Thursday, January 29, 2009

Barred Owls

Earlier this winter I was standing in the drive way chatting with my neighbor when an owl swooped down out from the trees near by and landed on a fence post in my neighbor’s yard. Apparently my neighbor was feeding some resident red squirrels, who had made their home in the covered patio furniture directly under the fence post where the owl was now sitting, so there was no mystery about what he or she was after.

The owl turned out to be a barred owl, Strix varia in the scientific nomenclature. Barred owls are quite common in Maine, they are certainly the ones I hear vocalizing the most. They are permanent residents of the state, meaning they do not migrate. They are generally permanent residents of their breeding grounds as well, so if you have barred owls around your house it is likely that they will remain. Most owls are active at night, called nocturnal, or during dusk and dawn, called crepuscular. The barred owl is active during all of these times, but may also be active during the day, especially if it is an overcast gray day, as it was the day I saw one on the fence post.

The barred owl is exquisitely adapted to do what it does, which is hunt silently and effectively, preying on small rodents and other animals. All animals have adaptations that allow them to fill their niches, some more so than others. On one end of the spectrum are animals (and plants too for that matter) that are rather cosmopolitan , with very general adaptations that allow them to function and even thrive in a wide variety of conditions and use diverse food sources. Humans, rats, and sea gulls are examples of these wide ranging species. On the other end of the spectrum are plants and animals with very specific or narrow niches—basically they are highly specialized to eat a certain food, be pollinated by just one specific pollinator, or live a certain way. Owls, though they can eat a relatively wide variety of foods, are generally thought to be on the highly specialized end of the spectrum.

The barred owl in my neighborhood, like barred owls all over Maine have their eyes on the front of their faces, like humans. Most other birds have eyes on the sides of their heads. The forward facing eyes do the same thing for owls that they do for us, that is give us excellent depth perception. This helps them hunt during low light conditions. Their ears are also specially adapted to help them hunt after dark. The ears of the barred owl are asymmetric. They have one on each side of their head, like we do, but they are not at the same level, one is higher than the other. This asymmetry helps them pinpoint the location of sounds. Barred owls tend to know their territory very well, so between their good depth perception, their acute hearing and their mental map of every perch in their hunting grounds, they are successful and opportunistic predators.

Pay attention in the next couple of months, Barred owls will be mating, which usually means a lot of vocalization. You may hear their familiar “who cooks for you?” call, or even something that sounds like a pack of monkeys has arrived in the Maine woods. Either way, its more likely that you will hear an owl than see one.

First Aired January 2008

Thursday, January 15, 2009

Snowshoe Hares

One of my favorite things about walking in the woods during Maine winter is seeing animal tracks in the snow. Deer, red squirrel, turkey and probably most reliably snow shoe hare. Snow shoe hares are common throughout northern north America, though their numbers can varied wildly from year to year as a result of predation pressure. If you want to see their tracks look in the snow anywhere in the woods there is dense underbrush or stands of conifers. Swampy alder thickets, boggy areas, these are great places to look for snowshoe hare tracks.

Snow shoe hares get their name from their big back feet—large in surface area, and covered with dense fur, they act like snow shoes and allow the hare to move around easily on the snow pack. They are also called varying hares—this name comes from the fact that they change color seasonally. In the winter the snow shoe hare is white, and in the summer it is brown to reddish brown. This is an adaptation to help them avoid their nearly inevitable fate—snow shoe hare are the all you can eat buffet of the northern forest. Essentially their job is to get eaten. They can live up to 5 years, but one study suggests that 85% of them make it barely a year—and this is what is described in the literature as being very good at avoiding predation. Clearly if they were any worse there wouldn’t be any left. But back to this seasonal color change. In the summer they have a thin brownish coat, they blend in well with their underbrush habitat. The change to white is controlled by photoperiod, or length of day. As the days start to shorten in the fall, the hare’s body senses it and responds by turning on a second set of hair follicles-the cells that grow hair and fur, this second set is the one that grow the thick white winter coat. The summer hair follicles, the ones that grown the summer coat, stop making brown hair, and the summer coat molts out and isn’t replaced. This transformation can take up to 10 weeks. And it reverses in the spring when the days get longer again. It is a great strategy when the timing is right, and the white coat coincides with the snow fall, and the brown coat coincides with the spring melt. When the snow is late, or early, or melts early, or hangs around late, the hare’s cammoflage can be compromised.

Today is a double whammy when it comes to cool facts. Because not only does the snowshoe hare experience a seasonal color change that is controlled by day length, they also engage in coprophagy. And what is this you may ask. Quite simply it means they eat their own dung. Yes, you heard me right. It turns out that what hares eat is relatively hard to digest. Grass, twigs, bark, buds, all things that are full of cellulose and other difficult to break down organic compounds that do not readily give up their nutrients. The bacteria that live in the hare’s gut work away at digesting this material, but it takes a long time, longer than this material actually can stay inside the hare. So the hare goes to all the trouble to forage, but can’t fully digest the material it eats, thus it does a lot of work for not so much nutrition. The way it solves this problem is, you guessed it, after the first pass through the digestive track the hare eats its own fecal material, and gives its intestinal bacteria a second chance to liberate all possible nutrition from the hard to digest fodder.

There are lots of animals I would love to be even if just for a little while, but between constant pressure of everyone trying to eat me, and having to survive by eating my own poo, I am glad I’ll probably never get to be a snowshoe hare.