Male Australian sea lions aggressively defend groups of females during the breeding season, using unique vocalizations—a series of sharp barks—to ward off rival males. Their breeding cycle is unusual, spanning over 17 months rather than occurring annually, and it’s not synchronized across colonies, meaning each breeding colony has its own schedule.
For my honours project, I set out to investigate whether mate-guarding males can recognise and respond differently to the calls of local males from their own colony versus those of foreign males from distant colonies.
Research Approach: The Playback Experiment
To test this, I conducted a playback experiment where I recorded the calls of males from two colonies: one local and one located 180 km away. I then played these recordings to males actively guarding their groups of females, carefully recording their behavioural responses to each type of call.
Findings
What did I discover? Male sea lions were indeed able to differentiate between the calls of local and foreign males. They based this recognition on differences in call characteristics, such as the duration of each bark, the time between barks, and pitch. This was the first study to demonstrate geographic discrimination in the vocalizations of sea lion colonies.
Interestingly, males responded more aggressively and swiftly to the calls of local males, suggesting that males from the same colony are seen as a greater threat and more likely to compete for access to females.
Listen to a male Australian sea lion’s barking call here.
An Unforgettable Fieldwork Experience
For this research, I traveled with two students to a remote, uninhabited island off the coast of South Australia called Lewis Island. We spent six weeks there, bringing only essential items: large cartons of water, food, and a single camping backpack each for our clothes, medical supplies, books, and laptops.
Each morning, we scouted the island’s perimeter, recording any newly arrived males and counting the number of females in each guarded group, or “harem.” One part of the island featured a steep, gorge-like area guarded by an especially territorial male we nicknamed “Bull’s Eye.” Unlike most males, who stay close to their harem, Bull’s Eye would chase us over long distances, making him quite the character to avoid.
How We Recorded the Calls
With the males being so aggressive, recording their calls was no small feat! Our method required teamwork and precise timing: one person would approach the harem to draw the male’s attention. As he barked and moved toward the intruder, I would quietly position myself, microphone extended, to capture his vocalisations. We learned quickly that most males wouldn’t go more than 20 meters from their females, so we had to stay alert and react quickly to capture the recordings safely.
Marie Attard 