Thanks, Norm, for posting the information. Here are some details. A group of about ten birders on a combined Wild Birds Unlimited/Rocky Mountain Bird Observatory field trip this morning studied the breeding birds at Chatfield S.P. The expected species (House Wren, Least Flycatcher, Yellow Warbler, YB Chat, etc, etc) were in full voice, and we found several nests.
At about 11 AM while the group heard and saw a singing male Plumbeous Vireo near a nest and sitting on the nest, two of the group, Becky Campbell and Nathan McAdam, spotted a different vireo high in the trees right above the path. They saw field marks compatible with Yellow-throated Vireo, so we all started searching the treetops. After initial skepticism, everyone had good looks at a Yellow-throated Vireo. It was interacting as a pair with the Plumbeous Vireo, coming to the nest site without being chased away. Larry Modesitt saw it right at the nest, and as I recall, saw it sitting *on* the nest at one point. Scott Menough, I and the others saw the birds well. The Yellow-throated Vireo was moving about sluggishly high in the tall cottonwood trees, offering multiple adequate views. It had the sturdy vireo habitus, a heavy vireo type bill, and we saw a bright yellow throat and breast, fading to white on the belly and vent. It had prominent yellow "spectacles," olive back, darkish wings with two white wing bars and a dark tail. These features separated it from other vireos, and although it was superficially similar to a Pine Warbler, that warbler has far less distinctive spectacles, a thinner bill and is virtually unknown during our spring migration. As you may recall, Becky Campbell showed a Pine Warbler to 58 birders in her back yard last December, and was recognized at the recent CFO Convention with the coveted Homeowner's Appreciation Award. Becky knows Pine Warblers, and this was not a Pine Warbler. On my way home I called Doug Kibbe, who did a little research on-line at Birds of North America. There he found no previous records of Yellow-throated Vireo pairing up or nesting with Plumbeous Vireo. The two species have no overlap in their usual breeding ranges, as they are separated by parts of the Great Plains. Even in the Northeast, where both Blue-headed and Yellow-throated Vireos breed in the same states, there was only one record of YT Vireo pairing with Blue-headed. (from North Carolina, BNA) CAUTION: This is a unique situation, and the pair could produce viable hybrid young. What might they look like? The nest will be monitored closely, and up-dates will be posted on-line at RMBO.org. I urge birders strongly to AVOID PLAYING RECORDINGS of either vireo's song or calls. You don't need to do that and the birds are conspicuous. This paved path is open to the public, so birders on it are far outnumbered by other visitors. Vehicles are on this trail during "improvements" of the trail farther south. Adequate commotion, although it is a pretty serene spot most of the time. The birds chose to nest right over the trail. So the *extra* impact by birders, compared to other human activities will be low. Joe Roller, Denver RMBO -- You received this message because you are subscribed to the Google Groups "Colorado Birds" group. To post to this group, send email to cobirds@googlegroups.com. To unsubscribe from this group, send email to cobirds+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/cobirds?hl=en.
