Brown Thrasher Toxostoma rufum

The Brown Thrasher is the shiest member of the mimic thrush family (Mimidae) to breed in Vermont. Less well known for its vocal abilities than the boisterous Northern Mock­ ingbird, the Brown Thrasher is nonetheless an accomplished songster and mimic of other birds (including the Northern Flicker, Tufted Titmouse, Wood Thrush, and North­ ern Cardinal). The thrasher's loud territorial song, generally distinguishable from that of the mockingbird because it has fewer re­ petitious notes, is given from the top of a shrub or low tree. A soft, more complex whisper song given while the bird is hidden al. I970). Clutches completed early in the may also be heard, particularly early in the breeding period tend to be larger. Vermont breeding season (Schafer I9I6; Graber et al. egg dates range from May 24 to June I6 I970 ). (eight records). Both parents incubate the Although a few hardy Brown Thrashers clutch for I2 to 14 days, and the nestlings linger in the Northeast each year past the fledge in 9 to I4 days. Data from Illinois usual mid October departure date, few suc­ (Graber et al. I970) indicate that most cessfully overwinter. Thrashers are among Brown Thrashers are not double-brooded; Vermont's earliest migrant songbirds to late nests probably represent renesting at­ return, arriving during the third week of tempts. Fledgling success has been found to April from their wintering grounds in the be low, averaging 4I% (Mayfield I96I). Al­ southeastern U.S. They probably commence though thrashers aggressively defend their breeding in Vermont early in May, as they nests, predation is probably the leading do in New York (Bull I974), before many cause of reproductive failure. The Brown other migrant passerines have returned. Thrasher is the largest passerine regularly They prefer shrubby, overgrown fields for victimized by the Brown-headed Cowbird breeding habitat, but forest edges and hedge­ (Terres I980), but the incidence and success rows may also be used. rate of parasitism is apparently low (Graber The bulky, basketlike nest lined with et al. I970). rootlets is usually placed in a thorny and/or The Brown Thrasher is generally dis­ very dense shrub 0.6-2 m (2-7 ft) above tributed throughout Vermont, but reaches the ground, occasionally as high as 4.6 m its greatest abundance in the lower eleva­ (I5 ft). Although ground nests are uncom­ tions of the Champlain Lowlands and Con­ mon, early nests tend to be built lower than necticut River valley. It was found in 75% of those started later in the breeding season all Atlas Project priority blocks. Atlas Proj­ (Graber et al. I970). Viburnum and haw­ ect workers in the Green Mountains and thorn are commonly used nest supports in Northeast Highlands encountered thrashers New York (Bull I974). From 4 days to 2 infrequently. Although Brown Thrashers in weeks may separate nest initiation and egg the Northeast have been decreasing by nearly laying. From 3 to 6 (usually 4 to 5) brown­ 3% per year according to U.S. Fish and speckled, bluish white eggs are laid early in Wildlife Service Breeding Bird surveys, no the morning on consecutive days (Graber et significant population change has occurred

256 Species Confirmed as Breeders in Vermont 73' ,,'

4S"

,," No. of priority blocks in which recorded TOTAL I35 (75%) Possible breeding: 33 (24 0/0 of total) Probable breeding: 40 (30% of total) Confirmed breeding: 62 (46% of total)

Physiographic regions in which recorded % of %of species' no. of region's total priority priority priority blocks blocks blocks

Champlain Lowlands 29 94 22 Green Mountains 31 57 23 North Central 16 84 12 Northeast Highlands 7 44 JO r II 4)' East Central IS 79 Taconic Mountains IS 94 II >0 20 20 I I ! Eastern Foothills 22 92 16

in Vermont (Robbins 1982b). Territory map­ est areas in Vermont may reduce Brown ping studies in farm and second-growth Thrasher populations slightly in the future, edge habitat in Vermont have recorded up to but the species adapts well to man's proxim­ 12 pairs per 40.5 ha (100 a) (Williamson ity and will probably continue to thrive in 1972 ). suburban and agricultural districts. The Brown Thrasher was probably rare DOUGLAS P. KIBBE in Vermont before land was cleared for ag­ riculture; clearance greatly increased the acreage of disturbed edge community avail­ able. The thrasher's status appears to have changed little in the past century, although in the early 1900s, when pasture was aban­ doned, the species probably flourished. The maturation of existing shrub and for-

Brown Thrasher 257