Move over Shakira and (maybe) Jennifer Aniston, there's a new celebrity baby-bumper in town ... and it's a bird. This ready-to-pop Mascarene petrel was spotted by researcher and bird photographer Hadoram Shirihai on a recent trip to study the critically endangered birds' behaviour at sea near their breeding grounds on Réunion Island.

"I spotted a petrel through my camera's viewfinder," he said in a press release. "Almost immediately I saw the outline of an egg, a huge bump at its belly. I called out to the other expedition members - 'she has an egg, she has an egg'..."

The swollen area is just above the cloaca, indicating that it is indeed an egg and not an abnormality or growth. Image: Hadoram Shirihai/Tubenoses project.

All birds lay eggs ... so why don't more bumps show up in photos? Petrels are known to produce disproportionately huge eggs and have smooth feathers that allow the bump to be seen more easily. But even when conditions are perfect, photographing one en route to lay is not an easy thing to do. 

According to Birdlife International (who partner with the IUCN to evaluate bird species), "this is thought to be the first record of any bird photographed in flight with an obvious egg inside the body."

This is also the first time this particular species has been photographed at sea – the sightings came only after meticulously mapping sea positions and attracting petrels to the boat with a specially made food lure. 

baby bump-map-2014-9-2
A map showing the landing zone (marked in yellow) for Mascarene petrels on Réunion. Image: Shirihai et al.

Past estimates suggest that 12 (or fewer) breeding pairs of Mascarene petrels exists in the wild, but this egg bump spells hope for the threatened species as it has given clues into the timing of the petrels' breeding season. The at-sea records also suggest there might be more individuals than we thought.

Knowing when petrels lay their eggs is only half the battle ... the mysterious colonies on Réunion have ensured the future of this species for now, but in order to protect them, the team first needs to pinpoint exactly where in the landing zone the birds are nesting. 

"[Taking that photograph] was a magical moment," recalled Shirihai.  " ...and to think that in less than an hour she would probably lay her egg and contribute to the future survival of this threatened species."