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Historic Status

The Olive-backed Thrush, as it was once known, was observed primarily as a migrant by Massachusetts’ bird observers during the 1800s. Late in that century, supposition arose that the species was breeding in the western portions of the state. As it turned out, those suppositions were correct, and eventually nesting verification was obtained primarily in Berkshire County, but also in the higher elevations of Franklin and Worcester Counties (Bagg & Eliot 1937). The cutting of the spruce forests in the early part of the twentieth century, however, gradually led to a population decline in Massachusetts (Griscom & Snyder 1955).

Atlas 1 Distribution

Swainson’s Thrushes were thinly distributed by the time of Atlas 1, as were the high-elevation conifer forests that they required for nesting. In all other situations, they were totally absent. The Taconic Mountains and Berkshire Highlands accounted for almost all Swainson’s Thrush breeding activity, and the birds completely skipped over the lower, more mixed woodlands characteristic of the Marble Valleys region. The species’ ethereal upward-spiraling song was heard in one Lower Berkshire Hills block, but its strong preference for high-altitude climates apparently made the rest of the state unsuitable for breeding.

Atlas 2 Distribution and Change

The Swainson’s Thrush is a classic habitat specialist, occupying a very narrow range in Massachusetts. It occupied the same percentage of blocks in Atlas 2 as it did in Atlas 1, and its stronghold was still in the Taconics and Berkshire Highlands. The Vermont Piedmont enjoyed modest occupancy, and using the effort-controlled data the Worcester Plateau gained 1 block, as did the Connecticut River Valley, increasing both regions by one sighting from none in Atlas 1.

Atlas 1 Map

Atlas 2 Map

Atlas Change Map