August 26 2017. Paletta Park, Burlington, ON. There are times when a bird is visible just long enough get some clues but not quite long enough to identify it with any certainty. That’s birding and it drives some people crazy, but I try to shrug, tuck the memory away and sometimes label it as a Bird-for-Another-Day. On one of my trips to Uganda there were lots of puzzlers and one day when I said out loud, “It’s a bird for another day” Emmanuel, one of my African companions, looking puzzled, took a while to process what I had said. I had thought it just an introspective comment but it puzzled him deeply, eventually he found it really quite funny and from then on a Bird-for-Another-Day met with broad smiles. We later invented Cup-of-tea Birds (to be identified from photos later over a cup of tea) and just plain Mystery-Birds (forever a Who-knows?).
I found and photographed a Mystery Bird today. Other birders might have named it in a flash but frankly I didn’t. At the time of writing I think it’s a juvenile female Tennessee Warbler. It was obliging in its tendency to pause from time to time and I was able to take several photos even though sharp focus was rare and the bright sky distracting. You’d think that identification would be easy matter with reasonable photos; well maybe. Here are four photos and some comments. 
In the photo above you can see the bird that it is bright lemon yellow below, has a greyish tail, a sharply pointed beak, a dusky line through the eye and a bit of a grayish cheek pattern. In the second photo, below, we can see an olive-yellow back, brownish yellow wing feathers and a yellowish-grey cap. The dusky line through the eye is clearer, the dark line slicing across the back is distracting but it’s just a shadow. All of the above is generally consistent with a juvenile female Tennessee Warbler although the yellow in this bird is I think unusually bright.
The third and fourth photos confirm some of the key points and you’ll see that its underside is quite bright yellow right to the grayish tail feathers; and there’s the sticking point, Tennessee Warblers are usually white under the tail although apparently a blush of yellow is not out of the question.
I’ve taken a few days to write this awaiting the thoughts of a few experts or near-experts; the consensus is that it’s a juvenile female Tennessee Warbler.
Mystery bird aside, the last couple of days have been a little on the cool side, good for birders because the first chills of late August set fall migration in motion. The woods, fields and skies, although still fragrant with summer, have been dotted with birds on the move. In my wanderings today I enjoyed watching a Yellow-throated Vireo, a couple of Magnolia Warblers, a Least Flycatcher and a Yellow–bellied Flycatcher, among others. They were all fueling up for the long journey in the weeks ahead, they’ll be heading to central America, anywhere from Guatemala to Panama; it seems so improbable, three to four thousand kilometers, half of it over water, on a diet of insects.