NORTHERN VIOLET-GREEN SWALLOW. Tachycineta thalassina lepida Mearns

Field characters.—Body size slightly less than that of Linnet or Junco; wings long and pointed, when closed reaching an inch beyond the slightly notched tail. Whole under surface of body, and sides of rump, pure white (pl. 46f); upper surface of body intense green, with violet tinge on rump discernible at short range. Voice: A plaintive tsee or che, sometimes repeated to form a twitter.

Occurrence.—Common summer visitant to Upper Sonoran and Transition zones on west slope of Sierra Nevada; also at east base of mountains. Recorded from Pleasant Valley and near Lagrange eastward to floor and walls of Yosemite Valley and to near Chinquapin; also in vicinity of Mono and Walker lakes; seen in migration near Washburn Lake. Forages in the open, roosting and nesting in hollow trees or in rock crevices. Often in loose flocks while foraging.

Of the six species of swallows found in the Yosemite section the Northern Violet-green Swallow is the one most likely to be seen by the summer visitor to the region. During the warmer months of the year it is common in Yosemite Valley (the only swallow regularly there, indeed), and it is plentiful in the blue oak belt of the western foothills. It occurs in some numbers east of the mountains in the same season, and it was observed at Washburn Lake in the fall.

In a general way the Violet-green Swallow resembles the Tree Swallow. Both species have pure white underparts and dark backs, and both nest in natural cavities of trees; but the Violet-green Swallow shows conspicuous white patches on the sides of the rump (pl. 46f). Sometimes the white feathers of these patches curl up so as to completely cover the rump, at least in side view, while again a dark space may show between the two. The pure white under surface readily distinguishes the present species from the remaining swallows found in the region.

In Yosemite Valley, and at certain places in the foothills, the Violet-green Swallow and the White-throated Swift may be seen together and the characteristics of the two may be compared closely. The swallow is seen to be of only about half the bulk of the swift and the hind margin of its proportionately broader wing is straight instead of concave as is that of the swift. In flight the Violet-green Swallow, while adept enough, is less speedy and never as daring as the swift, and its notes, even when uttered in series, are not given in the torrential manner characteristic of the swift.

The Violet-green Swallow arrives early in the Yosemite region. It was already present at El Portal upon our visit to that place on April 27, 1916, and was found in Yosemite Valley the following day. East of the Sierras, in 1916, it appeared on May 6, when a scattering flock was observed at the mouth of Rush Creek near Mono Lake. Throughout the summer months and until early September the species is much in evidence below the 7000-foot contour. At Washburn Lake on August 24, 1915, a troop of at least 12 was seen making its way high overhead down the cañon. Two were seen below Vernal Falls on September 1, 1915, and on September 10 the same year, five or more of these birds were noted near Walker Lake. Mr. C. W. Michael (MS) saw the species in Yosemite Valley during stormy weather on September 23, 1920. These are our latest records of the species.

Soon after arriving here the Violet-green Swallows begin hunting for nest sites. Unlike the Cliff and Barn swallows, they seek natural cavities in trees or crevices in rocks. On the blue-oak covered hillsides near Lagrange, on May 6 and 7, 1919, several pairs of these birds were prospecting, flying here and there, entering and leaving old woodpecker holes or cavities left by the rotting out of stubs, and doing much twittering. But our impression was that nesting would not commence in earnest yet for some days. The Violet-green Swallows seen on Negit Island in Mono Lake on May 27, 1916, seemed to be searching for nest locations in the cracks of the lava in the rougher parts of the islet. At Sierra Point on May 16, 1919, some of the swallows seen appeared to be settled for the season. Two, in particular, were again and again seen to alight on a certain little bench of rock near a cleft in the cliff. In Yosemite Valley, in 1915, a female was seen gathering nest material on May 31. Other pairs in the Valley that year were more advanced with their nesting program, as young were observed there on the wing, June 24. East of the Sierras, at Mono Lake Post Office on July 1, 1916, a female was found sitting on three incubated eggs in a nest on a cross beam in a barn, entrance to which had been gained through a knothole in the wall of the building.

Like other swallows the present species spends most of the daylight hours on the wing. Much of its hunting, as is noted often in Yosemite, is done high in the air. On the afternoon of May 29, 1911, there was a thunderstorm over the Valley, and another developed at late dusk. Just as the clouds were gathering and the sun was setting, large numbers of these swallows appeared over the meadows, where they alternately skimmed low and mounted almost out of sight, chasing one another, and giving their twittering notes which sounded faintly or loudly according to the distance of the birds from the observer. Probably the cloud formation over the Valley, preceding the shower, had forced the birds down from the upper air where they had been foraging.