. Brimleyana. Zoology; Ecology; Natural history. Tree Swallow Range Expansion 109 I960 1980 -;. Fig. 2. The expanding breeding distribution of the tree swallow (Tachycineta bicolor) in the southeastern United States (1894-1991). Possible Explanation for Range Expansion—Tree swallows might now be imprinted on bluebird boxes as nesting sites, and this imprint- ing possibly has allowed them to expand their range into areas where the lack of natural cavities would otherwise inhibit nesting. Plasticity in food habits may also be important in the range expansion of this swallow. Lee and Franz (1972)
. Brimleyana. Zoology; Ecology; Natural history. Tree Swallow Range Expansion 109 I960 1980 -;. Fig. 2. The expanding breeding distribution of the tree swallow (Tachycineta bicolor) in the southeastern United States (1894-1991). Possible Explanation for Range Expansion—Tree swallows might now be imprinted on bluebird boxes as nesting sites, and this imprint- ing possibly has allowed them to expand their range into areas where the lack of natural cavities would otherwise inhibit nesting. Plasticity in food habits may also be important in the range expansion of this swallow. Lee and Franz (1972) reported on a pre- migration staging flock of several thousand tree swallows feeding over a cornfield on the eastern shore of Maryland. Examination of the stomachs of a dozen birds revealed corn flea beetles {Chaetocnema pulicaria). No other food items were found. Food items were counted in one stomach, and 170 corn flea beetles were found. Although I am not aware of other direct observations of tree swallows benefiting from agriculture or agricultural pests, at the minimum the clearing of land for agricultural purposes has created foraging areas not available in the precolonial period. Several nesting sites are associated with man-made lakes and large impoundments constructed for waterfowl. Many hardwood trees killed by floodwaters contain cavities made by woodpeckers that provide multiple nest sites where the swallows form small colonies of a dozen or more pairs. Although the beaver was reintroduced by various state wildlife agencies and has made an explosive come-back, this generally precedes the period of range expansion of tree swallows outlined. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original North Carolina State Museum of Natural History. [Raleigh, NC : North Carolina State Museum of Natural Histor
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