This is interesting, and has to do with the basic "plumbing" of animals. Humans and many other animals have separate solid and liquid waste. Solid waste is the unprocessed remains of food through the digestive tract. Liquid waste, or urine, is waste that has been filtered out of the blood to regulate the chemicals that are in blood and keep you healthy. These two separate sources mean that there is no "separation" of liquid and solid waste, since they come from different places anyway, and it makes good sense that they leave the body separately.

Now that we know about people plumbing, do birds urinate? The answer is yes and no. In birds, both liquid and solid waste leave the cloaca (located on the butt). Birds have a urinary tract, but it is combined with solid waste before being released. So, birds urinate, but it is mixed with solid waste and removed at the same time. Having only one system for releasing weight may make birds lighter, and make flying easier.

That's a great question! Birds don't urinate. Flying requires a lot of energy, so birds have evolved to be as light as possible. Having urine means holding water, which is heavy, and makes flying more difficult. It doesn't make sense to carry around all that extra weight of water. Instead birds get rid of their waste through their poop. Urine in humans and other mammals contains urea, which is how we get rid of nitrogen in the body. Birds also need to get rid of nitrogen, so instead of urea, they make uric acid, which they get rid of in their poop. It takes a lot more energy to make uric acid than urea (which is why mammals don't make it), but it requires much less energy than trying to fly with all the extra water. The uric acid is slightly corrosive, which is why you should immediately clean bird poop off your car!

Sort of. Birds excrete urea, which is the main chemical in urine, but they suck the water out of it, so they excrete it as a solid instead of as a liquid.

Yes, they do urinate, but it is much different than how humans urinate.

In humans, waste flows into tubes called ureters and is then carried into the bladder for storage or release. We produce urine which contains salts and other materials our bodies don't need. Some of those materials are uric acid and urea which are toxic to our bodies. We have two openings to get rid of waste: one for fluid waste and one for solid waste.

Now, birds only have one opening to get rid of their waste and they do not have a bladder. Their opening is called a cloaca; this is where their waste and eggs with baby birds come out from. They absorb a lot of the water back from their waste so their "urine" containing uric acid comes out in a white crystalline form with their feces.

Birds actually combine their solid and liquid waste into a white paste with varying amount of green/brown color. The white part is mainly comprised of uric acid and the green/brownish parts are comprised of fecal matter.