Arch McCallum, Ph.D.
Applied Bioacoustics
P. O. Box 51063
Eugene, OR 97405

The Cordilleran Flycatcher (Empidonax occidentalis) and the Pacific-slope Flycatcher (Empidonax difficilis) are sibling species that are extremely difficult to distinguish in the field. Vocalizations are the only consistent means of distinguishing the two forms out of the hand, and even they are problematic. Since the two species were split from the former Western Flycatcher (E. difficilis) (American Ornithologists' Union 1989), many birders have complained that the purportedly diagnostic sounds are not distinguishable, and others have reported bilingual birds, i.e., single individual birds giving sounds these observers took to represent the vocal repertoires of both species. Intermediacy of songs in the Pacific Northwest is also mentioned often.

Although numerous authorities have addressed species-level vocal differences in print, and examples of the sounds of both species are found on many published compilations of bird sounds, side-by-side comparisons of the sounds themselves are rare to nonexistent. Web-style presentations are ideal for this purpose, and this site is an attempt to bring some clarity to the situation. My goals are to

  • Present side-by-side comparisons of major sounds from core populations of the two forms
  • Use these exemplars to stabilize the terminology applied to the major sounds.
  • Present samples of sounds from the Pacific Northwest and elsewhere that illuminate the problem of intermediacy.
  • Present several scenarios that may explain the observation of "bilinguality."

I welcome comments on both the content and format of this site.

                  --Arch McCallum
Site last updated on 11/29/2005

When you click below and enter the presentation of flycatcher sounds, you will see a lot of spectrograms (graphs of sound). Clicking a spectrogram will play its sound. Replaying a sound, once it is has loaded into the player, is faster when you use the "play" button on the player than when you click the spectrogram again, but you may need to resize your player. (See details below for help with that.) Mousing over the spectrogram (with Internet Explorer) will reveal the recording location and date.

The presentation has three frames, and you can navigate independently in each. There are two options for the size of the frames, depending upon the size (in pixels) of your monitor's screen. Try the "large screen" version first. If you do not see three frames, like this, try the "small screen" version. To enter now, click Large Screen or Small Screen.


What follows is offered in the spirit of helpfulness, but doesn't imply that I can provide technical support to each user. I would, nonetheless, appreciate receiving an email if you have technical problems using this site. I will try to correct any malfunctions, and compile some user hints to deal with challenges. Click the comments link above to send an email.

Screen Size

This presentation relies on frames. If you don't see three panels, like this, from top to bottom of your screen upon entering, it may be that your screen is not big enough for the page. Here are three possible solutions to such a problem:

  • Try the Small Screen presentation.
  • Try "Full Screen" mode on your browser. Click on the "View" button near the top of your browser window and select "Full Screen." (You can get out of Full Screen mode by clicking the Restore button, which looks like one sheet of paper on top of another one).
  • If you see all three frames, but want to increase or decrease the height of one of them, you can RESIZE two frames by grabbing the border between them and dragging up or down. This requires a light touch with the mouse. You should see a double-headed vertical arrow when you engage the border with your mouse.
Another possibility is that your browser does not support frames. If you have an extremely old browser this may be the problem. Download a new one. This site works best with Microsoft's Internet Explorer. OR, you can access each frame separately here. When you are ready to shift to a different frame, click the "HOME" link to return to this page.

Sound Player Software (Plug-ins)

Resizing the Player
Media files on the web, such as the dozens of sound files available to you on this site, are played with the help of software on your computer. The web browser software that displays the text and graphics of this site thinks of these helper software programs as "Plug-ins." My sounds are in Windows ".wav" format, so they will be played on your computer by the sound player software that you have chosen to play wav files. Many players can do this. The rub is, most of them want to take up most of your screen while playing. In general, you want to resize the player and drag it to the corner of your screen so you can still see the page. If you minimize the player, it will pop up and take its previous form every time you click a spectrogram.

I use Windows Media Player. Different versions of this player behave differently. I actually prefer an older version, because it has fewer bells and whistles and is easier to use. If you are using a recent version of Windows Media Player you can resize it by putting it into "Skin Mode." First, once you have clicked one of the sounds and found WMP on your screen, make sure it is not already in skin mode. Try resizing it by grabbing a corner of the player and dragging it toward the middle of the player. If this works, accept success. Find a convenient size and then move the player to the edge of the screen, so that you can still click the "Play" button. If it won't resize, click "Skin Chooser." (If you don't see that button, click an arrow pointing leftward along the left margin of the player. This should expose the "Taskbar," on which you can click the "Skin Chooser.") Highlight a skin and then click "Apply Skin." Most skins can be resized. I like "Corporate," because it can be made really small without sacrificing functionality.

Changing the Default Player
If you want to change the player for wav files, click Start, Settings, Control Panel, Folder Options, and then the File Types tab. Scroll down the list until you find WAV, highlight it, click Change, and then browse the list of programs ("applications") for one you recognize as a media player. If you don't know the names of any media players, you shouldn't be doing this. To return to the default player for your system, go back to the File Types window, find WAV again, and click the Default button. Please do all of this at your own risk. I can't provide technical support.

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