Montana Field Guide

Black-and-white Warbler - Mniotilta varia

Distinctly striped in black-and white plumage with a slightly decurved bill for bark foraging, the Black-and-white Warbler moves vertically along tree trunks, exhibiting characteristics generally attributed to nuthatches. The adult body length ranges from 11 to 13 cm, with an average wingspan of 21 cm. Body mass ranges from 8.8 to 15.2 grams, and bill length from 10.0 to 13.7 mm. The female is the smaller of the two sexes. Males, exhibiting darker, more contrasted markings than females in both breeding and non-breeding plumages, are defined by conspicuous black and white coloration. In breeding plumage, the male crown has a broad white median stripe, black sides, and a broad white superciliary stripe that extends to the nape. The lores and ear coverts are black, while the submustachial stripe is white above a black throat with black and white streaked sides of the neck. A white eye-ring contrasts with black ear coverts. The upper and underparts are streaked with black and white, the underparts being the more distinct and boldly marked. The wings are black with two evident wing bars. The feathers of this warbler's truncate tail are dull black marked with white, revealing white tail spots. The female's breeding plumage is similar to the males, but with pale gray lores and ear coverts and less contrasting black and white markings overall. A narrow, black eye stripe, white throat, and a less defined streaking on the back also distinguish the female from the male. Additionally, the female's tail spots are less distinct and a faint buff wash on the flanks and sides of the throat is generally present (Kricher 1995). The eyes have a brown iris. The feet in the juveniles are a pinkish-buff, becoming darker to black with age.

The vocalization of the Black-and-white Warbler is described as a thin, high-pitched two syllable squeaky "weesee, weesee, weesee," or "squeaky, squeaky, squeaky," repeated upwards of ten times (Kricher 1995). One of the highest pitched of the wood warblers, the song of the Black-and-white Warbler is described as resembling the sound of a wet rag wiped repeatedly across glass (Bent 1953, Lemon et al.1983, as cited in Kricher 1995). During breeding, a variation of the primary song is of a longer, faster, and more varied pitch (Bent 1953). Although varied, the call note of this species can be described as a sharp "chip," "pit," or sharp rattling "stick" (Terres 1980, Sibley 2000).

The Black-and-white Warbler is distinguished from similar warbler species by its distinctive black and white plumage and its nuthatch-like foraging behavior. Few other wood warblers forage in this manner, and those that do are not black and white in coloration. The two other black and white warblers in Montana, the Blackpoll Warbler and the Black-throated Gray Warbler, are noticeably different in plumage. The Blackpoll Warbler has an un-striped black crown and white cheek and throat, while the Black-throated Gray Warbler has a bright yellow spot in front of each eye, a solid black (or black and gray) un-striped head, and a mostly gray, un-striped back (Kricher 1985, Sibley 2000). Neither of these two species possess a decurved bill (Sibley 2000).

Montana Range

Less dependent upon flying insects, the Black-and-white Warbler generally arrives earlier in the spring and stays later in the fall than other warbler species (Johnsgard 1986). Birds have been recorded in Montana and southern Alberta from early May through early September. May is the earliest month recorded for Black-and-white Warbler observations in Montana. The majority of the latest season records are for August, although one record just south of Ninepipe National Wildlife Refuge indicates an individual present in October (Montana Bird Distribution 2003).

Information on habitat use in Montana is limited. Existing records indicate observations in riparian habitat and woody draws, those of mixed deciduous and ponderosa pine (Pinus ponderosa), in the eastern part if the state (Skaar unpublished data). One observation record indicates a female feeding on Douglas-fir (Pseudotsuga menziesii) northeast of Helena, while numerous records exist for the deciduous habitat in the town park in Westby, as well as that of several backyards, specifically in the northeast portion of the state (Montana Bird Distribution 2003).

In general, the Black-and-white Warbler inhabits young, medium-aged and mature deciduous and mixed forests during the breeding season (Bushman and Therres 1988, Kricher 1995). Studies of habitat selection have yielded conflicting results that appear to be due to geography, as well as variations in forest type and stand age. In the southern part of its range, this species appears to be most closely associated with relatively closed-canopied forests with low shrub density (Conner et al. 1983, Crawford et al. 1981, Noon et al. 1980, Wilson et al. 1995). In aspen forests in Alberta, however, stands with high shrub density were avoided (Westworth and Telfer 1993). Black-and-white Warblers were associated with high tree density and high canopy volume (indicative of mid- to late-successional forests) in mixed forests of central Ontario (Clark et al. 1983). The Black-and-white Warbler typically nests on the ground, often adjacent to a tree, shrub, rock, stump or log, under a shrub or dead branches, or, more rarely, atop stumps (Bent 1953, Kricher 1995).

A wide variety of habitats are used during the non-breeding season, from early successional disturbed areas to mature forests (Kricher 1995). Caribbean habitats utilized include coastal forest, dry interior forest, wet forest, forest edge, pine woods, riparian areas, wetlands, urban habitats that provide plant cover, and some open areas (Arendt 1992). Cacao, citrus, mango, shade coffee, and pine plantations in Puerto Rico, Jamaica, and Costa Rica are also selected (Robbins et al. 1992). Even though it showed a preference for undisturbed habitats, particularly forest, this species is considered a habitat generalist in western Mexico (Hutto 1992). Primary forest is preferred to other habitat types in the Yucatan Peninsula, Mexico (Greenberg 1992, Lynch 1989) and in Veracruz, Mexico (Rappole et al. 1992). In the Virgin Islands, they exhibited a preference for moist forest (90.5% of detections) over other habitat types (Askins et al. 1992).

Foraging principally by creeping along tree trunk and branches, Black-and-white Warblers also foliage glean (Bent 1953, Kricher 1995). The main food items are chiefly insects, including beetles (Coleoptera), caterpillars and moths (Lepidoptera), ants and other Hymenoptera, flies (Diptera), and bugs (Hemiptera), and may include spiders (Arachnida) and harvestmen (Phalangida) (Bent 1953). Lepidopteran larvae are important prey during spring migration (Graber and Graber 1983). The remains of a small lizard were found in the stomach of one Texas specimen, indicating further variety in their diet (Oberholser 1974).

Little information exists for this species in Montana.

In quacking aspen (Populus tremuloides) forest in Alberta, male pairing success was lower in forest fragments (56%) than in continuous forest (80%) but due to small sample sizes, the difference was not statistically significant (Sodhi and Paszkowski 1997). The Black-and-white Warbler occurs commonly in small, mixed species flocks of warblers in the Virgin Islands in winter where density in moist forest was less than 1 per hectare on St. Thomas and 1 to 2 per hectare on St. John (Ewert and Askins 1991). Conflicting reports of winter territoriality exist (Faaborg and Arendt 1984, Morton 1980).

Site fidelity is exhibited on the wintering grounds in Puerto Rico where 22% of banded birds were recaptured at the study site. The average time between banding and recapture was 1.9 years; the longest interval was 4 years (Faaborg and Arendt 1984). Twenty percent of birds captured in Cuba were birds banded there the previous year (Gonzalez-Alonso et al. 1992).

The average annual adult survivorship is estimated to be 71%, with the oldest known individual aged at 11 years, 3 months old (Klimkiewicz et al. 1983, Kricher 1995).

Known parasites on Black-and-white Warblers include blood parasites (Haemoproteus spp. and Leucocytozoon spp.), feather mites, a louse species (Myrsidea incerta), and one fly species (Ornithoica confluens) (Bent 1953, Kricher 1995). Bent (1953) indicates maggots destroyed a nestful of young.

One record of direct evidence of breeding was recorded in Valley County, but details of the nesting event appear lost (Skaar unpublished data, Montana Bird Distribution 2003). Additional observations that indicate behavior suggesting breeding have been recorded in Roosevelt, Sheridan, Daniels, Dawson, Richland, Rosebud, and Carter counties (Skaar unpublished data, Montana Bird Distribution 2003), but no details on these records are documented. No other information is available on the reproductive habits of the Black-and-white Warbler in Montana.

In general, breeding begins as early as mid-April at southern latitudes and as late as late July at northern latitudes. The female builds the cup-shaped nest of grasses, dry leaves, strips of inner bark, and pine needles lined with finer grasses, rootlets, hair or mosses (Terres 1980, Baicich and Harrison 1997). Clutch size is usually five, ranging from 4 to 6 eggs. Eggs are laid daily until the clutch is complete. Eggs are short, subelliptical, and range in color from white or cream-white, sometimes pale bluish or greenish-white, with finely speckled pigments of brown, and occasionally lavender and pale lilac, encircling the larger end. Dimensions average 15.50 to 18.46 mm by 13.02 to 13.64 mm with average weights of 0.076 gram (Kricher 1985).

Incubation, which requires 10 to 12 days, begins when the penultimate or last egg is laid and is conducted by the female only. When threatened, females may perform a distraction display described as the "rodent run," for its hunched posture and tail drag (Davis 1989, as cited in Kricher 1995). The young are fed by both parents and leave the nest at 8 to 12 days posthatching. This species is single brooded, though double broods are suspected (Kricher 1995). In Arkansas, 73.7% of 19 nests were successful (fledged at least one young) (Martin 1993). Age at sexual maturity is unknown (Kricher 1995).

No management activities in Montana specific to the Black-and-white Warbler are documented.