Winter Wren (left) // Pacific Wren (right)

In 2012, the august body known as the North American Check-list Committee, a branch of the prestigious American Ornithological Union, voted on a proposal to split a four inch, tiny wren, known in Europe, Canada, and the United States as Winter Wren, into three species. Two of the species occur in North America and both are seen on occasion in Colorado, especially in fall migration. In the eastern two-thirds of the U.S., the stub-tailed wren species is still known as Winter Wren but the new species in the western third of the U.S. has been named Pacific Wren (Troglodytes pacificus). A troglodyte is a person who lives in a cave or someone extremely reclusive and such is the case for all three species of stub-tailed wren. Their songs are loud and bubbly, but they are extremely difficult to view even when they are singing. Their call notes are distinct too, similar to the calls of the very common at this time of the year, Wilson’s Warbler, but still difficult to hear and even more difficult to find the wren making the paired call notes; short and doubled chat-chat sounds.

On 23 September a Pacific Wren flew into a Chico bird banding net and it was carefully measured to determine if it was a Pacific Wren or the more expected Winter Wren. Luckily there is one measurement, the length of the exposed culmen on the bill, which separates the two tiny wren species. As surmised based on the darker, more cinnamon coloration and with fewer white spots of the Pacific Wren, the bird was proven to be a new species to be added to the Chico Bird Checklist — Pacific Wren.

On October 5, 2012, three Winter Wrens flew into a mist net on Chico Basin Ranch and were banded so now there are photographs of those birds to be compared to the bird captured and banded on Saturday. Luckily, I was present on both dates and you can see the subtle comparisons between the two species (Winter Wren on left with the lighter throat and more white spots than the darker Pacific Wren on the right with the darker more cinnamon throat and fewer white spots).