Breeding

See Figure 4. One of the earliest warblers to arrive on its northern breeding grounds; breeding begins as early as mid-Apr in southern areas. Because of its habit of bark foraging, it may be less dependent than other wood-warblers on leaves opening.

In Alberta, courtship and nest-building start in late May and early Jun. Eggs are laid in the first week of Jun, hatch in the second to third week of Jun. Young leave nest late to early Jul. Leaves territories mid- to late Jul (N. Sodhi pers. comm.).

Usually in deciduous or mixed deciduous-coniferous woods, usually on ground against shrub or tree, occasionally in cavities at top of stumps (≤ 0.5 m above ground), but usually in a depression at the base of a stump, rock, or log. Nest is well hidden. Species often nests along hillsides or ravines, with a tendency to favor swampier places (Harrison 1978a Harrison, C. J. O. (1978). A Field Guide to the Nests, Eggs and Nestlings of North American Birds. Collins, Toronto, ON, Canada. Close ). In Ontario, nests in mixed woods (10 nests), coniferous woods (12), deciduous woods (1), black spruce (Picea mariana) bog (1), alder swamp (1), and unspecified woods (12), with nests at the bases of trees and stumps (19 nests), beside or under logs (4), under bushes or shrubs (4), under dead branches and leaves (1), and in mossy hummock (1), respectively (Peck and James 1983 Peck, G. K., and R. D. James (1983). Breeding Birds of Ontario: Nidiology and Distribution Volume 1: Nonpasserines. Royal Ontario Museum, Toronto, ON, Canada. Close ). Elevated nests were in stump cavities (5 nests), in upturned roots (4), in a rock crevice (1), in white cedar (Thuja occidentalis) trunks (3), and in a mossy bank (1) (Peck and James 1983 Peck, G. K., and R. D. James (1983). Breeding Birds of Ontario: Nidiology and Distribution Volume 1: Nonpasserines. Royal Ontario Museum, Toronto, ON, Canada. Close ).

Construction Process

No information.

Structure And Composition Matter

Dry leaves, coarse grass, skeletonized leaves, strips of inner bark (especially grapevine), pine needles, and rootlets; cup lined with finer grasses, horsehair, mosses, or even fine copper wire (Terres 1980b Terres, J. K. (1980). The Audubon Society Encyclopedia of North American Birds. Alfred A. Knopf, New York, NY, USA. Close ). Female scrapes bark from trees (N. Sodhi pers. comm.).

Dimensions

Outside diameter 9.5–11.4 cm; outside height 5.7 cm; inside diameter 4.4–5.1 cm; inside depth 3.8 cm; wall of nest 2.5 cm thick; bottom of nest 1.3 cm thick (Harrison 1975b Harrison, H. H. (1975). A Field Guide to Birds' Nests of 285 Species Found Breeding in the United States East of the Mississippi River. Houghton Mifflin Company, Boston, MA, USA. Close ). In Ontario (n = 8), outside diameter 7.5–13.0 cm; inside diameter 4.5–7.8 cm; outside height 4–12 cm; inside depth 2.5–6 cm; height of elevated nests 0.2–1.8 m above ground (Peck and James 1983 Peck, G. K., and R. D. James (1983). Breeding Birds of Ontario: Nidiology and Distribution Volume 1: Nonpasserines. Royal Ontario Museum, Toronto, ON, Canada. Close ).

Shape

Short subelliptical to subelliptical.

Size

Mean length 16.94 mm, range 15.50–18.46 (n = 99); breadth 13.38 mm, range 13.02–13.64 (n = 99) (Western Foundation of Vertebrate Zoology [WFVZ]).

Mass

Average shell mass 0.090 g, range 0.076–0.104 g (n = 99; WFVZ). Eggs laid first are reported to be larger than those laid last (Smith 1934b Smith, W. P. (1934b). Observations of the nesting habits of the Black-and-white Warbler. Bird-Banding 5:31-35. Close ).

Color

White or cream-white, sometimes pale bluish or greenish white, finely speckled with browns, but including lavender and pale lilac. Pigments tend to encircle the larger end.

Surface Texture

Smooth and somewhat glossy.

Egg-Laying

For New York State, 10 May–30 Jun (Bull 1974 Bull, J. (1974). Birds of New York State. Doubleday Natural History Press, Garden City, NY, USA. Close ); Massachusetts, 18–30 May (Veit and Petersen 1993 Veit, R. R., and W. R. Petersen (1993). The Birds of Massachusetts. Massachussetts Audubon Society, Lincoln, Massachusetts, USA. Close ); New Jersey, 18 May–8 Jun (Bent 1953b Bent, A. C. (1953). Life Histories of North American Wood Warblers. Bulletin of the United States National Museum 203. Close ); N. Carolina, 20–28 Apr (Bent 1953b Bent, A. C. (1953). Life Histories of North American Wood Warblers. Bulletin of the United States National Museum 203. Close ); W. Virginia, 6–29 May (Bent 1953b Bent, A. C. (1953). Life Histories of North American Wood Warblers. Bulletin of the United States National Museum 203. Close ); Ontario, 22 May–30 Jul (Peck and James 1983 Peck, G. K., and R. D. James (1983). Breeding Birds of Ontario: Nidiology and Distribution Volume 1: Nonpasserines. Royal Ontario Museum, Toronto, ON, Canada. Close ).

Eggs are laid on successive days; incubation normally begins when next to last or last egg is laid. Incubation requires about 10–12 d. Single brooded. Incubation by female only; male sometimes feeds incubating female. Incubating female sits tightly on eggs and moves only if touched or approached closely (<10 cm from nest; N. Sodhi pers. comm.).

Not observed.

Young leave nest 8–12 d posthatching. When they leave, they cannot fly well; use wings to help scurry across the ground (Smith 1934b Smith, W. P. (1934b). Observations of the nesting habits of the Black-and-white Warbler. Bird-Banding 5:31-35. Close ). As they gain the ability to fly, they tend to occupy low to mid-level branches, still in vicinity of the nest.

Both parents feed young and defend nest. Females observed performing “rodent run” distraction displays, in which the bird assumes a hunched posture and drags its tail (Davis 1989a Davis, Jr., W. E. (1989a). Distraction display or "injury feigning" in birds. Bird Observer 17:125-127. Close ). Both sexes monitor fledglings, which generally stay within 100 m of nest (Smith 1934b Smith, W. P. (1934b). Observations of the nesting habits of the Black-and-white Warbler. Bird-Banding 5:31-35. Close ).

Not known to occur.

Identity Of The Parasitic Species

Brown-headed Cowbird (Molothrus ater) is the only known brood parasite.

Frequency Of Occurrence

Once reported as an uncommon host for Brown-headed Cowbird, but now commonly parasitized. One report of 8 Brown-headed Cowbird eggs in a Black-and-white Warbler nest in Michigan; there were 2 warbler eggs, and the female warbler was incubating all 10 eggs (Byers 1950). Another nest was reported (H. Friedmann inBent 1953b Bent, A. C. (1953). Life Histories of North American Wood Warblers. Bulletin of the United States National Museum 203. Close ) with 5 cowbird eggs and 2 warbler eggs. Friedmann (Friedmann 1963 Friedmann, H. (1963). Host relations of the parasitic cowbirds. Volume 233. U.S. National Museum Bulletin, Washington, DC, USA. Close ) reported 38 occurrences of parasitism distributed throughout the Black-and-white Warbler's range, but the incidence of brood parasitism has undoubtedly changed since that study.

Many records of Brown-headed Cowbird parasitism are reported in breeding bird atlases and other nest records. In nest records supplied by the Western Foundation for Vertebrate Zoology, only 12 of 130 nests had cowbird eggs, but the records range from the late 1800s through the early 1900s. In Ontario, 9 of 43 nests (20.9%) were parasitized (Peck and James 1983 Peck, G. K., and R. D. James (1983). Breeding Birds of Ontario: Nidiology and Distribution Volume 1: Nonpasserines. Royal Ontario Museum, Toronto, ON, Canada. Close ). No evidence that this species rejects cowbird eggs.

Effects Of Parasitism On Host

Unknown.

Success Of Parasite With This Host

Few data, but Black-and-white Warblers have successfully reared cowbird young (Friedmann and Kiff 1985).

Little information; descriptions of fledgling appearance and behavior are needed. Fledglings are reported to be noisy but nonetheless difficult to find; they accounted for only about 10% of the confirmations of nesting in the Vermont breeding bird atlas project (Laughlin and Kibbe 1985 Laughlin, S. P., and D. P. Kibbe (1985). The Atlas of Breeding Birds of Vermont. University Press of New England, Hanover, NH, USA. Close ).

Behavior and movements are not well known. Immature birds generally resemble adult females, but upperparts are more mottled, blackish brown and buffy white, with throat, breast, and flanks pale olive-brown, underparts with diffuse brown streaking; bill and legs pinkish buff (Curson et al. 1994 Curson, J., D. Quinn, and D. Beadle (1994). Warblers of the Americas: an Identification Guide. Houghton Mifflin Company, New York, NY, USA. Close ).