Glaucidium gnomamountain pygmy-owl(Also: northern pygmy owl)

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Geographic Range

There has been much debate over the classification of Glaucidium gnoma californicum. Some experts now believe that these G. gnoma californicum deserves specific status as G. californicum, but the taxonomy of the genus Glaucidium is controversial. Evidence used in support of their specific status include their vocalizations. Because owls in general are primarily nocturnal, or active at dusk and night, their physical appearance and plumage patterns are believed to be less important than their calls and songs (Heidrich et al. 1995). Glaucidium gnoma californicum, unlike other G. gnoma populations, primarily hunt during the day. Glaucidium gnoma resides on the west coast of North America (extending from Canada, down to Central America) (Holt 2000), Glaucidium gnoma californicum inhabits a more compact region on the west coast, through the Rocky Mountains - from southern Alaska to southern California (Owl Pages 2000).

Habitat

These owls inhabit open coniferous and mixed forests, but are not found in dense, continuous forests. This may have to do with the use of open spaces and clearings where they dive down at their prey. They also hunt in open fields, wetlands, logged areas, and the edge of meadows (Owl Pages 2000). Because they rely so heavily on old woodpecker cavities for their nests, this selection of habitation may not be solely due to their preferences, but focus around where these woodpeckers reside as well.

Glaucidium californicum prefers to roost in quiet, shady alder thickets (Owl Pages 2000). (The Owl Pages, 2000)

Physical Description

The Northern Pygmy Owl's most distinguishing feature is its "extra pair of eyes" found on the back of its head. These two black teardrop-shape markings, bordered by white, resemble eyes. The rest of this owl's head is, depending on its habitation, gray, red, or brown in color - covered on the surface by small white dots. Glaucidium californicum's light belly is accented by thick brown stripes running vertically down its chest (Owl Pages 2000).

The males and females are fairly similar in appearance. Their average wingspan is 38 cm. The female's average length, however, is slightly larger: 18.5 cm, compared to 16.5 cm in males. Though very small in size, the Northern Pygmy Owl's tail, which when sitting is held slightly cocked upwards, is comparatively long and is striped six or seven times by light-white stripes (Owl Pages 2000). Both male and female have large yellow eyes, a yellow hornbill, and grayish yellow-feathered legs and toes.

Though the Northern Pygmy Owl's plumage doesn't show any seasonal variation, their coat colors from the north to down south demonstrates considerable differences. In the northern regions, this bird's upper parts are much grayer than in the south where the bird's feathers are browner (Holt 2000). The juveniles are similar in color to their parents, but with fluffier unspotted plumage, and grayer heads (Owl Pages 2000).

Reproduction

Glaucidium californicum breed from April to early June (Birds 2000). Though it is not known which sex is responsible for picking and building the nest, the actual sites are almost always old woodpecker cavities. The trees in which these birds nest are usually coniferous, and are found within boreal and deciduous forests. Glaucidium californicum have clutch sizes that range from 3 to 7, which the female incubates for about 29 days while the male is responsible for bringing back food to the nest. He also defends it from any predators. After the fledglings hatch, they grow quickly and reach almost adult size after 2 weeks. They fledge at approximately 30 days, but are defended and cared for by their parents for an extra 20 to 30 days (Owl Pages 2000).

Behavior

Glaucidium californicum is solitary (Holt et al. 1990). Very territorial, these owls -- especially the females -- fight by locking feet in the air, and falling to the ground (Holt 2000). This is very different from courtship, however, where these owls bring food to each other, and have been noted to snuggle together as well (Owl Pages 2000). Courtship again shows how important vocalizations are for owls. The Northern Pygmy Owl toot and trill in response to each other from nearby trees. The male then flies to the other, mounts, and copulates (Holt 2000). Mainly males use calls to defend territories, and are whistled hoots that sound like "too-too-too-too-too-too-too" at intervals of one or two seconds (Owl Pages 2000).

The Northern Pygmy Owl sleeps with its eyes open -- or so it appears. Actually, after settling onto a branch, these birds' clear-white eyelid (nictitating membrane) covers the eyes. This gives the appearance that it's still alert and watching, possibly to ward off potential predators or threats (Holt 2000). When awake, these birds erect their tuft feathers as a possible mode of concealment from prey and predators. These raised extensions of the eyebrows resemble twigs, and are accompanied by an elongation of their bodies, and pressing of their feathers against their bodies (Holt et al. 1990).

Communication and Perception

Food Habits

Unlike most owls that are active at night (Heidrich 1995) and rely mainly on sound or black-and-white vision, Glaucidium californicum hunts mainly by day. Therefore this bird relies mainly on its vision to capture its prey (Owl Pages 2000). Another notable difference between this owl compared to other owls is its noisy flight. Many owls have specially adapted feathers and wings for quiet flight. The Northern Pygmy Owl's wings not only make noise, but also whistle as it soars through the air (Holt 2000).

The Northern Pygmy Owl is a predominantly "sit and wait" type of predator. It sits and watches predominantly from the highest branches on trees (Owl Pages 2000) mainly for other birds, such as swallows, jays and chickadees, or sometimes mammals, such as shrews, moles and chipmunks (Holt 2000). When attacking its prey, it either dives down toward prey on the ground, or jump in a zigzag fashion from branch to branch before dropping onto its prey with its sharp claws (Holt 2000). These small owls, however, are much more vicious than they appear. They attack prey or run off predators that are up to several times their own size (Owl Pages 2000). After they catch a bird, they are plucked and either eaten entirely or only the brains are picked out (Owl Pages 2000).

Conservation Status

Glaucidium californicum is currently not endangered or targeted by shooting and trapping. As with most forest-dwelling species, they are susceptible to habitat loss due to logging and burning of forests.

Contributors

Gayle Soskolne (author), University of Michigan-Ann Arbor, Terry Root (editor), University of Michigan-Ann Arbor.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

chemical

uses smells or other chemicals to communicate

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

forest

forest biomes are dominated by trees, otherwise forest biomes can vary widely in amount of precipitation and seasonality.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

motile

having the capacity to move from one place to another.

native range

the area in which the animal is naturally found, the region in which it is endemic.

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

terrestrial

Living on the ground.

visual

uses sight to communicate

References

Heidrich, P., C. Koenig, M. Wink. 1995. Bioacoustics, taxonomy and molecular systematics in American Pygmy Owls. Stuttgarter Beitraege zur Naturkunde Serie a (Biologie)., 534: 1-47.

Holt, D., R. Kline, L. Sullivan-Holt. 1990. A description of tufts and concealing posture in Northern Pygmy-Owls. J. Raptor Res., 24(3): 59-63.

Holt, D., J. Peterson. 2000. Northern Pygmy-Owl. Birds of North America, 494.

The Owl Pages, 2000. "Northern Pygmy Owl" (On-line). Accessed Sept 14, 2000 at http://owlpages.com/species/glaucidium/californicum/.