The yellow-rumped warbler and Cape May warbler are two similar looking warbler species found in North America. They can be difficult to distinguish from one another in the field due to their overlapping ranges and similar plumage. However, there are some key differences between these two warblers in terms of distribution, habitat, diet, appearance, song, and behavior. Understanding the differences between yellow-rumped and Cape May warblers can help birders accurately identify them.
Geographic Distribution
The yellow-rumped warbler has a much broader distribution across North America compared to the Cape May warbler.
Yellow-rumped Warbler Distribution
The yellow-rumped warbler breeds across Canada and the western and northeastern United States. Its breeding range extends from Alaska and Canada south to California, Arizona, New Mexico, Minnesota, Wisconsin, Michigan, New York, Massachusetts, New Hampshire, and Maine.
During the winter, most yellow-rumped warblers migrate south to the southern United States, Mexico, Central America, and the Caribbean. On the Atlantic coast, they winter as far south as Florida. On the Pacific coast, they winter from California south to Guatemala.
Cape May Warbler Distribution
The Cape May warbler has a much more restricted range centered in the boreal forests of Canada. They breed across central Canada from Alberta to Quebec and the Maritime Provinces.
During winter, Cape May warblers migrate down to the southeastern United States south to the West Indies, Cuba, Hispaniola, Puerto Rico, and the northern coast of South America. Their winter range only barely overlaps with yellow-rumped warblers in Florida.
So in summary, yellow-rumped warblers have an expansive distribution across much of North America, while Cape May warblers are concentrated in the boreal forests of central Canada and the southeastern US in winter. The Cape May’s small range sits entirely within the much broader range of the yellow-rump.
Habitat
The yellow-rumped warbler occupies a broader range of habitats compared to the Cape May warbler which is more selective.
Yellow-rumped Warbler Habitat
During the breeding season, yellow-rumped warblers inhabit open coniferous forests, mixed woods, forest edges, and areas with scattered trees. They are very adaptable and occur in both mature and successional forest.
In winter, they occur in a variety of wooded habitats including pine forests, oak woodlands, cypress swamps, mangroves, parks, and shade trees in urban areas. They are one of the most flexible warbler species in their habitat use.
Cape May Warbler Habitat
Cape May warblers are specialists of the boreal forest. They prefer mature coniferous forests with spruce, fir, pine, cedar, and tamarack. They occur more in interior forests than along edges. In their winter range, they are mostly found in Caribbean pine forests.
So in general, yellow-rumped warblers use a broader range of open and semi-open habitats while Cape May warblers specialize in mature boreal and Caribbean pine forests. The Cape May is more selective in its habitat choices.
Diet
The diets of these two warbler species differ somewhat based on their habitat preferences and behaviors.
Yellow-rumped Warbler Diet
Yellow-rumped warblers are flexible and opportunistic in their feeding habits. They glean insects and spiders from foliage, bark, and branches. Common prey includes beetles, flies, moths, caterpillars, ants, bees, and wasps.
A unique aspect of their diet is the ability to digest waxes found in bayberries and wax myrtle. They are one of the only warblers able to consume these waxy fruits and make up an important part of their diet in winter.
Cape May Warbler Diet
Cape May warblers specialize in gleaning small insects from the needles of conifers, along branches, and among clusters of leaves. Their main prey includes caterpillars, sawfly larvae, spiders, bark beetles, aphids, and other small insects.
They eat fewer berries than the yellow-rumped warbler. But will sometimes eat conifer seeds and berries in winter. Overall, they target small arthropods found in boreal forests.
So the yellow-rumped has a more diverse diet including insects, spiders, and berries. While the Cape May specializes in catching tiny insects among boreal conifers.
Appearance
While these two warblers appear somewhat similar at first glance, a closer look reveals key differences in their plumage, coloring, and proportions.
Yellow-rumped Warbler
- Bill is short, pointed, and black.
- Face is gray with a white stripe above the eye.
- Throat and belly are white.
- Breast is gray to black with variable streaking.
- Back is bluish-gray.
- Wings are black with white bars.
- Tail is black with white spots on the outer tail feathers.
- Legs and feet are black.
The yellow patch on the rump (uppertail coverts) gives this species its name and is usually visible in the field. The male has bold black streaking on the flanks and breast. Females have fainter streaking.
Cape May Warbler
- Bill is fine, pointed, and black.
- Face is yellow with chestnut cheek patches.
- Throat and belly are yellow.
- Breast is chestnut.
- Back is olive-green.
- Wings are olive-green with white wing bars.
- Tail is olive-green with white tail spots.
- Legs and feet are black.
Males have a bold chestnut breast band. Females have fainter chestnut coloring. Their proportions are smaller and slimmer than yellow-rumped warblers.
So in summary, yellow-rumped warblers are blue-gray above with black streaking below and bright yellow rumps. Cape May warblers are olive-green above with a yellow belly and chestnut breast with no rump patch.
Song and Call
These two warblers produce distinct vocalizations that can aid in identification.
Yellow-rumped Warbler Song
The song of the yellow-rumped warbler is a musical trill or warble often described as “sweet-sweet-I’m so sweet.” It is a high-pitched, wavering warble, faster and more musical than the Cape May’s song.
Cape May Warbler Song
The Cape May warbler’s song is a loud, ringing series of musical notes typically described as “zee-zee-zee-zo-zeet.” It has a slower tempo and lower pitch compared to the yellow-rumped’s song.
Call Notes
The call notes of these species also differ. Yellow-rumped warblers give a flat, harsh “chip” note. Cape May warblers have a thin, high “seep” call note. These differences in vocalizations can aid identification when the birds are heard but not seen.
Behavior
Differences in foraging behavior, movements, and sociality also help distinguish these species.
Foraging Behavior
Yellow-rumped warblers forage more actively than Cape May warblers. They move quickly while searching for food, fluttering and hovering around vegetation as they pick insects. They are very restless and active foragers.
Cape May warblers forage in a slower, more methodical manner. They deliberately pick insects from pine needles and conifer branches while working their way through the foliage.
Movements
Yellow-rumped warblers wander more widely than Cape Mays during migration and winter. They roam open areas like roadsides, fields, and backyard feeders over a wide area.
Cape May warblers stick to denser, wooded habitats during winter. They move more slowly and cover less ground than the wide-ranging yellow-rumps.
Sociality
Yellow-rumped warblers form larger flocks in migration and winter, sometimes mixing with other warbler species. Cape May warblers tend to stay in smaller loose groups with their own species during the non-breeding season.
Conclusion
In summary, there are several key differences that distinguish yellow-rumped warblers and Cape May warblers despite some superficial similarities in appearance:
- Yellow-rumped warblers have a much broader distribution and habitat use across North America.
- Cape May warblers occupy a smaller range centered in boreal forests.
- Yellow-rumped warblers have more varied diets including insects, spiders, and berries. Cape Mays specialize in boreal insects.
- Yellow-rumped warblers have blue-gray backs with bold black streaking below. Cape Mays are olive-green with chestnut breasts.
- The songs and call notes of the two species sound different.
- Yellow-rumps actively forage over a wide area. Cape Mays deliberately pick insects from conifers.
Paying attention to distribution, habitat, vocalizations, and foraging behavior in addition to plumage can help birders confidently distinguish these often confusing warblers. With some practice, picking out a yellow-rumped warbler from a Cape May becomes much simpler.