With snow on the ground, it becomes evident that the urine of Eastern Cottontails, New England Cottontails and Snowshoe Hares is occasionally colored red or blue! This is not indicative of disease — it is a result of their diet.
Phytochemicals are responsible for this oddity. Plants contain compounds that contribute to the plants’ color, taste and smell. When the plants are eaten by a rabbit or hare, these compounds pass through the animal’s system and come out in its urine, affecting the urine’s color. I am not aware of which plants produce the more commonly seen red urine, but compounds in the twigs and bark (the fruit is not often eaten by hares and rabbits) of the invasive European Buckthorn (Rhamnus cathartica) can turn rabbit and hare urine blue. (Initially the urine is yellow, but after about ten minutes’ exposure to the sun, it turns blue.)
As winter progresses, your chances of seeing blue urine increase, as much of the easily accessible nutritious food has been harvested and rabbits and hares resort to eating the less desirable twigs and bark of European Buckthorn. (Photo: Snowshoe Hare tracks and urine)
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