Birds may be the most famous migrating animals, but they’re not the only ones, and they might not even be the most impressive. Many marine animals also make incredible migratory journeys each year, alternating between extensive foraging and returning to their original sites to breed.

Each year, after giving birth to a calf, female elephant seals undertake a trek of 10,000 kilometers over approximately 240 days to feed. Despite the great distances they travel, scientists have observed that seals successfully return home to give birth within five days of giving birth to a new pup.

In a new article published in the journal Current biologyRoxanne Beltran of the Department of Ecology and Evolutionary Biology at the University of California, Santa Cruz, and her colleagues studied elephant seals in hopes of better understanding how they accomplish this feat of planetary navigation.

The team collected data on 108 adult female elephant seals, tracking their migrations between 2004 and 2015, using sets of instruments mounted on the seals’ bodies.

“We have a long-term program run by Dan Costa at UC Santa Cruz where about 40-60 adult female seals a year are sedated on Año Nuevo beach and have instruments taped to them. Then they go on a trip, collect a lot of data and come back. Then we calm them down again, remove the instruments and upload the data,” Beltran told SYFY WIRE.

Scientific data collected has revealed that seals appear to have a robust sense of map that helps them navigate their 10,000 kilometer round trip each year. At present, it is unclear exactly how seals know where they are in relation to the breeding ground – whether they are using the earth’s magnetic field as birds do, or other cues – and it is possible that we never really know.

“That’s the million dollar question that no one has yet been able to answer,” Beltran said. “There are probably multiple signals used by animals, so there is no simple answer.”

Instead of answering how elephant seals navigate, the study sheds light on when and why individual seals make navigational decisions. It was thought that the decision to return home may have been based on foraging success. Female seals do not eat when nursing a pup and must rely on fat stores accumulated during the foraging period. Therefore, a potential explanation for the variable return times was that seals that were more successful at feeding might return home sooner.

Instead, the data revealed that return dates were strongly defined by the distance to home and the time required to get there. These decisions were made at the individual level, as the seals do not travel together or go to the same places as each other.

“Seals go to different places, but the same seal often goes to the same place year after year. There is a lot of consistency within individuals, but a lot of variability between individuals,” Beltran said. “Some seals go up to Alaska, some go to Japan, there’s probably a 20 degree difference in latitude between where they go.”

Therefore, the distance to the breeding site can vary greatly from seal to seal. Yet they all return within a week or two of each other. Whelping dates occur within a week of January 20, and female seals return to Año Nuevo with a high degree of accuracy around this date, although their return journey can take over 90 days, traveling over 150 kilometers per day.

Seals that are farther away turn home sooner than those closer to home, until they all converge on the beach to give birth to the next generation.

“How this kind of navigation ability develops when animals are young is an open question and I think we’ll learn a lot more about it in the years to come,” Beltran said.

Knowing exactly where they are on the planet and where they need to go, even months after leaving home, is an impressive ability, especially when humans regularly forget where they parked after an hour at the grocery store.