Fallible wild animals

More photos by Zac. Penny included for scale

What: On our tracking adventure at Bread and Butter Farm, we were also impressed at the density of coyote sign - they must be snacking on all them li'l rabs. We decided to trail one of the paths for a ways. Pretty quickly, we started noticing blood spots in quite a few places along the trail. Female coyotes are monoestrous (having only one period of "heat" per year). It's relatively short, about 3-5 days and happens sometime between late January and early March, so we got lucky in our timing. The females will scent mark with their urine (which has blood in it). It shows up as small reddish yellow drops on the snow. The female we followed seemed to be on a hunting foray, traveling in mostly straight lines with occasional detours to investigate something that caught her attention (for as long as we followed her, she was unsuccessful in her hunt).

Zac and I both wound up post-holing while trailing her along a small brook that was frozen over. I tend to take clumsiness in humans as a given, but never expect it from wild animals. It's always jarring to see a squirrel miss a branch it's jumping to and fall to the ground, or watch a beaver trip as it's stepping over a rock, or catch a cottontail running into a fence. In this case, not more than 30 yards from where both Zac and I broke through the ice, we saw the tracks in the image above.

It appears like the coyote postholed, then slipped with her right front foot. The track just below the dark circle (the posthole) is her rear foot swinging out wide to steady herself. That 3' provided us with a hundred little stories and questions that we only began to answer as we made our way along the trail over the next half mile or so. It's always refreshing to remember that every now and again wild animal show their fallibility.

Ecological notes: In Centennial Woods there's an abundance of fox (red and gray) and deer, but no coyotes and only a very few rabbits. It made me wonder if there was a correlation between the presence/absence of those species. I found some interesting studies that look into the relationships between these species (as well as bobcats and even Lyme disease). Here's a summary of what I found:

• Coyotes eat gray foxes (not sure I believe this, or at least that this has a significant impact on gray fox populations)
• There's an inverse correlation between fox and rabbit populations. Where cottontails are in great abundance, red foxes, an obligate generalist, will shift and specialize in hunting them (study)
• Bobcats prefer rabbits and rodents and will eat deer second (study)
• There's an inverse relationship between fox and coyote populations (coyotes apparently bully foxes out of their territories, called interference competition study, another study found that a third of kit foxes radio collared had been killed by coyotes, study)
• As a result, foxes can be found on the edge of a coyote's territory, but rarely within it
• Foxes out-compete coyotes in areas where human densities are higher
• Many predators will kill other predators (canids, it turns out are the most likely predators to kill other species of predators: study)
• More foxes=less Lyme disease, more coyotes=more Lyme disease (study)
• Red foxes have a significant impact on the European Roe deer, but those are much smaller than our native deer and it's likely that no such correlation exists
• Coyotes have a significant impact on deer populations (study)
• Coyotes are more successful in hunting deer in harsh winters (study)
• There's no hunting allowed in Burlington, so deer populations may be higher here as a result
• Deer seek refuge under conifers during winter for warmth, both habitats provide an abundance of hemlock cover, however

Rabbits are what they eat

Rabbit debarking bittersweet (all photos in this post by Zas Ispa-Landa)

What: You are what you eat. And in this case rabbits are a whole lot of things. Zac and I were impressed at the abundance of rabbit sign (from the introduced eastern cottontail, Sylvilagus floridanus, as opposed to the native New England cottontail, Sylvilagus transitionalis) when we went tracking on Saturday down at Bread and Butter Farm in Shelburne. We even spooked a cottontail as we walked past the driveway. Rabbits seemed to prefer shrubby non-natives, or at least those were the most prolific species in the area and so were the most foraged upon. We found feeding sign (debarking and/or twigs clipped) on forsythia, common buckthorn, barberry, domestic apple, honeysuckle, staghorn sumac, and oriental bittersweet.

45o angle snips on twigs, charateristic feeding sign from cottontails
on woody species (forsythia in this case)

The story got even cooler at the end of the day when we found another high traffic area for cottontails under the powerlines. Buckthorn predominates in that area and the rabbits must have been eating fallen buckthorn berries as their urine was died blue (image on the right is blue tinted urine, on the right is more typical orange). Buckthorn berries are unpallatable, if not inedible to most things so the berries persist into late winter, when they become a last resort for many winter active species.

Ecological notes: Many plants contain phenolics (tannins, which cause the dry taste in wines, the bitterness in aspen bark) as a defense against herbivory. During spring and summer these are concentrated in leaves and flowers, but during winter they are translocated to the bark. Animals have a variety of ways of dealing with these phenolics (e.g. beavers will soak witchhazel before eating to leach tannins, birds and will eat clay, which absorbs phenolics). Buckthorn (Rhamnus cathartica) is high in phenolic compounds. Rabbits presumably can handle the phenolics by breaking them down in their kidneys, or maybe eating clay. The anthocyanins (pigments in the fruits) are also excreted in the urine. I'd assume that eating buckthorn fruits later in the season gives more time for the tannic acids to break down and makes the fruits more palatable. That's speculation though, and I couldn't find any articles to confirm/deny that.

What do foxes eat?

What: A couple nights ago, Meryl, Julia, Brian and I were watching a couple of eastern cottontails chasing each other ferociously around in my backyard. For the 3 or so minutes we watched, one was definitely the pursuer. They would sprint for short periods followed by great acrobatic displays with one or both jumping straight into the air. Their breeding season is March through September, so this might be an early start on staking out breeding territory, a mating ritual between a male and a female, or it could be a late winter food-shortage spat. I'd only ever seen one rabbit at a time in my backyard so I didn't realize that their territories overlapped. I have no idea of gender, nor is there a reliable way of telling without having the animal in hand.

I left some food out to bait so I could get a photo of at least one of the rabbits. For the hour or so I watched the rabbit from my window, it spent about 95% of its time in surveillance mode and the other 5% eating, moving, or grooming. I love the above photo, because it shows those great big back legs and stubby little front legs.

Where: My backyard

Other notes: Eastern cottontails (Sylvilagus floridanus) are virtually identical to the native New England cottontail (Sylvilagus transitionalis), and can only definitively be identified if the animal is dead (genetics or skull morphology). NE cottontail populations have declined since Eastern cottontails were introduced to Vermont over 100 years ago. According to a publication on Eastern cottontails produced by Vermont Fish Wildlife, wildlife agencies and private hunting clubs were responsible for the introductions. Rabbit populations have declined as a whole over much of New England due to reforestation and loss of transitional habitat.

At the end of every trail...

What: Brian came downstairs yipping about a red fox in the parking lot. A minute later Meryl came down equally excited. We threw on our shoes and headed out into the beautiful snow. We picked up the tracks circling along the edge of cedars then along the powerline substation by UVM Facilities office and Centennial Field. In the photo below the fox demonstrates a near perfect direct register trot. In this gait the animal's rear foot lands exactly where the front foot landed. The 3rd, 5th, and 7th prints appear wider where the animal slips from the direct register just slightly. The front foot, which is larger (as with all canines) and appears under the imprint of the rear foot, is offset to the right, where the fox was probably looking to the right (up the road to East Ave).

We came to a very very small crack in the fence that it had scooted under. Weirdest thing is to think how that little opening got there, as it seemed deliberate. Could the foxes have worked up the fence over time? It'd be tough for even a human to bend that fence. The fence is other wise in perfect shape and it's on the side that doesn't have any traffic so it's hard to imagine it accidentally getting formed. Regardless, it makes for a nice escape hatch (as when being pursued by a pair of humans).

On the east end of the substation, there's another gap in the fence that the fox slithered through before making its way down the rocks towards the dumpster. See if you can spot the fox in the image below. Brian and I watched the fox for a bit tugging away at the ground before slowly stalking up on it. 

As we got closer, it looked like it was trying to get under the plow. When we got about 35' away we scared the fox off and were able to investigate what it was investigating. We found a dead squirrel tangled in a pile of trash (smelled really really bad). The fox ran around the fence and hid under the building you can see in the above image.

Where: UVM Facilities/Centennial Field

Other notes: As we approached another fox of equal size got spooked and headed over to the south where the mulch piles are. The weirdest thing was that the fox was white. Or rather, it seemed like a darker colored fox that had its coat covered in snow. Brian and I were both covered in snow after being out about 30 minutes, so not unlikely, but still seemed weird - albino foxes in CW?

Snake mountain and lake closings (freeze overs)

What: I hiked up Snake Mountain with Jon and his family yesterday. Looking out at the southern end of Lake Champlain, I was surprised by how the sharp line at the edge of the ice was. The ice seemed to be corralled into the southern bay, perhaps by the harsh northerly wind. The freezing point I think was between Potash Bay in Addison, VT and Mullen Bay near Westport, NY. The image to the right shows data collected on the lake between 1816. Rectangles on the left side, colored in red, indicate years in which the lake did not freeze over completely at the widest point (from Burlington Bay across the lake about 9 miles to Corlaer Bay; 6 miles if you don't include the 2 bays). In total, since data collection began, the lake has not frozen over 38 times in the past 197 years. 32 of these are in the last 54 years! While it might be convenient to readily assume that climate change is the culprit, there might be some confounding factors that have also changed over the past 197 years. Things that lower the freezing point of water could include increased: Turbidity (suspended solids absorb more heat from sunlight) Wind Turbulence (like flow in a river) Concentrations of salt, alcohol or any other substance that has a lower freezing point than water I don't know for sure if these have any bearing on the fact that the lake is consistently less likely to freeze over, but they are likely a part of the story. I found an article from Feb 15, 1993 in the Daily Gazette about Lake Champlain closing dates (when it freezes over completely). The article states: "Whether the lake freezes over or not has no effect on the fish and other creatues that live there, said George LaBar, a UVM fisheries biologist. 'The bays are always going to be frozen, those shallow areas are going to freeze over,' and the fish who live in those bays are used to that, he said. A frozen lake doesn't affect teh overall temperature of the lake water, he said. Winters with less ice cover might encourage fish to spawn earlier, he said, which allows the young fish to grow larger." I really doubt that the lake not freezing over has no effect. I think it probably means something pretty significant for some things and not so much for others. Complex system with complex feedback loops.