Vaux's Swift Life History

Habitat

Vaux’s Swifts use mature and old-growth coniferous and mixed forests for nesting, especially those with plenty of hollow trees. Forests with coastal redwood, grand fir, ponderosa pine, western hemlock, Douglas-fir, and western redcedar have the largest populations of this swift, as they tend to produce more nesting and roosting cavities than other tree species. Nonbreeding birds also use tree hollows during the summer, roosting communally in large trees especially. In many cases, old woodpecker holes serve as the roost entrances. In preparation for migration to wintering areas in the tropics, Vaux’s Swifts gather in large flocks and use both trees and chimneys (often in large metropolitan centers) for communal roosts. On the wintering grounds, Vaux’s use old-growth forest at many elevations. They feed over forest gaps and fields as well as towns. Very little is known about roosting of migrant Vaux’s Swifts, but the locally nesting populations in the Yucatán Peninsula sometimes roost and nest in natural limestone wells.

Food

Vaux’s Swifts forage in flight, eating tiny insects and spiders that they catch via rapid aerial pursuit. They eat flies, hoverflies, booklice, ants, bees, leafhoppers, planthoppers, aphids, spindlebugs, lanternflies, bark beetles, moths, mayflies, and true bugs. They forage in flocks, pairs, or singly, coursing back and forth over productive areas. On occasion, these swifts seem to flutter or stall over the tips of tree branches, perhaps to glean an insect resting there. When feeding young, Vaux’s Swifts capture over 100 insects and spiders per sortie, which they form into a bolus (ball) that they regurgitate to the young at the nest. They may make over 50 sorties per day.

Nesting

Nest Placement

Nest are built in hollows of live or dead large trees, usually coniferous trees, and much less often in chimneys or under rooflines. The species readily accepts artificial nest boxes in Oregon.

Nest Description

Both male and female construct the nest of small twigs, using saliva to adhere the twigs to the side of the nest cavity. Nest is a sloppy-looking, semicircular set of twigs (and sometimes other plant materials) measuring on average 4 inches across and 2.4 inches tall, with the interior cup 3.2 inches across by 1.2 inches deep.

Nesting Facts

Behavior

In spring, Vaux’s Swifts arrive in breeding areas in small groups, vocalizing frequently. They quickly pair up, usually with the same mate as in previous nesting seasons. A third bird sometimes joins courtship flights by pairs, though the reasons for such threesomes are not clear. On occasion, the lead bird performs a glide with wings held high in a V-shape. Vaux’s Swifts mate on the wing, the male riding on the back of the female for a few seconds as she glides. Vaux’s Swifts do not establish territories. Multiple pairs may nest peaceably in the same tree, and nonbreeding birds sometimes also roost in nesting cavities. Both parents feed the young in the nest, and in several instances, a third adult swift feeds young. Such observations suggest that Vaux’s may sometimes breed cooperatively, as in Chimney Swifts. Studies that used radio-tagged swifts discovered that Vaux’s mostly forages very near the nest site while feeding young and also that about half the adults and young continue to use the nest tree for roosting well after the young have fledged. Before migration to wintering areas, Vaux’s Swifts congregate in flocks that roost communally, often in large cities, where chimneys may serve as roost cavities. Their rapid return to these communal roosts at dusk has made them celebrities in some cities, where residents turn out in numbers to watch the spectacle, sometimes involving tens of thousands of swifts. On the wintering grounds, Vaux’s Swifts have been little studied but appear to forage and roost in much the same manner as on the nesting grounds.

Conservation

According to the North American Breeding Bird Survey, Vaux's Swift numbers declined by an estimated 1.8% per year between 1968 and 2015, resulting in a cumulative decline of 58% over that period. Partners in Flight estimates a global breeding population of 870,000 and rates the species a 13 out of 20 on the Continental Concern Score, indicating it is a species of low conservation concern. Modern forestry practices that reduce old-growth forests have a negative impact on populations of this species. Vaux’s Swifts are aerial insectivores, a broad group of birds that are undergoing severe declines, for reasons that have yet to be fully understood.

Credits

Bull, Evelyn L. and Charles T. Collins. (2007). Vaux's Swift (Chaetura vauxi), version 2.0. In The Birds of North America (P. G. Rodewald, editor). Cornell Lab of Ornithology, Ithaca, New York, USA.

Lutmerding, J. A., and A. S. Love (2017). Longevity records of North American birds. Version 2017.1. Patuxent Wildlife Research Center, Bird Banding Laboratory, Laurel, MD, USA.

Partners in Flight (2017). Avian Conservation Assessment Database. 2017.

Sauer, J. R., D. K. Niven, J. E. Hines, D. J. Ziolkowski Jr., K. L. Pardieck, J. E. Fallon, and W. A. Link (2017). The North American Breeding Bird Survey, Results and Analysis 1966–2015. Version 2.07.2017. USGS Patuxent Wildlife Research Center, Laurel, MD, USA.

Sibley, D. A. (2014). The Sibley Guide to Birds, second edition. Alfred A. Knopf, New York, NY, USA.

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