New research by the Marine Apex Predator Research Unit (MAPRU) reveals that Cape gannets, one of South Africa’s most charismatic seabirds, use both social cues and memory to navigate the open ocean in search of food.
SENTINELS OF THE SEA: Cape gannets are at the centre of a groundbreaking ocean predator study. Picture: Pierre Pistorius
“It’s a big ocean,” says MAPRU head Professor Pierre Pistorius, of the Department of Zoology, who co-led the recently published paper based on 11-years of data collected between 2010 and 2021.
“Prey is limited and patchily distributed (and there are also) global changes, such as climate change and human exploitation in the form of fisheries.
“Finding (food) resources that are scattered beyond direct perception range is a key constraint in the ecology and evolution of many wide-ranging animals.”
For more than a decade, Prof Pistorius and his group tracked Cape gannets breeding on Bird Island in Algoa Bay, home to around 95 000 breeding pairs. Using GPS tracking data, they uncovered a fascinating pattern: the birds rely on both past experiences and visual cues from other animals to decide where to hunt.
EDUCATION IN ACTION: Professor Pierre Pistorius training post-graduate students working on collecting tracking data used in the study of Cape gannets on Bird Island in Algoa Bay, Gqeberha, South Africa. Picture: Pierre Pistorius
The findings, published in the international journal Proceedings of the Royal Society in February this year, challenge previous assumptions that seabirds primarily depend on either social cues or memory.
“Until they directly perceive resources of interest, animals should follow some rules and/or cognitively process information about where their resources are likely to be found and how they should move to find them.”
Using Cape gannets as a subject, the study set out to investigate exactly how marine predators find food resources beyond spotting them visually.
MAPRU researchers collaborated with international colleagues from France’s Centre d’Etudes Biologiques, La Rochelle Université, Institut des Neurosciences Paris-Saclay, Université Paris-Saclay and Institut de Recherche pour le Développement, University of Montpellier in studying the birds.
Sentinels of the sea
Cape gannets are well-known for their dramatic hunting behaviour, often seen plunging into the ocean in large groups to catch fish.
The charismatic Cape gannet dives for a meal. Picture: Lloyd Edwards
But while earlier research by the research team demonstrated that they follow other birds and marine animals to locate prey, and don’t necessarily directly look for prey themselves, this study reveals a more complex strategy at play.
The birds feed predominantly on sardine and anchovy – school fish with a typically patchy, rather than even, distribution.
“Scientists have studied them more than any other seabird to document how they widely observe and copy each other to decide where to forage at sea,” says lead author Julien Collet, a recent post-doctoral student in Prof Pistorius’s research group.
“Here, we show that these birds also rely on ‘private information,’ presumably personal memory, but updated frequently so that after about ten days, the memory effect is no longer detected.”
This discovery suggests that Cape gannets aren’t just reacting to immediate social signals but are also recalling past experiences of where they successfully found food. The combination of both strategies helps them adapt to shifting food availability in a rapidly changing marine environment.
Studying them could reveal previously unknown foraging behaviours in other marine predators, including seals, sharks and dolphins.
Cape gannets foraging. Picture: Lloyd Edwards
Why this matters for conservation
Understanding how marine predators find food is critical for conservation, particularly in a world where human activity is reshaping ocean ecosystems. One major risk is the creation of “ecological traps,” where birds continue to return to previously rich feeding grounds that are now depleted due to climate change or overfishing.
“An ecological trap is when there used to be abundant prey in a specific area, but not anymore; and so, birds still go to these areas, but without much success,” explains Prof Pistorius.
Rapid changes in prey distribution and location can be influenced by shifts in oceanographic conditions and human fishing activities, he says.
By identifying how predators adapt their search strategies, scientists can better predict how they will respond to environmental changes and implement more effective marine protection measures.
Ongoing research at MAPRU will continue tracking Cape gannets to assess their responses to these shifts and explore the benefits of marine protected areas.
The bigger picture
By combining memory with social cues, these animals demonstrate an impressive level of adaptability—one that could inform future conservation efforts and deepen our understanding of life in the ocean.
How marine predators find prey in such a vast ocean landscape has always intrigued researchers, says Prof Pistorius.
“Previous research on Cape gannets demonstrated that, while foraging, gannets don’t look for fish but rather use other gannets – and other predators – to find this prey. Current research demonstrates that, although this is true, they also use memory in a complex strategy, and that these two mechanisms are not mutually exclusive.”
The study has uncovered that, contrary to widely-accepted theories, foraging seabirds are not directly looking for prey, but rather search for indicators of its presence, with movement patterns of foraging seabirds being heavily driven by processes that are unobservable with conventional methodology, he says.
Researchers found that the birds’ personal memory was updated frequently in response to changing prey distribution.
“It’s important to understand how they find food, as this enables better management of the species and the ecosystem.”
The science behind their search
The study examined how Cape gannets navigate the vast ocean, testing three key foraging strategies used by marine predators:
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Random opportunistic searching—roaming until they find food
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Following conspicuous social cues—tracking other predators
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Long-term attachment to reliable feeding grounds—returning to known hotspots.
The results indicate that Cape gannets use an updated memory system, rather than long-term site fidelity. The birds adjusted their search areas every few days (in combination with using social cues), suggesting they continually re-evaluate where food is most likely to be found.
This ability to combine social information with short-term memory gives them a survivaladvantage in unpredictable ocean conditions.