022 ( Table 1 ). During 19 of these occasions, all 3 members were present, showing a stable group structure over time and indicating a social unit of likely related individuals ( Table 1 ). All individuals were adults when first documented in 2012, and SN0540 has not been recorded with a calf of her own during our long-term study (2012–2022). The pilot whale calf was classified as a newborn and its body condition as “emaciated” ( Fig. 1 ). The pilot whale calf was observed in echelon position with SN0540 for the whole duration of the encounter ( Fig. 1 )—with the exception of two surfacings where the calf surfaced several meters away from SN0540. There were no visible interactions between the other group members (SN0089 and SN0092) and the pilot whale calf. The 92s displayed foraging behavior ( Table 1 ) throughout the encounter, which continued as the boat left the scene. The next confirmed sighting of the 92s was in March 2022, and the pilot whale calf was not observed to be present ( Table 1 ).
Fig. 1. Fig. 1 . Killer whale (Orcinus orca (Linnaeus 1758)) female SN0540 in echelon formation with a long-finned pilot whale (Globicephala melas (Traill, 1809)) calf. The pilot whale calf displayed clear signs of emaciation via a deep depression posterior to the blowhole and a narrowed trunk, indicating poor body condition and nutritional status (Joblon et al. 2014). The strong fetal folds, indicating that the calf was newborn (Auger-Méthé and Whitehead 2007; Augusto et al. 2017), are clearly visible on both sides of the body. All images were taken on 12 August 2021 (upper two images by M.-T. Mrusczok and lower image by S. Rodríguez Ramallo).
Table 1. Table 1 . Sightings of the focal group of killer whales (Orcinus orca) in the southern part of Breiðafjörður Bay and along the Snæfellsnes Peninsula, West Iceland.
Lagenorhynchus albirostris (Gray, 1846)) was sighted among the pilot whales and was observed porpoising with them toward the killer whales during the initial chase before disappearing from view during the subsequent part of the encounter. The killer whales exhibited non-aggressive avoidance behavior and moved away from the pilot whales in a tight formation at moderate speed. The pilot whales stopped at a distance of approximately 200 m from the killer whales and turned back toward northeast. As the pilot whales turned northeast, the killer whales also turned northeast and slowly moved toward the pilot whales, maintaining a tight formation. The pilot whales then turned southwest and started chasing the killer whales again, who reacted by also turning southwest. This chain of behaviors repeated itself twice more in the same way during the observation period. The group of killer whales included one killer whale calf (not associated with the individuals that had formerly been seen with the pilot whale calf), and the pilot whale group included several conspecific calves of various ages. Observations ended when the boat left as the killer whales were moving toward the pilot whales for the third time. On 19 July 2022, the 92s were observed as part of an association of 10 killer whales that interacted with a group of approximately 40 long-finned pilot whales ( Table 1 ). The observation period lasted 26 min, and the pilot whales were observed pursuing the killer whales southwest. In this encounter, a lone white-beaked dolphin ((Gray, 1846)) was sighted among the pilot whales and was observed porpoising with them toward the killer whales during the initial chase before disappearing from view during the subsequent part of the encounter. The killer whales exhibited non-aggressive avoidance behavior and moved away from the pilot whales in a tight formation at moderate speed. The pilot whales stopped at a distance of approximately 200 m from the killer whales and turned back toward northeast. As the pilot whales turned northeast, the killer whales also turned northeast and slowly moved toward the pilot whales, maintaining a tight formation. The pilot whales then turned southwest and started chasing the killer whales again, who reacted by also turning southwest. This chain of behaviors repeated itself twice more in the same way during the observation period. The group of killer whales included one killer whale calf (not associated with the individuals that had formerly been seen with the pilot whale calf), and the pilot whale group included several conspecific calves of various ages. Observations ended when the boat left as the killer whales were moving toward the pilot whales for the third time.
In the case presented here, the observation of the echelon formation between the adult female killer whale SN0540 and the pilot whale calf should be given special consideration, even though the pilot whale calf was not observed nursing. The echelon position allows a calf to make fewer tail fluke movements than when swimming on its own and overcome physical limitations during high-speed travel, as it is closely “drafting” alongside an individual, carried by the pressure wave created by the adult’s larger body ( Weihs 2004 Noren and Edwards 2007 ). As a form of aquatic infant-carrying behavior, echelon swimming is considered one of the most energy-intensive forms of parental care after lactation and may impact energy budgets, predator evasion, and foraging efficiency ( Noren 2008 ).
Long-finned pilot whale calves are frequently observed traveling alongside other pilot whale adults and juveniles, both males and females, in echelon position ( Augusto et al. 2017 ). These allocaring individuals have been found to be from outside the calf’s social unit, and pilot whale calves have been observed to switch between allocarers regularly ( Augusto et al. 2017 ). It is a possible explanation that the calves themselves may initiate some of these allocare relationships, which might make it easier for a killer whale to either intercept or adopt a newborn pilot whale calf. SN0540 may have also initiated the contact and deliberately, at least temporarily, adopted the pilot whale calf, considering the high-energy investment of caregiving. During the observation, SN0089 and SN0092 tolerated the presence of the pilot whale calf, but it is unknown how these individuals related to the calf specifically, as no interaction was documented.
Even though the 92s were observed foraging in the vicinity of the pilot whale calf, foraging benefits are unlikely to occur for the killer whales in this specific interspecies association, as the calf was a newborn and would still have to be nursed ( Augusto et al. 2017 Soto et al. 2017 ). Given the poor body condition of the pilot whale calf and the lack of nursing killer whale calves in the group at the time of observation, it is unlikely that the pilot whale calf received any nourishment.
While we do not know how the observed relationship between SN0540 and the pilot whale calf started, it does suggest a possible novel explanation for the regularly observed killer whale chasing behavior from long-finned pilot whales in Icelandic waters. The movements of the 92s in conjunction with other killer whales during the subsequent interaction between them and the pilot whale group on 19 July 2022 do not fit any formerly observed behavioral patterns described for these antagonistic interactions ( De Stephanis et al. 2014 Selbmann et al. 2022 ). It is possible that the movements of the killer whale group as a whole could have been influenced by an active effort of SN0540 to obtain another pilot whale calf through an approach of the pilot whale group, and the pilot whales may have reacted with a chase as a preventative measure to protect their young.
SN0540 with the newborn pilot whale is the first documented account of a long-finned pilot whale calf seen in echelon position with a killer whale. This observation also presents the first documented account of epimeletic and possible alloparental behavior of a killer whale toward a non-conspecific. Whether the attraction between SN0540 and the pilot whale calf was mutual or one-sided is not known, nor is the duration of the association, or how it started and ended.
We suggest that pilot whales and killer whales in Iceland may display repeated or long-term interactions on the basis of multiple drivers. More research on pilot whale–killer whale interactions, including on how pilot whale calves become associated with killer whale groups in the first place, is necessary to understand the complex interplay of these two delphinid species.