Common Poorwill

by Stan Tekiela
© NatureSmart
October 26, 2007

At the risk of sounding like a broken record, this week’s column comes to you from the desert of Arizona. As you may have guessed, I am currently working on several new field guides for the state of Arizona so I am spending a lot of time here in the desert.

During the day, I am working on locating and photographing several species of tree, cactus, wildflowers and small mammals. But at night I have some time to explore the desert. In fact if you ask me, night time is the best time to be in the desert. All the desert critters become active.

One night just after dusk, I came across a very unusual bird—the Common Poorwill (Phalaenoptilus nuttallii). When I say, unusual, I don’t mean uncommon I mean different from other birds. The poorwill occurs in the western half of the country but because it is a nocturnal bird and one that is also very cryptic in color it often goes unnoticed by the average person.

The Common Poorwill is a resident of high rolling prairies, desert scrub and rocky foothills at elevations around 4,000 feet. It is noted for its distinctive call and ability to enter a temporary daily hibernation called torpor. In fact this is the only known bird to spend long periods during winter months completely inactive, day and night.

In 1946, a California ornithologist found a Common Poorwill in a rock crevice one day during winter. When he picked up the bird he could not detect a heartbeat or respiration, yet the bird was not dead. The temperature of this bird was between 64-67 degrees F, whereas its normal temperature would be around 106 F. Over the next 88 days during which the air temperatures remained around 40-42 degrees the bird was examined, temperature and weight were monitored and returned to the rock crevice. The temperature and weight of the bird remained the same and after 12 weeks the bird woke up and few off, just as the air temperatures began to rise and its chief source of food, insects, became available. This was the first time that temporary hibernation (torpor) was reported in birds.

Since then, we have learned a lot about the Common Poorwill. We now know that they become torpid when the air temperatures range between 35-66 degrees F and will only use 0.35 ounces of stored fat over a 100 day period to keep alive. We have also discovered several other species of bird that use torpor to make it through cold temperatures. I have discussed Black-capped Chickadees in this column in the past. However the poorwill is the only bird that uses torpor for extended periods of time, kind of like hibernation. Recent studies show that poorwills in Arizona remain completely inactive on as many as 90 percent of all winter days and nights.

The poorwill is an insect eater who hunts from the ground or low perch at night just after the sun sets. They use the stars and moon to help illuminate the sky and to see flying insects in the night sky. They have extremely large eyes that allow them to see in the dark. When they see a large moth or beetle fly by they quickly fly (sally) up to capture the insect before returning to the ground and to wait for another insect to pass by. They use very little energy to obtain their high protein diet. They are such proficient hunters they only need to be active for a couple hours each evening after the sunsets to capture enough calories to last until the next night.

Back in the desert, I am driving down a dirt road just after sunset. The first poorwill that is illuminated in the headlights quickly flies off as well as the second and third one. However the fourth one holds still. I am able to quietly exit the truck and sneak up close enough to capture a couple images of this elusive night bird before it takes to the night sky and leaves me standing there in the glow of the headlights and the stars shining brightly above. Another great night in the desert. Until next time...

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