Breeding

See Figure 7. Males arrive on territory 2 to 7 d before females - for arrival dates, see Migration. Pairs form shortly after arrival of female, sometimes on day of arrival. After pair formation, nest building usually begins within a few days for early arrivals, almost immediately for late arrivals. Cold and wet weather may delay nesting by as much as 10 d (Will 1986 Will, T. C. (1986). The behavioral ecology of species replacement: Blue-winged and Golden-winged warblers in Michigan. Ph. D. diss., Univ. Michigan, Ann Arbor. Close ). Egg laying usually starts one day after nest completion, but can be delayed by cold weather.

First egg-laying: central Michigan (1981-83), 21 May to 1 Jun (13 nests; Will 1986 Will, T. C. (1986). The behavioral ecology of species replacement: Blue-winged and Golden-winged warblers in Michigan. Ph. D. diss., Univ. Michigan, Ann Arbor. Close ); se. Pennsylvannia, 5 May to 10 Jun (Jacobs 1904 Jacobs, J. W. (1904). The haunts of the Golden-winged Warbler. Gleanings 3:1-30. Close ); n.-central New York, 15 May to 7 Jun (JLC; 33 clutches observed 1990-91). Rarely up to early July. Will (Will 1986 Will, T. C. (1986). The behavioral ecology of species replacement: Blue-winged and Golden-winged warblers in Michigan. Ph. D. diss., Univ. Michigan, Ann Arbor. Close ) noted late second nests with bigamous males.

Usually 1 egg/d, sometimes 1 egg/2 d (Jacobs 1904 Jacobs, J. W. (1904). The haunts of the Golden-winged Warbler. Gleanings 3:1-30. Close ). Incubation may begin on the afternoon of the day when the penultimate egg is laid (Jacobs 1904 Jacobs, J. W. (1904). The haunts of the Golden-winged Warbler. Gleanings 3:1-30. Close ), as with the Kirtland's (Dendroica kirtlandii; Walkinshaw 1983 Walkinshaw, L. H. (1983). Kirtland's Warbler: The natural history of an endangered species. Bloomfield Hills, MI: Cranbook Inst. Sci. Bull. 58. Close ) and Prairie Warbler (D. discolor; Nolan 1978 Nolan, V., Jr. (1978). The ecology and behavior of the Prairie Warbler Dendroica discolor. Ornithological Monograph No. 26. American Ornithologists' Union, Washington, DC, USA. Close ). Incubation usually 10-11 d, exclusively by female; young in nest 8-9 d. Duration of both influenced by weather. All young usually fledge same day, rarely over 2 d. Frequent renests after loss of first clutch, but renests after fledging young not described.

Female appears to select the nest site, sometimes accompanied by the male. Nest usually on the ground, often at the base of a cluster of leafy plant material, e.g., Solidago or Ribes. Base of supporting plants often above the nearby ground level, with leafy material quite thick and obscuring the nest, especially later in the growing season. Nests sometimes built in a tussock of grass or sedge, so somewhat exposed. Most nests include a taller, thicker stem in the supporting basal material, which adults grasp when arriving at the nest. Adults feeding nestlings and detecting a nearby human may repeatedly carry food down nearby stems as if decoying potential predator (Bradbury 1991 Bradbury, R. C. (1991). Decoy behavior of Golden-winged Warblers at nest. Bird Observer 19:306. Close ). Brewster's and Blue-wings seem to build nests higher (0-30 cm) above ground than Golden-wings (JLC).

Nest sites for Golden-wings, Blue-wings, and their hybrids often located along the shaded edge of a forest-field. Edges in small forest openings, paths, or trails also used. Some nests within forests, ≤10 m from the edge of a field. Vegetation around nests appears to be the same for Golden-winged and Blue-winged warblers (Will 1986 Will, T. C. (1986). The behavioral ecology of species replacement: Blue-winged and Golden-winged warblers in Michigan. Ph. D. diss., Univ. Michigan, Ann Arbor. Close ). For 15 Golden-wing nests, the number of tree trunks > 2.5 cm DBH averaged 127 within 12.5 m of the nests. The number of shrubs for an 80 m2 transect extending 12.5 m from the nest averaged 190 (n = 9). Within 1 m of the nest, the mean height of stems near the nest was 0.52 m and ground cover and grass cover was 86% to 56%, respectively.

Construction

Entirely by the female, usually in 1 to 3 d. Females readily desert nests disturbed during construction; may build as many as four partial nests. Even nests with incomplete clutches may be abandoned if disturbed (JLC). After incubation starts, females often stay on a nest despite considerable disturbance.

Structure

Based on Jacobs (Jacobs 1904 Jacobs, J. W. (1904). The haunts of the Golden-winged Warbler. Gleanings 3:1-30. Close ), Eaton (Eaton 1910 Eaton, E. H. (1910). Birds of New York. Introductory chapters; Waterbirds and gamebirds. New York State Museum, Memoir 12, Part 1. NY State Education Deptartment, Albany University, Albany, New York, USA. Close ), Forbush (Forbush 1929 Forbush, E. H. (1929). Birds of Massachusetts and Other New England States, Part 3: Land Birds from Sparrows to Thrushes. Massachusetts Department of Agriculture, Boston, MA, USA. Close ), several hundred nest records provided by the Western Foundation of Vertebrate Zoology and the Nest Record Program of the Cornell Laboratory of Ornithology, and personal observations. Leaves form the base of most nests (>30 leaves in one instance), usually arranged with petioles outward. Coarse material next, e.g., bark from grape (Vitis spp.) or shreds of the reddish bark from Viburnum amomum (> 40 pieces of 5 to 15 cm in one nest). Thin, long threads of plant material 10-20 cm long often woven into the nest with a few leaves in the lower, outer portions. Inner lining of fine plant material arranged in circular pattern, often with reddish color, particularly apparent when wet. Most nests well concealed, occasionally with a leaf positioned to form a cap over the eggs and incubating female. A few nests are rather sprawling in shape.

Dimensions

Range of dimensions (n = 17; Jacobs 1904 Jacobs, J. W. (1904). The haunts of the Golden-winged Warbler. Gleanings 3:1-30. Close ): outside diameter: 9.1-15.2 cm; outside depth: 7.6-12.7 cm; inside diameter: 4.3-6.4 cm; inside depth: 3.3-6.4 cm.

Size

Length x breadth (mean and range in mm): 16.3 x 12.7, 14.5-17.8 x 11.9-13.2, n = 81 (Jacobs 1904 Jacobs, J. W. (1904). The haunts of the Golden-winged Warbler. Gleanings 3:1-30. Close ), 14.7-18.5 x 12.2-14.0 (Forbush 1929 Forbush, E. H. (1929). Birds of Massachusetts and Other New England States, Part 3: Land Birds from Sparrows to Thrushes. Massachusetts Department of Agriculture, Boston, MA, USA. Close ), 16.7 x 13.0, 15.9-18.6 x 12.3-13.0, n = 50 (Tyler in Bent 1953b Bent, A. C. (1953). Life Histories of North American Wood Warblers. Bulletin of the United States National Museum 203. Close ).

Color

Ground color from pale pink, especially when fresh, to pale cream. Markings in fine streaks to small blotches of burnt sienna to lilac color concentrated near the rounder end. (JLC).

Egg Laying

Time between nest completion and onset of egg-laying variable. Nests occasionally contain eggs the day after nest construction begins (Jacobs 1904 Jacobs, J. W. (1904). The haunts of the Golden-winged Warbler. Gleanings 3:1-30. Close ). In n.-central New York, during a wet but warm spring, the duration between the date of nest discovery and laying of the first egg ranged from 4 to 6 d (mode of 5 d); during a warm and dry spring, 1 to 4 d (mode of 1 d; JLC).

Female only. 10 to 11 d, occasionally 12 d according to Golden-winged Warbler Working Group.

Little information. Juvenile remiges emerge from their sheaths on the sixth day (Will 1986 Will, T. C. (1986). The behavioral ecology of species replacement: Blue-winged and Golden-winged warblers in Michigan. Ph. D. diss., Univ. Michigan, Ann Arbor. Close ).

Little information. Both sexes share in feeding of young.

Not known to occur.

Brown-headed Cowbirds the only known brood parasite; about 30% of nests have at least one cowbird egg (Coker and Confer 1990 Coker, D. R. and J. L. Confer. (1990). Brown-headed Cowbird parasitism of Golden-winged and Blue-winged warblers. Wilson Bulletin 102 (3):550-552. Close ), as determined by a survey of several hundred nest records. Effect of cowbird parasitism on success of these nests unknown.

In n.-central New York (1990-1991), 8 of 23 (35%) Golden-winged Warbler nests found (all stages of nesting cycle) had cowbird eggs or chicks (JLC). Omitting predation and assuming one warbler egg was discarded for each cowbird egg added, 61% of warbler eggs (n = 31) in parasitized nests failed to hatch while only 9% of the eggs (n = 57) in non-parasitized nests failed to hatch, about a 50% loss from egg-laying to hatching. In contrast, all known nestlings in parasitized nests fledged (JLC). For the entire study population, a 50% reduction in hatching for 35% of the nests reduces fledging by about 17%.

In central Michigan, cowbird eggs in 4 of 13 Golden-winged Warbler nests were studied by Will (Will 1986 Will, T. C. (1986). The behavioral ecology of species replacement: Blue-winged and Golden-winged warblers in Michigan. Ph. D. diss., Univ. Michigan, Ann Arbor. Close ). Two of these nests were abandoned by the warblers, but in one nest a single cowbird egg appeared 3 d before the first warbler egg; one Golden-wing female laid a clutch of 4 warbler eggs and fledged 3 warblers and the cowbird.

Brown-Headed Cowbird Success

Eight parasitized nests in n.-central New York had a total of 13 cowbird eggs: 3 in 1 nest, 2 in each of 3 nests, and 1 in each of 4 nests. One additional cowbird egg was laid after the warbler nestlings fledged. Six of the 14 cowbird eggs fledged. Most losses were due to predation. Will (Will 1986 Will, T. C. (1986). The behavioral ecology of species replacement: Blue-winged and Golden-winged warblers in Michigan. Ph. D. diss., Univ. Michigan, Ann Arbor. Close ) observed that "Cowbirds did not necessarily fare better than their warbler nestmates. Of 6 parasitized nests that fledged warblers, 2 did not fledge cowbirds. The two cowbird nestlings in one nest and a single cowbird in the other disappeared from the nests well before the warblers fledged."

Parents often divide fledglings, each group attended by only one parent; young disperse off-territory within a few days of fledging (Will 1986 Will, T. C. (1986). The behavioral ecology of species replacement: Blue-winged and Golden-winged warblers in Michigan. Ph. D. diss., Univ. Michigan, Ann Arbor. Close ). Parents may feed fledglings up to 31 d after fledging.

No data; difficult to study.