I assume you speak of the “croppers”? I actually had the same question, myself, when I started writing about fancies.

All pigeons inflate their crops (a sac-type structure in the throat) when they’re strutting in front of potential mates/rivals. In most pigeons, the crop is proportionate, and while you can obviously tell they’re “puffing out their chest” when they inflate it, it doesn’t look all that weird.

To develop the pouter/cropper class of pigeons, birds that loved to “puff up” in play, as well as those who had the largest crops were selected to breed. Over the decades it got pretty ridiculous. For the most part, a well-bred cropper is tall and balanced, but the thing is…most of them aren’t so well-bred? So while most of them possess the big crops and the desire/need to inflate them frequently, not all of them are actually balanced that well.

Here are some German croppers, some strutting, some not.

The Norwich cropper is one of the more extreme breeds.

And the Holle cropper takes the group standard in an entirely different direction.

Just like dogs and cats, ornamental/”pet” pigeons are prone to a lot of problems and complications because of their deformities.

They’re incredibly hardy birds, and I would expect that most of the birds that I posted (which would have conformed to late-19th century breed standards) to be able to function at least decently. Some of them would have trouble, but not the trouble we run into today.

Today, many of the “short-faced” breeds have beaks so short they can’t even feed their own young, which have to be hand-raised. The classes with feathered feet have such extensive feathering that ulceration is common when an owner assumes that the bird only needs as much care as a normal pigeon (they need to be cleaned and too-long feathers must be clipped…the latter of which is something show pigeons rarely have done). The exhibition fantails can hardly fly, and both the fantail and frillback birds lack protection from cold and water.

There’s far too much extremism in physical form going on today, but as breeds like the Archangel (below) show, you can be freaking *amazing* looking without being completely deformed. Just like today’s “show-quality” french bulldogs, basset hounds, and shar-peis are a far cry from the lovely form they were 100 years ago, pigeons have likewise been modified.

There are many lovely pigeon breeds, and a couple organizations that seek to bring very cool-looking breeds back to their “original” breed standard, so that they can survive as a happy and healthy pigeon, in a normal dovecote. But some are just way too crazy about accentuating and pushing the extremest, most-crazy-looking birds out there.

Pigeons are cool birds. They have taken well to domestication (and it’s posited that, like cats, they “domesticated” themselves, because of the benefit to their own kind). We don’t need to make complete freaks out of already-fascinating creatures.

"Useless" is a bit of an arbitrary judgement, especially when it comes to evolution - all "advanced" species have "useless" remnants from their eons of change, as well as having incredibly specialized and well-adapted traits and anatomical features.

The problem with giant pandas, is that they're incredibly specialized, and fill a very specific niche in the environment (mass consumers of bamboo forest) - they're as specialized as the koalas of Australia (consuming Eucalypts) and the sloths of South America, but WAY bigger, and much less inclined to reproduce. Even in the wild, when two compatible individuals run into each other (or find each other) during a female's heat, there have been observed instances where they just chill together for a while, "mate" (without penetration), and go their separate ways - unlike other species where mating is occasionally unsuccessful from the male end, there are rarely more than two attempts to mate by the male, and as such, birth rates in the wild are almost as low as non-IVF reproduction rates in captivity.

For what it's worth, I'm not crazy about spending over a hundred million US dollars (by all countries, mind you, not just the US) preserving a species that cant be bothered to get their shag on every once in a while. Habitat preservation is one thing, the active attempt at restoration of former population levels while the species has no interest in doing the sex thing in the wild is another.

Yes, humans led to their decline in the first place. But by committing ourselves to this cause, we're getting ourselves into a whole incredibly expensive mess regarding a species that's not considered ecologically necessary, in the mountainous bamboo forest habitat, while ignoring some of the less-cute, VERY necessary organisms that we're causing the extinction of just as quickly, like the frogs of Central America and many of the accidentally-caught fish and crustaceans of the ocean.