Black-throated green warblers range in size from 11.5 to 14 centimeters in length. A breeding adult male has a black chin, throat, and upper chest with a bright yellow face. The underside is mostly white with black lines running down the sides. A pale yellow color stretches across the lower chest and chin area. The wings are mostly gray with white streaks. Mature females are similar to males except not as bright and with less black on their chins. There is not much change in appearance during migration. A young female may have little or no black on its chin. Immature males and females have a yellowish belly rather than a white one. (Gough and Sauer, 1997; Morse and Poole, 2005; Peterson, 1983; Robbins, et al., 1983)
Black-throated green warblers are found through much of the Nearctic Region. In the summer they range from eastern British Columbia throughout southern Canada as far north as Alberta and as far east as Newfoundland. Their summer range includes much of the Appalachian mountains, as far south as South Carolina, Georgia, Alabama, and the Ozarks of northwest Arkansas. They are also found in the Great Lakes region and into Indiana and Illinois during the summer. An isolated subspecies, D. virens waynei, breeds in the cypress swamps of Virginia, North Carolina, and South Carolina. Black-throated green warblers migrate in the winter to southern Texas, southern Florida, and Central and South America. Some individuals have been known to migrate to the West Indies (Cuba), and some wind-blown individuals have recently been found in the British Isles. (Farrand, 1988; Farrand, 1988; Morse and Poole, 2005)
Black-throated green warblers breed from the coastal plains to mountain ranges, but are mostly found in coniferous and mixed forest regions of the northern United States and the Appalachian mountain range. In their winter range they also prefer woody habitats such as deciduous or coniferous forest edges.
Males reach the breeding ground first, with females following shortly after. Black-throated green warblers form mated pairs for a single breeding season. Mating begins with a male display to the female that includes fluffing, in which the male fluffs out his feathers. After mates are chosen, the male usually remains near the female to aid in nest building. After the young leave the nest, the male and female go their separate ways. Males are protective of the nesting area during mating season.
All mating takes place in the spring. This occurs in mid April in the Appalachian mountains, early May in the northern United States, and as late as mid-May in Canada. One brood is produced per year with clutch sizes of 3 to 5 eggs. After 12 days of incubation, it takes about 8 to 10 days for the birds to leave the nest. (Ehrlich, et al., 1988; Gough and Sauer, 1997)
Females spend 80% of their time with their eggs in the nest. Only females brood the hatched young (keep them warm), while males defend the nest. They brood the young less and less over the course of a few days. No brooding occurs within the last few days of the hatchling's time in the nest. Females feed the young, although the male may contribute by bringing some food to the nest. Parents carry the food (mostly invertebrates such as spiders and insects) in their bills and place it in the beaks of their young.
Black-throated green warblers survive well as adults, with 67% surviving from year to year. The longest known lifespan of a black-throated green warbler is 71 months (5 years, 11 months).
Black-throated green warblers hops around, usually on vegetation, but also on the ground. They tend to stay in wooded areas, but will fly across open spaces. (Morse and Poole, 2005)
Black-throated green warblers will bathe during the day in streams. This includes immersing themselves in the water and spreading the water over the rest of his body by shaking. Birds also spend time perched on branches in the sun. (Morse and Poole, 2005)
At dawn and dusk during the breeding season, males hunt for insects and sing to announce their territory. After the young have hatched, the female feeds periodically throughout the day. After hatching, females spend much of their time hunting for food to feed the young. (Morse and Poole, 2005)
Males tend to fight with other males over territorial boundaries. This includes jabbing each other with their wings or pecking at the opponents head with their bill. They often will latch onto one another and fall to the ground with their wings open and continue fighting. Females have been known fight over territories as well.
Black-throated green warblers are territorial and protect the area around the nest site. No information on size of territory was found. (Morse and Poole, 2005)
Males sing at territorial boundaries. A different song is used in the presence of the female or near the nest. The typical song is slow with a clear whistle on the third and fourth notes, while other songs are wheezy. Another form of communication occurs before mating, fluffing is usually performed by the male and is a form of visual communication (see Reproduction: Mating Systems). (Ehrlich, et al., 1988; Robbins, et al., 1983)
Black-throated green warblers eat mostly insects, primarily caterpillars, such as spruce budworms. They have also been known to eat poison ivy berries during migration and the pollen of Cecropia trees in their winter range. During the breeding season, black-throated green warblers eat exclusively insects. (Morse and Poole, 2005)
Predators include red squirrels and blue jays. These predators usually target eggs, hatchlings, or fledglings. The biggest threat to adults are hawks, mostly sharp-shinned hawks. (Morse and Poole, 2005)
Black-throated green warblers are insectivorous. They may help control insect populations in some areas. (Ehrlich, et al., 1988)
Black-throated green warblers have no negative impact on humans.
Black-throated green warblers, like most warblers, are popular birds for birdwatching and may be indicators of ecosystem health.
Black-throated green warblers are not currently considered threatened. However, destruction of forests in breeding and wintering ranges reduces their habitat and leads to the disappearance of the species in that area. Also, balsam woolly adelgids, small, sucking insects that prey on fir trees, are destroying forest habitats that black-throated green warblers rely on.
Tanya Dewey (editor), Animal Diversity Web.
Marina Migliore (author), Kalamazoo College, Ann Fraser (editor, instructor), Kalamazoo College.
Ehrlich, P., D. Dobkin, D. Wheye. 1988. The Birder's Handbook, A Field Guide to the Natural History of North American Birds. New York: Simon & Schuster Inc.
Farrand, J. 1988. An Audubon Handbook, Eastern Birds. New York: McGraw-Hill Book Company.
Gough, G., J. Sauer. 1997. "Patuxent Bird Glossary" (On-line). Accessed November 14, 2006 at http://www.mbr-pwrc.usgs.gov/id/framlst/i6670id.html.
Morse, D., A. Poole. 2005. Black-throated Green Warbler (Dendroica virens). The Birds of North America Online, 2: 55. Accessed October 15, 2006 at http://bna.birds.cornell.edu/BNA/account/Black-throated_Green_Warbler/.
Peterson, W. 1983. Old World Warblers to Sparrows. Pp. 142-143 in J Farrand, Jr., ed. Black-throated Green Warblers, Vol. 3. New York: Alfred A. Knopf.
Robbins, C., B. Bruun, H. Zim. 1983. A Guide To Field Identification Birds Of North America. Racine, Wisconsin: Western Publishing Company, Inc.