Seabirds called prions, which mate for life, find their nests by sniffing out their smelly partners, scientists say.
Prions are strictly monogamous, although they rarely get to spend any time with their partners
The birds make their nests in deep burrows, which are very dark, so they cannot rely on any other sense to find them, Science magazine reports.
The birds also actively avoid their own smell, which could be a way of making sure they do not breed with their kin.
Although this use of smell has been observed in mammals, it has never before been seen in birds.
Antarctic prions, Pachiptila desolata, are so-called tube-nosed seabirds.
They are strictly monogamous, although they rarely get to spend any time with their partners. Instead they take it in turns to incubate eggs and find food.
"All the shared life of the birds is inside the burrow because they don't stay together at sea - they just alternate on eggs," said co-author Francesco Bonadonna, of CNRS in Montpellier, France.
Sometimes a prion will forage at sea for up to two weeks, before returning to the nest to begin a stint of incubation duty.
When they fly in from sea, they have to reliably find their own nest among a medley of other nests.
But sight is not much use because they tend to come home at night and their nests are submerged in deep burrows.
"Their burrows are underground and really, really dark," said Dr Bonadonna. "They have nothing other than odour to find their way."
Luckily, prions are rather smelly, so returning birds can locate their nests by following their partner's distinctive smell.
"We found that the birds are able to recognise their partner's odour, and we think they use this odour to recognise their burrows," said Dr Bonadonna.
Not only are the prions attracted by their mate's smell, but they actively avoid their own.
When they return from sea, they have to reliably find their own nest among a medley of other nests
At first the researchers were surprised by this, because they assumed that following its own scent might also lead it to its burrow.
But since the birds spend such a long time at sea their nests are unlikely to smell of them, the team concluded.
But why the avoidance? Dr Bonadonna thinks it is a strategy to prevent inbreeding.
He said: "To avoid mating with a bird that smells too similar is to avoid mating with a bird that is related."