mammals – Page 4

Skull mystery

On occasion when hiking our 30 acres, which has minimal forest cover, I like to walk back along the narrow strip of mature forest that borders our western fenceline. For most of its length it’s only half a dozen meters/yards wide, although there are a handful of spots where it reaches out into the meadows. I wander through, looking for anything different going on there than I might see in the field a short distance away. I stick to our side of the fence even though it’s an old split-rail that would be easy to hop, primarily because we aren’t sure who owns that land and I feel uncomfortable trespassing unless I know the owners never visit the property. But there’s one spot where our section narrows and has become choked with the invasive prickly ash. If you’ve never had the opportunity to try crossing a prickly ash thicket, it’s rather like trying to push your way through a rose hedge. Yeah.

So I hop the fence there and just skirt around the small patch of prickly ash, and hop back and carry on my merry way. Today as I was doing my brief bit of trespassing I happened across this fragment of bone. Picking it up, I noticed it had the round knobs at the back which are the bit of the skull that articulates with the spine. But this clearly wasn’t a complete skull – the front half was missing. Sheared clean off, in fact. I puzzled over it, took a few photos, and left it where it was. What had it belonged to? What had sheared it away? Could a predator slice bone that cleanly?

It was only after I returned home that I had the thought that this might be a deer skull that a hunter cut. It was about the right size for the upper half of a deer skull, and comparing it to images on the web, it seemed to have a similar rear profile. I knew that deer antler trophies are sometimes mounted still attached to the poll of the skull. Further investigation (including this instructional video on how to prepare your own such mount, start to finish from a fresh deer head… not for the squeamish) revealed that the skull is cut with a hacksaw in a wedge behind and in front of the antlers, which pretty much confirmed for me what this bone seemed to indicate. Rather than just sever the poll, though, it appears our local hunter cut the back of the skull off first, and then removed the antlers second.

Although we’ve never met the folks who own that property, we’ve heard them out on their ATVs on rare occasion, and a couple of weeks ago I heard gunshots from that direction. This skull is much too old to have been this year’s, weathered and green with algae as it is, but it’s undoubtedly the remains of one of their kills. I’ve been through that area several times since last year’s hunting season, and as the fragment was lying out in the middle of a rocky bit, it’s unlikely I’d simply missed it before. Which presents another mystery: how’d this old bit of bone get there? It seems much too old for anything to have interest in chewing on it for the marrow. I have no answer to that question; it will have to remain a mystery.

The sawed-off portion does present an interesting cross-section of the bone, however, something not typically seen when examining skulls or other bones. We’ve been taught that mammal bones are solid while bird bones are hollow, but neither of these are strictly true. Bird bones are actually filled with many struts that brace the two walls and give the bones strength. Mammal bones are filled with tiny holes and channels that give it a very porous look. In addition to making the bone lighter to carry around, these holes serve an important function: they are the channels that carry blood vessels through the bone network so they can access the marrow inside (the part of the bone which produces new blood cells).

The meeting place

A quick announcement, first off, for the folks who use Facebook and might be interested. Starting today I’ve taken over day-to-day management of the Peterson Field Guide fan page on Facebook. I’ll be posting photographs with associated bits of information. If this blog is, let’s say, mostly lunch- or dinner-sized servings, the Facebook items will be snack-sized tidbits. The content will be otherwise largely similar, though. If you’re a Facebook user and want to follow my posts there, go to this page and click on “Like” at the top, and it’ll show up on your Facebook friends page. And if you’re not a Facebook user but still want to check in, I’m pretty sure you can go to that link and it’ll still show you everything even if you don’t have a Facebook account.

And a second announcement, regarding the Nature Blog Network. We (or, I should say, primarily the hard-working Wren of Wrennaissance Reflections) have been planning a reinvigorating of the NBN blog and community. One of the things NBN members indicated they’d like to see was an RSS feed of all of the posts from the NBN members’ blogs. Something similar to that Blogger sidebar widget what will show you the latest posts from a person’s blogroll contacts. The feed was launched today and can be found here. A Google Reader version containing complete posts is here. If you’re a Twitterer, new member posts will be tweeted at the NBN Twitter page. Unfortunately, blogs have to be added manually (we couldn’t find a bulk import option) and with over 1200 blogs in the NBN it’ll take a little while to get everyone added, but they’ll all get there eventually! It’ll be a great way to find new and engaging nature content.

I’ve noticed just recently a proliferation of trails in our meadows. They cut through the long grass, flattening it down with the creature’s passage. They criss and cross and double back and come together. Can you see them, in the photo above? Two trails, leading out of the forest and converging in a compressed patch of grass. A meeting place? Friendly hellos, or irritated confrontation?

I don’t know for sure who they’re made by, but I suspect porcupines. I came across a little pile of the distinctive macaroni-shaped droppings at the side of our human-made trail, where a creature-made trail intersected it, a few days ago (discovered primarily because Raven was rolling in it, otherwise it might have escaped my attention). Also, I think it’s more likely these trails were made by a low-bellied animal such as a porcupine or raccoon than by something taller like a coyote or a deer. When Raven wades (bounds) through the grass, or even, for that matter, when I do, we don’t leave such a distinct trail. Grass stands back up fairly quickly from a swishing-through, but takes more time to recover if it’s been flattened.

I’m not certain why there would suddenly be such an apparent exodus of porcupines from the forest just now. It’s possible that youngsters, who to this point have been able to share feeding territories with their parents, are now dispersing to find their own den sites and associated winter feeding grounds. Or, maybe it’s just a single individual or two who’s taken a liking to the shrubs growing in the field, and has been making trips back and forth and between plants.

(I was photographing a moth in the dark forest and set my camera to Manual mode while using the flash so the image wouldn’t get washed out. And then I forgot to change the setting back. So this image got washed out instead. I still like it, though.)

Sunday Snapshots: Dog in a field

Jumping mouse

I was hard at work on the moth guide this morning (three weeks to our deadline!) when Dan called up to me that there was an unusual mouse in the pool. Drowned, unfortunately; though we’re out at the pool two or three times a day, often, rodents that fall in overnight usually swim themselves to exhaustion. It’s a problem we’ve struggled to deal with; Dan put a board in the water today and we’ll see if that helps, but I think the best way to prevent critters from falling into the pool is to have an above-ground pool, or not have one at all. I assume they come to the pool looking for water to drink, but why do they fall in? Do they accidentally stumble over the edge in the darkness of night, not realizing the drop? It’s a bit of a mystery.

I grabbed my camera, despite the poor creature’s condition, because this wasn’t just any mouse: it was a Meadow Jumping Mouse, Zapus hudsonius, and it was a species I’d never seen before either alive or dead. When Dan described it to me he said it had a tail twice as long as its body, and really long back legs, which are the jumping mouse’s two distinctive characteristics. The hind legs, of course, are used to help it leap long distances, while the extra-long tail is used in balancing during these manoeuvres.

The only mammal guide I own is actually a section of the Reader’s Digest North American Wildlife, a hardcover book that I remember consulting growing up, and still find a useful reference for tidbits of information, or as a mammal or plant guide. Their image of the jumping mouse lacks the white underside or the buffy streak down the flank clearly visible on this individual, but there’s no mistaking that tail. Or those legs. And look at those long toes! They would also be an adaptation for stability in jumping.

The book indicates that the mouse “can leap across distances of 5 feet or more.” I’m not sure where they took their info from, but Wikipedia disputes that number, suggesting that 2-3 feet is more the norm (apparently at the start of the 1900s it was claimed they could jump as much as 8 to 10 feet in one bound! For a creature whose nose-to-tail-base is only a couple of inches this would be quite a feat. Studies in the 1930s actually observed the mice and came to the more modest values). What everyone does agree on is that the leaping is primarily an evasive manoeuvre, and the mouse usually moves in steps of only an inch or two when foraging, perhaps up to a few to several inches at a time when traveling.

Despite the name, Meadow Jumping Mice do occur in both meadow and forested habitats, though they typically prefer the open spaces. They are true hibernators, digging a burrow where they sleep away the winter in a low metabolic state. At more northern latitudes they may spend up to seven months of the year in hibernation. They mate immediately after emerging in the spring, and give birth to naked, blind young a mere 18 days later. A month after that the youngsters are independent and out on their own – it’s a turnaround that rivals many songbirds in its rapidity, and allows them to bear two litters in a summer.

Wikipedia notes that jumping mice are decent swimmers, and will often retreat to water when trying to escape danger. Could that be the reason this poor fellow ended up in the pool?

Groundhog day

One morning about a week ago, this groundhog spent a few hours hanging around close to the banding lab at Innis Point. We’d seen him, or we presume it was the same individual, once or twice a little farther out though still in the same general area, but this was the first time we’d noticed it so close to the buildings. One of my interns spotted him first, and pointed him out, and after watching him a few moments I went to get my camera. I sidled slooowly up toward him, and while he seemed alert and watchful, he didn’t seem overly nervous. He retreated to his burrow only once, and popped his head out again nearly immediately. When I paused and stood still, waiting for him, he eventually decided perhaps I was no threat after all, and came out to rest at the edge of his hole again. Through slow, non-threatening movements I was able to get within seven or eight feet of him. He remained there after I turned and slowly walked away again. I love encounters like that with wildlife.

That was the only time we’ve seen the groundhog at this burrow entrance, but that’s not to say he’s not still around in the area. A groundhog’s burrow may be fairly extensive, with up to five entrances from different directions, and 14 m (46 ft) of tunnels connecting to it. The entrance near our buildings may not be a favoured one. Burrows serve the dual purpose of sleeping and family-raising. They may use the burrow for hibernation, as well, or build a new one used expressly for that purpose; in either case, the burrow used for hibernation is dug deep enough to be below the frost line, where the soil remains above freezing through even the coldest months. Some may be as much as 1.5 m (5 ft) below the surface.

For the most part, except for the purposes of mating groundhogs are solitary animals. While the male keeps the female company during her month-long gestation period, he leaves before the young are born and she raises the pups by herself. The young are born in April or early May, which was about the time we started noticing this one around. I’m not sure if it’s a male or a female, as I admit I haven’t been able to get a good look at its back end.

The most famous groundhogs, of course, are those used in predicting the return of spring: Punxsutawney Phil and Ontario’s own Wiarton Willie. The original Wiarton Willie was an albino groundhog who lived in the town till the ripe old age of 22; he died during hibernation one winter. His successors have also been albinos. The first died at just six years, and while his death was attributed to an infection, six years is probably a more typical lifespan for a groundhog. Wild animals live on average about two to three years, with lucky or wily animals perhaps reaching six or more years before slowing reflexes, aging immune system, or other health problems finally catch up with them.

He was pretty comfortable with us there – so much so, that while I stood watching he stretched out one paw, flexing the little fingers, and yawned. I’m not sure whether this groundhog’s relaxed attitude will prove a good thing (conserve energy/metabolism) or bad (slow to retreat may result in being caught). In the weeks I’ve been there, though, we’ve yet to see a predator that would be a threat to a groundhog, so at the very least he seems to have chosen a good place to call home.