RE - Ceruleans. I did a lot of atlas blocks (04-08) in Sproul State Forest. I was surprised to find Ceruleans not at all uncommon on the upper parts of high steep slopes. My surprise probably came from a Lower-Trail influenced assumption, as you say, that they were on hillsides along rivers.
Re - Vireos. I wrote the atlas account for YTVI. I wondered why REVI so-outnumbered YTVI., two species so seemingly similar (tho of course with requirements we can't fully grasp). The best hypothesis (a hypothesis in need of factual backing) I could find was that REVI "out-competed" YTVI, pushing them from favored forest interiors to less favorable, more open margins of forests. Which sort of fits with where we tend to find YTVI.
In PH we find YTVIs in deep forest readily; they nest in basically the same areas as REVIs and BHVIs, though of course the latter nest earlier. A study that definitely needs to be done. We'll see what the Atlas turns up in terms of vireo numbers...
RE - Ceruleans. I did a lot of atlas blocks (04-08) in Sproul State Forest. I was surprised to find Ceruleans not at all uncommon on the upper parts of high steep slopes. My surprise probably came from a Lower-Trail influenced assumption, as you say, that they were on hillsides along rivers.
Re - Vireos. I wrote the atlas account for YTVI. I wondered why REVI so-outnumbered YTVI., two species so seemingly similar (tho of course with requirements we can't fully grasp). The best hypothesis (a hypothesis in need of factual backing) I could find was that REVI "out-competed" YTVI, pushing them from favored forest interiors to less favorable, more open margins of forests. Which sort of fits with where we tend to find YTVI.
In PH we find YTVIs in deep forest readily; they nest in basically the same areas as REVIs and BHVIs, though of course the latter nest earlier. A study that definitely needs to be done. We'll see what the Atlas turns up in terms of vireo numbers...