In a recent post on his excellent blog Earbirding, Nathan Pieplow points out an issue with the voice description of Buff-collared Nightjar in the Sibley Guide to Birds, which says:
Song of rapid, sharp, dry chips in crescendoing series tup to to tu tu ti ti trridip accelerating and rising to flourish at end; pattern similar to song of Cassin’s Kingbird but notes sharper and drier. Also rapid, dry, clicking notes.
As Nathan shows in his blog post, Vermilion Flycatcher should be mentioned as an identification pitfall, since the rhythmic pattern of its song is actually closer to the nightjar’s than is the song of Cassin’s Kingbird. Rick Wright, in a comment there, further suggests that Western Kingbird song is quite similar to the nightjar.
I agree that there are very real similarities between Buff-collared Nightjar and Vermilion Flycatcher, and that it’s misleading to single out Cassin’s Kingbird as the primary similar species, but Nathan Pieplow seems to suggest that, for decades, observers have misidentified Vermilion Flycatchers as Cassin’s Kingbirds, and then mistakenly written that Cassin’s Kingbird sounds like Buff-collared Nightjar.
I do not agree with this, but the situation is complex and, I think, interesting.
First, much of this disagreement comes from the fact that we are each selecting and emphasizing different aspects of the sounds. So while Nathan Pieplow says the song of Cassin’s Kingbird “doesn’t sound anything like” the song of Buff-collared Nightjar, I can actually hear some resemblance. To me the song of Vermilion Flycatcher is distinctively high and sharp, unlike the nightjar, while the kingbird’s song is about the same pitch and tone quality as the nightjar’s. On the other hand, to Nathan the song of Vermilion Flycatcher has a very similar rhythm and pattern to the nightjar, while Cassin’s Kingbird is utterly different.
Another important factor is that I am trying to hear similarities between Cassin’s Kingbird and Buff-collared Nightjar, as I have been since I read that in Phillips et al.‘s Birds of Arizona. I first went to Arizona with the idea firmly planted in my mind that Cassin’s Kingbird could be confused with Buff-collared Nightjar. So when I listened in the predawn darkness at Guadalupe Canyon in 1983 I was straining to hear something that was flycatcher-like and yet nightjar-like, and the strange dawn song of Cassin’s Kingbird fit perfectly.
It’s possible that Phillips et al., in trying to alert people to a potential source of confusion, unwittingly emphasized and perpetuated that confusion.
Our perception of sounds (just like sight) depends on many other factors besides the actual vibrations that reach our ears. It has long been known that we incorporate visual cues such as facial movements in our perception of speech, and in a recent study (reported in the New York Times on 25 Nov 2009 here):
…researchers had subjects listen to spoken syllables while hooked up to a device that would simultaneously blow a tiny puff of air onto the skin of their hand or neck. The syllables included “pa” and “ta,” which produce a brief puff from the mouth when spoken, and “da” and “ba,” which do not produce puffs. They found that when listeners heard “da” or “ba” while a puff of air was blown onto their skin, they perceived the sound as “ta” or “pa.”
This is similar to abundant research on visual perception showing that what we perceive can be fundamentally altered by other stimuli, including psychological factors.
So if a puff of air on the back of the hand can cause us to hear “ba” as “pa”, and “da” as “ta” imagine how the omnipresent expectations, hopes, and other psychological effects of birding can influence the bird sounds that we hear.
Finally, I think this debate may also highlight a subtle shift in the way birders learn and study bird songs. I learned bird songs decades ago through countless hours of field experience, supplemented by listening to a few recordings, reading detailed descriptions, and talking to other birders. It was a subjective, holistic approach to bird songs that led to a sort of gestalt style of identification – after you hear a sound often enough the identification just becomes second-nature.
Now, it still takes countless hours, but birders have a wealth of technological aids, allowing them to study and compare bird sounds with an ease and immediacy that was never possible before. In the modern world of ipods, sonagrams, and websites like xeno-canto, birders can examine the bird sounds directly, objectively, and in great detail. This may lead (as Nathan Pieplow admits) to a slightly greater emphasis on differences in pattern rather than the more subjective and hard-to-describe differences in tone.
Given how suggestible we are, and how tiny things can influence our perception, the detail-oriented objective approach to bird sound identification is probably better and more accurate. A similar shift happened in sight identification a couple of decades ago, and that shift can also be linked to technology. In the 1980s it was rapidly improving photographic equipment and optics that allowed more detailed study and comparison of living birds than ever before, leading to a whole new approach to identification based on feather details, molt, etc.
It may be that with modern technology Cassin’s Kingbird is no longer such a source of confusion with Buff-collared Nightjar. If so it has merely been replaced by another species (Vermilion Flycatcher) that is less easily sorted by the modern style.