Of all the small mysteries of avian life, I've spent most of my time wondering about why I've never seen a baby pigeon. But there is an equally important mystery of the bird lifecycle that I'd never paused to consider: given that eggs are fairly large, oblong objects, is it possible to see a bird with a baby/egg bump?

The answer is yes.

The world now has a clear image of a flying bird about to lay an egg, thanks to scientists studying the endangered Mascarene petrel near the island of Réunion in the Indian Ocean, east of Madagascar. The work was revealed in the latest issue of the Bulletin of the British Ornithologists' Club.

The lead author on the paper, Hadoram Shirihai, recounted the adventure to the conservation non-profit, BirdLife International. "I spotted a petrel through my camera's viewfinder. 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,'" he said. "She flew close to the boat which gave me the unique chance to photograph her just before the sun set. It was a magical moment, 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."

There was good reason to be excited. Taking a photograph of a bird with a visible egg bump is rare. BirdLife International believes it to be "the first record of any bird photographed in flight with an obvious egg inside the body."