A springtime thread: interesting things you may not know about bird reproduction
1) Only 3% of bird species have a penis. For the majority that don’t, sperm are transfer by the male and female touching their cloacas together. This is called “the cloacal kiss,” which I hate.
1) Only 3% of bird species have a penis. For the majority that don’t, sperm are transfer by the male and female touching their cloacas together. This is called “the cloacal kiss,” which I hate.
2) Birds that have penises include waterfowl, ostriches, and emus. In ducks, the penis can be extremely long and weird. In these cases the vaginas are likewise complex and weird. The reasons for this are very dark and discussed in more detail here:
3) Birds only have 1 ovary (usually on the left) and can generally lay 1 egg a day. If the strategy is to have all the eggs hatch on the same day, the female will wait until the whole clutch is laid before she starts incubating.
4) Some birds such as cowbirds and cuckoos don’t build their own nest but rather engage in nest parasitism, where they lay their eggs in the nest’s of other birds.
5) This works because most host targets can’t recognize the presence of additional or unusual looking eggs as strange. (📸 Ted Kinsman) 
6) That’s not always true though. There’s evidence that Eurasian magpies can tell when they been parasitized by great spotted cuckoos, but keep the eggs so the cuckoos don’t destroy their nests.
7) Some birds can build their own nests but still lay eggs in the nests of other birds. This is called egg dumping and occurs among waterfowl, turkeys, coots, starlings, and others. Coots try and prevent dumping by recognizing and keeping track of how many eggs they have.
8) Another strategy is to let microbes do the incubating for you by laying in huge compost mounds, like the megapodes do. The male Australian brushturkeys uses his beak like a thermometer and will add or take away material as needed to maintain the correct temp. (📸 Ian Davies)
9) Some birds hatch blind & naked, while others hatch sighted, covered in down & ready to leave the nest w/in a few hours. To facilitate the exit from the egg, chicks have a white “egg tooth” on their bill that allows them to bust out. This will later fall off. (📸 IWS)
10) Magapode birds like the brushturkey mentioned earlier, are so well developed though that they can kick their way out of the egg, and will be capable of flying within a few hours. (Maleo chick; 📸 Sam Woods)
11) As chicks, hoatzins are the only living birds that have functional claws on their wings. They use them for generally clambering around the rainforest canopy, and to climb back up trees if they end up on the ground.
12) To trigger feeding by parents, bb birds can have very flashy mouth interiors. For reasons we don’t fully understand, the mouth lining of grass finches like Gouldian finches, plum-headed finches, black-rumped waxbills, & double barred finches are BONKERS (📸 Hofmann&Scheffer)
13) Too feed their babies, flamingos and pigeons produce crop milk, a lactose-free, semi solid secretion. Because flamingos insist on being so extra, their milk is red. Cute, right?
14) The last thing I want to leave you with is that some birds leave the nest before they can fly. Please always check with a licensed rescue professional before removing baby birds from their environment. Otherwise you may accidentally abduct a kid from their busy parents.
