"A wise old owl once lived in a wood, the more he heard the less he said, the less he said the more he heard, let's emulate that wise old bird." — Flann O'Brien

Truth be told, owls are probably no more or less wise than most birds. Yet, perhaps because of their round head and those exceptionally large forward-facing eyes, they have a somewhat human-like countenance, and so “must” be wise. The true geniuses of the world of birds are ravens and crows, yet nothing about their appearance is human-like, and so they get no respect. A group of crows is called a “murder," a group of ravens is an “unkindness." However, a group of owls, if such an association ever occurred, is a “parliament." 

An axiom of ecology is that, assuming limited resources, no two animal species can occupy the same space at the same time eating the same food. The closer they get in space and diet the more likely they are to compete, and competition means winners and losers with the loser having to go elsewhere and find something else to eat. So hawks and falcons are the daytime birds of prey, eating daytime foods, while owls are typically taking the night shift, eating those things that go bump in the night. Across the North American deserts, you can find as many as seven species of owls living here, but adhering to that axiom, each eats something different or does so in a different place.

Deep within the Sonoran Desert, where iconic 30-50’ tall giant saguaro cacti decorate the hillsides, Gila woodpeckers and gilded flickers excavate homes in the cactus’ fleshy column. Once used they are abandoned, and those cavities form cool and dark abodes for miniature owls, small sparrow-sized elf owls, one inch longer ferruginous pygmy owls, and screech owls only slightly larger still. Elf owls eat moths, crickets, centipedes, and beetles. The pygmy owls seem to prefer dining on small birds. The cacti-dwelling screech owls consume small rodents, some birds, and scorpions. Same place, different menus. The ferruginous pygmy owls reach their northernmost range in Arizona near Tucson, otherwise occurring south into Central America. Screech owls can be found here in the Coachella Valley, living in the unburned, untrimmed skirts of native California fan palms. Elf owls sometimes will venture as far west as Corn Spring in the Chuckwalla Mountains, occupying cavities in the trunks of native palms once again excavated by a Gila woodpecker living at the western edge of its range.

Short-eared owls hunt during the late afternoon and early morning for voles in grasslands, marshlands, and agriculture fields. They fly with a distinctive wingbeat, looking like giant, prehistoric moths. I have seen one here in the Coachella Valley just once, coursing back and forth above the sand dunes. The more common desert owls include great horned (the only local species that actually “hoots”), long-eared owls, burrowing owls, barn owls, and screech owls (which do not screech, they trill, but barn owls do screech). Except for burrowing owls, the other four are commonly found living in native California fan palm oases, untrimmed and unburned, growing in dense clusters. When native palms are planted in suburban landscapes in clusters, untrimmed, they too can be inhabited by barn and great horned owls. In those cases, their diets are largely filled with non-native mice and rats.

Owls do something that makes them excellent subjects for studying their diets, they often swallow their prey whole, then in a section of their digestive tract before their stomach, acids strip away anything easily absorbed and everything else, feathers, hair, bones, and scorpion stingers, gets regurgitated in a little (or big) package called a pellet or casting. Watching an owl regurgitate a pellet, they yawn and stretch their necks, and sometimes use a talon to reach into their mouth to delicately ease out the casting. These pellets accumulate beneath their daytime roosts, providing a treasure trove of information about everything they’ve eaten. In 1986, when Katie, Colin and I arrived in the Coachella Valley, my “office” was in the “Palm House” in the Thousand Palms Canyon Oasis. Lots of palms, lots of owls, and lots of pellets. I decided to test that axiom of ecology.

Great horned owls, which also occupy rock nooks and clefts high on the walls of desert canyons, are more common living in the palms. This, our largest owl, regurgitates huge pellets – bigger than a pre-teen child’s fist – and had the biggest range of prey sizes, big scorpions were common, but so were woodrats, gophers and even cottontail rabbits. None of the other owl species touched the rabbits. Screech owl pellets were about the size of the last two joints on your little finger. Nearly half of their diet consisted of various arthropods, but there were also a few gophers, and lots of kangaroo rats and pocket mice. Very different sized owls eating very different food. The other two palm oasis owls, barn owls and long-eared owls, are almost identical in size and as it turned out they ate pretty much the same food. Mostly pocket mice and kangaroo rats with the occasional woodrat, although the barn owls did eat more gophers. I don’t remember ever having a barn owl and a long-eared owl occupy the same palm oasis, so perhaps they avoid competition by avoiding each other. Another possibility was that there were such plentiful pocket mice and kangaroo rats to be had that there were no limits.

The fifth owl species commonly occurring in the Coachella Valley is the burrowing owl, the one desert owl that wants nothing to do with palm oases or saguaro cacti. Burrowing owls want open, treeless landscapes. True to their name, these owls live in burrows extending well underground. They typically use abandoned burrows from ground squirrels, and enlarge them and decorate them, sometimes with horse or cow manure. The reason for the decorations could be twofold, to hide their scent from predators such as coyotes or badgers, and to insulate the bottom of the burrow from the cold winter earth. It would be interesting to know what, if anything, they used before cows and horses were brought here. Perhaps it is a remnant behavior from the Pleistocene Epoch when there was lots of manure available, from ground sloths and horses and camels and mammoths and mastodons. Burrowing owls can occur as isolated pairs, but are often found in loose colonies (parliaments?) of two to three, up to maybe ten pairs occur across several acres. Like with people, the burrowing owl population expands in the winter with migrants from the cold steppes of Saskatchewan, but there is a resident group of owls that are here all year long.

Burrowing owls will eat an occasional kangaroo rat, but when it comes to vertebrates, they strongly prefer pocket mice. However, by far their most common dietary items are solpugids, arachnids commonly called sun scorpions. They are not scorpions and have no stinger. Nor do they have the venom we associate with another group of arachnids, spiders. They have very soft, digestible bodies and if it wasn’t for one thing, I would never be able to detect them in the owls' pellets. That one thing is their mandibles. Their mouth parts include four independently moving jaws, each tipped in a hard exoskeleton. If Hollywood is looking for the next scary monster, they need look no further than the head and mouth of a sun scorpion. Fortunately for us, those jaws are designed to tear apart beetles and crickets, and so pose no threat to us. Dissecting burrowing owl pellets, they are often filled with tiny, less than ¼,” scimitar-shaped jaws. After finally identifying which beast the owls were eating, I then counted up the jaws and divided by four to have a count how many sun scorpions had been consumed.

Nullius in verba

Go outside, tip your hat to a chuckwalla (and a cactus), think like a mountain, and be safe.