Female Ruby-throated Hummingbirds seem to never stop feeding, even for simple body functions. But of course, what goes in has to go out. This is especially true for hummers.
Hummingbirds are unique ‘peeers’ in the bird world. Every day, hummingbirds ingest their body weight + in nectar. That nectar is 75 – 80% water. To deal with this excess water, specialized kidneys extract and retain all of the sugar content from nectar. Excess water is expelled as urine. Making hummers one of the few bird species that actually pee! And like everything else in their lives, they do this quickly – in as little as 20 minutes after feeding! They can’t afford the energy consumption of carrying around waste. They don’t even have a bladder.
Don’t forget that hummingbirds diets consist of 60% arthropods and spiders. These foods add microscopic solid waste to the ‘pee’.
With the notable exception of Ostriches, other bird species conserve water by converting nitrogenous wastes to uric acid or guanine which is most often excreted along with feces as a gooey white paste.
But if you have ever parked you car under a mulberry tree you are aware of other possible colors.