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Animal migrations are some of the most spectacular events on the planet.
From monarch butterflies collecting in huge droves as
they rest along their journey, to arctic terns, which travel
an impressive 40,000 kilometers or more.
But imagine traveling all that way, through potentially
dangerous seas, all while heavily pregnant.
So pregnant, in fact, that you’re giving birth in mere
days after arriving home, but you can make it just in
time thanks to your…GPS?
*That’s the story of female northern elephant seals.
Now, these animals are already pretty remarkable, from the noses they're named for to the fact
that they're the only known animal that makes two
migrations in a year.
*These pregnant elephant seals make their first
migration by swimming some 10,000 kilometers across the Eastern North Pacific Ocean, hunting
for food, before turning around and swimming through their second migration back to their
breeding beaches to give birth.
And those births almost always happen five days after returning.
There’s even been at least one recorded case
of a seal giving birth the night she arrived back.
So, knowing their way back is pretty important since future generations depend on it.
But how northern elephant seals decide when to U-turn
to make it just in time remained a mystery.
In February of 2022, researchers published some potential answers in the journal Current
Biology.
They thought maybe the animals have a kind of
internal map that tells them how far they’ve traveled, since that’s what other migrating
animals, like birds, have.
And researchers found something along those lines,
when the seals turned around had nothing to do with
how much body fat they had stored up.
See, the whole reason females spend all that time at
sea is to eat enough to get them through the next five
or so weeks on land.
That’s because females give birth, nurse their pups,
and mate again, all without eating.
So those fat reserves become pretty important.
The researchers’ other hypothesis was that maybe
seals who had had a good hunting season, and stored up enough fat, would head back earlier
once they were full.
So they tracked around a hundred female northern elephant seals to see when they returned home.
And it turns out the timing of the turnaround depended on how far away from the beach
the seals foraged.
If the seals started their foraging further away,
they’d start heading back to shore earlier than
seals who were foraging closer to the breeding beach.
By the end of the sea trip, female northern elephant seals ended up back at their breeding
beaches in waves.
So, it seems that northern elephant seal females have a kind of inbuilt map or GPS that tells
them, “Oh, it’ll take you this long to get back,
so better turn around now.”
It’s unclear, though, whether what’s guiding the
females is also guiding the males.
Because males are also out foraging in a totally different part of the ocean compared to females,
but they also manage to come back earlier to await
the females and stake their claim of who to breed with.
What’s also still unclear is what exactly is telling
the seals where they are relative to the beach.
Basically, what’s giving them their coordinates?
Researchers think it could be the Earth’s geomagnetic
field or the position of the stars.
Because other migratory animals have receptors that are able to sense Earth’s magnetic
field and they can use those receptors as a compass
to see where they need to go.
We have a whole video about how monarch butterflies use it for their long migrations.
So the next step for the researchers is to figure out
if that's how the seal’s GPS also works and what
environmental cues are important to them when it
comes to navigating.
And understanding northern elephant seals’ amazing
navigation abilities could help researchers better
understand other amazing animal migrations.
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