9 Warm Blood and Live Birth

Walden Pond was not wilderness in the 1830s, and Henry David Thoreau knew that. There were people to watch, and he watched with a keen eye.

Early in the morning, while all things are crisp with frost, men come with fishing-reels and slender lunch, and let down their fine lines through the snowy field to take pickerel and perch; wild men, who instinctively follow other fashions and trust other authorities than their townsmen, and by their goings and comings stitch towns together in parts where else they would be ripped. . . . Here is one fishing for pickerel with grown perch for bait. You look into his pail with wonder as into a summer pond, as if he kept summer locked up at home, or knew where she had retreated. How, pray, did he get these in midwinter? Oh, he got worms out of rotten logs since the ground froze, and so he caught them. His life itself passes deeper in nature than the studies of the naturalist penetrate; himself a subject for the naturalist.6

It may seem to be beyond the scope of this book, what philosophers would call a “category mistake,” to include phenological studies of humans. But why? As one among many mammalian species, humans are often the most easily observed. And while many of their behaviors are attributable to culture and habit rather than to instinct, these too have phenological interest and may be as useful for watching climatic change as those in many plants and animals.

Humans (Homo sapiens sapiens) are found in all forty-eight contiguous states, Hawaii, and Alaska. They display a wide variety of colorations in their hair, skin, and eyes. Bipedal, like most birds but unlike the typical mammal, humans often move through the landscape on foot or using technologies they have devised, such as the “auto-mobile,” which is linked in most cases to increased atmospheric carbon. Before the last century, animals, such as horses and oxen, were frequently used as beasts carrying burdens of benefit to people. Humans eat almost anything and have domesticated a wide number of plants and animals to provide a constant supply of food on a year-round basis, using technologies (again) to prevent spoilage during periods of transportation and storage.

Females enter estrus thirteen times a year, or about every twenty-eight days. Males are generally unaware of estrus, and, as females may be as well, sexual behaviors are not well coordinated with reproductive realities. If copulation leads to fertilization, gestation takes about nine months. At birth, an infant human is entirely dependent on the care of a parent (or surrogate) and generally does not leave the parent’s or surrogate’s care for eighteen years or more. Brain development is slow but steady over this time. Both females and males are biologically ready to reproduce at about twelve to fourteen years of age, but cultural standards generally favor a delay in reproduction for another ten to twenty years.

Human phenophases are not well understood. In the United States, annual curves displaying mortality show a spike at and near New Year’s Day, which occurs about two weeks after the winter solstice. In a small percentage of the population, there is a likely causal connection between short day lengths in winter and depression, combined with lethargy. Formal learning is generally a three-season activity in childhood; summers are given over to alternative behaviors of various kinds, not all of them designed to increase rationality. Greater exposure to sunlight may cause a darkening of some skin pigmentations during periods of longer day length, leading to “tanning” in some members of the population and “freckling” in a small percentage. Using technologies that some consider to be the earliest cause of increasing accumulations of atmospheric carbon dioxide, humans “clothe” themselves in materials of varied insulating value and reflectivity during the year.

Humans have varying degrees of awareness of their relationship with the rest of the natural world. In his signature work on the importance of nature for humankind, Biophilia, the natural historian and ant expert Edward O. Wilson wrote that “the naturalist is a civilized hunter.” An ironic choice of word: “civilized,” for Wilson describes his hunter afield, in a place utterly uncivilized, either by other people (the hunter ventures out alone) or by the works of humankind. So, whatever did Wilson intend? Did he mean that his hunter was peaceful, as opposed to predatory or warlike? I suspect that Wilson meant by “civilized” a synonym for scientific inquiry as Wilson sometimes practices it (that is, when he wasn’t extinguishing all life on an offshore island). I think I understand him to mean that the naturalist is a zen hunter, a mindful hunter. Still, I’m left wondering. Aren’t all skilled hunters at least this, or aim to be?

Wilson’s civilized hunter paid attention to the swarming of midges and to the smells in the soil, in order to collect salamanders, unlike the sort of twenty-first-century American hunter of game, who directs attention primarily to mammals and a few birds—and, more than any other mammal, at deer, particularly white-tailed deer.

Phenologists share a variety of strategies with hunters, such as tracking spoor. Spoor include tracks, the impressions that animals may leave as they move through a landscape. There is also scat, or excrement, which has a notable “signature” that varies from species to species. And there is other evidence, such as tree bark that has been marked by a bear scratching his or her back. An awareness of spoor is a more than suitable way to watch the movements of larger, predatory animals such as big cats, bears, and wolves.

There was a time when “civilized” hunters even sought after birds and large mammals with guns to collect them, but that sort of activity is considerably reduced from what it was a century ago. There are other ways to “collect” mammals and birds, and counting is among these.

Joseph Grinnell, first director of the Museum of Vertebrate Zoology at the University of California, Berkeley, was an old-school naturalist, collector, and hunter. Over the passage of four decades, he and his associates pieced together a collection of thousands of specimens to document California wildlife still extent in their own time, as well as wildlife no longer present. The collection includes a California grizzly bear, now extinct.

No mere hunter, civilized or otherwise, Grinnell took care to collect metadata with his specimens and set standards for record keeping as discussed in chapter 4. Today, the collection is a vast portrait, in cabinets, drawers, and notebooks, of Californian life zones as they were in the past, up to one hundred years ago. Much more recently, ecologists and conservation biologists have collected data from many of the same sites where Grinnell, his colleagues, and his charges collected specimens. The result is the Grinnell Resurvey Project, a record of California’s changing ecological conditions.

Grinnell devoted much of his career to birds, but his careful records of mammals, especially smaller mammals such as squirrels, mice, and shrews, have provided resurvey investigators with considerable evidence of climate change made manifest in alterations in the sizes, locations, and altitudes of ranges for California mammals.

Phenological observations augment these ecological field studies. More to the point, not every part of the United States had the luck to sponsor the work of a Grinnell. In many places, ecologists have much less to go on, and phenological observations, along with breeding surveys and other data, are essential for tracking the effects of climatic change.

Are mammals helpful in this? Mammals are attention-getters, without a doubt. That said, mammals are in some ways more difficult to observe than other fauna or flora. They are often more secretive and sometimes more dangerous; an encounter with a bear or a mountain lion is doubtless bracing but also threatening and ill advised, if for no other reason than that hunters may be afoot in the ranges of some mammals—armed hunters, some of whom cannot fully distinguish between two-legged mammals and four-legged varieties. The best way to experience behaviors associated with phenophases in large predators is to watch videos. For this and other reasons, observations of mammalian phenophases by citizen scientists and amateur naturalists tend, in most cases, to be dependent on opportunities, not on disciplined observing over seasons or years.

Even so, there are opportunities. Development in the United States has been such over the past seven decades that humans now increasingly dwell in places where there are large mammals, including bears, moose, bobcats, mountain lions, and elk. Deer have been garden-variety mammals for some time. Suburban dwellers regularly report coyotes, skunks, raccoons, possums, and (in some places) armadillos. Common suburban mammals include squirrels, chipmunks, voles, moles, rats, and mice. Wild dogs and feral cats are not uncommon.

Mammals are warm-blooded. Our bodies are covered with hair or fur. The female of mammalian species in the United States give birth to live offspring following a period of gestation specific to each species and suited by natural selection to be seasonally optimal. Fertilization and mating are similarly timed to produce the largest number of healthy offspring. But here, there are some differences among mammals. In some species, a newly fertilized egg forms an embryo that implants in the womb and develops through gestation to birth. In other cases, embryos are dormant for a period of time, implant later, and then develop to birth.

A number of mammals, such as bats and many rodents, hibernate as a way of adjusting their metabolic requirements to diminished supplies of food in winter. Others, such as bears, have similar instincts for surviving winters, although biologists may not class these strategies as true hibernation.

Hibernation and similar strategies are phenophases; they are regulated by astronomical and environmental cues, especially temperatures. Because hibernating mammals are usually not observable without invasive techniques—and are therefore assumed in the absence of observations—some phenological networks do not list hibernation and related inactivity as reportable phenophases.

In true hibernation, animals that control their body temperatures (ectotherms) lower them as a way of conserving energy. Heart rate declines, and respiration diminishes. Torpor is a similar strategy. While hibernation is not easily observed, certain clues that animals are preparing to hibernate are observable—the caching of nuts, for instance, or the development of winter coats.

Because of their place in the food chain, a wide variety of plants and animals (and mushrooms) have phenologies that have consequences for mammals. It is not safe for citizen scientists to engage with grizzly bears, for instance, except to make a note of the occasional sighting—ideally at a distance. But bears rely on huckleberries as a portion of their diet, so scientists with an interest in bears look to citizen scientists collecting data on huckleberries and other food sources. This is a useful way to make a contribution to science. Much the same sorts of observations are valuable even for mammals that are not dangerous. Food sources, whether for squirrels or bears, are likely to change and shift in coming decades. If you glimpse a rabbit nibbling at plants, or squirrels catching insects, try to identify not just the predator but also the prey and watch for change or stability of these relationships over time.

Squirrels, mice, and rats like our company, although they tend to be wary when we pay any attention to them. But since they get along so well with us, we can expect that changes in our life chances will reflect in their life chances as well.

Squirrels are squirrels, but so are woodchucks and prairie dogs. Chipmunks are squirrels and so are flying squirrels. Tree squirrels and ground squirrels are squirrels. Indeed, there are more than 250 species of squirrels, although only a fraction of them have a range in the United States. The reproductive cycles among the squirrels have many similarities from one genus and species to the other. After my initial discussion below, I will mention only differences.

Let’s start small. Eastern chipmunks range from the Mississippi River valley to the East Coast but are absent in parts of states bordering the Gulf of Mexico. Western chipmunks, a separate genus and divided into twenty or more species, are found in the rest of the United States, except in the Sonoran and Mojave Deserts, the Sierra Nevada mountain range, and the Central Valley in California. Eastern chipmunks hibernate in winter, while western chipmunks burrow and consume a winter store of foods. Both species mate in springtime and may mate a second time in fall.

Chipmunks, eastern or western, are worth noting. Make a note of food sources if you observe one or more chipmunks eating or gathering nuts in their cheek pouches.

Tree squirrels alone include dozens of species, best known of which in the United States are gray squirrels and red squirrels. But on the southern Colorado Plateau, the tufted-ear Kaibab squirrels and Abert’s squirrels pop up in the ponderosa pine forest on either side of the Grand Canyon, Kaibabs to the northwest of the Colorado River and Abert’s to the southeast. The two are considered subspecies, but they are isolated geographically and were once thought to be separate species. Kaibabs and Abert’s are dependent on the pinecones of ponderosa pines as well as fungi that live in the roots of the pines, and their survival is linked to the forest, which will have to recruit upslope to survive.

Gray squirrels range through the Eastern United States and the northern Mississippi River basin. Their expanding range extends into southern Canada. They excel at sharing human habitats, especially urban green spaces, where they are often common and observable wild mammals and taken for granted for that reason. Usually gray in color, there is considerable variation in parts of the range. Dark (melanistic) individuals are common in northern parts of the range. Their preferred foods are nuts, seeds, tree bark, and fungi. A more generalized diet, including insects, may signal periods of stress or may simply be a response to broad opportunities.

Mature gray squirrels may breed twice in a year, but when they are younger, the female might reproduce but once in a year.

American red squirrels are woodland mammals with a preference for pine forests. They are found through the Northern states and well into Canada, as well as in the Rocky Mountains. Red squirrels have an unusual mating behavior, in which several males chase a single female. Pine seeds make up a major part of their diet.

Mice of several species are common dwellers in dooryards and wherever humans reside. They are generally considered vermin, especially where crops (such as corn) are stored. Where they are unwanted, such as inside human habitations, especially kitchens, it is somewhat common to keep a predator such as a cat. Mice are favored food for a large number of predators across the chordates: owls, eagles, snakes, lynx, and others. Deer mice have been linked to both hantavirus in the Southwest and Lyme disease, which they get from ticks.

Rats seem to be especially well suited to urban environments. Any major change in the distribution or phenologies of rats would be interesting news, to say the least.

Rabbits and hares. Has this happened to you? You have an argument with a colleague, or the boss calls you on the carpet for some minor error. Or a home repair turns out to cost hundreds more dollars than you’d planned to spend. Maybe you just took an exam and worry that you’ve not done as well as you’d hoped. Sullen, you head for the nearest greenspace where you can escape the overcivilized world. And as you turn a corner in the path, you encounter: a baby bunny. This happened to me many times on the campus where I taught for many years, and each time it did, I felt renewed. It is very difficult to remain angry in the company of a baby bunny. And even though this setting was also coyote country, the presence of any youthful rabbit is proof that at least two adults rabbits made it safely to the age of reproduction.

Female rabbits (does) are capable of reproducing several times a year, beginning in late winter, mating with a male (buck) over a matter of a few minutes, at most. The gestation period is about a month. The young are born blind and without fur but develop in a little over two weeks and are weaned after about a month. Rabbits are entirely herbivorous, and the cellulose from the foods they eat is digested primarily in their lower digestive tract.

Eastern cottontails are widely distributed east of the Mississippi River, the Great Plains, and the desert Southwest. Desert Cottontails inhabit the western Great Plains and the desert and mountain West. It is worth making note of sightings of cottontails, counting them when there is more than one and paying attention to what they are eating. Although notorious for being prolific breeders, rabbits could experience consequences from climate change.

Hares, while superficially similar in appearance to rabbits, are quite different from them. Male hares (not bucks but jacks) must chase females (jills, not does), catch them, and then fight with them before mating. In hares, the gestation period is nearly two weeks longer than for rabbits, and the young (leverets) are born with fur and able to see.

Snowshoe hares (Lepus americanus) are quite interesting, phenologically, as they molt and, in doing so, change their fur color from brown to white, so as provide camouflage in snow cover, then back again when the snow melts. The primary mechanism in these phenophases appears to be day length, although temperature and the presence or absence of snow may play a role—but not enough of a role, perhaps, because there are increasing observations of mismatches in spring and fall in this species. Biologists hypothesize that natural selection will drive changes in populations of hares to accord with shorter periods of snow cover.

Snowshoe hares are found in mountainous areas in the Pacific Northwest and the Rocky Mountains, in northern Minnesota, Wisconsin, and Michigan, in the Appalachian Mountains north of Tennessee, and from New York through New England.

Jackrabbits, white-tailed and black-tailed, range through the Western states. All of the hares have longer life spans than rabbits do and are worth noting when observed. Be sure to record fur color.

Bats. There are around four dozen species of bats in the United States. Worldwide, bats are of two main types: megabats, and microbats or echolocating bats. Only the latter are found in the continental United States, including little brown bats and big brown bats, both common in most parts of the country. Echolocating bats emit sounds and instinctively process the return times of echoes in order to “see” objects, particularly prey, in their habitats. Both are insectivores and are therefore dependent on the phenologies of insects. A group of scientists from the University of Wisconsin, Milwaukee, working with Wisconsin state biologists, studies little brown bats and has found little change in the timing of their spring emergence from caves.

Along with most bats in the United States, little brown bats are difficult to observe and identify. They are active at night and move rapidly. But if you are certain of identification, you can look for first appearances in spring, after the bats emerge from hibernation. Although mating occurs in the fall, before bats hibernate, the females store sperm and are fertilized in spring. Gestation is about two months; young are born in summer.

Bobcats and mountain lions. A ranger in southern California once told me that whenever I was hiking in the region, I could be fairly confident that a mountain lion was watching me. In time, I got used to the idea, but I always feel more confident, if that’s the word, when I see mule deer on my hikes: a hiker or bicyclist may be interesting to watch, or at least worth keeping an eye on, but a mountain lion would much rather dine on venison.

Mountain lions, also called puma and cougars, occupy a range vastly reduced from what it was in the United States thanks to bounties placed on them in the not-so-distant past. Although lions will hunt and feed on smaller mammals, they prefer deer and thus inhabit similar habitats, individually, except in the case of a female whose young are still with her.

Jaguars are found at warmer latitudes, with infrequent sightings in the border Southwest.

The lynxes are a smaller species of wildcat, two species of which are found in forty-nine U.S. states and in Canada. Lynx rufus can be found throughout the contiguous forty-eight states, with the exception of the areas around the prairie states and the Great Lakes. They are commonly called bobcats. Lynx canadensis are primarily a more northern species, but overlap with L. rufus. The bobcat is considered a game animal in many states. Bobcats have a diet similar to that of coyotes (but with more success capturing birds), and their habitats may overlap. Bobcats mate in late winter. The females give birth to four to six kittens a bit over two months later, in midspring. Kittens will stay close to their mothers for about a year.

Bobcats are active in twilight, near sunrise and sunset, and one sometimes encounters them on early morning or early evening hikes. While hiking in bobcat habitat, one should be alert to bobcat spoor, tracks, and scat, making notes when you find these. If you are lucky enough to see a cat with prey, be sure to document the kind of prey.

Foxes, coyotes, and wolves. The red fox inhabits a large part of the contiguous United States but is absent from parts of Idaho, Washington, Oregon, California, Nevada, and the Southwest; in most of the range where red fox is absent, one finds gray fox. The red fox is an omnivore, hunting and eating other mammals as large as raccoons and juvenile deer, as well as other chordates. Fox supplement their diet with plants and some invertebrates. They prefer edge environments, and this brings them into urban areas where they forage in gardens and the middens of human populations.

Females (vixens) enter estrus in early winter; they copulate with a male for a period of about an hour, after which there is a gestation period of about two months. When the vixen gives birth to four to six kits, she is usually immobilized in a burrow for fourteen to twenty-one days, and the male feeds her while she suckles the kits. Vixen and kits emerge from the burrow after a month’s time and begin to hunt with the vixen and the male fox.

Because fox are wary, especially in areas populated by humans, it is exciting to see one and to jot down their numbers and the presence of kits, if present. The vocalizations of fox are varied, particularly when mating, and worth learning and chronicling when heard.

Gray fox look similar to red fox from a distance; it is best to learn to distinguish them in the company of an experienced observer. Gray fox are found throughout the contiguous states, except in the northern Rocky Mountains and the northern Great Plains, and are more inclined toward woodlands and other places with cover, unlike the edge-loving red fox. Vixens enter estrus in midwinter and gestate for six or seven weeks.

Coyotes are doing well and are likely to continue apace as climate changes. Inhabiting all of the contiguous United States and Alaska, they were absent from the southern Appalachian states and Florida but have expanded their range over the past half-century. They are broadly omnivorous animals and are among the set of species that thrive in proximity to human settlements, sometimes feeding on pets, such as cats and small or immature dogs.

Coyotes mate in middle to late winter; pups are born about two months later. Both parents play roles in rearing young into early summer, when the pups are weaned. The pups are mature by the middle of the fall of their first year.

Although it is not unusual to observe coyotes visually, particularly lone individuals, it is more common to hear coyotes. If you do happen to encounter a coyote visually, it is worth watching what is being hunted and marking it down. Also note the condition of coat and apparent weight (lean or well-fed).

Raccoons, skunks, otters, and badgers. Raccoons and skunks are among the Musteloidia, a superfamily that also includes weasels, otters, badgers, martens, and close relatives to raccoons such as ringtails and coatis. Of these, raccoons and skunks are most likely to frequent the American dooryard. They are generalists, and the skunk in particular has evolved a formidable system of defense against predators, real and imagined.

Raccoons’ ideal habitat includes streams, ponds, and lakes, and it is fair to say that the species was for a long time a free rider in beaver habitat. During the early period of European expansion into North America, many streams were transformed by humans into dam sites, and this as much as anything else contributed to the tendency for raccoons to associate with human populations and may have favored an expansion in the species’ range, albeit with a wariness about humans.

Raccoons mate in late winter. The phenophase seems to be controlled by length of day, although temperatures may also play a role. The period of active mating—courting and copulation—occurs in under a week’s time. In the aftermath, a fertile female will gestate for about two calendar months, at the end of which she will give birth to a litter of two to five young. At two months the kits begin exploring and will forage; they are fully weaned at about four months. In the fall, kits will go their separate ways, and males roam some distance from the places where they were born.

Raccoons have successfully adapted to a wide range of changes to habitat and will probably continue to do so. Shortened winters are likely to increase the extent of each year that they are active.

Make notes of sightings of raccoons. I was surprised one day to see a raccoon peering out from a storm drain in San Diego. Whether it was merely hiding there until I passed by or was living there, I had no way of knowing.

Skunks, too, are found in a variety of habitats across the United States, including urban areas, where they forage for foodstuffs discarded by human populations. In all habitats they are omnivorous. Adults mate in early spring, and females then gestate for a little over two calendar months. Males do not play a role in rearing offspring. In colder regions, skunks will occupy winter dens but they don’t hibernate.

Log sightings, as well as smellings, of skunks.

The rest of the Musteloidea are uncommon enough to deserve reports, in your journal at least, on any and all sightings. Weasels are common in rural landscapes, especially farms and tailored environments like golf courses. They can breed twice a year, in spring and again in summer. All sightings are worth noting. Badgers are omnivores. Their reproductive cycle is unlike other Musteloidea. Badgers mate in late summer or early fall. The fertilized embryo then remains in a dormant state, implanting in early winter and gestating over a period of less than two months. Shortened winters may have an effect on badger populations. All sightings of badgers, and especially of young, are worth documenting.

Deer and elk. Deer are the largest mammal that you are likely to see on a regular basis. I recall the thrill I felt one night, while sitting at a window gazing dreamily at a winter landscape in moonlight, as nine deer of varied ages emerged from the wooded yard across the street, crossed the road one by one, and passed through my dooryard to someplace behind my house.

To my taste, the carefully choreographed chain of deer was a gift. For many, though, deer are the largest nuisance they are likely to encounter, a menace to successful gardening, a big suburban pest. White-tailed deer range throughout the contiguous states, with the exceptions of the Colorado Plateau, the Great Basin, California, and the Puget Sound. They show a preference for “edge” environments combined with sources of water. For this reason, suburban landscapes bounded by woodlands are quite ideal—and the cause of suburban gardeners’ displeasure at seeing deer pose in a well-tended garden space. In the far West, mule deer are likely to occupy similar habitats. White-tailed deer seem to have expanded their range through much of the twentieth century and are popular and abundant game for hunters.

White-tailed deer and mule deer are members of a broader taxonomic unit that also includes elk and (in Canada) caribou.

Estrus occurs in female white-tailed deer (does) in the middle of the fall. Length of day seems to determine this phenophase, which is known as the rut. Mating with males is a fairly perfunctory affair; gestation is just shy of seven months in length. Fawns, one to three in number, are fed and sheltered by does for about a month, then begin accompanying the doe as she forages. They wean at about ten weeks. Females are ready to mate in a few months; males usually have delayed reproductive success until they are about eighteen months of age.

Because of their place as a managed game animal, white-tailed deer already provide a lot of data for phenologists. Even so, it is worthwhile to note sightings, especially in spring when does may be accompanied by fawns. Years with early springs are associated with better survival of fawns.

In the West, mule deer may migrate from warmer deserts and valleys in summer to mountains and mountain foothills in winter. Reproduction is similar to white-tailed deer, although the rut continues in early to midwinter.

Annual variations in conditions for mule deer in Western states, especially during periods of drought, may cause temporary range expansions of mountain lions, sometimes leading to incidents that bring lions and humans together.

The habitat for elk is primarily in the mountains and plateaus of Western states. Larger than white-tailed and mule deer, elk migrate from higher country in summer to lower altitudes in winter. With anthropogenic climate change, the lowest elevations at which winter elk are found are likely to increase, and elk are likely to migrate to higher elevations in summer as long as there are sufficient sources of food. For elk, the rut begins as early as late summer and continues through the fall. Female elk (cows) gestate eight months or more.

Because of their migratory behavior, notes on sightings of elk are worth keeping. Count numbers; make a note of cows, males (bulls), and young (calves). Very young calves have spots.

Moose are distantly related to deer and elk. Ranging through the northernmost contiguous U.S. states and into Canada, their reproductive cycles are similar to elk. Because moose found in the United States are at the southern extent of their range, it is possible and even likely that moose will be extirpated in the contiguous states in due course owing to anthropogenic climate change. All sightings are noteworthy, and details—numbers, genders, presence or absence of calves, apparent condition—are worth keeping.

Marine mammals. Although smaller than blue whales, gray whales are among the largest marine mammals. Eastern gray whales migrate along the West Coast of the United States, from the Bering Sea to the Gulf of California, responding to phenological cues—sunlight and water temperature. Because their migratory route takes them close to the coast of California, whale watching—usually from private or chartered boats—is a favored life event for naturalists. Other whales are more elusive.

Of the whales’ phenological cues, water temperature, in particular, will change as global climate warms and may cause changes in the timing of whale migrations and the availability of resources at migratory endpoints. Without private wealth or a research grant it may be difficult to monitor whale migrations for phenological data, but fortunately the popularity of the migration is such that changes in dates of migrations are likely to be reported by institutions such as the Monterey Bay Aquarium.

Miscellany. Ground squirrels and rodents in the mountains and foothills of California and Colorado have been found to host the fleas that carry bubonic plague. Usually, this occurs on public lands and is likely to be posted when there is concern. Changes in phenology could lead to changes in the vector for this disease.

If your commute is regular it is worthwhile to make notes about roadkills of armadillo, possums, skunks, and the like.

Domesticated animals: cows, goats, pigs. One of the reasons that certain animals were suitable for domestication was that estrus in these animals is subject to manipulation or is repeated within a yearly cycle. In sheep, estrus is seasonal in some breeds, less seasonal in others. Bovine females enter estrus for a period of eighteen hours every eighteen to twenty-four days. In pigs, estrus is manipulated by breeders. For these reasons, domesticated animals are not very interesting subjects for phenological study.