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For those who don't follow the ID Frontiers listserv, that forum has been alive with recent discussion of an interesting oriole found in Georgetown, South Carolina on 9 May of this year. Originally, the bird was identified as a Scott's Oriole, which would have been a first state record. However, after much debate and a flurry of conflicting expert opinions, the bird was re-identified as an Orchard Oriole, a species that occurs regularly in the "Palmetto State." Towards the end of the debate, David Sibley wrote a detailed analysis explaining why the bird was an Orchard and not a Scott's. More importantly, he offered some enlightened discussion about the psychology that shapes and sometimes biases our perceptions.
Just this evening I received an e-mail from a long-time birding friend that included two images of a "mystery bird" that someone he knows had photographed near San Diego, California. He had circulated the photos to me and two other veteran birders earlier in the evening in hopes of solidly identifying the bird. Thankfully, I was the last to take a crack at it. The original images showed a finch-like bird that appeared to be rosy-pink/purplish over much of its body (see below). Given the apparent color, my first inclination was to think that the bird was one of the Carpodacus finches (most likely a Purple Finch). However, beyond the apparent coloration nothing looked right for that species. The other three experienced birders who had looked at these photos were all reluctant to put a name on it, which was my first clue to focus on what didn't fit rather than lock in on what seemed obvious.
Realizing that things weren't adding up, I mentally backed up and tried to abandon my first impression, which was being driven by the apparent coloration. Almost immediately, it occurred to me that aside from the apparent pink and rosy tones, this bird looked like a female Blue Grosbeak. It had a bill that seemed much too large and pale fleshy colored for a Carpodacus finch of any species. Additionally, it showed strongly peaked crown and a spiked crest (a look often shown by Blue Grosbeaks), it had two conspicuous broad pale buffy wingbars, and it seemed to have a very large looking eye on an otherwise patternless face. Under closer inspection, I noticed that most of the color around the head, especially on the nape, seemed to be more cinnamon brown and that the parts of the bird that appeared pinkish and purple (including the bill) were either in the shade or in indirect light.
Once satisfied that the bird was a female Blue Grosbeak, I began playing around with the images in iPhoto. First, I cranked up the color saturation to the max. I've found that this sometimes helps bring out the true color of the bird and reduces those hues that are artifacts of the original camera or processing. In this instance it seemed to exacerbate the problem. Someone with a better understanding of the technology behind digital photography can probably explain how these color artifacts are produced.
Next, I took the image and turned the color saturation all the way down, resulting in a black and white photo. I've found that in cases where apparent coloration is leading me astray, looking at an image in black and white eliminates the biases created by the colors and allows me to focus more on pattern and shape. I believe that the others would have readily identified this bird had they first seen the black and white images that I created. I suspect that they were drawn off track by the apparent coloration shown in the original images.
As Sibley points out in his discussion, our perceptions are shaped by expectations and initial impressions. Abandoning our initial impressions and starting over after already looking at a photo is easier said than done. Had this bird not shown a couple of key features that pointed away from it being a Carpodacus finch, I probably would have narrowed my analysis of this bird down to species within that genus. Fortunately, I benefited from knowing that three birders whom I know and respect had already puzzled over this bird without coming to a consensus about its identity. That tipped me off to think outside the box and recognize that something was amiss. I've been on the other end of this equation more times than I care to admit.
In the coming days, our latest spring migrant, the Common Nighthawk, will finally make its way into the Pacific Northwest. Like the "Boys of Summer" referenced in the the late-90's song by Don Henley, nighthawks are birds of summer in higher latitudes. Their distinctive nasal "peents" are rarely heard in most of Oregon before the first of June.
Nighthawks and their relatives are members of the order Caprimulgiformes. The origin of this scientific name literally means "milker of goats" (Cleere 1998). Like other crepuscular creatures, which don't become active until the last few footcandles of daylight fade away, nighhawks and nightjars are the subject of colloquial lore. Traditionally, many believed that these birds suckled milk from goats and other livestock during the night. In fact, nighthawks and nightjars subsist almost entirely on a diet of insects and, so far as anyone knows, they don't ever suckle livestock. And yet, if you look in your field guide, you will still see them referred to as "goatsuckers."
As one might expect from a family of highly insectivorous birds, nighthawks and nightjars are primarily tropical. They migrate into temperate zones only during the breeding season, although some individuals may go into a torpor (a hibernation-like state) and remain through the winter months on or near their breeding grounds. Of the 119 species of Caprimulgiformes listed by Cleere (1998), only eight are known to occur somewhat regularly in the U.S. and Canada and three of those barely reach our southern boarders. The Common Nighthawk is the most widespread and most northerly breeder of the five species with extensive ranges in North America. They can be found from coast to coast during the summer months and their breeding range extends well north into Canada -- as far as southern Yukon in the west, southern Labrador in the east, and the northern reaches of the "prairie" provinces in the center of the continent (Poulin et al. 1996).
If you see a Common Nighthawk up close, you will likely notice that they have a comparatively tiny bill. However, this bill belies a yawning basket-like gape that can be opened wide as they fly about in pursuit of moths and other flying insects. Studies have determined that nightjars have a highly-evolved jaw mechanism that allows them to open their mouths both vertically and horizontally (Cleere 1998). In flight, they are more like a butterfly or a bat as they feed, with constant darting and changes of direction. One of the colloquial names for Common Nighthawk is "bullbat," again referencing the traditional beliefs about this group of birds.
Many species of nightjars nest or roost on the ground, where their cryptic coloration allows them to easily blend in among the dried leave litter. During the nesting season, male Common Nighthawks do a "booming" display, performing steep dives that result in an audible rush of sound as air passes through the primaries at the bottom of the dive. The sound produced is a descending hollow, reedy "fffooom" with a slight rise in pitch at the end. This sound has a humming or vibrating quality that is sort of like what is created when you purse your lips and blow on the edge of sheet of paper (though not nearly as high-pitched).
Thoughts of Common Nighthawks evoke memories of warm summer evenings, the buzz of insects, sitting around a campfire toasting a marshmallow, and the welcomed interruption of a "peent" overhead...a sound I don't hear as often as I'd like.
Cleere, Nigel. 1998. Nightjars: A Guide to the Nightjars, Nighthawks, and Their Relatives. Yale University Press, New Haven, Connecticut.
Poulin, R. G., S. D. Grindal and R. M. Brigham. 1996. Common Nighthawk (Chordeiles minor), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds.cornell.edu/bna/species/213doi:10.2173/bna.213