Chestnut-sided Warbler

One of the more famous anecdotes about the Chestnut-sided Warbler is that John James Audubon is reputed to have only seen two over his entire life. In the early 1800s this might not have been unrealistic, since this species of early successional habitats was likely much scarcer when forests still dominated much of the landscape in the Northeast. The Chestnut-sided Warbler is most common in the youngest stages of forest maturation, as well as in artificial habitats (e.g., power line corridors) that mimic its preferred low tangled habitat. Historically it probably occurred in scattered patches across the larger landscape, with birds shifting about as old clearings grew in and new ones were created (e.g., by fire, beavers, Native Americans). As such habitat became more common, so did Chestnut-sided Warblers, just not in time for Audubon to see more than a couple.

The fact that this warbler can respond quickly to changes in habitat availability likely explains the high variation in population trends shown across it range from central Canada to the Northeast (there are also some southward along the Appalachians). In northern New England and New York, the pattern is generally a decline through the late 1990s followed by a leveling off or slight increase, much as shown in the trend graph for New Hampshire. Farther west there are a mix of stable populations or ups and downs that don’t correspond to those in the Northeast. It is likely that these trends are driven, at least in part, by different histories and patterns of land use – especially forestry – in different regions, but more research is needed to get at the details.

Most warblers have two song types, and in the case of the Chestnut-sided these are noticeably different. Most familiar is the one usually described with the mnemonic “pleased pleased pleased to meetcha,” which ends on an accented syllable. This is the song used to attract mates and maintain a pair bond early in the nesting cycle. The second song is more warbling and lacks the accent, and is used in the context of territory defense. It can be confused with that of species such as the American Redstart and Yellow Warbler. Chestnut-sided Warblers winter in Central America, where they defend small non-breeding territories against con-specifics. They also join resident birds and other migrants in mixed-species feeding flocks as they pass through the warblers’ territories.