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Volume 39 Issue 4 • May 28-June 3, 2009
now in our 39th season

An Underground Surprise

by Dr. Sarah D. Oktay
Managing Director UMass Boston Nantucket Field Station

This week's subject was conceived after an enchanting discovery that we have been sharing with visitors to the Nantucket Field Station over the past month:  an Eastern Cottontail rabbit nest.  Our dog Jake found the well hidden nest while he was rooting around for food to augment his new, involuntary and mandatory, high-fiber diet. The nest was built in the grass and soil directly next to our foundation and was lined with bits of rabbit fur so the baby bunnies could stay warm. Sadly, one bunny went to cottontail heaven before Jake could be stopped from his one and only predatory adventure. 

The nest was concealed under a layer of grass forming a lid to the nursery cavity, which was simply a shallow dug-out indentation in the soil.  Both lid and nest were lined with fur and when the top was moved aside, the furry baby bunnies (known as kits or kittens) would start hopping and popping in reaction to the exposure.  At this point, a common reaction is to mumble “sorry guys,” admire the warmth coming off the nest in the chilled air, and put the “lid” back on as quickly as possible, which can be pretty tough to do as the kits continue to bounce like little jumping beans.  The terms cozy and cute  don't begin to describe it.  We'll talk more about the life cycle of these bunnies below and find out why although they are cute, the diseases they carry are less than enchanting.


1 week old kit

According to Wikipedia, the Eastern Cottontail (Sylvilagus floridanus, J.A. Allen, 1890 ) is a New World cottontail rabbit, a member of the family Leporidae.  It is one of the most common rabbit species in North America. It is native to many states in America, but not to New England and as an introduced species, it has pushed out its brethren, the New England Cottontail.  Like many other creatures found on Nantucket, rabbits were brought to Nantucket for hunting reasons.  In fact, Eastern Cottontails were first introduced to New England on Nantucket in the 1880s. We'll discuss below the consequences of the seemingly innocuous introduction.

The genus name “Sylvilagus” is from the Latin word sylva (forest) and the Greek word lagos (hare), and the species name “floridanus” refers to the state in which they are considered endemic (common and native).  The taxonomic ranks of the eastern cottontail show us they belong to the Phylum, Chordata (has a spinal cord); Class, Mammalia (usually but not always live birth, mammary glands, neocortex brain); Order, Lagomorpha; Family: Leporidae.  The name leporid is derived from Latin leporis, which is a possessive case derivative of the word “lepus” or “hare.”  Rabbits vary from rodents, so they were grouped into their own Order, Lagomorpha ( Greek for “hare form”). The members of Lagomorpha (rabbits, hares, and pikas) have an extra set of incisors (teeth) in their upper jaw, are strictly herbivores (plant eaters) and have a few other physiological (body related) differences.  Like rodents, their teeth keep growing so they have to gnaw constantly to keep them from getting too long.  There are 18 recognized subspecies of Sylvilagus floridanus scattered all over the world in a huge variety of habitats.  These little guys get around.

The Eastern Cottontail has large hind feet, long ears, and a short fluffy white tail. They typically have speckled brown-gray fur on their backs and sides, reddish-brown fur around their neck and shoulders and much lighter fur around their nose and abdomen.  They are distinguished too by their large eyes and, of course, the white coloring on their “cottontails.”  In the winter, their fur may be more gray than brown. The kittens develop the same coloring after a few weeks, but they also have a white blaze that goes down their forehead that eventually disappears as they get older. The average adult weighs about 2-4 pounds; however the female tends to be heavier. The females here at the Field Station look like tanks.

The Eastern Cottontail can be found in meadows and shrubby areas in the eastern and south-central United States, southern Canada, eastern Mexico, Central America, and northernmost South America. It is abundant in Midwest North America, and has been found in New Mexico and Arizona. Its range expanded north as forests were cleared by settlers. Originally, it was not found in New England, but it has been introduced here and now competes for habitat there with the native New England Cottontail. The New England cottontail (Sylvilagus transitionalis), is very similar to the Eastern Cottontail, except that it has a black patch between its ears and a different skull shape, among other less noticeable differences.


A rabbit nest.

The Eastern Cottontail eats a variety of different plants including grasses, clover, fruits, and vegetables. About half the cottontail's intake is grasses, including bluegrass and wild rye. In the winter it eats the woody parts of plants like the twigs and the bark of brambles, birch, oak, sumac, dogwood, and maple trees. The cottontail prefers an area where it can hide quickly but be out in the open. Cottontails are happy in forests, thickets, meadows, and edge environments between woody vegetation and open land. Its range of habitats includes areas with second growth shrubs, vines and low deciduous trees.

Many people use the terms rabbits and hares interchangeably, but they are distinct creatures. Rabbits are distinguished from hares in that rabbits are altricial, which means their young are born blind and hairless. In contrast, hares are generally born with hair and are able to see (precocial). All rabbits (except the cottontail rabbit) live underground in burrows or warrens, while hares live in simple nests above the ground (as does the cottontail rabbit), and usually do not live in groups. Hares are generally larger than rabbits, with longer ears, and have black markings on their fur. Hares have not been domesticated, while rabbits are often kept as house pets. In gardens, they are typically kept in hutches—small, wooden, house-like boxes—that protect the rabbits from the environment and predators.

A great website called www.bookrags.com has a excellent summary about rabbits of all kinds including our Eastern Cottontail and I learned some interesting facts there such as the fact the rabbits are “hind gut” digesters which means that portions of the digestion system following the stomach (small and large intestine and large cecum) are where all the action happens. Much of a rabbit's diet is composed of large amounts of cellulose, which is always in plants and can be hard to digest. Rabbits solve this problem by passing two distinctive types of feces or poop: hard droppings and soft black viscous pellets, the latter of which are immediately eaten (Yum! sounds like Jake's favorite). Rabbits reingest their own droppings (rather than chewing the cud as do cows and many other herbivores) in order to fully digest their food and extract sufficient nutrients. So yes, rabbits eat their own poop, a behavior called coprophagy. And if that is not gross enough for you, here is another fun fact: rabbits are incapable of vomiting due to the physiology of their digestive system. I bet you'll never forget that trivia!

Back to more appetizing matters. A cottontail’s sharp senses of hearing and smell are among its adaptations for survival. The eyes are located on the sides of the head for wide peripheral vision. The ears are large and pivotal and are cupped to detect faint sounds. The cottontail sometimes checks the surroundings by standing on its hind legs with its forepaws tucked next to its chest. When danger is sensed, the cottontail “freezes” and relies on camouflaged coloration to avoid detection. Another survival mechanism is “flushing” or basically, “running like the wind.”  If necessary, cottontails can move quickly (18-20 mph) for short distances. Their zigzag running pattern is meant to confuse predators. They mainly drive me crazy as they dart back and forth over and over again while I am driving down my dirt road.  Eastern cottontail rabbits do not hibernate in the winter and instead find hollows to snuggle in and stay warm.  They are also very nocturnal as any night time drive on the island will verify. Last but not least, the males can be very territorial and may occupy as many as 5-8 acres while driving off any other males trying to enter their territory. Like deer, male rabbits are called bucks, and females are called “does.”

During mating season, males often fight with each other. The male and female also perform a kind of mating "dance." The male will chase the female. Eventually the female will stop and face the male and box at him with her front paws. At some point, one of them will leap straight up in the air and then the other one will jump up in the air too. This is pretty funny behavior when you see it firsthand.

After finding it, we checked the nest every few days to see how the kits progressed. Cottontails are born with very little fur and their eyes sealed shut. As they grow, their eyes open and their ears perk up.  Once their eyes open, a young cottontail is capable of eating solid foods on its own, but will ordinarily remain with its mother and siblings for a short time. Young cottontails are very nervous and may even die of fright if they are handled by a human or caught by a cat or dog.  Knowing our dog's total lack of predatory behavior or hunting competence around the umpteen million bunnies here, my guess is the kit he found died of fright.

After the female has given birth to her offspring, she can mate again immediately, so she is off to do what we expect most bunnies to do.  She will come back to the nest to feed the young twice a day for the first three weeks, usually at dawn and dusk; she will not visit the nest in the daytime in order to avoid alerting predators to its location.  As she is practically an absentee mother, her milk is one of the most nutritious of all mammals. The female gives birth about a month after mating. She can have from one to nine babies, although she usually will have four to five young. The babies are weaned after about three weeks and leave the nest after about seven weeks. Females can have three or four litters a year. Eastern cottontails are ready to mate when they are three months old. Their lifespan is on average three years although they can live much longer in captivity.

The high birth rates and frequent mating of rabbits coupled with their short life span and tendency to be food for something results in a 80-85% mortality rate.  This high mortality rate is one of nature’s checks and balances as one pair of rabbits and their offspring could potentially produce five million young over a five-year period. Many mortality factors affect rabbit populations. Weather is a major factor in nest mortality as ground nests are susceptible to flooding in heavy rains. Rabbits are known as the “protein base” for the mammalian food chain and serves as lunch for raptors such as red tailed hawks, coyotes, and many other mammals, not the least of which is humans. The Eastern Cottontail is the most commonly observed game animal in the United States.

Populations of Eastern Cottontail and the New England Cottontail have varied across the country and through the years as a result of changes in land type. As the Midwest started to build big farms with just a few crops, the Eastern Cottontail populations dropped precipitously while in New England, farms could not compete well with the Midwest farms and therefore some farming land returned to forest sooner, providing a suitable habitat and enough diversity in grasslands for Eastern Cottontails to proliferate (from Wild Mammals of North America by George A. Feldhamer, Bruce Carlyle Thompson, Joseph A. Chapman, 2nd ed, 2003).  The Eastern Cottontail's ability to spread throughout most of the U.S. lies in its adaptation to many habitats, in the Northeast it tends to favor disturbed and early successional forests with dense understories, lots of forage and cover, and relatively immature trees. As a result, the New England Cottontail has been losing the habitat war with the Eastern Cottontail.

This MA Division of Fisheries & Wildlife site: www.mass.gov/dfwele/dfw/wildlife/living/living_with_cottontails.htm, describes the plight of the New England Cottontail and its status as an endangered native rabbit in New England. In New Hampshire and Maine, wildlife officials are attempting to restore some of the habitat favored by the severely deplete New England cottontail population. Mass Wildlife has lots of useful information including estimates of species distribution around Massachusetts, and they list the Black-tailed Jackrabbit or Lepus californicus as still found on Nantucket Island, although they have a caveat that it may be extirpated. The state listing indicates that snowshoe hares may also be lurking around, and they believe that the New England Cottontail has become wiped out on Nantucket and Martha's Vineyard.

The occurrence of tick borne disease and its association with our local rabbit population has been around for many decades. According to D.L. Belding and B. Merrill's 1941 paper in the New England Journal of Medicine (224:1085-1087), “Tularemia in imported rabbits in Massachusetts,” the sudden appearance of tularemia in the Cape Cod region was associated with the importation of 29,689 rabbits from 1937 to 1940 by various Massachusetts game clubs.  Three hundred and forty of these rabbits were released on Nantucket Island.  And as mentioned above, Nantucket got the first wave of imported rabbits back in the 1880s.  So when we imported these rabbits we also imported any nasty bacterium or parasites they may have been carrying.  Tularemia or "Rabbit Fever" was once known as "rabbit skinner's disease" since persons would skin rabbits infected with this bacteria and become infected through tiny lacerations in their skin.  For many decades extensive research has been conducted on the role the Eastern Cottontail plays in the spread of tularemia, European human babesiosis, and human granulocytic ehrlichiosis on Nantucket.  A Google search will bring up a variety of papers from the extensive work of Harvard Public health researchers such as A. Spielman, Sam Telford, and Heidi Goethert. A summary of the leaps in science is at www.hsph.harvard.edu/review/nantucket_fever.shtml.

Rabbits have been shown to harbor a suite of zoonotic organisms (those that can transmit infectious diseases from animals to humans and vice versa), including a Babesia species (Babesia divergens), Anaplasma bovis (agent of bovine-infecting Ehrlichia), and Anaplasma phagocytophilum (the agent of agent of human granulocytic ehrlichiosis). The rabbits often serve as a dead-end host, transmitting diseases to ticks that bite them without getting the disease or suffering ill effects. The vectors and transmission probabilities, successes, and failures between white footed mice, deer ticks, rabbits, dogs, birds, humans, deer, and other hosts is quite complex for each disease. We may explore this in depth in another column, but suffice it to say, when in doubt, be careful when removing dead rabbits on your property.  And put that lid of grass right back over the baby bunnies nest.

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