My next camping-place was on the western slope of the Rocky Mountains, near a lake, by the margin of which grew some cottonwood trees (Salix scouleriana), together with the alder (Alnus oregona), and the sweet or black birch (Betula leuta). My attention was called to the latter tree by observing numbers of wasps, bees, and hornets swarming round its trunk. The secret was soon disclosed: a sweet gummy sap was exuding plentifully from splits in the bark, on which hosts of insects, large and small, were regaling themselves. As the sap ran down over the bark, it became very sticky, and numbers of small winged insects, pitching on it, were trapped in a natural ‘catch-’em-alive-O.’
Busily occupied in picking off these captives were several very sombre-looking hummingbirds. They poised themselves just as the others did over the flowers, and deftly nipped, as with delicate forceps, the helpless insects. I soon bagged one, and found I had a third species, the Black-throated Hummingbird (Trochilus Alexandri). Were any proof needed to establish the fact of Hummingbirds being insect-feeders, this should be sufficient. I saw the bird, not only on this occasion but dozens of times afterwards, pick the insect from off the tree, often killing it in the act; and found the stomach, on being opened, filled with various species of winged insects.
The habits of the three species differ widely. The Red-backed Hummingbird loves to flit over the open prairies, stopping at every tempting flower, to catch some idler lurking in its nectar-cells. Building its nest generally in a low shrub, and close to the rippling stream, it finds pleasant music in its ceaseless splash. Minute Calliope, on the other hand, prefers rocky hillsides at great altitudes, where only pine-trees, rock-plants, and an alpine flora ‘struggle for existence.’ I have frequently killed this bird above the line of perpetual snow. Its favourite resting-place is on the extreme point of a dead pine-tree, where, if undisturbed, it will sit for hours. The site chosen for the nest is usually the branch of a young pine; artfully concealed amidst the fronds at the very end, it is rocked like a cradle by every passing breeze.
The Black-throated Hummingbird lingers around lakes, pools, and swamps where its favourite trapping-tree grows. I have occasionally, though very rarely, seen it hovering over flowers; this, I apprehend, is only when the storehouse is empty, and the sap too dry to capture the insects. They generally build in the birch or alder, selecting the fork of a branch high up.
All hummingbirds, as far as I know, lay only two eggs; the young are so tightly packed into the nest, and fit so exactly, that if once taken out it is impossible to replace them. Several springs succeeding my first discovery that these hummingbirds were regular migrants to boreal regions, I watched their arrival. We were quartered for the winter close to the western slopes of the Rocky Mountains. The winters here vary in length, as well as in depth of snow and intensity of cold, 33° below zero being no unfrequent register. But it did not matter whether we had a late or early spring, the hummingbirds did not come until the Ribes opened; and in no single instance did two whole days elapse after the blossoms expanded, but Selasphorus and Calliope arrived to bid them welcome. The males usually preceded the females by four or five days.
The Black-throated Hummingbird arrives about a week or ten days after the other two. Marvellous is the instinct that guides and the power that sustains these birds (not larger than a good sized bumblebee) over such an immense tract of country; and even more wonderful still is their arrival, timed so accurately, that the only flower adapted to its wants thus early in the year opens its hoards, ready to supply the wanderer’s necessities after so tedious a migration!
It seems to me vastly like design, and Foreseeing Wisdom, that a shrub indigenous and widely distributed should be so fashioned as to produce its blossoms long before its leaves; and that this very plant alone blooms ere the snow has melted off the land, and that too at the exact period when hummingbirds arrive. It cannot be chance, but the work of the Almighty Architect—who shaped them both, whose handiwork we discover at every step, and of whose sublime conceptions we everywhere observe the manifestations in the admirably-balanced system of creation!
The specific characters of these three species, whose northern range I believe was first defined by myself, are briefly as follows:—
Selasphorus rufus (the Nootka or Red-backed Hummingbird).—Male: tail strong and wedge-shaped; upper parts, lower tail-coverts, and back, cinnamon; throat coppery red, with a well-developed ruff of the same, bordered with a white collar; tail-feathers cinnamon, striped with purplish-brown. Female: plain, cinnamon on the back, replaced with green; traces only of metallic feathers on the throat. Length of male, 3·50; wing, 1·56; tail, 1·31 inches. Habitat: West coast of North America to lat. 53° N., extending its range southward through California, to the Rio Grande.
Stellata Calliope.—Male: back bright-green; wings brownish; neck with a ruff of pinnated magenta-coloured feathers, the lower ones much elongated; abdomen whitish; length, about 2·75 inches. Female, much plainer than the male, with only a trace of the magenta-coloured ruff.