Quick he is.  Just short of the roofs the taut wings flash a reverse, there is a lightning swoop, a startling hollow wind-sound, and the rushing bird is beating skyward again, hawking deliberately as before, and uttering again his peevish nasal cry.

This single note, the only call he has besides a few squeaks, is far from a song; farther still is the empty-barrel-bung-hole sound made by the air in the rushing wings as the bird swoops in his fall.  The night-hawk, alias “bull-bat,” does not sing.  What a name bull-bat would be for a singing bird!  But a “voice” was never intended for the creature.  Voice, beak, legs, head—­everything but wings and maw was sacrificed for a mouth.  What a mouth!  The bird can almost swallow himself.  Such a cleft in the head could never mean a song; it could never be utilized for anything but a fly-trap.

We have use for fly-traps.  We need some birds just to sit around, look pretty, and warble.  We will pay them for it in cherries or in whatever they ask.  But there is also a great need for birds that kill insects.  And first among these are the night-hawks.  They seem to have been designed for this sole purpose.  Their end is to kill insects.  They are more like machines than any other birds I know.  The enormous mouth feeds an enormous stomach, and this, like a fire-box, makes the power that works the enormous wings.  From a single maw have been taken eighteen hundred winged ants, to say nothing of the smaller fry that could not be identified and counted.

But if he never caught an ant, never one of the fifth-story mosquitos that live and bite till Christmas, how greatly still my sky would need him!  His flight is song enough.  His cry and eery thunder are the very voice of the summer twilight to me.  And as I watch him coasting in the evening dusk, that twilight often falls—­over the roofs, as it used to fall for me over the fields and the quiet hollow woods.

There is always an English sparrow on my roof—­which does not particularly commend the roof to bird-lovers, I know.  I often wish the sparrow an entirely different bird, but I never wish him entirely away from the roof.  When there is no other defense for him, I fall back upon his being a bird.  Any kind of a bird in the city!  Any but a parrot.

A pair of sparrows nest regularly in an eaves-trough, so close to the roof that I can overhear their family talk.  Round, loquacious, familiar Cock Sparrow is a family man—­so entirely a family man as to be nothing else at all.  He is a success, too.  It does me good to see him build.  He tore the old nest all away in the early winter, so as to be ready.  There came a warm springish day in February, and he began.  A blizzard stopped him, but with the melting of the snow he went to work again, completing the nest by the middle of March.