Category Archives: Mammals

Ring-tailed lemurs

A small population of ring-tailed lemurs lives on the north end of St Catherine’s Island. The animals are descendents of a handful of ancestors that originally lived in the Bronx Zoo and Duke University. The lemurs are free-ranging but receive daily dietary supplements (fruit and “primate biscuit”) and regular veterinary attention. They have been on the island since 1985.

The lemurs’ social behavior is very similar to that found in the wild — they live in matriarchal groups that keep to a home territory. The matriarch and her daughters are usually the dominant animals within the group. Social rank is therefore determined by kinship (and, secondarily, by reproduction — not having babies knocks down a female’s rank). Males are subordinate to females. They live with the group for their first few months, then disperse and try to join other groups.

The lemurs on St Catherine’s are not “tame” (no touching allowed) but they seem to have no fear of humans, frequently approaching very close. This opens the door to interesting studies of their lives and primatologists travel here from across the world to observe the lemurs’ behavior. Most of the animals have individually colored radio-collars. These chunky necklaces appear to cause them no discomfort and allow researchers to track each animal.

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Lyme disease, foxes, and coyotes

A gray fox swaggered across University Ave this morning, its bushy tail bouncing as it trotted. It was headed to the patch of woodland behind Otey Parish Hall and the Duck River Electric building. I’ve seen fox scat on the road there, so I think this must be a resident, perhaps the same animal that I saw last summer with a rabbit in its mouth.

This has been a busy few months for fox and coyote sightings in Sewanee. Now, a paper in the Proceedings of the National Academy of Sciences has added some insight into the tangle of interactions among these wild dogs and their prey. Apparently, tick abundance and Lyme disease risk is affected by the numbers of foxes and coyotes. The paper examines data from the northeast, but its results may also be relevant here.

Lyme disease (caused by the bacteria Borrelia burgdorferi) is transmitted to humans by tick bites (especially bites from nymphal stage of Ixodes scapularis, the black-legged tick) But humans are not the main host of these ticks, so the abundance of ticks is determined by the abundance of their other mammalian hosts, especially mice. Foxes and coyotes both prey on mice, so you’d think that more foxes and more coyotes would mean fewer mice, and therefore fewer ticks, and therefore fewer Lyme disease cases. But things are not quite so simple.

The abundance of foxes is indeed correlated with a decreased risk of Lyme disease. Foxes love to eat mice and fox populations can get quite dense, so mice fare poorly in areas with healthy fox populations. Coyotes also eat mice, but coyotes live at lower population densities than foxes. Coyotes also drive out foxes. So the overall effect of coyotes on Lyme disease is a positive one: more coyotes = fewer foxes = more mice (despite the few that get eaten by coyotes) = more ticks = more Lyme disease. And deer? There was no correlation with Lyme disease; mouse abundance drives the dynamics of the disease and deer abundance seems to have little effect (except in areas that have no deer — an unusual situation these days — that do have lower incidences of Lyme).

Excerpt from one of the paper’s figures, showing correlations (or lack thereof) between Lyme disease and either coyotes per fox (positive correlation), foxes (negative correlation), or deer (no correlation).

An important caveat: this paper examined correlations among estimates of the abundance of different animals. But correlations are slippery things. They seem to imply that we’ve discovered a cause-and-effect relationship, but this is often misleading. So I’m sure this story will evolve as scientists tease out the subtleties (does the effect of foxes depend on the availability of other prey?) and alternative explanations (might some unknown causative third variable be correlated with coyotes and Lyme?). I wonder how domestic cats play into all this. They are major predators on mice and often live at densities well above what could be supported without the subsidy of store-bought cat food. Do they also suppress Lyme?

Some notes for blog readers in the south:

1. We’re well outside the “hotspot” of Lyme disease, as shown on this CDC map. The disease does not seem to be increasing in many parts of the south. But, in Virginia and other areas that are close to the center of Lyme’s activity, the disease is increasing quite rapidly.

2. The south is blessed with other tick-borne diseases. Southern Tick-Associated Rash Illness is one; Rocky Mountain Spotted Fever is another.

3. Although we do have black-legged ticks here, lone star ticks and dog ticks are more common. These are not prime carriers of Lyme, but they can transmit the other tick-borne diseases.

For more info about ticks, the CDC site has some good links and great pictures (which will make your skin crawl). Obviously, if you have medical concerns about a bite, check in with an MD, not a Rambler.

Mammoths

The discovery of the remains of a miniature mammoth on the Mediterranean island of Crete was announced last week. These mammoths stood about waist-high and the reconstruction of the animal in the journal Nature must rank as one of the cutest scientific reports in a long time.

If Crete seems impossibly remote, the map below serves as a reminder that mammoths and mastodons (full-sized: three meters high) roamed North America until very recently. For three million years, this species wandered through forests in small bands, tearing up the vegetation. The “damage” left by the much maligned white-tailed deer is nothing compared to what these giant herbivores wrought. About ten thousand years ago the mammoths and mastodons disappeared. A combination of climate change (the last of many ice ages was ending) and predation (humans had just shown up on the continent) probably did them in.

So, we have to turn to our imaginations to experience what our forests were like for most of their evolution. We sit on a mountain ridge and watch a group of huge elephant-like beings work their way across the valley, twisting at tree trunks with their five meter tusks, ripping and nibbling at branches with their mouths. Their calls? Stirring, no doubt.

Each dot is the location of a fossil. Image from FaunMap: http://www.museum.state.il.us/research/faunmap/ This map is for the American mastodon. The fossils from Crete were mammoths, a different genus.

Strolling on the beach

Two days ago these white-tailed deer sauntered out of the woods near Lake Cheston and walked the length of the beach, stopping occasionally to drink from the shallow water. They skipped off after a couple of minutes, leaving some crisp tracks in the sand.

There is nothing quite like the sight of ungulates ambling in the dawn light to take you back to the good old days.

Red fox kits

Jeff Heitzenrater sent me these photographs of a red fox mother and her kits (Vulpes vulpes). The foxes had little fear of humans and played openly even as Jeff approached with the camera. They were denning near his house, but have now grown up and moved on. The family group will stay together until late summer or autumn. At first I thought that this must be a gray fox — the tip of the tail seems to be dark, a distinguishing characteristic of the gray fox (red foxes have white tips). But the actual tail tip is hidden in the photos. The shape of the face (narrow muzzle, with large ears), the dark legs, the white wash that extends up the belly to the throat, and the bushiness of the tail all indicate that this is a red fox. If blog viewers have other ideas, please don’t hold back on correcting me in the comments section. In Sewanee, gray foxes are more common (they are woodland creatures) but red foxes do occur here and are fairly common in the valley. The red fox is the most widely distributed canid in the world, occurring on five continents. [update added later: Jeff has now sent me another photo (last one below) that clearly shows the white tail tip]

Coyotes

Harold Goldberg sent me these great photos of coyotes taken from his house in Sewanee. You can also see the photos in this week’s Messenger (I’ve held off on posting until the latest edition of the Messenger went live — no natural history scoops from me! :) )

At this time of year, coyotes are pairing up and breeding. Unlike many mammals, the male sticks around to help raise the young, as do some non-breeding pups from previous years. These family groups get very vocal when they reunite after hunting forays. I’ve heard their crazy yips and howls near our house for the last several nights – an acoustic dose of the wild. The goats and Junebug the Hound are not amused.

Coyotes have invaded our region from the Western states, partly replacing the ecological role of the wolves that used to roam here. But wolves sat atop the food chain, specializing in group hunts of large animals. As deer and forests were decimated in the wake of European arrival, the wolves disappeared, helped along by vigorous persecution. Coyotes are more flexible, eating small mammals, berries, insects, and whatever else is available and nutritious. This flexibility allows them to thrive in the fragmented, unpredictable world that we have created.

For those concerned about the abundance of deer in Sewanee, the arrival of coyotes is good news. Although they seldom take adults, coyotes do prey on fawns. For cat-lovers with outdoor pets, coyotes are cause for concern. Cats are a delicacy for most canids, including coyotes. This has some interesting ecological consequences. In California, areas with coyotes have thriving native bird populations, the result of predation by coyotes on cats (and behavioral changes in pet-owners – people are more likely to keep kitty indoors if they know that coyotes are on the prowl). This is a classic example of a “trophic cascade” in ecology – the effects of a top predator “cascade” down through the “trophic” (feeding)  levels in the system. My enemy’s predator is my friend.

Coyotes and wolves occupy interestingly different places in our cultural imagination. The wolf lives in that tense place between fear and desire (the Big Bad Wolf…ends up in bed…then slain…). Coyotes are more ambiguous. Most tales of coyotes regard them as playful, devious tricksters. These imaginings are fair reflections of ecology: the focused predator versus the jack-of-all-trades opportunist.

Listen for the trickster’s yodel…

Coda to Chuck D’s birthday

…the unity and diversity of life, illustrated by skull replicas of living primates (back row) and extinct putative human relatives (front row). Unity of form is plainly visible (short snouts, bony brain case, binocular vision, jaw arrangement) = the mark of kinship. Variations on the primate “theme” are also in evidence (teeth, skull size, muscle attachments, brain size) = ecological diversity. We measured these skulls and talked about their significance in Intro Bio this week.

A few cool living relatives:

Tarsier: a nocturnal (BIG eyes) insectivore (sharp little teeth)

Capuchin — strong premolars for cracking nuts, big ol’ canines for social “interactions”

The largest living great ape — massive sagittal crest (ridge of bone on top of head) for attachment of HUGE chewing muscles used to chomp on stems and leaves. The ape-cow.

Solstice Quiz

The theological overlay has changed over the years, but the underlying principle is the same: Sun = Life. So, on this most life-affirming day of the year, Happy Solstice to you (11:30pm CST is the hour, for those who like some precision).

In celebration, let’s have a quiz. These photos are all from along the Elk River, taken earlier this week.

Who made these tracks in the sand (each print would nestle easily in the palm of your hand)?

The same animal, showing back and front feet:

How about this one (a bigger track, about human hand-print sized, or a little smaller)? Normally, this creature has a fourth toe, pointing backward, but this time the mystery track-maker must have been walking daintily.

Now, look up. Whose nest is this?

Answers: here, here, and here.

I’ll close this ramble with a shot of the dawn mist on the Elk. Around my feet was strewn the plastic detritus of Homo sapiens (fishing tackle, TVs, bags of household junk, oil cans — all the usual suspects, minus needles this time), but the place was still beautiful.

Sewanee armadillo

The Sewanee network of road-kill aficionados (thank you, Rachel), pointed me to this freshly killed nine-banded armadillo (Dasypus novemcinctus) on the side of Rte 41A, outside Stillpoint (a name that, for this little animal, came with uninflected irony).

The “armored” skin of the armadillo is tessellated with striking patches of contrasting color. These patterns are made from little bony plates covered with leathery skin.

Armadillos are a recent arrival here in Sewanee and are still quite uncommon, although they are becoming abundant in the surrounding valleys. The first one was seen here about ten years ago on Gudger Rd. I then found one on the main highway through town, the first record in Sewanee itself. This latter specimen was also road-killed and is now in the mammal collection at the University of Tennessee. This week’s find is interesting because it comes at the start of winter. All the previous sightings have been in the warm months, suggesting perhaps that armadillos are moving up here from the valley in summer, but are not established year-round. Well, at least one made it to nearly the winter solstice.

Armadillos are champion diggers. Apparently, they can ruin a nice vegetable garden in one night. They excavate burrows to sleep in during the day and the entrance holes to these burrows are perfectly sized to catch unwary human feet, plunging unfortunate walkers into leg-twisting tunnels. The armadillo’s feet are well-equipped for this task:

But despite their tendency to dig where we don’t want them to, we should regard them with some awe, not with irritated condescension. They are members of a wonderfully strange group of mammals, the Xenarthrans, that originally evolved in South America. When the land bridge formed between North and South America, about three to five million years ago, these animals moved north, colonizing what is now the United States. This Sewanee armadillo had come a long way. Other members of the Xenarthra include additional armadillo species (incl. “pink fairy armadillo” and “screaming hairy armadillo” — did someone say “Muppets”?), sloths, and anteaters.

Is the resemblance to E. H. Shepard’s drawings of Piglet coincidental?