Saturday, April 27, 2013

Fly Portraits

The warm weather has blown in at last, and with it arrives insects! Yesterday afternoon, the flies discovered the buck head hanging in the backyard, as well as a dead white-footed mouse I'd left outside. At first, they busied themselves with feeding — coming out of a wintertime torpor, their tiny fly stomachs were probably quite empty.


As the day progressed and the air warmed further, more flies arrived, and they began to swarm the buck head and lay their eggs.

Esophageal Egglaying   
Yesterday, when the temperatures were hovering around 50°F, there wasn't too much competition for egg-laying space. The flies had their pick of prime ovipositing spots, and their favorites seemed to be the esophagus, mouth, and eye sockets. Today, as temperatures climbed into the low sixties, the flies arrived en masse and laid their eggs wherever they could — on fur, eyelashes, whiskers. 

Once the buck head was pretty well-loaded with fly eggs, I relocated it to the ground, tied it to the base of a balsam fir, and concealed it with the branches of last December's Christmas tree. The brush cover will help keep the smell of decomposition at bay, deter unleashed dogs from bothering the head, and protect the maggots and other insect scavengers from cold nights and hungry birds.

On the topic of hungry birds: shortly before relocating the head, Steph and I watched a yellow-rumped warbler execute an impressive aerial maneuver to catch one of the egg-laying flies. It's incredible just how many different species of animals a single corpse can feed, both directly and indirectly.

Monday, April 22, 2013

Cold Decay

Spring may have officially started one month ago, but that doesn't mean much in Michigan's Upper Peninsula — especially not this year. In 2012, we experienced a spring unlike anything I've ever seen before: 80°F temperatures, early flower blooms, and little snowfall to speak of. This year has been the exact opposite. We've had snowstorm after snowstorm and weeks of daytime temperatures barely scraping 32°F; now, in what's getting to be late April, spring looks like it might finally be on its way. Maybe.

Toward the end of March, I put the head of the Ann Arbor buck outside, and tied it to a post: I had the hope that the chickadees, nuthatches, and bluejays would scavenge at it. Well, the birds saw it, gave it a few suspicious looks, and promptly ignored it — and the buck head has been hanging there, relatively unchanged, ever since.

Once the temperatures hit the mid-50s and 60s — and stay there — the beetles and flies will no doubt discover this food source and consume it quite quickly. I do still hope that the birds, at the very least, will use the fur to line their nests. I witnessed some of that behavior last spring, when I was stretching a deer hide, and it was neat to see the chickadees and warblers stuff as much fur as possible into their tiny beaks.

Despite the sky being gray and the temperatures not exceeding 40°F, the snow is melting — slowly. Much of our backyard is still covered. I did see an old friend today, though, thanks to the work of an off-leash dog. Last October, I picked a raccoon up off M-28, skinned it, and later put the body out back. At some point in late November I checked in on it, and was surprised to see maggots squirming around beneath the corpse. We received our first substantial snow in mid-January or so, and the raccoon has been covered ever since — until today.

The body's state of decomposition was quite putrid, with meat and fat sloughing off the bones. In some places, mold had started to grow, and it came in a vast array of colors, ranging from pink to white to blue. The off-leash dog had really torn into the carcass — and I've observed this, time and time again: (wild) scavenging mammals want nothing to do with carrion when it's in this state. Domestic dogs, however, seem to love it.

In any case, because spring has been slow, posting has been slow. I hear that temperatures might actually reach the low-60s this weekend, and maybe by mid-May the snowbanks will have melted.

Friday, April 5, 2013

From the Collection: Fisher Identification

This is a Fisher (Martes pennanti) skull:

It should not be confused with an American Badger (Taxidea taxus) skull:

... or a Raccoon (Procyon lotor) skull:

Fishers are a large member of the weasel family, Mustelidae. An uncommon and shy animal, they are agile tree-climbers and prefer coniferous forests. Fishers are well-known for being one of the very few predators of porcupines! They also prey upon snowshoe hares, squirrels, and other small mammals, and are known to eat carrion. Despite what their name suggests, fishers do not seek aquatic meals.

Here is another view of the fisher skull. Note the canine tooth was not quite fully erupted at the time of the animal's death:

And, a closer look at that canine tooth:

This is an interesting skull — the rest of the teeth appear to be adult teeth, fully grown-in. Some of the nasal sutures are fused, and the sagittal crest, while small, is still rather well-developed. It's possible that the canine tooth was just late in appearing, a pathology unique to this particular individual.

A fisher skull should not be hard to identify. Shape and size aside, there is an easy-to-find feature that is unique to this species' teeth:

The upper molar, second from the back, has an exposed "rootlet". No other animal skull of similar size or shape possesses this same characteristic. Nevertheless, fisher skulls seem to get confused with those of raccoons and badgers, at least in my experience.

As you might remember from the previous post about the badger skulls in my collection, they were a case of mistaken identity: the shop owner swore that they belonged to fishers. Here's a side-by-side comparison of the two:

click for larger view

Though fishers and badgers both belong to the weasel family, their appearance, habits, and skulls are quite different! The badger skull is larger and stockier; the fisher skull is thinner, with an overall more delicate appearance. While badgers are digging, burrowing animals restricted to the ground, fishers are skilled climbers and possess retractable claws.

When I purchased this fisher skull, it was misidentified as that of a raccoon. Shown together, they are quite different in shape, as well:

click for larger view

Again, the fisher skull is longer, thinner, and flatter than the stocky, domed raccoon skull. Raccoons, like fishers, are dexterous climbers, but their omnivorous diet is far more varied — hence the not-so-sharp teeth of the raccoon.

For good measure, here is a side-by-side comparison of the raccoon and badger skulls, as these two are often confused, as well:

click for larger view

Badger and raccoon skulls are actually pretty similar in appearance! But raccoon skulls are smaller, and badger skulls have a more "square" profile. Raccoons are not mustelids, and instead are part of a family that includes coatis and ring-tailed cats.

I've never seen a live fisher in my travels, and likely never will — they are a very wary animal. I came very close, however, last summer: Steph and I were backpacking along Pictured Rocks in Alger County, and near the beach we discovered the fresh tracks of a fisher:

It was likely that the fisher had been there no more than half an hour before us. Despite searching extensively, we never found the owner of the tracks.