That was the first time dialects were documented in a nonhuman mammal. Fifty years later, however, those dialects are lost.

Half a century ago, Le Boeuf and his colleagues were documenting the size of the elephant-seal population, which had shrunk to almost nothing during the 19th century. The population now counts more than 210,000 individuals, three times as many as in 1969. Such a dramatic expansion, after the species had been so close to extinction, might have affected how these males talk to one another.

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Little is known about the abundance of northern elephant seals prior to 1840. “There were apparently quite a lot of them,” A. Rus Hoelzel from Durham University told me, but “then they were noticed as a nice resource for oil.” As with other seals and whales, they were hunted for their blubber. The oil obtained from this thick layer under the skin served as fuel for lamps or was used to make soap. A single large male could provide up to 210 gallons of oil.

By 1850, northern elephant seals were scarce. Two decades later, individuals were barely seen, even on Isla Guadalupe, a volcanic, somewhat lonely island in the northwest region of Mexico, where most of the seals had escaped from poachers. It is, even today, not easily reached. But the remoteness of the place did not discourage collectors, whose interest in the species increased as the seals became rarer.

“They were keen to get samples,” Hoelzel said, adding that “1892 was probably the nadir.” That year, an expedition to Isla Guadalupe found nine individuals: a surprise, given that the seals were presumably extinct. The collectors killed seven of them for the Smithsonian’s museum collection. Decades later, Alfred W. Anthony, who had been part of the team, argued that this type of action was “considered justifiable at the time, as the species was considered doomed to extinction … and few, if any, specimens were to be found in the museums of North America.”

By the turn of the century, the population had been driven down to a tiny number—maybe 100 individuals, perhaps even fewer than 20. All the northern elephant seals that exist today are descendants of the small herd that survived on Isla Guadalupe.

The first decades of the 20th century proved to be kinder to the species, and in September 1922, the Mexican government sent a patrol boat to Isla Guadalupe “to post a large sign in both Spanish and English, informing those that might land at that point that a heavy penalty followed the killing or capture of any elephant seals,” Anthony wrote. A month later, the island was declared a biological reserve. The number of northern elephant seals has only increased since then.

As that tiny population grew, northern elephant seals started to recolonize former breeding locations. It was precisely on the more recently colonized islands where Le Boeuf found that the tempos of the male vocal displays showed stronger differences to the ones from Isla Guadalupe, the founder colony.