The image of wild animals visiting a salt lick is probably a familiar one to you if you are a regular watcher of television natural history documentaries. The scene is repeated over and over again, as large African or Indian mammals approach this particularly rich source of minerals.

One of my long-time colleagues and friends, a researcher of primates, pachyderms and amphibians, has even documented a phenomenon he calls "elephantine speleogenesis." Years ago, he and his wife spent some time living in the entrance of a large cave system on Mount Elgon in northern Kenya. There he slept with a long piece of thread tied to his toe, ready to awaken if an elephant put in a nocturnal appearance. From the photographs he took, tuskings on parts of the cave roof, and particles in the elephants' copious droppings, he was able to determine that not only had huge areas of the cave system been mined by elephants and other game, but that the very caves themselves may have been created by their mining activities (hence speleogenesis).

Carbohydrates, proteins and fats make up the bulk of a mammalian diet, but without the addition of trace elements, minerals and salts, even the best-fed animal may weaken, sicken and die. We only have to examine our own human populations in parts of the world where strife has impoverished the local diet to find the implications of a lack of calcium or potassium, for example.

Mammals are not the only creatures who seek out trace elements and salts. I have seen photographs taken of macaws, those hugely spectacular, long-tailed South and Central American parrots, taken at riverside cliffs where they gather to ingest mineral-rich soil. The predilection for swarms of tropical butterflies in South America, Africa and tropical Southeast Asia to gather at the urine splashes left by local large mammals surely reflects an interest in the minerals present -- after all, moisture is not in short supply in rain forests.

That a wide range of species seeks out dietary supplements is perhaps not surprising. Consider the rows of such things on our own supermarket and pharmacy shelves. What, though, is the mechanism whereby individuals recognize, and act, on that need? How do elephants know which minerals they need and where to find them? How do macaws recognize their needs and know which cliffs to nibble, and butterflies which urine tastes best? As a child, I was regularly reprimanded for attacking the salt pot in the pantry, but in my craving it tasted almost sweet -- perhaps revealing a simple deficiency.

I remain surprised by the intensely Japanese love affair with that quintessentially cold, unappealing and neutral building material: concrete. More is poured here each year than in the whole of the U.S. While Mount Fuji, cherry blossoms and shrine gates may be the enduring images of Japan's past, their modern counterparts are the concrete structures that cover the country from Hokkaido to Okinawa.

The obsession with concrete and hard engineering is in spite of the poor track record of some of those structures during major earthquakes and floods. Interestingly, a number of brick structures have survived innumerable earthquakes, yet the positive value of brick as a building material in a quake zone seems to have been overlooked.

Among these brick structures, dating back I believe to the late 1800s, are the pillars for the old railway line running into the hills up to Karuizawa. A trail runs parallel to the modern railway line; the deciduous forests here are rich, diverse and fun to wander in. One never knows what will appear next; perhaps a Japanese green woodpecker will call from the treetops, a copper pheasant may explode from cover to whirr away across the hillsides, or a troop of monkeys may come wandering across the path.

I was struck one day by what seemed like odd behavior on the part of the local monkeys.

Japanese macaques share many similarities with us; indeed, many hundreds of them are used each year in laboratory research, testing the efficacy or dangers of chemicals that may affect us. Naturally they share some of our phisiological needs, including minerals. I had never given any thought to where monkeys here obtain their dietary supplements, however; I had merely assumed that the range of plant species they consume would contain everything they required.

They have been widely studied. Some groups have been continuously watched for more than 50 years, making them among the best and most intimately known of all species. Their every move has been recorded; their social interactions and social rankings have been examined and analyzed; their genetic relatedness has been exposed by DNA testing and their innovations have been splashed across newspapers and magazines worldwide.

Where do macaques wash sweet potatoes in seawater? Japan. Where do macaques throw grain and sand on to water to separate the two? Japan. Where do monkeys live in deep snows during winter? Japan. Where do they spend time in hot springs, for all the world like human bathers enjoying a rejuvenating spa? Japan. Even where other species in other parts of the world might emulate them, it is the Japanese macaques that do it most famously.

One behavior that I had not come across when reading about macaques, however, was that they also climb railway pillars. Scaling a sheer brick pillar is no mean feat, and so when I saw several individuals fleeing the old railway pillars as I approached, I was intrigued. What could they have been doing?

Through my binoculars, I could see that in places there seemed to be small damp patches on the pillars. Retreating a little, I waited and watched, and soon the animals were back. The cause of the damp patches was revealed: The macaques had been licking at the bricks and mortar.

I've met geologists who lick rocks -- the moisture helps reveal their colors and texture more readily to the eye, and gives some clues as to the mineral contents. The macaques were not geologists though. When I investigated the brick pillars I found that here and there, exuding from tiny fissures and from the mortar layers were crystalline crusts -- salts.

How do I know?

Well, I too licked the bricks.