The animal alliances reshaping our understanding of intelligence

In nature, interactions between species are often framed in terms of survival — those that hunt and those that are hunted. But research is showing some animals form surprising partnerships, reshaping scientists’ ideas about how intelligence evolves in the animal kingdom.

Take Octavia and Finn, a striking duo hunting along a coral reef. I observed this pair while exploring a research site on the Great Barrier Reef as part of a project to understand complex behaviour in the wild. Octavia moves with fluid grace, slipping between the rocks, while Finn zips through the water with bursts of speed. They work as a team. Each of them brings a unique skill to the hunt – Octavia with her dexterity, Finn with his quick strikes. Octavia is a day octopus, and Finn is a coral trout.

This kind of collaboration isn’t unique to the ocean — on land, other species have also developed remarkable partnerships. Take, for instance, the relationship between the greater honeyguide bird (Indicator indicator) and humans. Honeyguides call and flutter to lead humans to bee nests. Once the humans harvest the honey, the bird swoops in for the leftovers, beeswax and larvae – a treat that it couldn’t easily access without help. The two species engage in a kind of cross-species conversation, each relying on the other’s skills.

Other collaborations show how different species can use trust and deception to their advantage. The fork-tailed drongo (Dicrurus adsimilis) acts as a sentinel for meerkats (Suricata suricatta), issuing alarm calls to warn them of approaching predators. Drongos sometimes give false alarms, sending meerkats scattering so the bird can steal their abandoned food. Even so, the relationship is beneficial for both parties: meerkats gain an extra set of eyes, while the drongo secures an occasional meal.

In the underwater world, similar dynamics are at play. Cleaner wrasse (Labroides dimidiatus) remove parasites from the bodies of larger “client” fish, such as groupers and manta rays. Client fish will congregate at underwater “cleaning stations”, often atop coral heads, and will even queue up for their turn. But these partnerships aren’t always fair. Sometimes, cleaner wrasse sneak a nibble of their client’s protective mucus instead. When this happens, the client fish can cut the interaction short and leave. This disruption suggests that these relationships involve strategic decision-making.

Perhaps the most captivating example of marine collaboration happens between octopuses and fish. Initially, scientists assumed fish took advantage of octopuses, snatching prey they flushed out. But thanks to advances in tracking technology, a richer, more cooperative dynamic is emerging. Combining data from two cameras allows researchers to study highly accurate movement patterns. One of my collaborators applied this method to study the octopus-fish partnership, published in Nature Ecology & Evolution in 2024.

The day octopus (Octopus cyanea) collaborates with fish such as coral trout (Plectropomus spp.) and goatfish (Parupeneus spp.) during hunts. The 2024 study found these fish don’t just follow the octopus, they participate in the hunt. Scientists have even observed octopuses “punching” fish that aren’t pulling their weight. Fish like the coral trout produce signals by using their bodies. They perform a “head-stand”, tipping their heads downward and hovering above crevices to indicate hidden prey. This prompts the octopus to flush it out with its dexterous arms. Although octopuses are solitary animals, these brief partnerships reveal a degree of social sophistication.

A blend of ecological and cognitive factors probably underpins these partnerships. Dietary overlap plays a crucial role, as partnerships are more likely to form when animals of different species feed on similar prey.

Cognitive abilities are equally important. For these partnerships to work, both species must recognise each other as reliable partners. Octopuses demonstrate behavioural flexibility, adapting their tactics in real time, based on their partner’s actions. Fish show self-control by holding back until the octopus has flushed prey from hiding.

Habitat complexity also shapes the partnership. Coral reefs, with their maze of crevices, make hunting alone difficult). Timing may also help make these partnerships work. Since both species are active during the day they can capitalise on daylight to communicate using visual signals.

Rethinking animal intelligence

It remains unclear whether octopuses truly understand the meaning behind their partner fish signals or follow them instinctively. But either way the interaction hints at a surprising level of cognitive sophistication. Research in animal cognition suggests that behaviour such as perspective-taking – (understanding that others may have different views) and theory of mind (the ability to attribute thoughts, beliefs, or intentions to others) – could be involved in referential signals.

These abilities are typically seen in social animals (such as chimpanzees, crows, or jays) that live in groups or among family members, where understanding one another’s intentions can offer a real survival advantage. Animal alliances are challenging the traditional view in research that intelligence and social skills develop solely through interactions within the same species.

This idea broadens the way in which scientists think about social intelligence, showing that the capacity to collaborate can arise wherever there’s something to be gained from working together. A project funded by the National Geographic Society through the Meridian Grant Program aims to push these ideas further. A team of behavioural ecologists, comparative psychologists (including myself), robotics researchers, and underwater storytellers are developing a robotic fish to interact with day octopuses. By controlling one partner in the interaction, we can test responses and decode the signals exchanged between octopuses and their fish collaborators.

Just like the octopus and fish, this project is a reminder that some tasks can only be achieved through collaboration. No single species, or team, can do it alone.

Alexandra Schnell receives funding from the National Geographic Society.