Social behaviour research asks how Galápagos cetaceans organize themselves — who travels with whom, how long bonds last, and how groups coordinate to hunt. Most of what's known comes from killer whales, the best-studied species here, tracked through years of photographs rather than direct observation of vocal communication. These patterns reveal how resilient a small, tightly bonded population really is.

A small population that depends on specific individuals and tight bonds to hunt cooperatively is more fragile than it looks. If key individuals are lost, the groups that rely on them to take down large prey — or to pass on hunting knowledge — could be disrupted. Understanding social structure shows exactly how resilient this population really is.

• Galápagos killer whales live in fission-fusion societies — small subunits merge into larger pods, and different pods associate and fuse depending on circumstances (Denkinger et al., 2020).

• Most sightings are of small groups: pairs (21%), triads (19%), or singletons (17%); the average group size is 4 animals.

• Groups of 7 or more individuals occurred in 12% of sightings, with a maximum of 15 animals recorded on two occasions.

• Social network analysis of 18 resident individuals identified three distinct associated units, plus one looser association of 6 whales (1 male, 5 females or juveniles); one individual showed no strong ties to any group.

• Bonds between individuals are long-lasting, averaging 5.8 years, with some pairs — including two males — staying associated for 5 or more years.

• Groups temporarily merge into much larger hunting parties (5–10 or more animals) specifically to take on large prey like Bryde's whales or sperm whales.

• Fusion isn't only about big prey: one local killer whale joined nonlocal individuals to feed on sea turtles at Kicker Rock, showing flexible, situational associations.

• Feeding (54%) and traveling (27%) are the most commonly recorded behaviours across all Galápagos cetaceans; bow riding (12%) is mostly seen in bottlenose dolphins (Alarcón-Ruales et al., 2023).

• Hunting/harassing behaviour was recorded exclusively in killer whales among all Galápagos cetaceans, at 1% of all described behaviour.

• Mating or nursing behaviour is rarely documented (1% of sightings), mostly in humpback and Bryde's whales travelling with a calf.

• The local killer whale population is male-biased (38%), an unusually high ratio compared to most other studied populations worldwide.

Complex, long-lasting bonds mean this is not a loose collection of individuals but a small, interdependent population — losing even a few whales to bycatch or vessel strikes could break apart the cooperative groups needed to hunt large prey. Mapping which pods fuse together, and when, also helps predict where and when large gatherings will occur, informing seasonal protections. Over time, tracking this social network gives researchers an early warning system: a fraying network can signal population stress before a decline in numbers becomes obvious.

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