Birds Make Their Own Milk, And It's Gross
On the second day of Christmas, my true love gave to me
Two turtle doves ...
Unlike some bird gifts that come up later in "The 12 Days of Christmas," two turtle doves kind of make sense as a present from your true love. Turtle doves (named because they make a "tur-tur" sound) have been a symbol of love since biblical times. If someone gave you two of them, that's probably because they're mates who've paired for life.
Those two turtle doves might instead be siblings. Two is the maximum number of chicks in a turtle dove nest, one for each parent. Because if there are more than two, the parents can't produce enough milk for all of them.
That's right: Birds make milk. Not all birds, but members of the pigeon family like turtle doves, and also flamingos and some penguins. They don't squirt it out of nipples, since only mammals have mammaries. But we call the stuff milk, and they make it in the crop, a sort of second stomach that generally just stores food before digestion.
So if you see a pigeon coughing up something into a baby pigeon's mouth, then 1) congratulations, many people go their whole lives without seeing a baby pigeon, and 2) that’s crop milk. They aren't vomiting, which is how some other birds feed their young. The crop milk (made by both male and female birds) consists of just their own secretions and also a fair number of living cells. The result actually smells even worse than vomit, thanks to all the bacteria in there, which is why we've yet to package and market bird milk as an all-natural substitute for oat and almond milk.
Turtle dove milk is still less disgusting than flamingo milk. Flamingo milk is pink. "Hey, that's not disgusting at all," some would say. "It's probably strawberry-flavored. Or, it's pink because flamingos are pink, duh." But no: Flamingos are pink thanks to the carotenoid pigment that's in a lot of stuff they eat, while their crop milk is pink because it's got so many red blood cells mixed in there. We mammals may all be little cannibals thanks to our diet of breastmilk, but birds are cannibals and vampires.