Pine Warbler

The Pine Warbler is very well named, since even outside the breeding season it is rarely found far from pines, especially the white pines that comprise a significant portion of New Hampshire’s forests. It is one of the first warblers to arrive each spring, sometimes as early as late March and slightly ahead of our other two early warblers, the Palm and Yellow-rumped. At this time and through the summer it is typically heard before it is seen, and herein lies a frequent source of confusion. The song of the Pine Warbler is a somewhat monotonous trill, and easily confused with that of the Chipping Sparrow and Dark-eyed Junco. Of the three, the Pine Warbler is arguably the most musical, but practice is required to keep them straight. April is a good time to become more familiar with these overlapping songs, since the warblers and sparrows are arriving while juncos are still in southern New Hampshire.

Except in the extreme southern United States, Pine Warbler populations are stable or increasing, in contrast to many other warbler species. Increases tend to be strongest in the north, including Canada and the states that border it, suggesting a potential influence of climate change. As recently as the 1980s, Pine Warblers in New Hampshire were limited to the southeastern third of the state and a narrow band along the Connecticut River, and now can be found statewide wherever there are stands of white pine (although still scarcer in the north). They may also be increasing as a winter species. Roughly 100 were reported during the winter of 2023-24, compared to an average of five per year in the preceding five years. That winter was exceptionally warm, but since warmer winters are becoming the norm we can expect Pine Warblers to be more frequent in the future.

Pine Warblers may be better suited to survive northern winters because they are the only warbler that regularly consumes seeds (several others will eat fruit), including both pine seeds and those found at feeders. Laboratory studies have shown that these warblers can change their digestive systems depending on their diet. For instance, birds fed primarily seeds had larger gizzards (the muscular stomach in birds) than those fed fruit or insects, presumably because more grinding force is needed to process relatively hard seeds. When their diet was shifted to something else, these warblers were quickly able to alter how they processed the new food internally.