Reading about porcupine courtship made me think about how other animals use this metabolic waste product. Urine is an excellent vector for delivering scents and hormones that are signals involved with courtship (as in porcupines) and territorial defense. Many mammals, as well as some fishes and invertebrates, makes use of this convenient and readily available delivery system for olfactory communication.
We are all familiar with domestic dogs lifting a leg to urinate on a tree or fencepost. Such scent marks are sniffed by other dogs, who can learn the identity of the mark maker from the unique mix of scents, and often leave their own marks atop the original one. We sorry humans, with our relatively poor sense of smell, sometimes have a hard time imagining the scented world of dogs and many other animals, but these other beasts can identify individuals, as well as sexual and social status, from scent marks.
Both members of the dominant pair in a pack of wolves use urine to scent-mark the borders of their territory; newly formed pairs superimpose urine-borne scent marks on each other’s previous marks, probably as a part of courtship. Territorial borders marked with urine deposits are a regular feature of behavior in a variety of mammals, including coyotes and tigers. Beaver families make small, black piles of debris marked with urine and anal gland secretions to establish claims to particular waterways; other beavers are thus given notice that the place is occupied.
Males of many ungulates (such as moose, bison) either urinate over their own legs or wallow in urine-soaked dirt as a way of chemically signaling their status. Stallions urinate on established dung piles to advertise their dominant status. Male elephants and giraffes actually taste a few drops of female urine to detect hormones that signal readiness (or not) to mate. Female crayfish and swordfish send out a chemical signal via urine to attract willing males. Urine is used for certain forms of chemical communication among individuals of some species of primates (the taxonomic group to which humans belong).
Human campers sometimes urinate all around a camp site in hopes of deterring unwelcome four-footed visitors (although I don’t think the efficacy of this boundary marking has been fully determined), but human uses of urine go way beyond simple boundary marks. In the course of history, urine has been used in several inventive ways. Perhaps best known are the roles of urine in tanning hides and as a mordant to bind dyes to cloth. In sixteenth century England, whole casks of urine were shipped across the country for use in the dye industry.
The ammonia in urine can cut dirt and grease, and so it has been used as a cleaner. Even after soap became available, urine from chamber pots was used as a household stain-remover. In ancient Rome, urine collected from public urinals was hauled to laundries, diluted with water, and poured over dirty clothes in a tub; a person then stood in the tub and stomped on the wet pile to thoroughly mix the cleaner with the dirty clothes. Commercial persons who made a business of collecting and selling vats of urine were even subject to Roman taxes.
A traditional Scottish way to treat woven wool was to soak a length of the cloth in household urine to clean it and set the dye, and then pound it on a board. The process is called ‘waulking’ and still continues in the Hebrides (and in Nova Scotia by descendants of Scottish emigrants) as a cultural celebration.
Urine has been used as a tooth-whitener and for making gun-powder. Hormones extracted from pregnant mare’s urine are one way of treating fertility and menopausal problems. More recently, stem cells extracted from urine have been re-programmed to grow new nerves and other tissues. Many other medical applications are part of folklore, and indeed may be efficacious, but they could use verification by scientific study.
Very versatile stuff!