Not infrequently two tits will engage in what may be called a "responsive exercise," swinging their two-part song back and forth in the woods like a silvery pendulum. Not soon shall I forget a winter day on which I listened with delight to such an antiphonal duet. I was standing in a road that wound along the foot of a steep, wooded bluff, and the two minstrels were in the woods above me, one of them singing very high in the scale, the other responding in the same tune, but almost, if not quite, an octave lower. At first they were about twenty rods apart, but as they swung back and forth, they gradually approached each other until the distance between them was only a few feet. The music seemed like a slender thread of silver which was being wound up at both ends, gradually drawing the little fluters together. Sometimes one of them would miss one note of his dissyllabic song, and at times the refrains were repeated in a leisurely way, at times in quick succession; but the performers never sang simultaneously, each waiting until his fellow minstrel had given his reply. The pleasing duet lasted for many minutes; indeed, it was kept up long after I left the immediate neighborhood, for when I had gone quite a distance the sweet cadenzas still fell rhythmically on my ear. To my mind the two-part aria seemed like a voluntary performance, and I cannot doubt that it was. There was too much of an air of purpose about it to permit of the thought that it was a mere accident or coincidence; but whether it was a musical contest between rival vocalists, or the love song of a tomtit and his mate, I could not determine.
Cunning in other ways, it would be strange if the tomtits did not display acuteness in the selection of nesting sites. A cosy hollow in a dead snag or stump is especially acceptable. Sometimes it is a deserted woodpecker's cavity made trig and clean, while quite often, when the wood is soft enough, the tits themselves chisel out a little hole in a tree or stump or fence post. I recall having once watched a pair of chickadees hollowing the upper end of a truncated sassafras tree that was half decayed. They would fly into the cavity, pick off a chip, dash out and away a rod or two, drop the fragment, then dart back to the hollow for another piece. In this way the busy couple worked hour by hour without resting for an instant. Their reason no doubt for carrying the chips some distance away from their nest was that they did not want any telltale fragments to betray their secret to their enemies.
It would be impossible to tell how many chickadee nests I have found in all the years of my bird study. One of them was in an old stump near a path along which I was sauntering. My attention was attracted by the little husband's flying from the stump and calling nervously, thus unwittingly "giving away" his secret. Had he been quiet, my suspicions would not have been aroused; but many birds, like a few people here and there, find it very hard to keep a secret. And this, by the way, is one of the strangest things about Nature—that she has not taught her feathered children to go with apparent unconcern about their employment when a nest is near, but impels them to chirp and flit about in such a way as to excite the suspicion of an enemy.
Moralizing aside, however. On examining the stump, I found a deep cavity just inside of the decaying bark. Though it was quite dusk within, by slightly pressing the bark aside I could see the little mother sitting on the nest, unwilling to leave it in spite of my proximity. I almost touched her with my hand, and still she did not move. Unwilling to disturb so brave a heroine, I stepped back and walked quietly away a few rods to see what would happen, when she popped out of the orifice like an arrow and, joined by her mate, set up a loud chattering, which sounded as if they were saying that I was the nosiest and most impudent man in the whole countryside.
No doubt they were right, for I went back, in spite of their protest, and peeped into the nest, and found four gleaming white eggs studding the bottom like pearls. Alas! when I visited the place two weeks later, the little domicile had been raided, the half-decayed walls having been broken down. A tuft of gray hair hanging to a splinter proved the invader to have been a predatory animal of some kind, probably a cat. The birds were nowhere to be seen—unless a pair chirping in the woods on the other side of the valley were the same couple, trying to rear a family in a safer place.
What a persistent sitter the female blackcap is! One day I discovered a nest in a fence post by the wayside. Pressing the bark aside, I could plainly see the little owner snuggling close to the bottom of the cup. I thrust my finger through the aperture and gently stroked her head and back. Still she hugged the nest, pressing her head close to the grassy bottom, as if she thought she would be safe if her head were hidden. Thinking she must have little ones, or she would not cling so tenaciously to the nest, I pushed my finger under her and partly raised her from her seat. Even this rude treatment she bore for a few moments—but it was going too far even for her courageous little heart; she lifted her head, glanced wildly at me for an intense moment, then sprang from the cavity with a piercing cry.
Imagine my surprise to find the nest entirely empty, not even an egg having yet been deposited. The brave little lady had doubtless just entered the nest to lay her first egg, and was not going to be driven off without knowing the reason why. The tomtit is game every time.
The entrance to most of the chickadee's nests is lateral, but I found one nest whose doorway was in the top of a fence post, so that the owners had to go down into it vertically. The hole was quite deep, and the birds would drop down into it as you have seen swifts dropping into a chimney, but whether they went down head first or tail first I could not learn, their movements were so quick. Another feature of this nest was that it had no roof, for the doorway was open to the sky, so that a cloudburst would have filled up their little nursery and drowned its inmates.