Dr. Isis responded by asking if turkeys can pee. So today's post addresses bird urine and a bit of embryology.
Normal Human Urogenital Development
Studying human embryology makes one wonder how any of us come out normal. So many things can go wrong as all of these cells divide and migrate and die.
Initially the urinary tract, genital tract, and gastrointestinal tract all empty into a common opening called the cloaca.
In the later part of development, cells must migrate to form "walls" between various structures in humans, giving us the 2 or 3 openings expected. Sometimes this process goes wrong, and babies may be born with a persistent cloaca.
Bird Urogenital Systems
Birds skip this division of openings; their urinary, genital, and gastrointestinal tracts open into a cloaca that then exits the body. Birds also maintain internal gonads; in the absence of sex differences in plumage, it can be very difficult to tell a boy bird from a girl bird, short of surgery to examine the internal glands. Birds thus empty both urine and feces into this common pouch which exits the body via a single opening or vent (which is also used for sex).
Anatomy of Bird Droppings
When birds empty the cloaca, they both poop and pee. The dark portion of the dropping is fecal material which reflects the bird's diet. Clear urine evaporates quickly; bird owners may collect droppings on blotting paper to evaluate the volume of urine, as shown in the figure. The white material in droppings is composed of urates. Birds and some reptiles excrete these crystals in the feces rather than in urine via a process that allows maximal water conservation.
The Answer Is...
Our feathered friends do have kidneys and make urine. We just may not perceive it because they always do #1 and #2 simultaneously and the poop lasts longer than the pee.