See video: Mothers decide when orcas should dive

“It is the adult females that most often initiate a deep dive,” says marine researcher Carla Freitas.

In more than 80 per cent of the killer whales' collective deep dives observed in the Hardangerfjord, a female initiated the dive. The others in the group followed – quickly and in an orderly fashion.

This may be an important trait when conditions at sea change.

Faced with climate change, human impacts, or changes in food availability, killer whales depend on rapid and effective decision-making.

In such situations, clear leadership may be key.

The hierarchy

The findings are based on drone observations in the Hardangerfjord, collected from February to April 2025. The results were recently published in Animal Behaviour.

“In total, we collected 594 minutes of drone footage of the different killer whale groups,” says marine biologist Marie-Laure Veys.

She lived in Ulvik for three months during the fieldwork for her master’s project at the Institute of Marine Research.

The fjords of western Norway are popular habitats for killer whales during the spring. Many of the whales return year after year.

Killer whales are social animals that live in closely connected family groups, composed of mothers and their offsprings. Determining the internal hierarchy of these groups can be challenging.

“We have investigated how killer whales make collective decisions and the more subtle social interactions between them,” says Veys.

Watch drone footage of the killer whales:

14.6 seconds from the first to the last dive

The researchers analysed 45 collective deep dives by killer whales and 274 social interactions between individuals.

The results show that females initiate the vast majority of collective dives.

“This supports the hypothesis that killer whales do not make these decisions collectively or at random. Instead, leadership appears to be linked to both age and sex, with adult females most often taking the lead," says Carla Freitas.

In roughly half of the cases, the whale that dived first was positioned at the front of the group, but in 40 per cent of cases, the starting signal came from the middle of the formation. This shows that the leader is not necessarily positioned at the front of the group, as assumed in previous studies.

Once the decision to dive has been made, the rest follow one after another.

From the moment the first killer whale takes a breath and dives until the last one does the same, the average delay is 14.6 seconds.

“The dive lag is relatively short, suggesting a high degree of cohesion within the groups. This may indicate that the killer whales have strong social bonds and are coordinated like a well-oiled machine,” the researcher says.

The matriarchs

The results are not unexpected, as killer whales are known to live in matriarchal social units. The researchers also saw this reflected in the whales’ interactions.

The team recorded 274 social interactions – including physical contact between killer whales and synchronised surfacing.

“These interactions were most common between adult females and calves,” says Freitas.

The fact that these interactions occurred primarily in mother-calf pairs may indicate that calves stay close to their mothers to learn how to behave – whether that involves social norms, vocal traditions, or hunting strategies.

The researchers note that the study covers a relatively small number of killer whales over a short period of time.

Nevertheless, it demonstrates the value of combining drone observations with long term monitoring of known individuals to study the whales’ nuanced, close-range interactions.

“The study also demonstrates the central role adult females play in structuring the group’s collective behaviour and in maintaining the social bonds among killer whales,” says Freitas.

Source:

Veys et al. Female-centred decision making and social interactions in killer whales revealed by drone-based observations, Animal Behaviour, 2026. DOI: 10.1016/j.anbehav.2026.123732

How do the researchers know which killer whale is which?

The Norwegian Orca Survey (NOS) has built up an extensive archive over several years, documenting photo-identification records and life-history information about orcas in western Norway.

This allows researchers to identify individual orcas from drone images. They can determine each animal’s sex, age class, reproductive status, and family relationships.

“This long-term knowledge of individual animals has been crucial to interpreting leadership and social interactions within the groups,” says Eve Jourdain of NOS.

The Institute of Marine Research (HI) and NOS have collaborated on orca research on several occasions. For example, during field work conducted in 2024 and 2025 with UiT as well:

• På sporet av vestlandsspekkhoggarane (Norwegian only)

• Vestlandsspekkhoggarane et gjerne niser og sel, i tillegg til den meir sedvanlege silda. (Norwegian only)

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