The many uses of urine

courtship and defense, signposts and bragging rights… and a few human uses too

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!

Parental care by males, part 2

these are not deadbeat dads!

This essay will consider male parental care in birds and mammals. Both birds and mammals evolved from reptiles, and some ancient reptiles did have parental care by at least one parent, but modern reptiles have no record of male parental care, so they will be ignored here. As is true for fishes and amphibians, the factors that govern the evolution of patterns of parental care are no doubt several and still subject to debate and future research.

Biparental care is the usual thing among birds: both parents tend the young in over ninety percent of bird species. Females often do the incubating of eggs, but her male may feed her while she does so and the males generally help feed the chicks. This is the case for American dippers, for instance; as one of my field techs said, during our intensive study of this species: there are no dead-beat dads! In fact, we even know of one hard-working dad who raised at least a few of his chicks by himself, after his mate disappeared. The emperor penguin male goes a step further: he incubates a single egg on his webbed feet while his mate goes off to sea and feed; then they both tend the chick.

In some taxonomic groups of birds, including hummingbirds and grouse, females generally do all the work while the males run off to find more females. But even in these groups, there are unusual species in which both parents provide parental care; the willow ptarmigan is a local example.

Still more unusual are avian species in which males both incubate and tend chicks by themselves. Here a few examples. Spotted sandpiper females often lay one clutch of eggs and leave it to the male to do the incubation and guarding while she proceeds to lay another clutch (with the same or a different male) that she incubates and tends; this is a pattern found in several shorebirds.

spotted-sandpiper-nest-Kathy
Spotted sandpiper nest–is this tended by the dad? Photo by Katherine Hocker

In two of the species of kiwi in New Zealand, the Australian emu, and several other species, males incubate and tend the chicks alone. The cassowaries of Australian and New Guinean rainforest also have hard-working males, who incubate the eggs for weeks and then tend the chicks for months. They are fierce defenders of their little families: One day in the Australian rainforest I encountered a cassowary family; we were all looking for fallen fruits. Imagine looking up from the forest floor and seeing a very large bird, almost as tall as you and with claws that could rip you open, glaring at you from just a few short yards away. You can bet I apologized for my presence most abjectly and discretely retreated rather quickly!

What about the mammals? Virtually by definition, females are the ones that feed the infants, and lactation is considered to be the single most expensive thing a female mammal ever does. Dependence of the infants on mother’s milk means that females are always involved in parental care, so uniparental care by males is not an option. Biparental care is not common, but males are reported to be closely involved with parental care in about five percent of all mammal species. The best known cases include carnivores and primates, but regular male care occurs in other groups too. Here are some examples:

Among the carnivores, the males of foxes and wolves regularly bring food to their young. Asian raccoon dog males participate in all forms of parental care except lactation, and also tend the female during the birth process. Male members of packs of African wild dogs bring food to lactating mothers and young pups.

Male baboons and macaques carry babies around, which may help protect the infants from predators or intruding strangers. However, this situation is more complex than that, because the male may obtain direct benefits too: a male with a baby in his arms suffers less aggression from other males and may also gain favor with the infant’s mother. And if there is a fight between males, the infants are in great danger. In some small New World primates called tamarins, including the cotton-top tamarin, males regularly carry and care for babies. Males of the endangered pied tamarin reportedly do most of the parental care except for lactation.

Wild horses and zebras live in groups, often a male’s harem of females plus foals. Males defend their foals and females from predators.

It’s a rare herbivore that helps feed the young ones, but male beaver do: they regularly help build winter caches of branches on which the whole family, but especially the still-growing young ones, feed; they also help maintain dams that make the pools that protect the lodge and facilitate transport of branches. They stay with the rest of the family in the lodge over the winter, interacting and providing body warmth. Among the smaller rodents, males of the California deer mouse reportedly brood the young, keeping them warm until they can regulate their own body temperature. Prairie vole males cache food, brood and groom the babies, and even retrieve them if they wander out of the nest.

Hunting success

… you can’t win ’em all

One day this fall I watched a juvenile great blue heron that was fishing in Steep Creek. In typical heron fashion, it stood motionless for long minutes, then quickly jabbed its long bill down into the water after some hapless little fish that passed by. When one hunting spot petered out, the bird moved over to a new perch and waited again. Altogether, it made over a dozen tries to capture a fish and succeeded about one third of the time. A success rate of about thirty-three percent is not too bad, although an adult, with more experience, would likely have done better.

Those observations got me thinking about the success of predators in general. How often are they successful in prey capture? What proportion of capture attempts is successful?

Perhaps the best-studied wild predator in North America is the wolf, so that is a good starting place. Admired for their strength and intelligence, respected for their close family life, wolves are sometimes reviled as competitors to human hunters. Just how successful are wolves, when they go hunting? I focused on wolves hunting ungulates (such as moose, deer, sheep), because that interaction has been the most studied. Wolves also eat beavers, hares, mice, and fish, of course, but there are no data available on those interactions.

Hunting success of wolves obviously varies with many factors, including prey density, wolf pack size, physical condition of the prey, snow depth, escape routes for prey, and so on. Reviewing a number of research reports, I found that, for wolves hunting moose in winter, as many as 38% of hunts might be successful, but usually fewer than 10% of hunts are successful. And captured prey is sometimes lost to scavenging ravens or bears.

It is interesting to compare those figures with those (courtesy of ADFG) for human hunters of moose. The average recorded success rate over a ten-year period for much of Southeast was less than 25% (with the notable exception of one subunit in which humans were successful 63-100% of their hunts!). To take two examples from farther north: In Kenai and Talkeetna, 10-22% of moose-hunters were successful.

It is harder the find data on the frequency of moose kills by wolves, which also varies enormously. Although wolves are capable of killing two moose in one day when hunting is easy, far more commonly there are three or four days between kills (sometimes even eleven days or more). Records for human hunters show that it often takes two to four days for a successful hunter to get a moose.

Although statistical comparisons are not feasible, the data suggest to me that human hunters often have higher success rates than wolves, when hunting moose. In addition, there are at least three salient differences between wolves and humans as predators of moose. Wolves are not constrained by regulations; in the absence of regulation, the human success rate would probably be still higher. Each human hunter generally takes only one moose per season, but of course the wolves hunt repeatedly throughout the year. Hunts by humans tend to be heavily concentrated in areas that are easy of access (around settlements, or a short boat ride from town, for example), sometimes to the point that the prey population is quite depleted in those areas. In contrast, wolf hunts are typically widely spaced, often many miles apart, as each wolf pack ranges over its large territory.

Wolves hunting deer in winter are recorded to be successful on fewer than 20% of their hunts, although occasionally they may succeed up to 50% of the time. By comparison, humans in Southeast were successful 30-71% of their hunts (in various management units), on average. For Dall sheep, wolves caught one in fewer than 33% of their hunts, and humans averaged 28-46% success. Again, the numbers suggest that humans often may be somewhat more successful than wolves.

Bald eagles are another fairly well-studied wild predator, and data are available from all over North America. There are a few reports that eagles are more successful in capturing fish than waterfowl (for instance, 90% vs 20%, respectively), but most reports do not separate the two sorts of prey or the age of the eagles. Nevertheless, when fish comprise at least 90% of prey taken, the success rates tend to be quite high, ranging from 47% to 73%. In these cases, there was no information on what species of fish were caught, and I found no data on eagles catching salmon or herring, which would be very relevant here in Southeast.

For fun: here are a few other serendipitous bits of data: Coyotes hunting snowshoe hare succeeded 28-69% of the time, compared to 20-40% for lynx hunting hare in the same area. Orcas hunting minke whales off the shores of British Columbia and Southeast Alaska were successful in four of nine observed hunts (45%); orcas hunting humpback whales in Argentina were successful 21% of the time in open water and 34% of attacks on beached whales. Great blue herons in Nova Scotia were successful in 29-100% of their strikes on fish prey.

One striking feature of such observations is that hunting success for any species varies enormously, which must have huge consequences for the predators. I did not find information on how much energy is expended on a hunt (and perhaps how much energy is spent defending the catch from competitors) compared to how much each predator gains by eating the captured prey. Some times or places might make it easy to obtain the energy needed for daily maintenance and for reproduction. But many predators must sometimes be close to starvation, and thus be faced with the hard choice of whether to hunt harder or to rest in order to conserve energy. The critical importance of getting enough food is one reason that juvenile animals commonly have a high mortality rate, before they learn to become proficient hunters. Some predators, including orcas and wolves, often use sophisticated strategies and complex tactics in capturing prey, and in such cases, the learning period for juveniles is extended to several years.