Pine warblers are wood warblers, which are small and often colorful songbirds. They are about 14 cm long, which is larger than many wood warblers. Their wingspan is about 22 cm. They weigh about 12 g, but can weigh anywhere from 9.4 to 15.1 g. The speed of their body processes, or their metabolic rate, is 30.6 cm^3 oxygen per hour. (Baicich and Harrison, 2005; Chapman, 1907; Dunne, 2006; Sibley, 2003)
Pine warblers are less brightly colored than many other wood warblers, and males are more brightly colored. In the summer, males are olive or yellow on the top of their head, around their ears, and on their back. They have bright yellow feathers around their eyes that continue down to their bill and wrap around their throat. Their breast is yellow with olive streaks, fading into a white belly with faint olive streaks. Most of their wing and tail feathers are gray, and their legs, feet, and beak are dark. (Baicich and Harrison, 2005; Chapman, 1907; Dunne, 2006; Sibley, 2003)
Males in the wintertime and females in both seasons are not as brightly colored. The feathers are more olive and brown. First-year females have very pale feathers but the same markings. Newborns don't have feathers at first, and their first feathers are soft and downy dark brown ones. (Baicich and Harrison, 2005; Chapman, 1907; Dunne, 2006; Sibley, 2003)
Pine warblers live in most of eastern North America. The farthest north they live is in the southern parts of Manitoba, Ontario, and Quebec in Canada. They live as far south as Florida and the southern tip of Texas. They live as far east as the coast of the Atlantic Ocean, and as far west as Minnesota, Wisconsin, Illinois, Missouri, Arkansas, and Texas. They stay in most of this area to breed in the summer, except for southern Texas and Louisiana. In the winter, they are mostly found in the parts of this area that are further south, which is unusual among wood warblers. In the winter, the farthest north they are found is Arkansas, southern Tennessee, and southern Virginia. (Chapman, 1907; Dunne, 2006; Harrison, 1984; Rodewald, et al., 2011; Sibley, 2003)
Pine warblers are almost always found in pine forests. They prefer open pine forests, but are also found in thick groups of pine trees or in groups of pine trees within a forest of leafy trees. When traveling between summer and winter habitats, they can also be found in forests with leafy trees. (Chapman, 1907; Dunne, 2006; Ehrlich, et al., 1988; Harrison, 1984; Sibley, 2003)
Males and females form a mating pair during the breeding season. During this time, males can be aggressive toward other males and guard their mates. Scientists don't know if pairs stay together for more than one season. (Morse, 1989; Rodewald, et al., 2011)
In the north, pine warblers usually start building nests between late March and early June. They build nests in pine trees that are normally 8 to 12 m off the ground, but can be 3 to 35 meters high. Their nests are small and shaped like cups. They are made from strips of bark, plant stems, pine twigs, and leaves. They are bound together with silk from caterpillar cocoons or spider webs and lined with feathers, hair, and soft plant material. Females do almost all the nest building, but males often keep them company while singing. (Baicich and Harrison, 2005; Chapman, 1907; Dunne, 2006; Ehrlich, et al., 1988; Harrison, 1984; Reed, 1965)
Pine warbler females usually lay 4 white spotted eggs, but can lay 3 or 5 in rare instances. Females sit on the eggs and keep them warm for 12 to 13 days, and males often feed females during this time. Newborns are ready to leave the nest after about 10 days. Pine warblers have 1 to 3 sets of eggs per year. Scientists think the chicks are able to have their own young after the first year, but there isn't much evidence of this. (Baicich and Harrison, 2005; Chapman, 1907; Dunne, 2006; Ehrlich, et al., 1988; Harrison, 1984; Reed, 1965)
Females build nests and take care of keeping the eggs warm. Males sing to defend the territory and occasionally bring food to the females. Chicks are unable to take care of themselves at first, so both parents feed them until they are able to leave the nest. Parents probably continue caring for their brood for several days after they can fly, but scientists don't know the exact amount of time it takes them to become independent. (Baicich and Harrison, 2005; Ehrlich, et al., 1988; Rodewald, et al., 2011)
Pine warblers are active during the day, hopping, climbing tree trunks, and cleaning their feathers. They sometimes pump their tails. Like many other warblers, their wings beat in an irregular pattern when they fly. Most pine warblers migrate, or travel between different areas for the summer and winter. They migrate during the night. Farther south, they might stay in a similar area during the whole year. Some southern populations may remain in relatively the same area year-round. During the breeding season, they are most active at dawn. Males sing enthusiastically from the tops of trees within their territories. (Baicich and Harrison, 2005; Chapman, 1907; Rodewald, et al., 2011)
Scientists don't know much about the size of their territories. The largest territory found was 1 hectare while the smallest was 0.1 hectare. The quality of habitat probably has a large effect on territory size. (Rodewald, et al., 2011)
Like most warblers, only males sing. Different from most warblers, males sing throughout the year. They do sing more often during the early part of the breeding season. Their songs are short, only lasting one or two seconds. Their song is a short, rapid trill that can be improvised, or changed on the spot. Its notes have similar pitches and are a little bit slurred together. Both males and females also make contact calls, which are short, high chirps. Rarely, they make a noise while flying that sounds like “seet”. Because this call is weak, it is not heard very often. (Chapman, 1907; Dunne, 2006; Rodewald, et al., 2011; Sibley, 2003)
Like almost all kinds of warblers, pine warblers eat mostly insects and spiders. They search for food in the middle or upper parts of pine trees and sometimes in leafy trees. If insects and spiders are scarce, they also eat pine seeds, fruit, and berries. During the winter, they have been spotted eating corn, sunflower seeds, and suet from feeders. They probably get all their water from food because they have never been seen drinking and commonly have nests far away from water. (Ehrlich, et al., 1988; Harrison, 1984; Rodewald, et al., 2011)
Pine warblers sometimes join other species and migrate together in mixed groups, or flocks. There might be other warblers or songbirds in these flocks. Occasionally, brown-headed cowbirds lay eggs in their nests. Female brown-headed cowbirds may take out warbler eggs or add in their own. Some pine warblers notice the difference and bury the brown-headed cowbird eggs in the bottom of the nest. Pine warblers also have parasites in their bodies including species of Plasmodium (which causes malaria), Leucocytozoon, and Haemoproteus. They can also have rabbit ticks, louse flies, flies, and deer ticks. (Dunne, 2006; Rodewald, et al., 2011)
Pine warblers aren't known to cause any negative economic impacts. (Rodewald, et al., 2011)
Pine warblers may create a small amount of income from birdwatchers. They may also consume insects which are pests to humans. (Rodewald, et al., 2011)
Pine warblers live in a large area and are listed as "least concern" on the IUCN Red List. They are most threatened by loss of habitat that happens because of logging and spread of buildings onto land that used to be forest. (Dunne, 2006)
Jacob Keck (author), Northern Michigan University, Mary Martin (editor), Northern Michigan University, Rachelle Sterling (editor), Special Projects, Catherine Kent (editor), Special Projects.
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Beane, J., S. Alford. 1990. Destruction of a Pine Warbler brood by an adult cowbird. Chat, 54: 85-87.
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Dunne, P. 2006. Essential Feild Guide Companion. New York: Houghton Mifflin Company.
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Reed, C. 1965. North American Bird Eggs. New York: Dover Publications.
Rodewald, P., J. Withgott, K. Smith. 2011. "Pine Warbler" (On-line). The Birds of North America. Accessed April 15, 2011 at http://bna.birds.cornell.edu/bna/species/438/articles/introduction.
Sibley, D. 2003. Sibley Feild guide to Birds. New York: Alfred A. Knopf Inc.