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Mixed Diglossini, Sept. 30, 1962, IV 10

About 3 minutes after this, I hear burst of PR Atlapetes song in direction in which Rufs went. But no more Ruf song.

[[left margin]] Laf Ruf [[/left margin]]
There was a single Laf in tree about 30 ft. away from Rufs when Ruf song occurred. The Laf remained silent. Then sang after Rufs flew away (but not immediately afterwards). So did several other Lafs in neighborhood.

[[left margin]] Humer [[/left margin]]
11:00 am. Down below Guasca, where I was yesterday afternoon. See a small black Diglossa. carbonaria shape, but with humeral patches. The patches look blue, but this bird must be humeralis, ("Humer"). Quite silent.

[[left margin]] Humer [[/left margin]]
Then in another area, appr. 1/4 mile away, can bear another Humer singing. Quite like some Glor songs (the kind in which doublets are least noticeable). Twittering, fairly short phrases

Both birds in areas of thick, but low, uncovered scrub.

[[left margin]] Humer [[/left margin]]
The second Humers song may have had R components within some phrases, but definitely no terminal R's

A few minutes later, in a similar environment, about 1/2 mile away, I see a pair of black Diglossas flying. Possibly or probably also Humers.

[[left margin]] Humer [[/left margin]]
It is obvious now that the "hybrid" I saw yesterday morning up above Guasca in the Laf region was a Humer. 

[[left margin]] Laf [[/left margin]]
All the time I have been in the upper Laf region, I have been paying special attention to songs, and looking at every black Diglossa as closely as possible. I am quite certain; therefore, that I have not encountered any other Humer there except the "hybrid." So Humers must be very rare there. Relatively much rarer than Aters on top of Atacaso.

[[left margin]] Humer [[/left margin]]
As far as I know, the one song uttered by the "hybrid" yesterday when close to me is the only Humer song that has been uttered in the Laf region during any of my periods of observation. 

[[left margin]] Humer [[/left margin]]
Why are such songs so rare?

They are not rare because the Humer(s) cannot get a word