Dendroica pinus
pine warbler

Pine warblers, Dendroica pinus, range throughout most of eastern North America. Their northern range extends to the most southern portions of Manitoba, Ontario, and Quebec in Canada. The southern extent of their range extends from Florida, to the southern tip of Texas. The eastern border of the range is the Atlantic coast of the United States (US) and Canada, while its western range runs through the US states of Minnesota, Wisconsin, Illinois, Missouri, Arkansas, and Texas. The breeding range of pine warblers covers much of their general range with the exception of parts of southern Texas and Louisiana. Despite the large breeding range, it is worth noting that breeding populations are often quite isolated in the central parts of their range. The winter range of pine warblers includes much of the southern portion of their breeding range which is unusual for a wood warbler. Their winter range extends as far north as mid-Arkansas, southern Tennessee, as well as southern Virginia. (Chapman, 1907; Dunne, 2006; Harrison, 1984; Rodewald, et al., 2011; Sibley, 2003)

Pine warblers can be found almost exclusively in pine forests except during migration, when they may be found in habitats with few or no conifers, in addition to pine forests. There appears to be a preference for open pine forests; however they have been found in dense conifer stands or in small pockets of pines in a predominately deciduous forest. (Chapman, 1907; Dunne, 2006; Ehrlich, et al., 1988; Harrison, 1984; Sibley, 2003)

Pine warblers are larger wood warblers with an average wingspan of 22 cm and average length of 14 cm. The average mass of pine warblers is around 12 g, however, individuals have been recorded with body masses ranging from 9.4 to 15.1 g. The average metabolic rate for pine warblers is 30.6 cm^3 oxygen per hour.

There is no data about sexual dimorphism in size for pine warblers however their sexual dimorphism in plumage is well known. Pine warblers exhibit much more subdued tones than many other warblers. Male breeding plumage includes an olive to yellow crown with this same coloration shared by the auriculars and the mantle. In contrast to the slightly drab crown there will be yellow orbital feathers and yellow lores, malar, and throat. The breast is yellow with olive streaking that fades into a white belly with some continuation of the olive streaks. The coverts, primaries, secondaries, tertials, and tail are grayish in coloration with some faint wing-bars. The legs, feet, and beak are dark in coloration.

Non-breeding males and females tend to be somewhat similar in plumage which is similar in pattern to the female breeding plumage except more subdued in coloration with more olive and brown tones. First year females are very subdued in coloration although they maintain the same characteristic markings.

Newborn pine warblers are altricial and eventually develop dark brown, downy feathers. (Baicich and Harrison, 2005; Chapman, 1907; Dunne, 2006; Sibley, 2003)

Little is known about the courtship behaviors of pine warblers. There is some evidence to suggest that mate guarding takes place and males have been observed to be antagonistic towards other males. It is believed that they are monogamous throughout the breeding season with no extra pair copulations being recorded. It is unknown if pairs remain coupled for more than one breeding season. (Morse, 1989; Rodewald, et al., 2011)

Nest building normally begins in late March to early June in the north. Nests are almost always built in one of 15 species in the genus Pinus. Nests are constructed normally between 8 and 12 meters off the ground although finding a nest between 3 and 35 meters high is not that uncommon and there is one report of ground nesting. Nests are built almost exclusively on horizontal branches, often at a fork which gives a sturdy base to build a nest. Their compact cup nests are constructed from strips of bark, plant stems, pine twigs, and leaves bound with silk form caterpillar cocoons or spider’s webs. Nests are then lined with feathers, hair, and soft plant material. Nest building is done almost exclusively by females, however males often accompany their mates while singing frequently.

A clutch of 4 white spotted eggs are laid, although in rare cases 3 or 5 are laid. The eggs are incubated almost exclusively by females, but males are known to feed mates during egg incubation which lasts for a period of 12 to 13 days. Newborns are ready to leave the nest after about 10 days. A pair of pine warblers may brood 1 to 3 clutches per year.

It is believed that individuals are sexually mature after one year however there is no direct evidence to support this. (Baicich and Harrison, 2005; Chapman, 1907; Dunne, 2006; Ehrlich, et al., 1988; Harrison, 1984; Reed, 1965)

Females both construct nests and perform all incubation duties. During these periods, males will occasionally bring food to their mates as well as sing to defend the territory. The chicks are born altricial and are fed by both parents until they are ready to leave the nest. Time to independence is currently unknown, but parents likely continue to care for their brood for several days post-fledging. (Baicich and Harrison, 2005; Ehrlich, et al., 1988; Rodewald, et al., 2011)

Little is known about the lifespan of pine warblers, but the oldest recorded banded individual was 6 years old when it was recaptured for the second time. ("Longevity Records Of North American Birds", 2011; Rodewald, et al., 2011)

Pine warblers will hop both on substrate and on trees. They will also climb and descend tree trunks to get from branch to branch. Pine warblers will regularly preen themselves for up to 15 minutes. Individuals will display occasional tail pumping. Pine warblers have flight that is fairly typical for warblers with irregular wing beats. This is a migratory species that relocates to spend a different portion of the year in two different regions. Some southern populations may remain in relatively the same area year-round. Pine warblers complete most activities during the day, but will migrate nocturnally. This species is most active at dawn during the breeding season when males sing vigorously from treetops within their territories. (Baicich and Harrison, 2005; Chapman, 1907; Rodewald, et al., 2011)

little is known about the territory size maintained by pine warblers. The largest recorded territory was 1 hectare while the smallest was 0.1 hectare. It is believed that habitat quality greatly affects territory size. (Rodewald, et al., 2011)

Like most warblers, only male pine warblers will sing. Unlike most other warblers, males can be heard singing throughout the year although there is a noticeable increase in the frequency of their songs during the early part of the breeding season. Songs are short, and typically only last a second or two. Their song is characterized as a short rapid trill that can have a fair amount of improvisation. Notes are often similar in pitch and slightly slurred.

Pine warblers' contact calls, which are made by both sexes, are high chirps of short duration. There is also a flight call “seet”, however this call is often very weak and therefore rarely heard. (Chapman, 1907; Dunne, 2006; Rodewald, et al., 2011; Sibley, 2003)

Like almost all warblers, pine warblers diets consist mostly of insects and spiders. Most foraging is done in the mid to upper regions of pines and occasionally in deciduous trees. When arthropods are scarce they are able to have more varied diets that include pine seeds, fruit, and berries.

During the winter individuals have been noted to eat corn, sunflower seeds, and suet from feeders.

It is believed that pine warblers obtain adequate water from their diet because there are no reports of individuals drinking and they are often found nesting far from any water source. (Ehrlich, et al., 1988; Harrison, 1984; Rodewald, et al., 2011)

Little information exists about predation on pine warblers. There is at least one account of egg predation by blue jays. Pine warblers are also uncommon hosts for brown-headed cowbirds. Female brown-headed cowbirds may remove the existing warbler eggs or simply add their own. In response to this, some pine warblers have been noted to bury the foreign eggs within in the bottom of the nest. (Beane and Alford, 1990; Ehrlich, et al., 1988; Harrison, 1984; Rodewald, et al., 2011)

There has been very little research about the ecological roles of this species. Pine warblers have been known to join mixed-species flocks during migration which contain both warblers and other passerines. Pine warblers are known hosts of endoparasites from the genera Plasmodium (causing malaria), Leucocytozoon, and Haemoproteus. Pine warblers are also known hosts of the rabbit ticks, louse flies, flies, and deer ticks. (Dunne, 2006; Rodewald, et al., 2011)

There are no known economic uses for pine warblers however there may be a small amount of ecotourism from birders. Pine warblers may also benefit people by consuming insects which are pests to humans. (Rodewald, et al., 2011)

There are no known negative economic impacts from pine warblers. (Rodewald, et al., 2011)

Pine warblers are currently listed as a species of least concern. This species occupies a large range throughout most of the eastern United States, however its range is threatened by logging and development causing habitat loss and fragmentation. Future studies should focus on the impacts of this habitat loss and ensure that populations are large enough to persist. (Dunne, 2006; Rodewald, et al., 2011)