Introduction

Perhaps no bird is more characteristic of the pine forests of eastern North America than is the Pine Warbler. This species rarely occurs in purely deciduous vegetation, except uncommonly during migration and occasionally during winter. The Pine Warbler is a common breeding bird and permanent resident in the southeastern United States. Its breeds at lower densities as far north as southeastern Canada and northeastern United States, where it is migratory and among the earliest warblers to arrive in spring and latest to depart in fall.

Pine Warblers are unusual among theParulidae (wood-warblers) in that both their breeding and wintering ranges lie almost entirely within the United States and Canada, although resident races are present in the Bahamas and on Hispaniola. Migrants from North America are rarely recorded in the West Indies, and very rarely in northern Mexico and Central America. The annual extent of migration into the West Indies by northern migrants is poorly known.

In winter, Pine Warblers can be especially abundant in pine forests of the southeastern United States when numbers are increased by migrants from the north. In some areas, up to 50–100 or more individuals can be seen in mixed-species foraging flocks. Agonistic encounters between Pine Warblers and with other bird species frequently occur in these flocks. Male Pine Warblers may sing in all months of the year and commonly within fall and winter flocks, although less frequently on cold winter days.

The Pine Warbler is the only wood-warbler known to regularly consume seeds (often pine seeds or seeds at bird feeders) in any significant amount. However, few data exist on the frequency of this behavior away from feeders and the importance of seeds in the fall or winter diet. Some recent research (Levey et al. in press) has examined ways in which this primarily insectivorous bird may make the seasonal physiological changes necessary to allow for digestion of seeds.

Even though the Pine Warbler is widespread and common in parts of eastern North America, surprisingly little is known about its natural history, and its nesting biology in particular. This is likely due to its propensity to nest high in pine trees, mak-ing nests difficult to observe. As a result, it remains one of the more under-studied North American breeding wood-warblers. However, several studies focusing on the species have been conducted. Foraging relationships of Pine Warblers within mixed-species bird flocks in Louisiana (Morse 1967, Morse 1970) and with Yellow-throated Warblers (Dendroica dominica) in Maryland (Ficken et al. 1968, Morse 1974) have been examined in detail. In addition, their ecology and foraging behavior have also been studied in the Bahamas (Emlen 1977, Emlen 1981, Emlen and Dejong 1981) and in the Dominican Republic (Latta and Sondreal 1999).