There are many species of whales and dolphins in our seas, with incredibly diverse behaviour, culture and social structure. Baleen whales, or mysticetes, are generally solitary whales and large groups are very uncommon. However, smaller groups of two or three do occasionally occur, particularly when grouping together for feeding. Baleen whales don’t echolocate but they do make vocalisations to remain in acoustic contact with one or more others. Toothed whales, or odontocetes, communicate using a series of clicks, calls and whistles and use echolocation to navigate and hunt. As a general rule, all toothed whale species are social, though the degrees of sociality differ between species, and can even be different within species!
Orcas, or killer whales, are the largest species of dolphin. The social structure and culture of orcas is incredibly sophisticated, and said to have no parallel apart from human societies. The orca pod is a matriarchal society and pods have strong matrilineal connections. Bonds are extremely tight between pod members and last for a lifetime. Calves stay with or near their mothers throughout their lives, and whilst female offspring may break off to start their own pods, they usually stay near to their mother’s. Related pods will often join up and come together to form what is known as a clan. Sometimes a single pod can contain four generations, and can number up to 50 individuals.
One apparent exception to this rule is the population of orcas that occur in the seas around the Galapagos. These orcas appear to demonstrate a fission-fusion society, which means that the size and composition of the social group changes as time passes and animals move throughout the environment. This could be because the seas in this area are less productive and food is less abundant. Within these societies, group composition is dynamic, though the majority of interactions occur between related individuals. (Denkinger et al 2020).
Orca mating systems are usually polygynous or polygynandrous – having more than one mate – therefore the majority of the care of offspring falls to the females. (Rendell et al 2019). However, within their family groups all adult whales take part in raising the calves. Other orcas within the pod will babysit youngsters, behaviour which is known as alloparenting. This altruistic behaviour helps take the pressure off the mother, strengthens the bond between the orcas and allows for the passage of knowledge and culture from orca to orca and generation to generation. Pod members of both sexes teach the youngsters essential skills such as hunting techniques, social interaction, knowledge of feeding and breeding grounds and migration routes. Each pod has its own distinct calls and vocalisations, a special dialect that is learned and passed down from one generation to the next. Clans all share similar vocalisations and calls, although there are some that are exclusive to individual pods.
“Overt violence or aggressive behaviour between individuals, even among males, has never been observed. Instead, orca society is marked by cooperation, coordination, communication, trust and acceptance.”
Orcas work together to hunt, and they can eat a variety of food. However, different pods have different feeding preferences, and some may eat a variety of food whereas others specialise on one prey type. This could be because it is more readily available, or because these orcas have adapted to become adept at catching it. For example, some orca pods feed solely on fish, and others specialise on other marine mammals, such as seals. Interestingly, orcas that eat other mammals live in smaller pods and hunt silently so as not to alert their prey to their presence. In comparison, fish-eating orcas live in much larger pods and communicate constantly as fish cannot hear their echolocations.
The most studied orcas in the world are the resident orca pods off the west coast of Canada and the USA. These resident pods are so named because they stay in inland or nearby coastal waters. There are two sub-groups of residents, the Northern Residents who range from Vancouver Island to southeast Alaska, and Southern Residents who occupy greater Puget Sound. These two groups are separate to each other and tend not to overlap. Both populations are clans made up of several pods that are all related matrilines.
In comparison to the resident orcas, there is another population in the Pacific Northwest known as transients. Transient orcas range over wider areas and further out into the open sea. Their pods are still made up of matrilines, however they tend to have fewer individuals. This could be due to the fact that their prey consists entirely of mammals, who would be alerted by a large group. Transients and residents are distinct genetically and are not thought to interbreed. They also do not share any calls or vocalisations, proving them to be unique populations.
The Icelandic Orca Project carries out research and monitors the orcas that are seen around Iceland, in order to aid in their conservation and protection. They have found that the orcas do not always remain in the area all year and some regularly travel to the north of Scotland. This means that it is possible to see orcas in the UK! Around Orkney and Shetland there is a fairly large community of orcas, and it is thought they belong to a population that also ventures to Iceland and Norway. Photo ID is being used as a tool to compare individuals seen in both Icelandic and Scottish waters.
Around the UK there is also a small pod in the Hebrides known as the West Coast Community, which is the only resident pod of orcas in the UK. This pod now only numbers eight individuals, four males and four females. These individuals can be identified by the size, shape and marks on their dorsal fins as well as other distinguishing markings. The Hebridean Whale and Dolphin Trust have been monitoring this population for almost twenty years, and have established an extensive catalogue of photos of the orcas to ID the individual animals and track their movements. Sadly, the future is uncertain for this pod of orcas, as some individuals have not been seen for years and no calves have been born since monitoring first began. One member of the pod, known as Lulu, died in 2016 after becoming entangled in fishing gear and stranding. Her necropsy showed incredibly high levels of PCBs, which are harmful contaminants that affect health and fertility. This explains the lack of calves, and means that this pod could become extinct in the near future.
The Sea Watch Foundation carries out a dedicated Orca Watch each year – a week where volunteer observers conduct land-watches around Sutherland, Caithness, Orkney and Shetland monitoring the orcas there. This year’s Orca Watch is taking place as an online event due to uncertainties regarding Covid restrictions and safety – the programme will be announced very soon!
Sea Watch Volunteer
Sources and further information
- Orca Social Organization : OrcaLab
- Orca (Killer Whale) – Whale and Dolphin Conservation (whales.org)
- Microsoft Word – Killer Whale.docx (seawatchfoundation.org.uk)
- What Is The Difference Between Transient and Resident Killer Whales (Orcas) | Orca Spirit
- Resident and Transient Orcas | Port Townsend Marine Science Center (ptmsc.org)
- Orca Network – Transient orcas
- Killer Whale — Hebridean Whale & Dolphin Trust (hwdt.org)
- Northern Residents Orca — BC Whales
- Pod‐Specific Demography of Killer Whales (Orcinus Orca) – Brault – 1993 – Ecology – Wiley Online Library
- Social structure of killer whales (Orcinus orca) in a variable low‐latitude environment, the Galápagos Archipelago – Denkinger – 2020 – Marine Mammal Science – Wiley Online Library
- Preliminary analysis of the social structure of killer whales, Orcinus orca, at subantarctic Marion Island – Tosh – 2008 – Marine Mammal Science – Wiley Online Library
- Social network correlates of food availability in an endangered population of killer whales, Orcinus orca – ScienceDirect
- Social cohesion among kin, gene flow without dispersal and the evolution of population genetic structure in the killer whale (Orcinus orca) – PILOT – 2010 – Journal of Evolutionary Biology – Wiley Online Library
- influence of ecology on sociality in the killer whale (Orcinus orca) | Behavioral Ecology | Oxford Academic (oup.com)
- West Coast Community Catalogue — Hebridean Whale & Dolphin Trust (hwdt.org)
- RESEARCH | Icelandic Orcas (icelandic-orcas.com)