It was a wet and foggy day in April.  I was standing in a damp little nook in dense woods, long before the first leaves would even think about opening, weeks before most migrating birds would get within a thousand miles of southeast South Dakota, listening to a cascade of musical notes that seemed like it would never end.  It was echoing off the trees and the mossy banks, coming from somewhere tantalizingly close — but from exactly where, I couldn’t for the life of me figure out.  After I stood there for perhaps ten minutes, I finally spotted it: a tiny brown bird singing from a pile of leafless brush, fifteen feet in front of me in plain sight.  My first Winter Wren.

By some strange coincidence, the details of that experience almost perfectly match the details of my first encounter with Pacific Wren, when, on another wet and foggy day in April, I spent another ten minutes trying to find the amazing vocalist hidden among the dense, damp vegetation, this time on the slopes of Skinner Butte in Eugene, Oregon.  At the time I had little idea I was seeing a different bird than the one I knew from the east.  The song was familiar, or so I thought — unmistakable, really.

To this day, in the field, I have some difficulty separating the songs of the two forms (which may be separate species soon, for those of you just tuning in).  Both are remarkable vocalists, with long-running musical strings of jumbled high-pitched notes and trills:

It’s not as easy as separating them by call, but with practice, Winter and Pacific Wrens are usually distinguishable by song.  Here are some points to consider:

• First of all, in the above examples, don’t let the shorter Pacific song fool you.  Strophe length is variable in both forms, and Pacific’s songs may actually average longer than Winter’s.  Pay no attention to duration!
• Although I can’t vouch for this across the board, the sample I’ve studied strongly suggests that Pacific Wren tends to sing with more trills given closer together, so that the song is composed of >50% trills, while Winter Wren tends to sing with longer jumbles of individual notes and fewer trills more widely spaced, so that the total song consists of <50% trills.
• Tone quality is key. Many people consider the song of Pacific to be “drier,” or, in the words of Sibley, “more mechanical-sounding” and “buzzy” with “hard trills.”  The difference is one of musicality.  To my ear Pacific’s song sounds higher-pitched, but you’ll note on the spectrograms that the maximum and minimum frequencies of both songs are almost exactly the same.  The difference is that Winter Wren shows very little frequency change within individual notes (with the trills usually clustered at the bottom of the song), while almost every one of Pacific Wren’s individual notes sweeps from below 4 kHz to about 8.  Thus the difference is roughly equivalent to the difference we saw between the songs of Field Sparrow and Black-chinned Sparrow.  The Pacific Wren’s notes, especially its trills, are less musical because they are changing pitch too rapidly.  Practically every single one of the Winter Wren’s notes has a bell-like, musical quality, but the Pacific Wren has a much lower percentage of musical notes.

A good way to think of the difference in tone quality is to listen for the trills inside the wren songs and compare them in your head to the the “classic” song of Dark-eyed Junco and the “classic” song of Chipping Sparrow (which are, of course, themselves often difficult to separate by ear).  The Winter Wren tends to have the more musical, junco-like trills, while the Pacific Wren often trends towards an unmusical, Chipping Sparrow-like (or even Brewer’s Sparrow-like) lisping rattle.

Song delivery also differs, although this can be difficult to ascertain unless you have a great auditory memory.  Winter Wren males have only a few stereotyped songs in their repertoire; successive strophes of song are almost always identical.  Pacific Wren males sing with far more songtypes, and they also recombine their songs — the beginning notes of successive strophes are frequently identical, but the endings vary widely.

For more practice, and to hear some more of these fantastic bird songs, head over to Xeno Canto’s Winter/Pacific Wren collection.