Visit any town or city, and you’re likely to see them everywhere; pigeons, those most ubiquitous of urban birds.

Those grey, white, black and brown-feathered friends that sit or walk, bobbing their heads, on pavements, walls, parapets and buildings cooing sweetly, raining down their excrement and odd feather.

In prehistorical times, baby pigeons were often seen, and on the menu

But there is something odd about pigeons. We see them old and hobbling, mature and wise, young and a little foolish, playing a game of proverbial chicken with the oncoming traffic. Yet we never see their babies.

Which, given the abundance of pigeons, begs the question why?

We asked you, our audience, on social media for your thoughts. We also did a little research ourselves. And here’s what we discovered.

“The more affluent pigeon parents tend to rent high-end private maternity coops to give birth,” suggests Thomas Keith.

Fledgling pigeons are everywhere, but they are not easy to identify

It’s a nice idea. But as Jennifer Austin, Kelly Mahan and others are correct to point out, the answer is rooted in the origin of the pigeon itself.

Feral pigeons – the ones we see in our cities – are descended from rock doves, and remain essentially the same bird. Their tastes might be a little more cosmopolitan, but when it comes to reproduction they still take after their wild rock dove ancestors, which are very secretive when it comes to situating their nests.

The rock dove Columbia liva likes to construct its nest on the ledges on cliff faces. “In its natural and wild state,” we are told by William Yarrell in A History of British Birds, the rock dove “inhabits high rocks near the sea-coast, in the cavities of which it lives the greater part of the year.”

On the island of Orkney, in Scotland, UK, for example, 19th Century ornithologists observed that the rock dove “is very numerous, breeding in the crevices of the rocks, but the nests are placed at such a depth that it is impossible to reach them.”

When squabs finally fly the nest they are fully grown

Over on the neighboring Scottish island of Shetland, others noted rock doves occupying “deep subterranean caverns, the mouths of which are open to the sea.”

Way back when humans spent more time hanging in and around caves, nobody would have batted an eyelid at the sight of a baby pigeon, often called a squab.

In fact, the excavation of a cave in Gibraltar reveals that Neanderthals were keen on eating pigeons before modern humans even reached Europe. Much later, after Neanderthals had vanished and Homo sapiens took over this same site, they too were dining out on pigeon flesh. In prehistorical times then, it’s likely that baby pigeons, or squab, were not only often seen, but often on the menu.

But today, with an absence of edgy cliffs, rocky crags and dingy caves in our cities, the feral pigeon must make do, constructing its nest in whatever out-of-the-way, covered spots it can find, such as church towers, abandoned buildings or beneath bridges.

Alison Goggin has only ever seen baby pigeons once, “in a crack in the stone stairs” at Carmarthen Castle in Wales. “Maybe they like the security of out of the way places where they’re difficult to see and get to,” she suggested on the BBC Earth Facebook page.

Since we don’t often enter such spaces, we don’t often get to see the contents of a pigeon’s nest.

You never know, when you look at a pigeon it might be a baby in disguise

Perhaps this is just as well. As Sarah Rochelle politely puts it, “They are butt ugly.”

What about young pigeons that have recently fledged? Surely we see these?

Well, yes. Fledgling pigeons are everywhere, but they are not easy to identify, as many of you appreciated. This is largely down to the fact that squabs, as if ashamed of their appearance, stay in the nest for a very long time: the nestling period from hatching to fledging typically lasts more than 40 days, roughly twice that of most garden birds.

During this time, the parents feed their chicks with a regurgitated “crop milk” rich in protein and fat. So when squabs finally fly the nest they are fully grown and virtually indistinguishable from adults.

With a keen eye, however, it is possible to spot a fledged but still-juvenile pigeon.

I left so that its parents could take over the baby sitting

It won’t have the shimmery greens and purples around its neck and the cere – that wattly growth that sits on top of the bill – will be a pinky grey rather than bright white as it is in adults.

“You never know, when you look at a pigeon sitting on a window sill or under a park bench, it might only be a baby in disguise,” writes Brian Waas.

In spite of the rarity of sighting a baby pigeon, many of you have been lucky.

Gwen Obertuck’s sister, for instance, had a pair of pigeons nesting on her balcony in Germany. Amy Dunkley got to watch the entire pigeon life cycle from her bedroom window. “It was wonderful,” she says.

The big window ledges outside one of the libraries at the University of Texas in Austin are perfect for nesting pigeons, notes Toni Salazar Loftin. And only last month, Judi Mcintosh encountered a baby pigeon – “half feathered and half fluffy” – en route to the compost heap at the bottom of her garden in Hampshire, UK.

“We had a quiet chat and then I left so that its parents could take over the baby sitting,” she writes. “It was gone when I went back hours later so hope all was well.”