Sucklebirds: Brood Parasitism Gone Too Far

Sucklebird chick art done by Tortoiseman on reddit

Sucklebirds (family musavemidae, mouse bird) a strange and horrifying family of birds that make it their job to be as unbirdlike as possible until the time is right. Instead of being brood parasites to other birds, these birds take advantage of bats. These brood parasites are found throughout North Asia.

Evolution

Sucklebirds are descended from Great Tits. When the holocene extinction hit and trees disappeared in siberia, the birds started to nest in the mouths of the newly formed caves, which was also home to bats. The birds were already somewhat tolerant to lactose due to their love of cream from milk bottles and built up a complete immunity to lactose from chicks  drinking the milk from resting bats when food was scarce. As time went on the parents started to become less and less involved with their chicks and let the bats feed and care for them. To blend in with the bats while growing so that they didn't get found out and kicked out,   they developed a lot of traits to look like a bat.

Biology

Adult sucklebirds are fairly unremarkable, the chicks however, are very strange.

Chicks feed off of milk until their ready to leave the bat colony, but obviously birds dont suckle, so the sucklebird chicks have a piston-like tongue to drink milk. 

There are other batlike attributes as well. Sucklebird chicks have 2 small triangular shaped feathers facing upwards in order to look like the bird has bat ears. There is also a cere covering the outside of the beak that looks like a bat snout. Lastly the wing feathers are completely black other than 3 brown feathers that make it look like the bird has bat wings. The last and most important adaptation is the prescence of a keratin thumb spike on the first digit to allow the bird to move like a bat and hang on while nesting in the mouth of the cave.

Once the sucklebird hits maturity. It will lose its batlike adaptations and become a normal generalist passerine.

Behavior

As stated earlier, sucklebirds are brood parasites, however, they don't lay their eggs in the bat colonies. They first build their nests and allow their young to hatch. The young are covered in tiny hairs upon hatching and are practically indistinguishable from newborn bats from afar. The mother will then pick the hatchling up with her beak and drop it off in a bat colony. The hatchling will then "remove" a baby bat and replace it. Once the bird hits maturity and leaves after a month, it will mate and repeat the cycle.

If the bat colony finds out about the chicks, they will be killed. This rarely ever happens since the chicks parents will attack the bats if their young are killed so the bats are practically forced to take care of the chicks if they don't figure out they're being tricked.

The species of sucklebird depends on the species of bat that it tricks into raising its children.