The Chestnut-sided Warbler is one of the few warblers that has benefited from forest cutting since European arrival in North America [Bent 1953, Richardson and Brauning 1995]. Because it is restricted to shrubby, second growth areas and forest edge habitat, its range and population have expanded in the last two centuries [Richardson and Brauning 1995 (BNA)]. While it was considered rare in the 1800s [Bent 1953], it is now one of the most common warblers of second growth woodlands in eastern North America, although populations have undergone a slow decline since the early 1960s [Richardson and Brauning 1995 (BNA)]. Chestnut-sided Warblers breed in the northeastern U.S. south to Georgia, with southern populations occurring at high elevations [Richardson and Brauning 1995 (BNA)]. In Canada, they are limited to the more southerly regions and extend farther west than in the U.S., into south central Saskatchewan [Richardson and Brauning 1995 (BNA)]. Their wintering range is considerably smaller than their breeding range, extending primarily from southeastern Mexico to Panama [Howell and Webb 1995]. Skutch [in Bent 1953] noted that within the wintering range, they are extremely abundant, particularly in Costa Rica and Panama.
In spring, Chestnut-sided Warblers enter the U.S. using either a trans-Gulf or a coastal route, although the trans-Gulf route is more common [Dunn and Garrett 1997]. From the southern states, they head north on a broad front from the Rocky Mountains eastward [Richardson and Brauning 1995 (BNA)]. Migrants arrive in the southern states in mid-April [Dunn and Garrett 1997] and in Massachusetts by early May [Veit and Petersen 1993]. By the end of May, most migrants have passed through Massachusetts [Veit and Petersen 1993] and arrived on their northernmost breeding grounds [Dunn and Garrett 1997]. Like many other species of warblers, Chestnut-sided Warblers migrate at night [Richardson and Brauning 1995 (BNA)] and the males typically arrive on their breeding grounds in advance of the females [Francis and Cooke 1986]. Fall migration generally begins in mid- to late August in northern breeding areas [Dunn and Garrett 1997]. These warblers again migrate on a broad front east of the Rockies, but typically avoid the Atlantic coastal plain [AOU 1998]. They reach peak numbers in the southern states by late September or early October [Dunn and Garrett 1997] and are usually absent from northern breeding areas at this time [Veit and Petersen 1993, Dunn and Garrett 1997]. In fall, the trans-Gulf route is most commonly used to reach Central America, where the warblers arrive by mid-September [Richardson and Brauning 1995]. During migration, these birds occur in a variety of forested and shrubby habitats, including the deep forests that are avoided during the breeding season [Bent 1953, Richardson and Brauning 1995].
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Observations
This rather late spring migrant breeds in disturbed and regenerating forest habitats. Our censuses showed high variation in A, B and C sites; there were many zero counts, some with a few small flocks. C sites in NH detected remarkably few Chestnut-sided Warblers, while B sites in MA were well above average.
The few early birds arrived in period 2, numbers peaked in period 4, and then dropped somewhat as migrants moved through and many stayed to breed. The northern breeding limits of the species are from Saskatchewan to Nova Scotia. Highest mean densities were observed in VT at A and B sites during period 4. |
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