Long shot, but maybe someone can suggest some ideas...

[KevinC]

I'm going to sound like someone who has never birded before, but this one is bothering me a little: it goes "hooowheeoo". Can anyone tell me what it is? 

It's a pretty clear whistle with a whispery quality that may just be caused by distance, with the starting and ending pitches about the same, but the middle pitch about 4 or 5 notes (on a musical scale) above them. About 2 seconds long. The sounds are very slurred together, so it is just one long sound, with a bit of emphasis on the "whee" and a touch more time spent on the lower and higher pitches. I don't know how to explain the "slur" better, except to say that the lower and higher pitches are what you really hear, with the transition just a rapid but smooth transition as if you whistled a low note, then a high note and back again without any pause at all, but you can still hear the transition.

I haven't been able to record the sound as it has been pretty faint and my camera will pickup up all the background noise instead.
I'm hearing it from my backyard, which is on Glenn Mountain, Abbotsford, at about 400' ASL. We've got a pretty steep slope, so the noise could be coming from something far below, or something flying, although it doesn't sound like it is moving.
I've listened to a bunch of birds on the "likely" list for my backyard in eBird, but nothing sounds close.

I pretty much guarantee I should know what it is and will feel stupid when someone points it out, but I just cannot put my finger on it.

Any ideas?

What techniques or websites do folks use when only hearing a strange or new bird? How do you explain a sound to others without appearing totally crazy?

[nickinthegarden]

Did you check Swainson's Thrush?
Do not feel silly about the challenges of bird ID via sound, I struggle with it every time I am out. Some birds calls are only used in spring, some birds have a huge repertoire of sounds, some bird calls are so similar to others and some birds are less common than others and the sound is new to you. I struggle when background noise is loud enough to make me unable to focus on the bird sound. When out birding I have the Ibird app on my phone and I try to compare sounds but that almost never works, my hearing is not good enough and I get confused. The apps that project bird calls should be used sparingly you do not want to confuse a bird sitting on a nest or gathering food for young ones. Some birds will respond to them and others ignore them completely, it is better to err on the side of caution. I know of some birders who are very much against them but will still make bird calls with their mouths. Birders!
I have met a few birders who have remarkable hearing and have some background in music and are maybe able to help you more. Good luck!

[Randy]

Eurasian collared dove?

If not, is it higher or lower pitched than ECDO?

[paulos]

Is it nasal sounding at all? What about a Western Wood-Pewee or a Starling? Willow Flycatcher?

[Randy]

Olive-sided flycatcher?

[KevinC]

Thanks, Nick. I am with you on all of that. I don't have a phone that can play songs, so that helps me avoid that issue entirely anyway! Unfortunately it also means I have to try and record it with my camera and if that fails, try to remember the song when I get home. I do try to make a "drawing" of it while I am out, as that sometimes helps my memory.
Thanks, Randy. It is roughly the same starting pitch or a bit higher than the ECDO, but not nearly as full a sound and there are no distinct breaks in the sound. It might be more like (still a much thinner sound) the Mourning Dove's "coo-OO" part of its song, as that is more of a single sound with an upward-slurring jump, except this one goes back down again to its original starting pitch. I should have used pitch instead of tone - I'll edit that above.
Thanks, Paul. I'd say it was more of a whistle (I can almost make the sound myself), but with a slightly airy quality to it? Not really nasal. But then that might mean different things to different people - the joys of describing sounds, eh?! Almost as good as when I try and tell the mechanic what is happening with my old clunker.

I only heard it a couple of days in a row, so I am hoping it happens again and I'll try and get a recording. I'm pretty sure it isn't any of the suggested birds based on the initial recordings on allaboutbirds.org, but that isn't a definite no either, as the Bewick's Wren around my yard doesn't sound like any of the recordings I've heard online.

I really appreciate the contributions, as it all helps me learn more!

The first song at www.allaboutbirds.org/guide/Long-billed_Curlew/sounds recorded on June 12, 1995 in Oregon, with 6 seconds left in the recording is somewhat like what I heard, except my sound was much slower (probably half as fast) and a bit airier. Maybe that just muddles it further...

[Randy]

Killdeer?

How does it differ from olive-sided flycatcher? I ask because I had one at my place this morning in Abbotsford and its call seems to match what you describe...

[KevinC]

Jun 9, 2019 5:03:05 GMT -8 Randy said:

Killdeer?

How does it differ from olive-sided flycatcher? I ask because I had one at my place this morning in Abbotsford and its call seems to match what you describe...

The plaintive quality of the Killdeer is quite similar, especially when they don't "enunciate" - for lack of a better word - and say "ki-eer" instead of "killdeer", if that makes sense. That may well be what it was after all.
Like an Olive-sided saying "qui-ee-eer", running all the sounds together smoothly, instead of the more staccato "quick three beers".
Definitely hoping I hear it again!