It must be noticed, however, that the goldfinches, referred to above, afford a partial exception to this rule. The young at the two nests of this species, which I have studied, were invariably fed with a white or greenish, sometimes frothy, semi-liquid seed-pap, each bird getting some, and at times from two to four doses, at each visit. Such birds react with great uniformity, and are remarkably uniform in their growth (Figs. 9 and 10). The feeding is extremely rapid, and so little of the pap is ever lost, that on only one or two occasions have I been able to get a drop of it for examination. It consisted of very small, immature seeds of some plant like the bull thistle or mullein.
Fig. 6. Cedarbird beginning to Regurgitate. Final stage in reaction (opening response) of young. Feeding is by regurgitation and direct, several being fed at each visit.
While all the common passerine birds of the country feed their young in the way described, at nests of the cuckoos a most singular and remarkable performance may be witnessed, for these interesting birds not only test the throats of their clamoring brood in the usual way, but practise what may be called mouth-feeding also. Thus we have repeatedly seen the female black-billed cuckoo bring to her nest caterpillars, or larvæ of some of the larger moths, from two or three inches long, already limp, and pinched at a point just behind the head. At the food response or opening reaction, she would lay the insect in the mouth of the young one, and without relaxing her grip, hold it there, mother and child standing immovable from two to five minutes by
