Tay Meadows Tidbit – tiny bones

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About a week ago, before we got all that snow (as you can see from the photos), I was hunting for a ball I’d thrown for Raven that had disappeared into the woods and she seemed unable to find. I circled wider and wider, completely puzzled about what happened to the ball (it took a funny bounce, it later turned out, and ended up on the other side of the driveway yards away from where we were looking). Eventually my circles brought me to a track in the forest, barely more than a tree-less gap, that ran between the natural forest and the artificially-planted pines at the foot of the drive.

Out in the middle of this, I spotted some poop. It looked like hawk or owl poop. I remember reading on Julie Zickefoose’s blog some time ago about the difference between hawk and owl poops, in that one (I think owl) drops it straight down from their perch, while the other (hawk) expels it at an angle. The first ends up as a blob on the leaf litter, while the latter results in more of a streak. These ones looked definitely blob-ish, so I suspect owl, and a good-sized one at that given the amount of poop. Perhaps the Great Horned that we’ve heard from time to time and whose pellet Dan found under the maple in the front yard.

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Looking closer, I noticed there was a pile of bones beside the poop. They were completely cleaned off. I couldn’t tell how long they (or the poop) had been there – possibly even since that first pellet was found in early October. Although we tend to think of bird poop washing away quickly, if it had been a dry spell, the poop might have hardened making it harder to wash off the leaves. My suspicion is that these bones used to be in a pellet, but that rain that we’ve had since (and quite a bit of it at times in November) combined with the work of scavenging beetles and other invertebrates, have decomposed and washed away the hair that used to be matted up with it.

I can’t tell what they used to belong to. Most of the bones were broken or fragmented, and the only skull bone I could pick out was a portion of a lower jaw bone, below. I didn’t think owls broke the bones when they were digesting their prey and forming the pellet, and I briefly toyed with the idea that this might be a snake poop, but aside from the broken bones there was nothing else to conclusively support that. I saw a few vertebrae in the pile, but the rest were generic long bones, or at least looked that way. The jaw bone was tiny, and quite long relative to its size. Shrew, perhaps?

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The Dark is Rising – or is it?

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The full moon is Thursday this week. They’re forecasting overcast skies and precipitation for the next several days, so I’m not sure we’ll see it at its peak, but right now, two days before full, the moon is pretty bright, enough that we don’t need to wear a headlamp to walk down to check the owl nets. Moonrise this evening was timed with dusk, and as I was looking out over the lake an hour or two after the sun had gone down, the rising moon caught my eye, hanging behind the silhouettes of the tall trees in the yard. I grabbed my camera and set it up on a tripod out on the deck. Uncertain about what exposure was necessary to capture the scene, I took several at different settings. The above was the one that most closely resembled what my eye saw. All the photos were taken at F/5.6 and ISO800, with just the shutter speed changed – this was at 1 second exposure.

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Some animals can see a lot better in the dark than we can. This is largely due to the structure of the eye. The vertebrate eye contains two types of cells in the retina – rods and cones. Rods are used in capturing light, and cones are used in detecting colour. Humans have more cones than rods, which is why our colour perception is so good. We have some rods, but being primarily diurnal species we don’t need a whole lot. Other critters, on the other hand, who do a lot of moving around at night tend to have more rods than cones – colour isn’t as important at night. Cats, for instance, frequently hunt at night and are known for their excellent night vision. The average cat has about six times more rods in their retina than a human (which translates to about six times more light captured, allowing them to see about six times better). I fancy that this is what the world looks like to a cat at night. This was a 4 second exposure, so not quite six times difference, but close.

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Owls are well-adapted to hunt at night, and may have among the best night vision of any land creature. Their retinas have as many as 10 times the number of rods that those of humans do, so they can see exceptionally well in the dark (this is helped by their exceptional 3-dimensional hearing, which results from their ears being off-centre from each other). Owls also have very large eyes relative to the size of their head – so large, in fact, that there’s hardly any room for eyeball muscles to move them around, and so the eyes are fixed in the skull. To look around the owl moves its whole head, and although it doesn’t have a complete 360 degree range of motion, it does come fairly close. These large eyes provide a greater expanse of retina for light collection, also contributing to their excellent night vision. This was a 15 second exposure. It might as well be daytime, you can even make out the colours of the trees across the lake.

In doing some of these long-exposure photos I often find it astounding how much light is actually available to the camera that our eye just can’t detect. It may look like the dark is rising at sunset, but it really isn’t.