Bluebird and Small Cavity Nester Conservation
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All About Violet-green Swallows
(Tachycineta thalassina)

Contents: Species, Interesting Facts, Identification, Song, Distribution, Preferred Nesting Habitat, Diet, Nesting Behavior, Nestboxes, Nestbox Location, Recommended Distance Between Nestboxes, Monitoring, Nesting Timetable, Longevity, More Info. Also see PHOTOS of nests, eggs and young.

Violet-green Swallow.  Wikimedia commons photo by Wolfgang Wander
Male Violet-green Swallow. Photo by Wolfgang Wander, Wikimedia Commons.

Species: Three subspecies of the Violet-green Swallow (alpha code VGSW) are recognized: Tachyncineta thalassina lepida, T. t. brachyptera and T. t. thalassina.

Interesting Facts:

  • Not much is known about VGSW breeding behavior compared to other swallows.
  • They are fairly abundant, with an estimated 11 million worldwide (Rich et al 2004.)

Identification: Smaller than many other swallows, narrow wings, short tail, wingtips stick out beyond tip of tail. Sides of rump are white. White above eye (less noticeable on drab adults). Adult male has a multicolored upper side with an iridescent emerald green back, sometimes with violet gloss on the upper tail coverts. Juveniles have a dusky face and look sort of like adult females. Juveniles have a dingy throat and chest that blends gradually with darker areas on the head. Females are drab colored. Acrobatic and graceful flyers.

In comparison, the Tree Swallow (TRES) is larger (by about 0.5", weighs 0.7 oz. vs. 0.49 oz. for VGSW), with broader wings, longer tail (wings shorter than tail when perched), a small white crescent on the sides of the rump, and the back of the adult male is more bluish-green, and there is no white above the eye, and they soar more. (It's hard to tell juvenile VGSW and TRES apart.) Tina Mitchell of Coaldale CO (where VGSW and TRES ranges overlap) notes that on the wing, male VGSWs have bright white patches on each side of rump that almost meet across the overtail coverts (sometimes referred to as "saddlebags.") TRESs have solid dark backs. You can't see the white when they're perched; in that case, VGSWs also have more white on the face--but that's considerably harder to pick up at 65 mph.

Song: Mono or bi-syllabic calls (chee-chee), chatty twitters and alarm calls.

Distribution: Breeds in western North America (mostly west of the Rockies), from central Alaska and Western Canada to Mexican highlands. BBS Map. Migrates in large flocks to winter in Mexico, Guatemala, El Salvador and Honduras.

Preferred Nesting Habitat: Open or broken deciduous, coniferous, and mixed woodlands. Likes trees in open areas (e.g., woodland edge.)

Diet: They only eat insects caught in flight. Food includes leafhoppers and leafbugs, ants, wasps, wild bees, beetles, etc. They also drink on the wing.

Nesting Behavior: A gregarious bird that may nest in pairs or colonies of up to 25 pairs. Monogamous?

Nestboxes: Often nests in tall dead snags. May be less likely to use a nestbox compared to the Tree Swallow. See recommended specs. Oval hole for Violet-Green Swallows from Malcolm Rodin

  • Malcolm Rodin has experimented with sideways oval holes for Violet-green Swallow boxes which he found deters adult HOSP if it is NO TALLER than 7/8". He makes the hole using a 7/8" and a 5/8" Forstner wood bit. Drill three hole, using he 7/8" bit for the center hole, and the 5/8" bit for the holes on either side. Then file and sand to get a good oval shape, but do not exceed 7/8" in height. The width will be between 1.5 to 1.75" inches. (Note: TRES require a 15/16" inch hole for the center.) He paints a round shape hole around the oval hole to attract swallows. See video on how to make the entrance hole.
  • See typical boxes used by Mitchell. Mitchell experimented with a diamond shaped hole (1.5" high at center, 3" wide) on a couple of boxes, and they were used by VGSW (but may also be accessible to Starlings.)

Nestbox Location: Some monitors mount boxes as high as possible (at least 5 feet off ground, but Tina Mitchell and Zell Lundberg have had great usage at 6 feet, mounted on trees in CO. Provide for a clear, open flight path from nestbox to sky. May nest near Tree Swallows, and near humans (in backyard gardens or near residences). Also found in roadside habitats and meadows, orchards, parks, golf courses, etc. May prefer boxes mounted under the eaves of buildings rather than on poles or posts? (Birds of British Columbia) May prefer to be near lakes or streams, wetlands and shorelines? Heights of 3-5 meters (9.8-16.4 feet and up) are used.

Recommended distance between nestboxes: ? Have nested 1 km apart. Breeding densities of 2.5 to 15 pairs have been reported in a 99 acre area in northern Arizona, and up to 50 pairs in the same size area, but in thinned forest with added nestboxes (Brawn and Balda 1988). Tina Mitchell of CO generally finds they do not choose boxes within sight of each other. On their trail, they may sometimes have 10-17 pairs nesting on 40 acres.

Monitoring: ? Tree Swallows are not likely to prematurely fledge, I don't know about VGSWs. Tree Swallows (TRES) will sometimes swoop at a monitor. May grab feathers offered by humans. Here is info about monitoring TRES that MAY apply to VGSWs:

TRES: Do not disturb nestboxes after nestlings are 15 days old, to avoid premature fledging. (You may be able tell the age because the parents stop removing fecal sacs when they are 14 days old). Tree Swallow adults are generally tolerant of humans and monitoring. Sometimes incubating females refuse to leave the nest, even if the nest is taken out of the box. However, they can also be quite territorial, and may not like it when humans approach the nestbox, and may swoop, dive bomb, click their beaks and make a racket. Neighboring TRES may gang up to bomb monitors (e.g., 6 at a time), especially if eggs are in the process of hatching. Although they seldom, if ever, connect, all the same, it can be a disconcerting,and some monitors wear a hat or carry a broom or stick their hands over their heads to avoid a collision. Try to monitor the box quickly and quietly to minimize stress. If boxes are monitored regularly, Tree Swallows usually adjust, and aggression may lessen after the babies hatch.

Nesting Timetable (typical):

  • Excavation or nest site selection: Pairs probably form in the spring. Secondary cavity nester. May nest in an abandoned woodpecker cavity, rock or cliff crevices, holes in columnar cacti, and holes in dirt banks, or opportunistically in posts or poles, stone and brick walls, bridges, fiberglass batting in attics, under tiles on ridges of house roofs, between logs in log buildings, in chimneys, in a trailer hitch, in plumbing, ski-lift machinery, and old nests of Cliff or Bank Swallows, and even in a sailboat boom. They often return to the same breeding site. Swoop and chatter around a box, landing on it, looking in, and going in and out a few times. It may take them days to decide on a box. The female probably selects the site. They often share "apartment trees" with other birds like woodpeckers, bluebirds and Purple Martins.
  • Nest construction: Mid-April through mid-May (early June in CO some years.) Both help, but female gathers most of the material. Work usually done in morning and early afternoon. May take 6-20 days, up to 3 weeks. Shallow, loosely constructed, sloppy nest made of straws, dry grasses, strips of bark rootlets, pine needles, lined with abundance of feathers (white preferred?). ( Tina Mitchell's blog shows female in a sea of feathers and notes "The nest of this female looks as if she had murdered a Band-tailed Pigeon and stuffed all of its feathers in her nest.")  Occasionally fur or horsehair? Sometimes wood chips, plant down, fiberglass insulation, string, rope and paper. Cupped middle? May add feathers after egg laying. May just add their own touches and feathers to existing nests. One recorded at 0.75" deep, 3" across, or filling about 25% of the 5x5" floor of a nestbox. May build a "dummy" nest in an adjacent box, or use it for a second brood.
  • Egg laying: 4-6, one report of 7, laying one egg per day. May to early June (mid June through Mid July in CO.) May begin before the nest is finished to 1-2 days after. Subelliptical to oval white eggs, no markings, smooth to non-glossy to slightly glossy, about the size of a penny. (Indistinguishable from Tree Swallow.) Photos. Female may roost in box during egg laying. Male often guards mate.
  • Incubation: 14-15 days, 15 days average, up to 18 days. Only female incubates. May be away from nest a lot.
  • Hatching: Eggs usually do not hatch in one day - one report of 5 day hatching period (Edson 1943). Mitchell notes that eggs are almost translucent until just before hatching. Parents remove eggshells.
  • Development:
    • Day 0: Altricial hatchlings with slight wisps of creamy or grayish down on back, crown and scapulars, pale pink skin, creamy-whitish gape (which Mitchell describes as "clown lips"), eyes closed.
    • Day 5: skins darkens to ashy dray, feather follicles visible.
    • Day 7: make a faint single note peep
    • Day 8-9: eyes open. Feather remiges almost breaking through sheaths. Parents may stop removing fecal sacs, young may defecate in far corner of box.
    • Day 9-10: faint double note peep.
    • Day 10: White feathers appear along sides of body. Blackish speckling shows among expanding gray feathers on back. Female may brood up to this age.
    • Day 13: primaries 1" long, half out of sheath, sides well covered with silky white feathers, plumage on back is black, primaries are halfway down tail.
    • Day 16: young stop gaping.
    • Day 18: look like adults. Abdomen still sticks out.
    • Day 22: abdomen reduced, only scanty down left, wings and tail are at full length.
  • Fledging: 23-24 (25?) days after hatching, sometimes over a couple of days. May return to the nest over the next few days?. Young are fully developed. ?Dependent on adults after nest for unknown period - maybe 3 days?
  • Dispersal: ?. High nest site fidelity (44-84% (BNA).
  • Number of broods: A single brood is typical, but second broods have been reported. May not reuse nests?
  • Longevity:

References and More Information:

  • Brown, C. R., A. M. Knott and E. J. Damrose. 1992. Violet-green Swallow (Tachycineta thalassina), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http:// bna.birds.cornell.edu/bna/species/014 doi:10.2173/bna.14
  • Sibley Guide to Birds, 2000.
  • James Reserve bluebird trail (San Jacinto)
  • Tree Swallow biology
  • Malcolm Rodin's Violet-green Swallow webpage with YouTube Video on how to make an oval hole
  • Cornell Nestwatch
  • Birdweb - Birds of Washington State
  • Rich, T.D., C.J. Beardmore, H. Berlanga, P.J. Blancher, M.S.W. Bradstreet, G.S. Butcher, D.W. Demarest, E.H. Dunn, W.C. Hunter, E.E. Inigo-Elias, J.A. Kennedy, A.M. Martell, A.O. Panjabi, D.N. Pashley, K.V. Rosenberg, C.M. Rustay, J.S. Wendt, and T.C. Will. 2004. Partners in Flight North American landbird conservation plan. Cornell Lab of Ornithology, Ithaca, NY.
  • Brawn, J.D. and R.P. Balda. 1988. Population biology of cavity nesters in northern Arizona: do nest sites limit breeding densities? Condor 90:61-71.
  • Campbell, R.W, et al, The Birds of British Columbia, Canadian Wildlife Service
  • Kingery, Hugh E, editor, Colorado Breeding Bird Atlas, 1998
  • Sipapu Blog by Tina Mitchell of CO
  • Nest and Egg ID (with links to species biology and photos of nests, eggs and young) for other small cavity nesters
...we will call them children of heaven.
- W.L. Dawson, 1923, The Birds of California

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