Tuesday, July 01, 2008

The Natural History of Fox



Natural History, January, 1985

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THE LITTLE FOXES by J. David Henry
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They may look endearing, but young red foxes fight violently and, when necessary, steal food from one another.


It happens during the coldest part of the year -- a time when northerners bundle up against twilight days and -- 40 degree air with parka and wind pants, gauntlet and mukluk. It is a time when darkness pervades the forest, when everything seems brittle.

Yet, during this inhospitable period in late January or early February, while most animals are simply trying to survive the frozen wastes of a boreal winter, red foxes begin to court. It is not difficult to know when the foxes are feeling amorous; a musky odor begins to emanate from the urine they leave in the snow. This scent is particularly strong in the urine of males. In Prince Albert National Park in northern Saskatchewan, where I do my research, foxes develop this breeding odor over the course of a week or so. Then, for the next month or six weeks, a skunky fragrance permeates the woods wherever a red fox and his vixen have established their territory, the area they use for hunting and scavenging and defend against other foxes. After studying foxes for years, I can say with confidence that it is my nose, more than anything, that first tells me the foxes are courting.

During this amatory interlude, the dog fox and vixen, both of which have been leading solitary lives on the territory, now begin to seek one another out. They travel together for several weeks, becoming increasingly confident about touching one another, until they finally breed. During the courtship period, the vixen visits and cleans out several lairs on the territory, one of which she will choose as her whelping den.

Why does a vixen choose to give birth to her pups in one place rather than another? What does she see in a particular piece of earth? After surveying thirty-five whelping dens, I found that they have certain typical characteristics. The den is usually located on a hillside in sandy loam. It is often in the forest but close to a meadow or open slope. And it usually has multiple entrances, the largest one about ten inches in diameter. Finally, the den retreat is normally within one hundred yards of a water source, although this source can be anything from a large lake to a humble pool in a muskeg. With these requirements, vixens have to be selective about where they bear and raise their cubs.

Certain features, such as the nearby drinking water, have obvious advantages; but I was not sure I understood the others. Why are they so common? After reflecting about them, I feel that vixens probably select sandy loam because they can dig into it more easily, but it could also be that this soil, combined with the hillside location and nearby open area, may make for a site where snow melts early, frost leaves the ground quickly, and drainage is always good. Vixens use the surrounding forest for shelter and escape; they can sun themselves in the adjacent meadow and their rambunctious pups can play there.

A vixen may use the same whelping den year after year, and when she dies, the site may be passed on to one of her daughters. One fox lair near my cabin, for instance, has been active for nine of the last twelve years. Since adult foxes in the wild usually live only three to seven years, this den was probably occupied by several different fox families. On the other hand, abandoned lairs that deteriorate may be renovated by foxes after a long vacancy. The first den I ever studied in detail, in 1972, was active until 1974. After that, it lay vacant until a young fox couple reoccupied it and raised a family there during the spring of 1980.

Foxes never seem to rely on just the whelping den, however. In my area, they always have other, smaller burrows hidden away on their territory. If disturbed or threatened at the whelping site, the vixen or dog fox will simply move the pups to a new location. Frequently, the vixen initiates the move, which sometimes leaves her mate in a quandary.

I remember one such experience when, for an extended period, I was observing foxes at a den twenty-four hours a day in order to document how the six-week-old pups were being raised. One afternoon, in an attempt to get some photographs, I unwittingly crossed an invisible but important vulpine boundary, and the vixen reacted as if she had decided enough was enough. She waited until the middle of the night and then moved the pups, not carrying them as other canids do but marching them along behind her. About first light the dog fox returned to the den with a rabbit in his mouth. He went to the main entrance and called the pups with the rapid "wuk . . . wuk . . . wuk" chortle that foxes use, but no one came forth. Setting the rabbit down, he began to smell around the area. He apparently was able to figure out what had happened by the odors that remained on the ground. Sniffing the site thoroughly, he finally detected the trail that the vixen and four kits had taken through the forest. He returned to the den, hid the rabbit, and then began to track down his family, following their scent through the bush. On the other hand, I, not being blessed with the nose of a fox, spent the next seven days searching in vain for the new den site.

But I am getting ahead of myself. Let me backtrack and follow the pups through their eventful early life. After a gestation period of fifty-two days, the kits are born; in my study area this occurs during late March or early April. The average litter comprises five whining, hungry mouths, but a litter of nine cubs is not uncommon. Regardless of the size of the litter at birth, some cubs usually die. The number that survive depends, among other things, upon the amount of food the adult foxes can find on their territory.

When the kits are born, they are helpless and weigh less than a quarter of a pound. Except for their smaller size, they are remarkably similar to newborn coyote and wolf pups--with one important exception. Even at birth, most young foxes have a curious white tip on the tail. Red foxes retain this white tag throughout their lives, and they are the only North American canid species to show this distinctive marking.

During their first month of life, young foxes do not possess the brilliant red coat that is the hallmark of the species; instead, their coats are charcoal gray. Foxes are not the only canids with this feature. At birth, the whelps of coyotes, wolves, and other species of wild canids are also cloaked with dark gray fur. As far as I can determine, this special natal fur does not have any physiological function. It may serve as camouflage while the young canids remain in the darkness of the den.

Fox kits grow slowly during their first few weeks; their eyes do not open until they are ten or twelve days old. During early life, the vixen constantly attends them. In many areas, the vixen may venture out of the den after only two days, but in northern Saskatchewan she remains inside constantly from a few days prior to birth until the kits are approximately ten days old. She is completely dependent on the male for her food during this period. This he provides with regularity.

Why is the vixen unwilling to leave the kits? David Macdonald, who has studied red foxes extensively in Britain, suggests that the kits are so small and vulnerable during early life that the vixen must surround them with her warm body if they are to survive. This maternal protection becomes increasingly important the farther north one goes. At the time the kits are born, the ground in northern Saskatchewan is still frozen and covered with snow. The den is damp, and the air temperature inside is a chilly 32 degrees Fahrenheit or colder. The vixen acts literally as a thermal blanket, protecting the cubs in their frosty underground chamber. One could almost say the incubates them. By then they are well furred and large enough to maintain their own body temperature. She now spends more and more time away from the lair hunting for prey for herself, but she continues to receive some food from her mate. And she does return to the den at regular intervals to nurse the kits. While in the den, she attends to her other maternal duties as well. She plays or naps with the cubs and then grooms them--cleaning out their ears, licking their groin regions, and eating their waste products. She maintains this routine until they are five weeks old, when she begins to wean them.

The early life of a kit fox is not the care-free, leisurely existence that one might imagine. It is business from an early age. During their second week, the kits begin to grow faster and their milk teeth start to come in--canines first, followed by incisors, and finally, premolars. During their third week, they begin to experiment with their teeth. They chew and suck on meat that the parents have brought them and learn to enjoy the juices found in a freshly killed rabbit. Now they enter an important phase of their development.

At this time, the fox kits are far from fully coordinated and have been above ground only for short periods. Yet at about twenty-five days of age, they begin to fight viciously; they clash with each other in short, serious, and sometimes fatal contests. (Fatalities are rare, however.) Fox kits do not act like cute, cuddly puppies such as those of the domestic dog; rather, they have always seemed to me to have a slightly demonic character about them. They are tough, month-old thugs, little street fighters that initiate fights and, over a period of ten days, establish a strict dominance hierarchy. The alpha (or dominant) member of the little establishes itself, and the process continues all the way down to the weakest animal.

Evidence suggests that these dominance relationships among the cubs remain stable and have a great bearing on their survival. If the adults are bringing the kits only a limited supply of food, competition for it is keen. By establishing a hierarchy, the kits determine who can steal food from whom. The largest member of the litter, whether male or female, usually becomes the alpha pup. Using either intimidation or direct attack, this animal steals food from its litter mates. Each pup steals food from littermates below it in the hierarchy. It is a blunt fact of a fox's life that the dominant pups get a larger portion of the food and have the best chance of surviving, while smaller and submissive ones may perish. The runt of the litter usually dies first, then the second lowest in the hierarchy, and so on. It is a brutal process; but given the constraints of the hierarchy, it is the only way healthier kits can survive. Nor have parent foxes evolved to interfere with this sibling rivalry, since the competition results in a litter composed of the healthiest whelps. Pared down, the litter size is also now in balance with the food resources of the territory.

By early May the fox kits in my area begin to come above ground for longer periods of time. At this point, the hierarchy is solidly established and, with that crucial matter out of the way, the aggressiveness of the cubs actually diminishes. Gradually, they become more social, playful, and puppylike. It is at this time that most people first see young foxes. How much has happened in their lives before we are even aware of them!

When a parent fox returns to the den during early May and chortles for the pups, they stumble out--unsteady on their feet, blue eyed, and still dark coated. But at about this time an important change takes place: at about five weeks of age, they start to lose their dark natal coat and get a new pelage. Once again it is not the brilliant red of an adult fox, but a sandy-colored juvenile coat that almost perfectly matches the sandy soil of the den site. This coat helps to camouflage the pups around the den and protect them from occasional predators, such as hawks, owls, and coyotes.

Reflecting on the sandy-colored coat, I began to realize that this juvenile pelage had come about from an interesting series of events. I can imagine it evolving something like this: At first the vixen tended to dig her whelping den in sandy loam simply because it afforded good digging. But over time, the fur of the kits slowly evolved to match the soil's color. Evolutionary theory states that, if the sandy-colored pups have even a slightly better chance of surviving, all fox kits will eventually develop this coloration. As this happened, there was great pressure on the vixen to locate her den in sandy-colored soil. Consequently, the selection of the den by the vixen and the juvenile pelage of the kits are co-adapted to protect the young during their vulnerable first month outside the den.

This buff coat of the young foxes is actually a specially colored underfur (the underwool of adult foxes is a dark gray). The kits keep this juvenile coat for approximately five weeks, but starting in early June, outer red guard hairs begin to grow through. By the end of June, kits display the bright red coats normally associated with adult foxes.

When the kits are five weeks old, they begin the transition that will launch them into adult life. The pups now begin eating solid food, and the vixen starts to wean them. Weaning fox pups is an uncomplicated procedure. If the kits try to nurse, the vixen rolls over on her stomach. If they persist, she threatens them and runs off a short distance. She becomes increasingly unreceptive to their suckling, and by the time they are eight weeks old, the pups are completely weaned. But being weaned doesn't mean being cut off. The parents continue to hunt and scavenge at different times of the day and night in order to supply the kits with sustenance. These adults bring in an assortment of prey and present it to their pups. For example, in one week the menu included rabbits, mice, voles, squirrels, groundhogs, songbirds, grouse, and a spawning long-nosed sucker.

Distributing this food is a household ritual in a fox family and always happens in the same way. Carrying the item in its mouth, the adult fox arrives at the den, chortles, and one or more of the pups rush out to greet it. The first pup to reach the parent crouches low and beats its tail about wildly. The kit whines and creeps toward the adult and then reaching up, it smells, licks, bites at the corners of the adult's mouth.

There seems to be a consistent rule in fox families that the adult will give the food to the first pup that begs for it. This way, supplies are more or less evenly distributed. Basically, the hungriest pup keeps the best watch, gets to the parent first, and is given the food. However, once it has received its ration, the kit still has to defend its prize against litter mates, either by running off or by threatening any siblings that come near. As I explained earlier, a dominant pup will frequently challenge and steal the provision from its subordinate litter mate.

Food-begging behavior, by the way, also appears many months later but in a completely different context--as part of the submissive behaviors shown by adult foxes. When two full-grown animals meet, the subordinate fox often acts as if it were a young pup, begging to be fed. It crouches low, whines, and beats its tail madly in every direction. This keeps the white tip of the tail in constant motion (much like waving a white handkerchief) and lets it function as an attention-getting device. The subordinate fox slowly creeps up to the dominant fox and carefully reaches up to smell and lick the corner of its mouth. This use of infantile behavior by adults is not unique among red foxes. Embracing among adults, which is used as a greeting and reassuring gesture not only among humans but also chimpanzees and baboons, may be derived from infantile grasping. People in love sometimes coo and baby-talk to each other; we sometimes stammer or show shy juvenile behaviors when introduced to famous people.

The role of the dog fox in raising the kits has been debated among naturalists and field biologists. Some state that the male fox is never seen around the den, while others conclude that he supplies most of the food for the pups. There must be considerable variation among red foxes of different areas. The causes of these differences are not fully understood. But in Prince Albert National Park, an area where the foxes are almost completely protected from hunting and trapping, I have consistently observed male foxes bringing food to the pups until they are approximately ten weeks old.

In addition to the parents, other foxes will occasionally feed the pups. These "helper" foxes are an interesting phenomenon. Most often the assistant appears to be a daughter from the previous year's litter that has stayed on the family territory but not given birth to pups of her own. When she is present, she makes a definite contribution to rearing.

This helper illustrates an important point about evolution. Evolutionary theory states that individuals of a species that are most physically and behaviorally fit will leave the greatest number of offspring. But twenty years ago, British biologist W.D. Hamilton stressed that an individual's relatives are also important. For example, red fox helpers are as closely related to their full siblings as they would be to their own offspring. If an assistant increases the survival rate of her younger brothers and sisters, she helps some of her own genes survive into future generations.

Foxes that aid in raising their younger brothers and sisters may also derive other benefits. For example, they may gain experience that will help them rear their own offspring more successfully. In a few cases, they may also inherit part of their parents' territory.

Hamilton's theory makes another prediction about these young vixens. It states that if food is scarce, the daughter will help raise and feed her mother's litter. However, if food is abundant, the male fox will breed with both the older vixen and his daughter, and both vixens will raise litters on the family territory. The male will bring food to both litters, and the vixens, instead of competing, will tolerate each other. Why does the theory predict these events? Because when food is abundant--considering the genetic relationships involved--each fox will pass on more of his or her genes to the next generation if multiple litters are reared on the territory.

My field observations tentatively seem to support these predictions. In my study area, during years when prey was abundant (one year, for example, there was a peak in the snowshoe hare population), I have occasionally observed two vixens raising separate litters several hundred yards from each other, and once, within the same den. In both cases the vixens got along amicably and one dog fox brought food to all the pups. These observations suggest that the vixens were acquainted and may have been related. These preliminary data are interesting, but before we draw any final conclusions about this aspect of the fox's family life, more detailed research is needed.

During middle and late June, the pups' transition to adult life continues. They have grown to be nearly two-thirds the size of adults; they are fully coordinated and exhibit a bright red coat. During this period the parents start to visit the den less frequently, and the amount of food they bring starts to diminish.

At this point, as in many species, a classic conflict between parent and offspring arises. The fox kits appear perfectly content to remain at the den, play continually, and be fed by the parents. However, the adult foxes, which have been run ragged, seem to have some other arrangement in mind. And fortunately for them, they control the situation.

During June the pups wait endlessly for the adults to arrive with food. When an adult finally does appear, one pup gets the food, which he quickly consumes. Then the adult often takes one or several of the pups on exploratory trips away from the site. At first the parents lead the kits away and later accompany them home. But after a few of these excursions, the kits return on their own. I wish I could have gone along, but the parent foxes never tolerated me on the expeditions, and this aspect of fox life has always eluded me.

The kits, while hanging around the den, begin to eat wild fruit and to hunt insects and whatever other prey they can find. Gradually they become more confident, venturing forth slightly farther each day and spending less time at the lair. Thus it seems that a combination of boredom and hunger eventually drives the kits away from the den site, whereupon they start a predatory, scavenging life of their own.

At first the pups travel in twos or threes. However, since the prey they hunt are small and quick, to capture one, the fox must hunt in a stalking, catlike manner using a surprise attack. These constraints slowly force the young foxes to become solitary predators.

Occasionally, the vixen and pups will rendezvous on the territory during late summer and early fall. When this happens, the foxes greet, play, and generally enjoy each other. By this point, however, the dog fox is intolerant of his cubs. During September, the male kits begin to mature sexually, and this increases the competition between father and son.

No one is certain what causes the kits to finally leave the territory altogether. Adult foxes have not been seen aggressively driving their young away, but they may exclude them from the best hunting and scavenging sites. Whatever the cause, during late September or October, the kits begin to disperse. Males leave first and travel the farthest. Each tends to travel in one direction until he has found an available territory. Once male kits have left their birthplace, they usually don't return. Female kits may remain on the family territory into December, and if food is plentiful, one or several female offspring may stay on.

Such is the way it happens. Each spring, kits are born; as helpless as embryos, they would freeze without their mother's constant attention. In the course of six short months, these tiny, helpless creatures grow into self-sufficient, graceful, flame-colored predators that leave their families and seek out their own part of the forest. When a young fox leaves, it becomes self-reliant and takes on the ways and manners of adults. It claims a territory and inhabits it with another fox--its prospective mate. During the frozen darkness of winter, the pair set up the territory and court, and the cycle inherent in a fox's life completes itself.
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1 comment:

terriertrio said...

Great information for our JRTCA Youth Handlers -- future terriermen and women! Thanks for sharing.