- Minnesota Breeding Bird Distribution
- Breeding Habitat
- Population Abundance
- Literature Cited
A regular breeding resident, and migrant, the Tree Swallow was abundant during the Minnesota Breeding Bird Atlas (MNBBA).
The Tree Swallow is widely distributed and common to abundant across the United States and Canada. It is uncommon or absent from many parts of the southern United States and beyond the tree limit of northern Canada (Figure 1). Among the highest densities observed in North America are those in central and southwestern Minnesota and east-central Wisconsin.
Assigned a Continental Concern Score of 10/20 by Partners in Flight
Short-distance to long-distance migrant that over-winters in the southern United States, Mexico, through Central America, and the Caribbean.
Flying insects; rarely fruit except during inclement weather and in winter.
Secondary cavity nester in trees, nest boxes, and occasionally holes in a variety of unusual locations.
Nests have been found throughout the state, but Roberts (1932) stated the species was found less commonly in the prairie region, where he suggested it is replaced by the Barn Swallow. He emphasized that where there is a nest site, “there must be water not far away.” He reported confirmed nests over widely scattered portions of the state from Goodhue County in the southeast; Lake County in the northeast; McLeod, Grant, and Otter Tail Counties in the west; and Lake of the Woods County in the north. His confirmed nesting observations illustrated the Tree Swallow’s widespread distribution in the state.
Many years later, Green and Janssen (1975) simply stated it is a resident “throughout the state” and “numerous in all regions.” They did not provide a map of confirmed nesting in the state. Several years later, however, Janssen (1987) presented a map of confirmed nesting activity that included 49 counties in Minnesota since 1970. Hertzel and Janssen (1998) expanded the confirmed county nesting records since 1970 even further to 60 of the 87 counties in Minnesota. Given the high densities reported by the federal Breeding Bird Survey (BBS) (Figure 1), many counties in which confirmed nesting was not reported by Janssen (1987) or Hertzel and Janssen (1998) is noteworthy. The areas lacking confirmed nesting were primarily in the agricultural regions such as the southernmost two tiers of counties and counties in west-central Minnesota.
The Minnesota Biological Survey (Minnesota Department of Natural Resources 2017) included 1,242 breeding season locations from counties where they have completed inventories. Breeding observations were limited to one location in Chisago, Goodhue, Olmsted, Rice, and Sibley Counties. However, many of the counties without confirmed nesting activity identified by both Janssen (1987) and Hertzel and Janssen (1998) since 1970 had multiple breeding observation locations, such as in southern and west-central Minnesota.
The MNBBA included 4,820 records with confirmed nesting in every county and illustrating the Tree Swallow as one of the most widely distributed species in Minnesota (Figure 2). It was recorded as potentially nesting in 53.2% (2,541/4,779) of the blocks and confirmed nesting in 21.6% of those blocks (Figure 3; Table 1). The MNBBA documented extensive breeding activity throughout much of southern Minnesota and especially in the central and west-central regions of the state. Breeding records were less numerous in the northeastern forested regions because the species avoids dense forested areas. The MNBBA probability modeling supported these observations with highest densities predicted in the transition region between the forested areas of the northeast and the agricultural, open landscapes of the western and southern regions (Figure 4). Higher densities were also predicted along many of the large river floodplains such as the Minnesota and Mississippi Rivers. Less suitable habitats were predicted to be in the heavily forested regions in the northeast and north-central regions of the state.
The distribution of the Tree Swallow has likely not changed substantially from the past in Minnesota. Intensive agriculture and urbanization that has resulted in a landscape devoid of suitable nest sites, whether it be trees or nest boxes, have likely reduced local distributions and overall populations in the state. The placement and maintenance of nest boxes for the Eastern Bluebird have aided successful nesting for the Tree Swallow in otherwise unsuitable habitats. Because of the lack of detailed distributional data in Minnesota from the late 1800s and early 1900s, it is impossible to decipher specific population changes.
Widely distributed nesting also has occurred elsewhere in the region, in Michigan (Chartier et al. 2013), Ontario (Cadman et al. 2007), and Wisconsin (Cutright et al. 2006). Brewer et al. (1991) referred to a 1912 publication from Barrows in Michigan that stated it is “our most abundant and uniformly distributed breeding swallow, with nests in every county but less plentiful in the south.”
Winkler et al. (2011) in their review of the Tree Swallow in North America stated it was uncommon south of Maryland before the 1920s but now is a regular nesting species southward into South Carolina and Georgia, and westward to Texas and Oklahoma. They further commented that expansion is continuing likely due to land clearing, reintroduction of beaver, expansion of its diet, colonization of bluebird houses, and damming of streams.
*Note that the definition of confirmed nesting of a species is different for Breeding Bird Atlas projects, including the definition used by the Minnesota Breeding Bird Atlas, compared with a more restrictive definition used by the Minnesota Ornithologists’ Union. For details see the Data Methods Section.