February 2010 – Page 2 – Seabrooke Leckie

Tay Meadows Tidbit – Pseudoscorpion

When I went to brush my teeth last night, I noticed this guy hiding behind the faucet. I put down my toothbrush and hurried to grab my camera and macro lens instead. The macro because it’s tiny, perhaps just half a centimetre (less than 1/4″). He was pretty obliging about hanging out for some photos, and the white porcelain sink made a nice, uncluttered background.

The critter is a pseudoscorpion. As you might guess by the number of legs on the body, pseudoscorpions are relatives of spiders, also found in Class Arachnida. Like spiders, they produce venom and silk, although the venom is injected through the pincer, and the silk is produced by a gland in their jaws rather than on their abdomen. Although they look just like scorpions without a tail, the similarity is superficial, as scorpions belong to a different Order (Scorpiones instead of Pseudoscorpionida).

There are some 3300 species of pseudoscorpion around the world, with potentially upward of 350 species in North America north of Mexico. Most of the diversity occurs farther south; up here there are probably fewer than 50 species that occur in Canada. They are found in virtually every habitat, from the deserts of the southwest to the northern taiga and tundra. There is one species that is so closely tied to human settlement that its habitat is described as “Houses, building, barns”, and is “often found crawling on the walls of older homes, particularly in humid locations”. That species would be Chelifer cancroides, and is the species that I believe my pseudoscorpion to most likely be, although apparently being able to definitively tell the difference between it and another Chelifer species requires being able to count the setae (hairs) on the pincer and examine the venom gland.

Pseudoscorpion, Chelifer cancroides — Also superficially resembles a crab, except crabs have tails that curl underneath their abdomens. No tail on this guy. (This is his underside. I flipped him gently with a Q-tip for this photo.)

When prodded, the pseudoscorpion goes into a defensive posture, pulling its pincers back toward its body. Its pincers aren’t limbs in the traditional sense, but are actually modified palps, mouthparts, much the way male spiders have swollen “mitts” in front of their faces. They use the palps primarily for hunting, stinging and immobilizing the prey with the venom gland located on the thumb-like inner pincer (the outer one is fixed). They apparently do not ingest the prey whole, but rather secrete digestive enzymes onto the prey and then “suck up” the liquified remains (this isn’t that different from the dietary habits of a spider, except the spider usually wraps its prey up with silk, first). Pseudoscorpions prey on dust mites and book lice, so are good to have around the home. Once it reaches maturity, an individual may live as long as two to three years.

Where the moths are

8926 - Syngrapha octoscripta - Dusky Silver Y

The last little while I’ve been hard at work making a push to wrap up the last of the maps for the moth field guide. This is partly because I’ve been itching for spring and the return of moths and wanted to focus on something moth-y, but mostly so that we will still have lots of time to review them before our deadline this summer. It’s been a bit of an undertaking – we plan to cover some 1300 species in the guide, and hope that some 800 of those will have range maps accompanying them. This will be the first guide to comprehensively provide maps for the majority of macro-moths, for the entire northeast region. Guides that have gone before have simply offered text descriptions of range (a few have maps, but of just the state and/or a subset of moths) but these can be so hard to interpret, especially when you’re not one of the corner states/provinces given in the text. We wanted to include something that would be faster and easier to interpret than text, more “user-friendly”.

The downside to this decision is that there just isn’t the data out there for moths that there is for other organisms, such as trees or birds. The data that does exist is in a highly scattered form. It includes records that may be extralimital occurrences (ie., vagrants), but with so few data points it’s hard to know for certain which ones are and which ones aren’t. I have a number of resources I’m referencing, both printed and web, as well as checklists and collection data from private moth’ers. I wish I had the sort of information at my disposal that birders have, but I’m making do.

There are a couple of approaches to presenting the data on a map. We could just plot points for locations we had data for. While this is easy to do and is guaranteed not to lie, it also doesn’t tell the whole truth as the species may occur in other areas where it just didn’t happen to be collected. We toyed with filling in states and provinces in a presence/absence presentation based on the data we had, but once again, while it was easy to do, this approach would also be misleading – even if a species only entered a state along one side or corner, it would still be displayed as though it occurred throughout. We really wanted to do smoothed range maps, because they look the nicest, but they require that you have a strong body of data in order to accurately define the boundaries.

After considerable thought and discussion, we decided to combine the latter two approaches. However, rather than using political boundaries to define our areas, we took an ecological approach. The map above shows ecoregional boundaries as defined by the North American Atlas project, a partnership between the Commission for Environmental Cooperation, and the governments of all three North American countries (you can download their maps for free here). The data I had for each species of moth was matched to the ecoregions on the map, and a range drawn encompassing all ecoregions that the species was known or believed to occur in based on collection data as well as information on habitat or food plants. Fortunately, because moths are so tied to their host species, ecoregions works better for them than it might for some other organisms.

Some assumptions are necessarily made in mapping ranges this way, and the depicted ranges may over- or under-estimate occurrence, but in a group of organisms for which data is sparse, this is almost inevitable. One of the hopes we have with the publication of this guide is that there will be an increase in interest in moths as a result of an easy-to-use ID guide, which will in turn create a bigger database of observations as people go out to look. Hopefully the second edition, down the road, would be able to refine the maps. In the meantime, I’m happy with how they’re turning out. Here are a few for a bunch of species that I’ve mentioned in the past here on the blog. I’ve also included the text range description from the original Peterson guide to moths by Charles V Covell, so you can see how they compare. The moth images below are the ones that accompanied the post, not the ones that will be in the guide.

*****

The Infant, Archiearis infans
These are early spring fliers, sometimes out even before the snow has completely melted from the ground. I typically see them in open areas near patches of birch. I wrote about them last spring, in a post I did about birch trees.

Text range description: N.S. to N.J. and Pa., west through Canada south to Minn.

*****

Morrison’s Sallow, Eupsilia morrisoni
This was my very first moth last spring. They’re encountered late in the fall and early in the spring, and occasionally in mid-winter on very warm days/evenings. They overwinter as adults, so they’re able to emerge from hiding to fly as soon as temperatures are warm enough.

Text range description: N.S. to Wash., D.C. and e. Ky., west to Ont., Minn., and Mo. [after carefully studying ecoregion boundaries compared to the rest of the described range, my other data points, and the species’ hosts/habitat, I decided not to include Missouri. I had no other data points for Missouri besides Covell’s.]

*****

Eastern Tent Caterpillar Moth, Malacosoma americanum
I’ve posted about tent caterpillars on a few occasions, but the first was on encountering a number of tents early in the spring during my first year of writing this blog. The adults fly in late June and July, after the caterpillars from the tents have pupated.

Text range description: Common throughout our area. [True; doesn’t occur in the northern Boreal, however.]

*****

Maple Spanworm, Ennomos magnaria
Back in September I participated in National Moth Night, a UK initiative that I was encouraging North Americans (and other countries) to adopt, too. Our two nights were cold here, and I got very little to my lights. The species that turned up in highest numbers was Maple Spanworm.

Incidentally, National Moth Night 2010 will take place on May 15. The date gets moved from year to year to sample different seasons. Don’t worry, I’ll remind you again before then.

Text range description: Nfld. to n. Fla., west across Canada, south to S.D., Mo., and Miss. [Actually found in a broader range within the east than the tent caterpillar, because it also occurs in the Boreal, however note that this species’ range was defined, while the tent caterpillar’s was not. My suspicion is that Covell started out trying to detail the ranges for everything, than then halfway through decided nuts to it, the common stuff he’d just save himself some time and put “Common throughout”.]

Tay Meadows Tidbit – Tree rings in snow

We’ve been having some warmer temperatures over the last couple of weeks. Warmer being a relative term, of course – most days it’s still at or below freezing, though perhaps not by much. We’ve had sprinklings of snow on a few days, though it hasn’t accumulated to much. Most days, however, have been sunny. Today is yet another sunny day. I’ve been noticing some snow melt as a result of all the sun, which can warm surfaces up above the freezing point. On our driveway and areas that receive a lot of traffic you can actually see the bare ground now. Also around the edges of the buildings where the snow doesn’t pile up as much because of drift patterns and the overhanging eaves. There’s bare ground under the evergreen trees, whose spreading boughs prevent deep accumulation of snow. And of course, there are the melt rings at the bases of tree trunks.

When I snapped these photos out in the 100-acre woods I thought this would be a pretty quick and easy post. Short, not much to say, right? There had to be dozens of posts talking about this exceptionally common phenomenon, right? Surprisingly, no. When I googled it today, most of the pages asking about it were things like Yahoo Answers, WikiAnswers, Answerbag, and similar. And judging from the great number and variety of answers posted to these questions, no one really seems to know.

The answer that seems to be mentioned the most is that the dark tree trunks absorb the warmth from the sun (even on cloudy days, some light still makes it through) and re-radiate it back into the environment; even just the slight rise in temperature from this is enough to melt the snow. Other explanations put forth were that the area under trees receives less snow to begin with; that the snow in the boughs of the trees melts and causes water to run or drip down the tree, melting the snow at the base; less grass means more geothermal heat rises from the ground under a tree than in the open; and turbulence caused by the wind breaking around the tree carries moisture away faster than in open areas.

I don’t know if anyone has done a rigorous scientific study to really say definitively. However, I found this study, which measured snow depth and ground surface temperature (where the ground and the snow meet) to a radius of 6 meters (20 feet) from a tree trunk. Their results showed that early in the season, snow under the pine tree being measured was only a third of what it was in the open, and by late in the season it was just a fifth. Probably because there was less insulative snow cover under the tree, ground temperatures closer to the tree were colder than those farther from the tree (this also meant the ground was frozen to a deeper depth under the tree than away from it).

To me it’s the re-radiation of heat from the trunks that makes the most sense, especially since in many cases the sunnier south side of the tree showed more melt than the north side. I’m surprised not to find anything definitively explaining the phenomenon, though.

Handiwork of a hunter

On my way from the second den site to the feeding location, the trail that I was following went down a rocky slope to a little creek, which the hemlocks were growing beside. Though the rocks were covered with snow, the slope was still steep, and the hard crust made footing uncertain, so I was keeping an eye on my step and not really paying attention to the surrounding woods. About halfway down I noticed a feather that had blown across my path. I stopped to pick it up; it was pretty, so I took a photo. Then I noticed another, and took a photo of that one, too. Then a couple more. As I looked, I realized they seemed to be originating from the top of the slope I’d just started down.

I climbed back up (just a short distance, a few feet), and discovered, at the top of the rocks, probably less than 2 meters (6 feet) from where I’d been walking, this mess of feathers left over from somebody’s meal. How I missed that, I don’t know. I was really focused on finding out where that porcupine went, I guess.

I identified the victim as a Ruffed Grouse by the tail feathers, whose thick, dark band is characteristic of the species. This was not a surprising find for me. On my walks in the 100-acre woods, as well as farther back from our house in the woods behind our back fields, grouse are the number one bird species I encounter. I don’t come across many, but I still have more meetings with them than I do with anything else, and that includes the ubiquitous chickadees.

I checked out the feathers for evidence of damage caused by the predator, either tooth marks from a mammal or crushed quills from a raptor, but couldn’t see anything definitive. I was about to just leave and label it “unknown” when I noticed the above: a very clear, very distinctive bit of whitewash that had blended in with the snow when I first examined the scene. The poop would have been left by the predator as it departed, and very clearly eliminates a mammal from consideration. A number of raptors will take grouse if given the opportunity, but the grouse’s biggest threat comes from either Great Horned Owls or Northern Goshawks, which probably account for the largest proportion of adult mortality.

There are a few reasons that I think this is a hawk kill and not an owl kill. The first, and primary one, is simply that the bird was plucked. Goshawks always pluck their prey, but I’ve found mixed reports on whether Great Horns do or not. Online there seem to be some references to the behaviour, but nothing consistent. I couldn’t see anything in the Birds of North America (BNA) account on the species indicating whether they do or don’t, although it does note that the Great Horn “Dismembers larger prey before swallowing… Dismembers larger mammals and birds with feet and bill; swallows the pieces. Generally discards head and feet of larger prey.” Nothing about plucking.

The way the poop is a line rather than a blob also suggests hawk to me, although I admit I have no experience with how owl poop looks when the bird is on the ground, not on a branch. I also don’t know whether owls defecate as they depart; I don’t recall ever having seen the behaviour in owls, though I have occasionally seen it in hawks. This may simply be a function of the greater frequency of observing hawks than owls. Third, though Great Horns will hunt in the forest, the BNA account suggests they prefer open areas, either woodland clearings, forests with open understories, or forest edges for hunting. Goshawks, meanwhile, are quite at home in denser woods. Although I wouldn’t exactly call the woods there dense, neither are they especially open. Finally, according to the BNA birds only make up about 10% of a Great Horn’s diet, on average, while they compose a much greater percentage, in some studies up to half, of a goshawk’s. Interestingly, the illustration in the goshawk account of hunting behaviour showed a goshawk chasing two Ruffed Grouse through the woods.

Ruffed Grouse by ru_24_real on Flickr; borrowed through Creative Commons license

I don’t know if it’s possible to know for certain who the hunter was. I know there are Great Horns around here, but goshawk isn’t an impossibility – they’re uncommon but present year-round throughout most of Ontario. They were recorded in the square immediately north and the one immediately east of us, as well as others in the area, during the recent Ontario Breeding Bird Atlas. And I actually thought I might have seen one cruise by the house one day a few weeks ago, but it was gone before I could get a good look.

I was amazed by the variety of patterns present in the feathers, and I took photos of many, all so beautiful. Can you figure out where on the bird they’re from? Here’s a tip: the ones with the squared off ends usually tend to be breast/belly feathers, while the ones that are longer and more rounded are typically from the back and shoulders.

Tracking the porcupine

I took Raven over to the 100-acre woods this afternoon. I hadn’t been over there in a little while, except for a quick hike through one day without camera or binoculars (I know, I know – you’re asking, why would I ever go for a hike without my camera? Sometimes, I guess, I just like to enjoy the forest for itself, and leaving the camera at home gives me more freedom to do that. Something like that, anyway.). The south portion of the property is completely forested, while the north end has open meadows chained together. There are access points at both sides of the property, one from the road, on the south, and the other from the rail-bed trail, on the north. Today I took the road, deciding I wasn’t really in a meadow mood. When I arrived I thought I would perhaps do a loop through the trails that stuck to the woods and return to the road entrance.

I started off according to plan. I headed down the west loop first, with the intention of taking that to one of the cross trails that would lead me to the loops on the east side. I got halfway down the west loop and then changed my mind. There was what looked like a small clearing set back from the trail, on the other side of some wild roses. Maybe I’d go check that out, and just cut through the forest to pick up the cross trail instead. So I changed course, pushed gingerly through the roses, checked out the clearing, and kept going.

And then, a short distance farther, I stumbled across the above, a very dirty track in the snow leading to a hole at the base of a dead tree.

Oh, what a fabulous discovery! My immediate first thought was that it was the nighttime den of a Snowshoe Hare, given the well-worn track that led right up to the doorway. It reminded me of the hare highways I blogged about a bit earlier this winter. I started to have doubts as I got closer, though. For one thing, the den was completely surrounded by, and filled with, the animal’s droppings. They weren’t droppings I recognized. Too big for rabbits, definitely too big for squirrels. Those of raccoons more resemble dogs or cats, and raccoons would be unlikely to be out and about anyway.

What was left? Porcupines? But they didn’t look like the porcupine poop I was used to seeing, either, which is a light sawdust colour, narrow, and curved like macaroni. Of all the droppings I know, these ones reminded me most of deer, actually – but there was no way a deer would fit in that little hole.

I decided to try following the trail to wherever it led to, and maybe seeing if I could pick out any tracks on it along the way. It wound through some dense rose shrubs, which I decided to skirt around instead of push through, and then carried on through the forest. Eventually the trail led up to the large tree here. Recognize it? It’s the same tree that Raven discovered a porcupine in back in the fall. That pretty much confirmed the identity of the critter for me.

At the base of this tree, more piles of droppings. These usually accumulate over the course of a winter underneath den trees or feeding sites, since the porcupine can’t be bothered going far when it’s snoozing. Dens are used through the entire winter, so the piles can grow quite large. They’ll break down over the summer, and will be nearly or entirely gone by next winter.

There was a narrow cedar log propped up on one side of the big tree, with its own small pile of droppings at its base. I wondered if the porcupine would sometimes climb up using that, which was at a shallower incline than going straight up the tree. It might be possible that there are two (or more) porcupines denning in this tree, and one of them prefers the log while the other uses the trunk. Porcupines are usually solitary creatures, but if den sites are at a premium they’ll sometimes come together and share a den in the winter.

Just like at the first den, there are packed-down droppings right in front of the den’s door. In doing some research on the porcupine’s habit of defecating on its front stoop, I learned that the reason I didn’t recognize these droppings is that the shape of the pellets is diet-related. Tough bark makes up more of the porcupine’s diet in winter, and so the droppings are more compact; in the summer, when it incorporates more soft food like leaves or grasses into its diet, its droppings resemble those that I’d found before. I’ve encountered a few of these paler sorts through both this winter and last, as well, so presumably they’re the result of different diet preferences between individuals.

There was another trail that led away from the big tree in a different direction from the one that I’d followed in. I decided to follow this one, too, to see where it went. Although I didn’t find this out until I came back home and poked around a bit, porcupines rarely travel farther than 100 m (300 feet) between their den and their feeding sites in the winter (summer ranges can be considerably larger). I figure the first trail I followed was about 60 m (200 feet) between the first den and the second.

After a similar distance, this second trail stopped at the base of a group of hemlocks that lined the small creek that cuts through the forest. Underneath the hemlocks were all these branch ends. I’d seen this before, and I’d just assumed that the poor trees had had a rough time of it in the last ice storm or something. Now I looked a bit closer.

All of them appeared to be snipped off neatly. I learned, again after returning home, that here in the northeast Eastern Hemlock is a favourite winter food of porcupines, such that some will feed on it nearly exclusively. They chew on the inner bark of the trunk, but they’ll also forage on the needles and small twigs of the branches. Given that one doesn’t encounter many trees with their trunks chewed apart, my guess is that the branches make up the bulk of their winter diet. White Pine is another favoured species, which makes me wonder if the hemlock-feeders have the dark, compact droppings and the pine-feeders have the narrow, paler droppings. I’ve also seen some evidence in our little bog to suggest that at least one porcupine was feeding on the tamarack (also pale droppings there).

In my poking around, I turned up this video of a porcupine feeding on hemlock twigs, taken and posted by Dave at Via Negativa last winter. Check out the narrow little branch the animal decides to climb! It’s practically tightrope-walking.

I ended up using up my alloted hiking time tracking the porcupine, and I never did make it around to pick up the cross trail. After I’d found the feeding site I returned back to the trail I’d come in by and headed back home. However, during that short bit of wandering around off-trail I collected up a number of blog-worthy photos, so I’ll have some stuff to share for the next little while!