I love going out on summer evenings to the Hogbacks near my home to listen for Common Poorwills. It is always a beautiful experience, and sometimes extra interesting, too, with good visual or auditory encounters with the poorwills. But on the whole, I don't learn a whole lot about what the poorwills are up to in that evening time. They are hard to view, often heard only a distance up the slope. and the oft unseen calling birds reveal little obvious about age, sex, nesting status, local breeder v migrant, etc. And most of what I encounter are calling birds, heard some distance away, and most often unseen.
-- But I don't feel too bad. The limited literature on Common Poorwill biology and natural history shows there are many unknowns. The Birds of the World species account offers a good summary of what is known and not known, and for the Common Poorwill the sections on behavior, foraging and nesting are pretty slim.
There is not a lot of detailed information. Under "Priorities for Future Research" it begins "Poorwills are one of the least understood of North American birds, probably owing to their small size, cryptic coloration, nocturnal habits, and long periods of dormancy during winter. Future research on the species should address issues along two distinct avenues: the basic biology of the species, which is unclear..." [longer excerpt under my signature line]
For one example, the account indicates a lack of information from the wild on how or if poorwill parents feed their young after fledgling, or how long parents tend to their young after fledging, if young remain in the natal area for some time after fledging, and how young beg or solicit feeding.
Dakota hogback slopes on the left, Lyons hogback slopes on the right.
Now, at the end of summer, there are usually good numbers of Common Poorwills in the hogbacks of Ken Caryl Ranch. They live on the slopes of the higher, eastern Dakota formation hogback, and on the slopes of the western Lyons formation hogback. Both slopes are mostly grassland, with areas of foothill scrub, oak woodland, and lots of exposed rocks in some areas. Last night I tallied about 12 poorwills as I walked along a 0.6 mile segment in the vale between the two hogbacks. The first calling poorwill began 25 minutes after sunset and the last poorwill was noted 43 minutes min after sunset. The dusk bout of calling was typical for late summer, with individuals overlapping their vocalizations, and some calling very near to each other. The calls are the primary call 'poor-will' but the quieter third element of the call is usually very hard to hear now from most calling birds. I also have noticed that individuals calling for a time will make periodic shifts in frequency. - calling steadily, then increasing the frequency for a several seconds, before returning to the somewhat slower rate of delivery.
This view shows the slopes where I observed two poorwills, described below.
Last night things unfolded as per usual. I made my way to my starting point and waited until sunset came and went. There is very little bird sound out in the hogbacks at evening now, and I only heard Lesser Goldfinches and several scrub-jays. The poorwills began calling after sunset, and eventually I began to walk back over my 0.6 mile segment. Part way along, a poorwill was calling from a slope on the Lyons side where I have had many sightings of poorwills. I paused and scanned with my bright flashlight. Far off, I caught the eyeshine the poorwill, calling from a perch about 100 yards up the slope from the valley bottom. I moved closer and could see the bird was perched on the tip of a mullein stalk, which they like to do. It was now over half an hour past sunset, and pretty dim. At this distance, even with a bright light, the body of the poorwill is hard to see through the binoculars, but its bright eyeshine showed exactly where the bird was. Often there is just one dot of eyeshine, as I can often see only one eye. So you see one bright dot shining back. Now, a flying bird shows eyeshine, too, but its dot of light drifts around over the dark slope as the bird flies low over the grassland.
So I'm watching the perched bird dimly, and listening to its call (recordings on the eBird checklist above). Then I notice the glowing eyeshine dot of a second poorwill that is flying low over the same slope. This flying bird is foraging and is not calling. Whenever the flying bird approached the perched bird, the perched bird briefly increased its calling rate, The flying bird flew right up to the perched bird, and there seemed to be very brief contact or nearly so, and the flying bird then drifted off and resumed foraging low over the slope. I saw at least 5 such close visits by the flying bird to the perched bird over a few minutes. Then the foraging poorwill moved out of view, and the calling bird took flight and flew across the valley between the hogbacks, landing somewhere up the Dakota slope.
So I saw one perched bird calling regularly, and a second bird foraging in flight nearby. The flying bird repeatedly visited the perched bird, at which time the perched bird responded by changing the nature of its calling. The rate of calling can be heard on the 2nd recording on the checklist, at 3 seconds and again at 34 seconds. It is subtle.
As I thought about what I had seen, I realized that it was not different from what juvenile swallows do (for example): They sit on a perch, sometimes begging, and wait to be fed. The adult comes around and feeds them and flies off to get more bugs. I am wondering if my perched poorwill was a juvenile being fed by an adult. The Birds of the World species account indicates there is no information about how young are fed or for how long. If that was what was happening, it suggests to me (based on character of calls) that many calling poorwills I hear now in the dusk chorus could be young of the year, and that they are from local nestings on or near their natal territories (vs. migrants moving through).
In the end, I try to fit a piece into the puzzle of a mysterious, little known, but prominent species of our Front Range region. But I'll have to go back out again to see and hear more.
David Suddjian
Ken Caryl Valley
Littleton, CO
From Birds of the World species account:
Excerpt from "Priorities for Future Research"
Although widely distributed, poorwills are one of the least understood of North American birds, probably owing to their small size, cryptic coloration, nocturnal habits, and long periods of dormancy during winter. Future research on the species should address issues along two distinct avenues: the basic biology of the species, which is unclear, and the physiological aspects of heterothermy by poorwills, many of which are particularly intriguing.
Reproductive success -- both numbers and factors influencing -- is essentially unknown except at the northern periphery of the range and findings there, where some populations could be ephemeral, are unlikely to be representative of the species as a whole (Csada and Brigham 1994a, Macdonald et al. 2003). Data on long-term survival of individuals are also lacking, although results in Arizona suggest this species is not an especially long-lived bird (Woods 2002). Juvenile survival and natal fidelity are unknown, as no banded poorwill nestling has been recovered in a subsequent year. More importantly, no migratory bird banded on its breeding grounds has been recovered in winter, and thus the winter ranges of migratory populations are entirely speculative.
Although widely distributed, poorwills are one of the least understood of North American birds, probably owing to their small size, cryptic coloration, nocturnal habits, and long periods of dormancy during winter. Future research on the species should address issues along two distinct avenues: the basic biology of the species, which is unclear, and the physiological aspects of heterothermy by poorwills, many of which are particularly intriguing.
Reproductive success -- both numbers and factors influencing -- is essentially unknown except at the northern periphery of the range and findings there, where some populations could be ephemeral, are unlikely to be representative of the species as a whole (Csada and Brigham 1994a, Macdonald et al. 2003). Data on long-term survival of individuals are also lacking, although results in Arizona suggest this species is not an especially long-lived bird (Woods 2002). Juvenile survival and natal fidelity are unknown, as no banded poorwill nestling has been recovered in a subsequent year. More importantly, no migratory bird banded on its breeding grounds has been recovered in winter, and thus the winter ranges of migratory populations are entirely speculative.
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