Naturespeak A naturalist's view of the world

December 20, 2009

Please Open Before Christmas

Filed under: Uncategorized — wykes @ 9:23 pm

I rarely pass up the opportunity to dissect an owl pellet. Such peristaltically propelled predatory packets are keys to unlocking the secret nightlife of our neighborhood owls. I remind you that pellets aren’t poop. They consist of the undigested remains of prey animals – mostly hair, bones, and feathers – which are compacted in the crop and ejected out of the bird’s mouth. Pellets are propelled, in other words, from the north end of an owl looking north whereas everything else is propelled from the south end. So, picking apart a pellet is not as nasty as you might think.  If viewed with proper attitude, pellets can be considered as little presents packed full ‘o fun and mystery. You never know what’s going to be inside. What a great Christmas idea for that special someone.

My last opportunity to do some pellet picking occurred just before our recent snowfall. A Great Horned Owl tossed his offering down onto the sidewalk behind the nature center building. Apparently the bird was perched on the roof edge and felt compelled to let ‘er rip right then and there. The pellet broke upon impacting the hard surface below, but it would have been about three inches long (see here). This size range put it firmly in the Great Horned Owl category.

I’ve often wondered what it feels like to eject a pellet. Based on the birds I’ve seen, they don’t appear to like it. They shake their head about, and with half-closed eyes, open up and fire. After the deed is done there are usually a few lip smacks followed by a slight re-focusing of the eyes. Perhaps the only comparable human experiences are those nasty soda pop burps and up-chucking, but I doubt they are truly the same.

While pondering the above question I carefully pulled the “little mystery packet” apart. I went for the big obvious bone first – like shaking the money out of a birthday card before reading who it was from. In this case the big piece turned out to be a complete lower leg bone (called a tarsalmetatarsus) from a bird. The rest of the pellet consisted of bird remains as well – over 124 bone fragments from two different types of birds (see below). All of this, including an intact feather, was packed in the talcum like powdery matrix of digested feathers.

Great horns are primarily mammal killers. They will go after anything from tiny shrews to fuzzy lap cats. But, if there is one thing that can be said about this bird’s diet, it is eclectic. Records show that virtually any kind of smaller animal can find itself on the dinner list. This list may include a variety of fish, bats, amphibians, and a whole host of birds. There is even a circumstance where one of these owls descended into a chimney in order to pick off a few of the Chimney Swifts nesting there.

After a bit of detective work involving a text on bird osteology and comparative samples, I determined that the pellet bones represented a foot form a diving duck and the better (or worse part) of a small perching bird. The small bird, complete with a tiny wish bone, was probably a Starling and the identity of the duck centered on a Ruddy Duck.

Each evening for the past month the marsh adjacent to the nature center has been the gathering and roosting spot for thousands of blackbirds. Most of these sooty fellows are Starlings. The birds circle about like shifting schools of fish for about 20 minutes before settling for the night on the branches of the cottonwood trees. I now had proof positive that at least one Great Horned Owl was conducting nocturnal raiding parties on this bountiful bird offering.  In order to confirm the duck identification, I was lucky enough to come upon the fresh remains of a Ruddy Duck out by the lakeshore (you’ll hear more about this one in the next Naturespeak).  I boiled down the foot (see here) from that bird and rendered the bones for comparison.

The bone match, especially on the tarsometatarsus, was exact (see comparison above – the pellet bones are on the bottom). In fact, I was even able to figure that the pellet remains were form the right foot of some unfortunate Ruddy duck (see here). The only thing missing was the outermost toe. What I don’t know is how the owl obtained his duck meal. There is a chance that the owl scavenged the fowl just like I had. Since they’ve been recorded as taking live ducks, however, there is no reason to suppose our Ruddy wasn’t taken via a stealth attack on the ice. in short, it was a duck that didn’t duck in time!

I can’t wait for the next pellet. I’m looking forward to finding one that contains a little buckle in it from a cat collar.

4 Comments »

  1. Ooo – very cool. I love pellet dissections – and try to convince many students every year that it is a really cool activity. The strangest thing I’ve found were mandibles from Jerselum crickets – we found them in 2 or 3 pellets one year. Most it’s mice, with the occasional shrew, mole or bird thrown in. Never a duck, though – ambitious owl!

    Comment by Ellen — December 21, 2009 @ 2:05 pm

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  3. Have I mentioned I love your blog? Awesome post! I’m astonished you were able to determine that it was a Ruddy duck. Seriously impressive – both your detective work and the owl’s ambition!

    Comment by Holly — December 22, 2009 @ 12:40 pm

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