The Phoebes of Leon

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Ebony and Ivory…

The half-lit world of Leon Creek under Old US 90 in San Antonio: dingy, dripping, and draped in vines and poison ivy. Debris is lodged at all levels of the road supports, showing how high the waters can flood after a storm.

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But even so, this is reliable nesting habitat for phoebes:  emphatic, charismatic winged flycatchers, the ones with the constant calls and the emphatic tail-wagging. They affix their nests to the concrete beams under road bridges with dabs of mud, mostly safe from wind and weather. They re-use the same nests year after year, lining them with grasses for a more comfortable bedding.

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Eastern phoebes are to be expected under any bridge, but it was a surprise to find a bunch of black phoebe fledglings crowded on a branch at the beginning of May — a rare breeding record for Bexar County. Unlike their grayish cousins, black phoebes are smartly black-and-white, with entirely dark heads and backs and stark white plumage crisply demarcated across the breast. Their “phoebe” calls are much sweeter and higher-pitched than the comparatively hoarse eastern phoebe.

After years scanning grayish juvenile phoebes for possible phoebe hybrids, it was nice to see straight-up black phoebe juveniles for once: not at all gray or indistinct, but sharply defined and unmistakable.

I stopped back to check on them at the beginning of June. Only one black phoebe was left under the bridge. In fact he was back at the nest with an eastern phoebe, with a couple of fresh fledglings teed up inside.

In this case, the parents seemed to be a mixed pair, both of them landing at the nest repeatedly and carrying food. I’ve puzzled over black and eastern phoebes hanging around a common nest before, and it seemed to be the same pattern here: an aggressive black phoebe chasing a more-retiring eastern phoebe around a nest.

Similar interests, apparently, but a noticeable failure to communicate.

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Phoebes tend to be loners, and not terribly companionable even in intimate settings, so the impression of hybridization would be difficult to back up with actual evidence. But this time, the fledglings were already visible inside the nest, so it should be just a matter of waiting around to document a Black x Eastern Phoebe, if that’s what was in fact occurring here.

I returned day after day hoping for a better look.

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As it turned out, however, this was the best view I was to catch of the fledglings. They left the nest around June 20 — but unfortunately for my wildlife study, they went without a trace. There were still phoebes calling loudly under the bridge when I returned, but no answering calls from hungry fledglings.

Would their hybrid offspring even recognize their parents’ respective calls? Part of the interest in a hybrid phoebe would be hearing how their vocalizations turned out. Phoebes, like all flycatchers, are sub-oscines — sub-songbirds — meaning their “songs” are basically hard-wired at birth, rather than learned from a parent. So the vocalizations of a hybrid juvenile would presumably sound different from either parent.

At the very least, if I was going to document a hybridization among phoebes, I wanted to see fledglings being fed by their mixed-species parents. But the adults weren’t even carrying food anymore.

 

 

 

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Here was one of the eastern phoebes seen interacting with the black phoebe around the nest. Without close looks, individual phoebes can be pretty difficult to tell apart.

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Both species actively patrolled the area, vocalizing constantly. “They’re countersinging,” commented Mike Scully, who stopped by to check it out. One eastern phoebe generally posted at the western end of the bridgeway, with the black phoebe posted on the eastern end, near the nest.  He chased off the eastern phoebe a few times, as well as a group of cliff swallows who passed through his area under the bridge; evidence, at least, that he was attempting to maintain the territory around the nest…

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… a nest where the chicks looked more like eastern phoebes than black, with pale throats and grayish, not black, plumage.

He allowed two dark-breasted eastern phoebes (hybrids? mates? or just juveniles?) to chase eachother around in vicinity of the nest, giving buzzing flight calls — which got me excited, as I was still looking for the missing fledglings and presumed he was, too. But these immatures didn’t have the yellow gapes of recent fledglings, and their relationship with the black phoebe didn’t seem quite filial. Eventually he chased them off.  I’ve seen phoebe offspring foraging with their parents before, and this interaction didn’t have much of that quality.

So despite my vigilance at the nesting site, I didn’t in the end have concrete evidence of much, and the parentage of the two missing fledglings couldn’t be pegged.

It seemed possible that eastern phoebes could have borrowed the black phoebe’s nest and used it to fledge a summer brood — despite the continued presence of one of the remaining black phoebes at the same site. Hence the complex defense of the same nest by both eastern and black phoebes.

UPDATE JULY 6.

I finally obtained a shot of one of the immatures in early July, about two weeks after they’d fledged:

 

 

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Closeup of a recent fledgling near the black phoebe site, July 6.

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Closeup of a recent fledgling near the black phoebe site. July 6.

 

UPDATE DECEMBER 6. Today a distinctly yellow-bellied, grayish black phoebe was hanging around the bridge. It appearred yellow-bellied in every posture and every lighting scenario; below, a sample of some of the best images.

It seems possible that the yellow (unusual in a black phoebe) be either an artifact of the lighting, or a result of some kind of staining on the belly feathers.

But the overall gray cast to the plumage, and the indistinct demarcation between dark and light feathers on the breast, is also unusual for this species.

No vocals were obtained; the individual was silent.

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Just wait till next year! It’s a safe bet they’ll all be back.

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