Cape May Warbler Life History

Habitat

Cape May Warblers breed in forests of spruce and balsam fir, especially in areas where spruce budworms are abundant. Although red, black, and white spruce habitats are all acceptable, these warblers nest only in relatively mature forests, about 25–75 years old (trees usually over 35 feet tall). During migration, they turn up in just about any woods, scrub, or even thicket. Look for them toward the edges, where insects and their larvae are most abundant. Wintering birds in the Bahamas and Greater Antilles also use a great variety of habitats and may be most numerous in shrubby gardens, coffee plantations, and parks, though they can also be found in xeric (dry) forest, scrub, pine forest, broadleaf forest, mangroves, and second-growth of many kinds.

Food

Breeding Cape May Warblers feed almost entirely on invertebrates, chiefly spruce budworm, which may form half of the diet or more. They might be considered spruce budworm specialists, as their populations rise and fall sharply with the prevalence of this pest of the boreal forest. They also consume spiders, beetles, wasps, flies, ants, bees, moths, leafhoppers, scale insects, aphids, and many other sorts of insects. They capture most prey by probing and picking while perched, but they also chase flying insects and occasionally hover-glean prey from the tips of branches. They share their habitat with other warblers, including Bay-breasted, Blackpoll, Magnolia, and Blackburnian, but during the breeding season, Cape May tends to forage in the treetops, in the outer portion of the tree. As their delicate, slightly decurved bill shape might suggest, Cape May Warblers are adroit in probing blossoms for insects and for taking nectar from flowers, which they do aided by their long, curled tongues. Migrants take nectar from plants as diverse as tulip poplar, black cherry, and willow, and wintering birds sip nectar at bottlebrush, agave, and many native and ornamental flowers. Cape May Warblers also eat fruit. In tropical areas, they take Cecropia fruit and other small berries including grapes. In backyards, they relish hummingbird nectar, fresh fruit, fruit jelly, sap (from wells made by sapsuckers), and mealworms. Fruit and nectar make up about a third of the diet in the nonbreeding season. During the nonbreeding months, Cape May Warblers frequent all levels of the forest and are often seen at eye level in coffee plantations and ornamental plantings.

Nesting

Nest Placement

Cape May Warblers nest in spruce (and occasionally balsam fir) trees, near the top and near the trunk, usually 40­–50 feet above the ground. Among other northern warblers, only Blackburnian regularly nests at comparable heights.

Nest Description

A cup, often bulky and oval-shaped, of spruce twigs, grass, pine needles, cedar bark, and plant down lined with animal hair, rootlets, and feathers; the exterior is often clad in sphagnum moss. Nests average about 4.1 inches in diameter and 2.4 inches high, with interior cup averaging 2 inches across by 1.5 inches deep.

Nesting Facts

Behavior

Very few people have reported observing courtship in Cape May Warblers. Ornithologist James Bond reported in 1937 seeing a male flying “with rigid wings” above a female as she was building the nest. Like other warblers, male Cape Mays are territorial during the breeding season and will chase rival males from the territory, which is about an acre in size, a bit larger when spruce budworm is scarce. Males guard females as they build the nest but do not assist them; females incubate the eggs, and both parents feed young. Adults and young remain in the nesting area for several weeks before migration, sometimes joining mixed-species flocks of woodland birds. Wintering birds are territorial in some but apparently not all habitats, and migrants may defend resources in some contexts, with males especially confronting each other by racing at each other with raised tails and drooped wings.

Conservation

Cape May Warbler populations declined by an estimated 2.5% per year from 1966 to 2015, resulting in a cumulative decline of 70% over that period, according to the North American Breeding Bird Survey. Partners in Flight estimates a global breeding population of 7 million and rates the species a 12 out of 20 on its Continental Concern Score, indicating it is a species of low conservation concern. Use of certain insecticides to control spruce budworms causes steep declines in Cape May Warbler numbers. Logging, especially in the western portion of the species’ range, may pose risks to the Cape May Warbler because of reduced availability of the mature forests needed to support spruce budworms. Cape May Warblers, like most songbirds that migrate nocturnally, often strike buildings and other structures and are killed. Feral and domestic cats probably kill small numbers during migration, though Cape Mays tend to forage higher than most cats hunt.

Credits

Baltz, Michael E. and Steven C. Latta. (1998). Cape May Warbler (Setophaga tigrina), version 2.0. In The Birds of North America (P. G. Rodewald, editor). Cornell Lab of Ornithology, Ithaca, New York, USA.

Bond, J. (1937). The Cape May Warbler in Maine. Auk 54:306-308.

Lutmerding, J. A. and A. S. Love. (2020). Longevity records of North American birds. Version 2020. Patuxent Wildlife Research Center, Bird Banding Laboratory 2020.

Morse, D. H. (1978). Populations of Bay-breasted and Cape May warblers during an outbreak of spruce budworm. Wilson Bulletin 90:404-413.

North American Bird Conservation Initiative. (2014). The State of the Birds 2014 Report. US Department of Interior, Washington, DC, USA.

Partners in Flight (2017). Avian Conservation Assessment Database. 2017.

Sauer, J. R., D. K. Niven, J. E. Hines, D. J. Ziolkowski Jr., K. L. Pardieck, J. E. Fallon, and W. A. Link (2017). The North American Breeding Bird Survey, Results and Analysis 1966–2015. Version 2.07.2017. USGS Patuxent Wildlife Research Center, Laurel, MD, USA.

Sibley, D. A. (2014). The Sibley Guide to Birds, second edition. Alfred A. Knopf, New York, NY, USA.

Stephenson, T. and S. Whittle (2013). The Warbler Guide. Princeton University Press, New Jersey, USA.

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