You don’t see them very often, but California has more kinds of owls than you might realize. Fifteen species in fact, give or take a few. This uncertainty makes a lot of sense when you consider that owls often live in remote areas and are mainly active at night, when most of us are asleep.
Fortunately, owl biologists love to prowl around at night and ask hard questions about how owls survive in the dark – bringing these near-mystical creatures at least partially into the light for the rest of us.
One of the first things you might notice about owls are their prominent eyes, forward-facing in the skull to give them superior binocular vision. An owl has huge eyes (and a very small brain as a result) that comprise 32% of their skull weight, a far cry from the 1% of skull weight found in humans. Imagine a human carrying around eyeballs that weight several pounds
For all their visual acuity, owls seem to have a problem with close-up vision. One captive Western Screech-Owl (Megascops kennicottii) had to back up for a better look and a second try if it missed a tossed ball of wadded paper on the first pounce.
Hidden under an owl’s feather are highly specialized ears that allow it to track sound with pinpoint accuracy. On the right side of an owl’s head the ear sits below eye level and points upward, while on the left side the ear is above eye level and points downward, resulting in a discrepancy in the arrival of sound waves at each ear. Our common Barn Owl (Tyto alba) can detect arrival intervals of 10 millionths of a second and precisely locate mice in the absence of light.
We tend to think of owls as fierce hunters, but owls are actually fairly vulnerable to predators and must stay hidden during the day in order to avoid being eaten. In fact this is probably the main reason why owls are so expertly camouflaged in brown, gray, and white tones. This fact, coupled with persecution and habitat destruction wrought by humans, makes an owl’s life harder than you think.
In general, however, owls are a ubiquitous component of the landscape, even in suburban neighborhoods where Great Horned Owls (Bubo virginianus) and Western Screech-Owls fill the night air with their varied hoots, trills, and screeches. Every California county has at least 2 to 3 species of owls, while oak woodlands of the Coast Ranges average around 6 species per site.
There are some species like the Spotted Owl (Strix occidentalis), Great Gray Owl (Strix nebulosa), and Burrowing Owl (Athene cunicularia) which are declining in numbers, even though their populations are carefully managed by wildlife biologists. And then there are other species whose presence in California remains a mystery. For example, biologists strongly suspect that there might be populations of the Boreal Owl (Aegolius funereus) in the montane forests of northern California or Sierra Nevada, but very few people venture into these habitats during the winter months when boreal owls are actively calling. And the desert Elf Owl (Micrathene whitneyi) was until relatively recently found clinging to survival in fragmented slivers of habitat along the Colorado River but seems to have disappeared in the last couple years.
With the coming cold nights of winter, many owl species are rising from their drowsy summer quiet and actively calling for mates, making this a fantastic season for discovering the owls of your neighborhood. Great Horned Owls in particular can be extremely vocal and active, and their large hulking shapes make them easy to spot in the daytime. Sometime in late December or January, female Great Horned Owls settle down on abandoned red-tailed hawk nests and start incubating their 2 eggs, so this is a good time to start checking out every bulky nest of sticks for a distinctive “two-horned” face peering down at you.
David Lukas, co-author of Sierra Nevada Natural History