In a review published in Animal Behaviour, an international team of researchers examined how animals use calls, body movements, visual displays, and other signals to coordinate cooperative relationships across species. The findings reveal the many ways animals exchange information to synchronize their behavior and maintain partnerships that benefit both sides.

Different species can cooperate in surprisingly diverse situations. Some birds lead humans to bees' nests in exchange for access to beeswax. Cleaner fish remove parasites from larger reef fish and receive a meal in return. Drawing on examples from birds, fish, insects, and mammals, the researchers show how communication helps these relationships function and endure.

How Animals Coordinate Across Species

For cooperation to succeed, animals must often match the timing of their actions to achieve a shared goal. This can be especially challenging when the species involved perceive the world in different ways.

One example is the greater honeyguide bird (Indicator indicator), which uses specialized calls to attract humans and lead them to bees' nests. The bird also responds to calls made by humans. In another case, warthogs use distinctive body postures to invite birds and mammals to clean them.

"From the examples we know, individuals coordinate their actions to access shared resources, like food, or to exchange resources for services, such as protection from predators," said Dr. Katie Dunkley, lead author and researcher at the University of Oxford. "We were particularly interested in how sharing information allows such close coordination between species."

Communication Helps Manage Risks

Signals and behavioral cues do more than initiate cooperation. They also help animals identify trustworthy partners and reduce the risk of being exploited.

Interactions with another species can be beneficial, but they can also be dangerous. Communication allows animals to distinguish between partners that offer a genuine service and those that might take advantage of them.

For instance, some cleaner fish (e.g. Labroides dimidiatus) and shrimp (e.g. Urocaridella sp.) display bright colors and perform distinctive movements that signal their role to predatory fish, allowing cleaning interactions to occur safely. Likewise, lycaenid butterfly larvae use chemical and vibrational signals that encourage ants to protect them rather than eat them.

The review also highlights the importance of looking beyond visual signals. Many species rely on information gathered through multiple senses, suggesting that scientists may overlook important forms of communication if they focus only on what animals can see.

Flexible and Adaptable Signals

Not all communication systems are the same. Some remain highly consistent, while others vary depending on location and environmental conditions.

Fish seeking cleaning services often use predictable postures, such as headstands or tail stands. In contrast, fishermen working with dolphins may interpret different dolphin behaviors as cues for when to cast their nets, and those signals can vary from one region to another.

"In some forms of interspecies cooperation, cues and signals vary depending on the ecological context, the species involved, and whether the signal is inherited or learned," said senior author Dr. van der Wal, a researcher affiliated with UCT's FitzPatrick Institute of African Ornithology. "This highlights just how flexible and adaptable interspecies communication can be."

How Cross-Species Communication Evolves

The researchers also explored how communication systems between species may develop over time.

Some signals may begin as simple cues, meaning traits or behaviors that influence another animal's response even though they were not originally meant to communicate information. Over generations, those cues can become more specialized signals.

Other communication signals may start out serving entirely different purposes, such as helping animals care for offspring or resolve conflicts. Eventually, those behaviors can be adapted for use in cooperative interactions between species.

"Studying how information flows between species gives us a powerful window into how communication systems originate, change and sometimes coevolve," said Dr. Dunkley.

Large Collaborative Research Effort

The review grew out of an interdisciplinary workshop focused on interspecies cooperation that took place in Cambridge in July 2023. Researchers studying a wide range of systems participated in the event.

The resulting paper includes 58 authors from multiple fields, including anthropology, biology, and linguistics. It also brings together experts studying animal cooperation across species, mixed-species interactions, and systems in which humans actively train non-human animals.

What Scientists Hope to Learn Next

According to the researchers, the review highlights promising new directions for studying how communication evolves between species and how these interactions influence ecosystems.

The authors emphasize the need for broader studies involving more groups of animals, along with additional experiments aimed at understanding how signals arise, persist, and shape cooperative behavior.

"We still have much to learn about how these systems function and evolve," said Dr. van der Wal. "We look forward to future research revealing both these interactions and other forms of interspecies cooperation yet to be discovered."

The study was published in Animal Behaviour under the title, "The ecology and evolution of cues and signals in animal interspecies cooperation."