Naturespeak A naturalist's view of the world

April 8, 2008

At a Flying Tiger’s Lair

Filed under: Uncategorized — wykes @ 8:34 pm

Great Horned Owls are unconventional even among that circle of peculiar fowl known as owls. They nest so early in the spring that they actually end up nesting in the wintertime and they do so as squatters. Even though they are quite capable of doing their own stick work, these resourceful birds are dependant upon the nest building skills of red-tailed hawks, great-blue herons, and bald eagles for a well-made platform. They take over the old nests made the previous season by these other builders and claim them for their own. Their status as “great” birds seems further diminished when you consider that their kids are expected to eat each other in the event of a food shortage.

  In truth, the nesting and rearing strategy of the Great Horned (a.k.a. Flying Tiger and Big Cat Owl) is a stroke of native genius. Owls are among the dumbest of all birds, by the way, so this genius is strictly instinctive. By starting early, they have their choice of free nest space and an exclusive supply of groceries when the young hatch out (getting to the store, so to speak, while the shelves are relatively full and before the morning shoppers arrive). 

  Normal birds wait until their full clutch is laid before they begin to incubate them. In this way all the young come out at the same time and grow up at the same rate. A winter parent owl can afford no such luxury and must begin incubating the eggs immediately upon laying (they can lay up to 6 eggs, but usually hold it to two or three) to keep them from freezing. The young emerge in sequence after each has completed its 30-35 day incubation and the youngest arrival must compete with its older larger siblings at feeding time.  Should the cruel hand of nature deal out a skimpy crop of mice, the older owlets will engage in sibling-icide upon the younger family members in order to stay alive. If the mouse crop is robust, then all owlets will thrive. This is a stark form of high risk life insurance that puts sibling rivalry in a whole new light.

  I am happy to report that my local family of Great Horned risk-takers has entered this spring season with a brood of healthy owlets in tow.  The pair took over a large Red-tailed Hawk nest high atop a sturdy oak and they have weathered all that the weather demons have hurled upon the landscape.

  I approached their lair a few days ago and discovered that my approach did not go un-noticed. One of the parent birds was perched nearby (look here). It nervously shifted about from tree to tree and occasionally issued a loud worried “Wonk” call. Knowing full well that these sizable predators are active nest defenders and can pack a wallop with their talons, I kept an eye on this bird during the entire time I was in the vicinity of the nest tree.

  The nest itself is a large twiggy affair nestled in a crotch about 50 feet from the ground.  There were two fluffy young peering out over the edge (look here – the second one is peeking up over the edge on the right hand side). I would estimate them at over a month old because of their size and the fact that an adult is no longer on top of them (there is simply no room).

  Directly under the nest platform, the ground is speckled with whitewash and pellets. After a month of feeding, things can get pretty messy around an owlery with stuff coming out of both ends of the resident birds.  Just to clarify things, let me remind you that whitewash is actually the chalky “pee-poop” that comes out the back end and the pellets are the regurgitated hair/bone packets that come out the front end.

  Each and every meal results in a pellet of undigested bones, hair, whiskers and toenails after a 6-10 hour digestion period.  Even a cursory glance at the pellet contents relays the story of an abundant food supply.  Most of the pellets contained the skulls and limb bones of Meadow Voles (look here and you can see the bony remains of several animals).  Some of them contained larger bone fragments (see here) which turned out to be the mortal remains of a Cottontail Rabbit (based on the distinctive skull cap from that animal seen here).  It somehow seems fitting that the Easter Bunny ends up as an egg-shaped hairball.

  Not wanting to tempt fate, I quickly moved away from the nest site and left the guardian owl and her young to peacefully ponder their own pellets. The parent birds will continue to feed their owlets for another three to four weeks, but the crew will soon abandon this nest.  The owlets spend their last several weeks wandering about the nearby tree limbs- climbing about like tufted monkeys until developing their full flight abilities. I suppose you could say that they will be branching out at this crucial stage, but that would be a cheap pun.  

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