November 10, 2011 Spotted Owl’s loss a wake-up call
The wild forests of western North America are awesome. Lush rainforests, renowned for gigantic trees, extend from the tip of northern Alaska to the San Francisco Bay. Equally breathtaking are the mountain forests that range into northern Mexico.
Rapacious destruction of old growth forests, global warming and invasive Barred owls are driving the fearless Spotted owl to extinction in Canada and uncomfortably low levels in both the U.S. and Mexico.
There are three subspecies of Spotted owls. The Northern Spotted owl ranges from southwestern British Columbia to northern California. The Californian Spotted owl is endemic to that state. And the Mexican Spotted owl lives in the mountains of Utah, Arizona, Colorado, New Mexico and northern Mexico.
All Spotted owls require old growth forests with large trees, a diverse array of lichens (half algae and half fungus), large dead standing trees, large fallen trees, large fallen dead trees in streams, small gaps in the canopy created when individual trees fall and an open under-storey.
The northern Spotted owl requires the largest amount of old growth at least 7,500 acres; the Californian Spotted owl needs 3,400 acres; and the Mexican Spotted owl has the lowest requirements of just 1,800 acres of ancient forests.
The size of their habitat is directly related to their main food source. Northern Spotted owls predominantly hunt smaller and less common northern flying squirrels and tree mice. Whereas the Californian and Mexican Spotted owls prey on an abundant source of wood-rats.
Spotted owls are cavity nesters. They need big standing dead trees in order to reproduce.
Females weighing 650 grams are significantly larger than males at 550 grams. This strategy allows smaller males increased agility in hunting diminutive flying of jumping prey, enabling them to deliver more food to nesting females and ravenous chicks.
Diversity of lichens growing on branches in old growth forests is an critical winter food source for flying squirrels and tree mice. In addition, decomposing nitrogen-rich lichens nourish nitrogen-poor soils.
A Spotted owl eats about 11 percent of its body weight a day. That translates into 57 pounds of prey a year or about 100 flying squirrels per owl. A nesting pair consumes 300 flying squirrels a year.
The owl’s stomach digests fleshy parts quickly but it cannot process fur, bones or feathers. Therefore, prior to eating it coughs up an oval pellet – containing indigestible prey parts. Incidentally, it’s these pellets that enable biologists to understand the exact food sources.
Spotted owls have black eyes, round heads and cryptic chocolate and white plumage. They blend into the dappled shadows of the forest and roost in the understory during the day.
These critters are especially designed to function at night with eyes supremely adapted for low light levels.
They pinpoint prey with acute hearing; their ears are positioned asymmetrically with the right ear being a different size and shape from the left.
The leading flight feathers are velvety in texture, providing silence in flight. During the night, Spotted owls perch silently in the forest and listen for prey.
Northern Goshawks and Great Horned owls are their predators.
A breeding pair of Northern Spotted owls produce two eggs (but sometimes only one egg), while the southern subspecies is more likely to incubate three. If the young chicks survive to juveniles then about 14 weeks after hatching they leave their native territory and strike-out in search of a new home, flying as far as 60 miles .
Between 67 and 100 percent of the young Spotted owls die during the dispersal phase. An adult has an 80 percent chance of surviving each year. Despites these odds, Spotted owls can live for more than two decades.
In 1986, the Northern Spotted Owl was listed as endangered in Canada. In 1993, the Northern Spotted and the Mexican Spotted owls were listed as threatened in the U.S.
In the 1990s there were approximately 100 breeding pairs in British Columbia. down from the historical records of 500 pairs. By 2000 the number fell to 50 pairs, and in 2006 it plummeted to only 3 known pairs.
Predators near the top of the food chain, like the Spotted owl are clearly more sensitive to senseless destruction of old growth forests than many other species.
The loss of the Northern Spotted owl in British Columbia is a wake-up call. Maintaining healthy ecosystems around the globe is of paramount importance for our quality of life and ultimately for our survival.
Earth Dr Reese Halter is an award-winning Science Communicator: Voice for Ecology and distinguished conservation biologist at California Lutheran University. His latest books are The Insatiable Bark Beetle and The Incomparable Honeybee
Text © by Dr Reese Halter 2011. All rights reserved.
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