- Minnesota Breeding Bird Distribution
- Breeding Habitat
- Population Abundance
- Literature Cited
A regular breeding resident and migrant; occasionally has been observed lingering into early winter at bird feeders in Minnesota. Cape May Warblers were uncommon during the Minnesota Breeding Bird Atlas (MNBBA).
Found patchily distributed across Canada from Labrador to British Columbia and in the northern portions of the Upper Midwest and the northeastern United States. Highest densities have been observed in eastern Quebec and central Ontario (Figure 1).
Assigned a Continental Concern Score of 13/20 by Partners in Flight. The Cape May Warbler is a Partners in Flight Yellow Watch List species because of a steep decline in its population and several threats. It is also listed as a Species in Greatest Conservation Need by the Minnesota Department of Natural Resources.
Long-distance migrant overwintering in the Caribbean, southern Mexico, and Central America.
Invertebrates including insects (especially caterpillars such as spruce budworm), spiders, and fruit and nectar during the winter. Forages primarily while perched but also known to hawk, hover, or fly-catch for prey.
Cup nest usually high in a coniferous tree and close to the trunk.
In Minnesota, Roberts (1932) quizzically stated about the Cape May Warbler that “if nesting at all in Minnesota it must be in very limited numbers and in restricted localities.” His only report of potential nesting activity was an observation by T. Surber on June 19, 1919. Surber observed 3 or more pairs in Pine County that he described as behaving with “actions” that provided evidence of a nest nearby. Roberts also reported a Cape May Warbler specimen taken on July 16, 1914, near Gabbro Lake in Lake County by Dr. C. E. Johnson.
Years later, Green and Janssen (1975) reported that Cape May Warblers were primarily a resident in the northern part of the northeastern region of Minnesota. Observations during the breeding season had been noted as far south as southern St. Louis County and west to Itasca State Park. They identified confirmed nesting in northern St. Louis County and inferred nesting in Cook County.
A few years later, Janssen (1987) described the Cape May Warbler’s distribution as primarily the northern part of northeastern Minnesota in “normal” years but stressed that its numbers can fluctuate widely with spruce budworm outbreaks. During these infestations, the species can be found in scattered locations in northeastern and north-central regions of the state. Janssen did not identify any confirmed nesting since 1970 but outlined its breeding distribution from Cook County to Clearwater County, northwest to eastern Roseau County, and southwest to northern Hubbard County; the southern boundary was defined by northern Itasca and southern St. Louis Counties. Hertzel and Janssen (1998) included only St. Louis County with a confirmed nesting record since 1970.
The Minnesota Biological Survey (MBS) recorded 155 breeding season locations for the Cape May Warbler (Minnesota Department of Natural Resources 2017). The vast majority of their locations were clustered in northern St. Louis and western Lake Counties. One location each was found in southern Lake and St. Louis Counties, and two were found in northern Aitkin County. These locations probably coincided with the distribution of spruce budworm outbreaks at the time of the MBS fieldwork.
The MNBBA reinforced that the major breeding distribution of the species is in the northeastern counties of St. Louis, Lake, and Cook but reported possible nesting as far south as Morrison County, west to Becker County, and northwest to Beltrami and Roseau Counties (Figure 2). The MNBBA extended the distribution presented by Janssen (1987) farther south in north-central Minnesota. The Cape May Warbler was confirmed nesting in 11 blocks within Lake, Lake of the Woods, Roseau, and St. Louis Counties. There were 59 blocks (1.2% of surveyed blocks) with probable nesting, which included the 4 previously named counties plus Aitkin, Cook, Itasca, and Koochiching (Figure 3; Table 1). Possible nesting was reported from an additional 169 blocks.
Baltz and Latta (1998) reviewed the Cape May Warbler in North America. They attributed historical changes in the distribution of the species to responses in budworm outbreaks. In Wisconsin, Cutright et al. (2006) found that the species’ population fluctuated in response to spruce budworm populations, especially in the southern margins of the breeding range. They confirmed nesting in 10 counties in northern Wisconsin from Douglas to Door Counties. In Michigan the story was similar. Nesting was not confirmed until the 1970s. The first atlas, from 1983 to 1988, identified breeding evidence in 137 townships, mostly in the Upper Peninsula, but also in the northern Lower Peninsula (Chartier et al. 2013). They noted that no significant changes were found between the state’s first atlas (1983–1988) and second atlas (2002–2008).
The distribution of the Cape May Warbler in Ontario was similar to Michigan’s. There was no significant change in Cape May Warblers in the northern regions or in Ontario as a whole between its first atlas (1981–1985) and its second (2001-2005), but there was a significant decrease in the second atlas within the province’s southern regions. The decline was largely attributed to the lower incidence of spruce budworm during the second atlas. Morse (1989), primarily from his research in the northeastern United States, suggested that Cape May Warblers may have been at or near their maximum historic population levels in the 1980s. It is unclear whether this observation is applicable to the northern Great Lakes region.
The historical status of the Cape May Warbler is difficult to assess in Minnesota. The atlases from Michigan, Ontario, and Wisconsin all note the difficulty in censusing the species and in the identification of its nesting behavior. The Cape May Warbler’s song is high, weak, and usually delivered high on the top of a coniferous tree, often in remote areas. Its nest is hidden high in a coniferous tree near the trunk, where observation is almost impossible, or as noted by Roberts (1932), where the nest is “invisible from the ground.” Thus, the documentation by Cottrille (1962) is impressive; her party was able to identify “eight small young three or four days old” that were “three and one-half feet from the top of a 23.5 foot black spruce.” They discovered the Cape May nest after eight days of searching in an area with a spruce budworm outbreak. Fortunately the nest was only 20 feet high in the tree, so it was possible to observe.
In summary, the status of this species begs for additional research, but it is a challenging task to study a species that is rare and highly variable in its population and distribution.
*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.