A medium-sized (5-5 ½ inches) wood warbler, the Worm-eating Warbler is most easily identified by its dull olive back, dull yellow underparts, and conspicuous black head stripes. In some respects, this species resembles the Northern Waterthrush (Parkesia noveboracensis), which may be distinguished by its darker brown back, brown head stripes, and streaked breast. Male and female Worm-eating Warblers are similar to one another in all seasons. The Worm-eating Warbler breeds in the eastern United States from Massachusetts south to Louisiana and west to Missouri. Although its breeding range covers a wide area, this species breeds only locally within this range where appropriate habitat exists. In winter, Worm-eating Warblers migrate south to southern Mexico, Central America, and the West Indies. Worm-eating Warblers breed in large areas of unbroken deciduous forest with extensive shrubby undergrowth. In winter, this species primarily inhabits humid tropical forests. Ironically, Worm-eating Warblers rarely eat worms, preferring to eat caterpillars and other small insects. In appropriate habitat, Worm-eating Warblers are most easily observed while foraging for food. This species hops through vegetation close to the forest floor, jumping down to catch prey hidden in dead leaves on the ground. Worm-eating Warblers are primarily active during the day, but, like many migratory songbirds, this species migrates at night.
occurs (regularly, as a native taxon) in multiple nations, but breeds in a single nation
Regularity: Regularly occurring
Type of Residency: Breeding
Global Range: (>2,500,000 square km (greater than 1,000,000 square miles)) BREEDING: discontinuously from northeastern Kansas and southeastern Nebraska east across southern Great Lakes region to southern New England, south to northeastern Texas, southcentral Alabama, northwestern Florida, and South Carolina (AOU 1983). NON-BREEDING: southern Mexico (Oaxaca, Chiapas, Veracruz, and Yucatan Peninsula) south along the Caribbean slope of Middle America to central Panama; also in the Bahama Islands, Greater Antilles, and Virgin Islands (AOU 1983) (uncommon in Puerto Rico and St. John, rare on other Virgin Islands).
- Clements, J. F., T. S. Schulenberg, M. J. Iliff, D. Roberson, T. A. Fredericks, B. L. Sullivan, and C. L. Wood. 2014. The eBird/Clements checklist of birds of the world: Version 6.9. Downloaded from http://www.birds.cornell.edu/clementschecklist/download/
Length: 13 cm
Weight: 13 grams
Strongly streaked crown against olive-green body; often seen hopping and climbing on or hanging from shrub and subcanopy branches while foraging. Often forages in clusters of dead leaves, especially on wintering grounds.
Habitat and Ecology
Comments: BREEDING: Well-drained upland deciduous forests with understory patches of mountain laurel or other shrubs, drier portions of stream swamps with an understory of mountain laurel, deciduous woods near streams; almost always associated with hillsides (Gale 1995, Bushman and Therres 1988). Coastal plain habitats in Maryland include well-drained oak and oak-hickory forests, flatland white oak forests along river terraces, and drier islands of nontidal forested wetlands (Stasz 1996). Dense patches of shrubs or saplings may be an important component of territories (Patton and Hanners, unpub. data; Bushman and Therres 1988). Most abundant in mature woods but also may be common in young and medium-aged stands (see Bushman and Therres 1988). Nests on the ground, usually on hillsides, in cryptic nests among dead leaves, usually against roots or stems of shrubs or saplings, in a slight cavity (Harrison 1978), or up against rock outcrops. Nests are constructed of skeletonized leaves and lined with sporophyte stems of hairy cap moss (POLYTRICHUM sp.).
NON-BREEDING: In migration, occurs in various forest, woodland, scrub, and thicket situations, but specific habitat requirements are not known. In winter, inhabits undergrowth shrub and subcanopy layers of forests. Wunderle and Waide (1993) reported that worm-eating warblers are forest specialists but use a variety of forest types in the Caribbean, including "montane pine and broadleaf forest, wet limestone and dry forest, and dry scrub and residential habitats in the Bahamas." On the Caribbean slope of Central America, habitats include scrub and broadleaf and gallery forests (Rappole et al. 1983).
Non-Migrant: No. All populations of this species make significant seasonal migrations.
Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).
Locally Migrant: Yes. At least some populations of this species make annual migrations of over 200 km.
Arrives in North America during spring migration in early April, and at breeding grounds in West Virginia, Pennsylvania, and Connecticut in late April or early May. Departure dates from breeding grounds not well known but some birds may depart by mid-July (Patton and Hanners, unpub. data). Fall dates in southern United States range from 30 August to 1 October (Chapman 1907). Extreme dates in Central America range from 31 August to 18 April in the Honduras (Monroe 1968). Arrives in Puerto Rico in October, departs by end of April (Raffaele 1983). Arrives in Costa Rica early September, rarely late August, through October, departs by mid- to late April (Stiles and Skutch 1989).
Comments: Eats primarily caterpillars, various insects and spiders. Obtains food from live and dead foliage in spring and summer using an array of foraging techniques including gleaning, reaching, hanging, probing, gaping, pecking, prying, pulling, leaping, sallying, and flutter-chasing (see Remsen and Robinson (1990) for definitions). Reaches into dead leaf clusters to remove caterpillars and spiders. Feeds at tree tops with early leaf-out and moves into subcanopy and understory as the summer progresses. In the nonbreeding season, most prey is obtained from dead curled leaves in the forest understory; also gleans prey from dense foliage, vine tangles, sometimes ground litter, or pecks into rotten twigs for termites (Stiles and Skutch 1989). See also Rappole and Warner (1980).
Number of Occurrences
Note: For many non-migratory species, occurrences are roughly equivalent to populations.
Estimated Number of Occurrences: 81 to >300
10,000 to >1,000,000 individuals
Comments: Occurs in relatively low densities rangewide, and populations appear to be patchily distributed (Rosenberg and Wells 1995).
In Missouri, density was 2.13 males per 10 ha in continuous forest (Wenny et al. 1993). In Connecticut, density ranged from 4.46 males per 10 ha at a 300-ha TNC preserve to 0.26 per 10 ha at a wooded 56-ha site (Gale et al. 1997). Territorial in winter in Mexico (Rappole and Warner 1980); may forage in mixed-species flocks with resident, tropical forest birds (Greenberg 1987).
Life History and Behavior
Lifespan, longevity, and ageing
Eggs are laid in May, will lay replacement clutches through June. In the middle Atlantic region, nests from mid-May to mid-July (Bushman and Therres 1988). In Connecticut, extreme egg dates for first or subsequent clutches range from 13 May to 21 June, with nestlings last observed on 11 July (Patton and Hanners, unpub. data). Clutch size is 5-6 for first clutches; replacement clutch size is usually 4. Single-brooded. Incubation lasts 13 days, by females only. Young are brooded by the female and fed by both parents. Mean nestling duration is 8.5 days but young may fledge as early as day 5 if disturbed (Patton and Hanners, unpub. data).
Molecular Biology and Genetics
Barcode data: Helmitheros vermivorum
Below is a sequence of the barcode region Cytochrome oxidase subunit 1 (COI or COX1) from a member of the species.
See the BOLD taxonomy browser for more complete information about this specimen and other sequences.
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Download FASTA File
Statistics of barcoding coverage: Helmitheros vermivorum
Public Records: 4
Specimens with Barcodes: 8
Species With Barcodes: 1
IUCN Red List Assessment
Red List Category
Red List Criteria
National NatureServe Conservation Status
Rounded National Status Rank: N5B - Secure
NatureServe Conservation Status
Rounded Global Status Rank: G5 - Secure
Reasons: Fairly large breeding range in the eastern U.S.; numerous occurrences; relatively stable population in recent decades.
Global Short Term Trend: Relatively stable (=10% change)
Comments: North American Breeding Bird Survey (BBS) data indicate a significant population decrease in eastern North America, 1978-1988 (Sauer and Droege 1992); no significant change, 1966-1989 (Droege and Sauer 1990); nonsignificant increase of 7% from 1966 to 1993, nonsignificant decline of 4% from 1984 to 1993 (Price et al. 1995). In the Northeast, long-term population trends have declined the most in regions where the greatest proportion of the population occurs (West Virginia, Kentucky, Tennessee). Species has shown increases in southern New England. Estimated population trends for this species based on BBS data are suspect because sample sizes are small in most areas (Rosenberg and Wells 1995).
Degree of Threat: B : Moderately threatened throughout its range, communities provide natural resources that when exploited alter the composition and structure of the community over the long-term, but are apparently recoverable
Comments: Dependence on large forests for nesting may make this species highly vulnerable to population decreases. Considered "highly vulnerable" to population decline because of anthropogenic alteration of tropical, broadleaved forests (Petit et al. 1993).
Preserve Selection and Design Considerations: Probably requires large forest tracts for successful reproduction. Large contiguous areas with a minimum of nonforested edge produce the highest densities of breeding individuals (Gale et al. 1997) and increase reproductive success by decreasing cowbird parasitism and nest predation (Robinson et al. 1995). Several studies suggest that viable populations occur in forest tracts of 300 ha or more (Robbins et al. 1989, Wenny et al. 1993, Robinson et al. 1995). Reported as rare or absent in forest tracts smaller than about 20-70 ha in Maryland (see Bushman and Therres 1988). In Illinois, occurred in a forest tract of 65 ha but not in tracts of 25 ha or 14 ha (Robinson 1992). In Missouri, bred in a large continuous forest tract but not in two similar but smaller (300 ha) isolated sites (Wenny et al. 1993). In Connecticut, may nest in tracts as small as 20 ha but density is very low (Gale et al. 1997). It is unknown whether individuals nesting at small sites contribute offspring to future generations.
Robinson et al. (1995) suggested that a good regional conservation strategy for worm-eating warblers and other migrant songbirds, at least in the Midwest, is to identify, maintain, and restore the large tracts that are most likely to be population sources. Fragmentation of large forests into smaller ones may result in loss of local populations that will need to be replenished from birds from large, unfragmented forests.
Management Requirements: Further studies are required to assess effects of various logging practices on both wintering and breeding grounds. However, this warbler probably is tolerant of many different forest management and logging practices; selective logging and thinning "overmature" trees may create favorable conditions; may nest in clearcut areas as young as 7 years old where several hardwoods have been left standing in the clearcuts (see Bushman and Therres 1988).
Global Protection: Unknown whether any occurrences are appropriately protected and managed
Relevance to Humans and Ecosystems
Stewardship Overview: Principle management concern is that large tracts (300-1000 ha) of unfragmented suitable habitat are required for nesting and must be protected. Primary habitat requirements on the breeding grounds are mature deciduous forest, understory patches of dense shrubs (e.g., mountain laurel), and a topography of moderate to steep slopes. Winter habitat requirements are less well known but believed to be dependent primarily on mature moist to wet broad-leaved forests. Specific habitat requirements during migration are not known.
The worm-eating warbler is a small New World warbler. It is 13 cm long and weighs 13 g. It is relatively plain with olive-brown upperparts and light-coloured underparts, but has black and light brown stripes on its head. It has a slim pointed bill and pink legs. In immature birds, the head stripes are brownish. The male's song is a short high-pitched trill. This bird's call is a chip or tseet. Worm-eating warblers are sexually monomorphic. Males and females can only reliably be sexed during the breeding season by the presence of a brood patch in females or a cloacal protuberance in males. These birds are also difficult to age. Hatch year/second year birds have rusty tips on tertials that wear off by March of the following year. Juveniles can be distinguished by duskier head markings, and cinnamon wingbars.
This bird breeds in dense deciduous forests in the eastern United States, usually on wooded slopes. The nest is an open cup placed on the ground, hidden among dead leaves. It is one of five species of new-world warblers that nests on the ground including the black-and-white warbler (Mniotilta varia), the ovenbird (Seiurus aurocapilla), the northern waterthrush (Parkesia noveboracensis), Louisiana waterthrush (Parkesia motacilla), and the Kentucky warbler (Geothlypis formosa). The female lays four or five eggs. Both parents feed the young; they may try to distract predators near the nest by pretending to be injured. Worm-eating warblers are often parasitized by brown-headed cowbirds (Molothrus ater) where forest fragmentation occurs. Reducing forest fragmentation may prove vital if populations of worm-eating warblers suffer large declines.
Habitat and distribution
These birds breed in the Eastern United States. Their selected habitats vary significantly between populations. In much of their range, worm-eating warblers are associated with mature hardwood forests on steep slopes. However, recent attention has been focused on coastal breeding populations, as little is known about their ecology or status. Historically, coastal populations would select for pocosin ecosystems. More recently, however, these populations have shifted to frequent use of pine plantations. Current use of pine plantations has resulted in densities higher than in areas previously thought to be their natural habitat. This shift in habitat selection likely demonstrates that worm-eating warblers are more closely associated with shrub structure than stand age or size. If this is the case, the landscape changes that occurred on the Atlantic coastal plain may have had less of an impact on these birds than previously described. Maintaining this species habitat may require managing for dense shrubby midstory and understory. Due to their reliance on shrub structure for foraging, and ground nesting behavior, frequent fires have a negative impact on this species. Other management strategies that reduce the shrub mid-story, increase herbaceous growth, and decrease canopy cover are likely to have a similar effect. More information is needed about their breeding habits in coastal regions as these forests are likely to represent different conditions from their inland counterparts. Fat deposits play a key role in allowing for long distance migration in most passerines. Stopover habitat, or areas that allow birds to replenish their fat stores, are also critical.
In winter, these birds migrate to southern Mexico, the Greater Antilles, and Central America particularly along the Caribbean Slope where they occupy both scrub and moist forests.  Worm-eating warblers have disappeared from some parts of their range due to habitat loss but their ability to use both scrub and moist forest ecosystems may be beneficial to the long term conservation of this species.
The diet of worm-eating warblers varies across habitat types.  This variation can be attributed to different predator avoidance strategies employed by common prey items. On their breeding grounds, worm-eating warblers glean mostly from live foliage, searching for arthropods. On the wintering grounds, this species gleans insects almost exclusively from dead plant material. The name "worm-eating" refers to the numerous Lepidopteran larvae that this species consumes; they rarely if ever eat earthworms.
Use of pesticides, especially those broadcast over a wide area, is likely to have an effect on most insectivorous songbird species, including the worm-eating warbler. These pesticides decrease the species' primary food source and could result in long-term toxicity.
- BirdLife International (2012). "Helmitheros vermivorum". IUCN Red List of Threatened Species. Version 2013.2. International Union for Conservation of Nature. Retrieved 26 November 2013.
- Helmitheros vermivorum on Avibase
- Curson, Jon; Quinn, David; Beadle, David (1994). New World Warblers. London: Christopher Helm. p. 163. ISBN 0-7136-3932-6.
- Helinaia swainsonii on Avibase
- Pyle, Peter (1997). Identification guide to North American Birds. Bolinas, California: Slate Creek Press. pp. 499–500.
- Robinson, Scott K.; Thompson III, Frank R.; Donovan, Therese M.; Whitehead, Donald R.; Faaborg, John (March 31, 1995). "Regional forest fragmentation and the nesting success of migratory birds". Science 267 (5206): 1987–1990. Bibcode:1995Sci...267.1987R. doi:10.1126/science.267.5206.1987. PMID 17770113. Retrieved 26 February 2014.
- Watts, Bryan D.; Michael D. Wilson (2005). "The Use of Pine Plantations by Worm-eating Warblers in Coastal North Carolina". Southeastern Naturalist 4 (1): 177–187. doi:10.1656/1528-7092(2005)004[0177:tuoppb]2.0.co;2.
- Artman, Vanessa L.; Sutherland, Elaine K.; Downhower, Jerry F. (July 7, 2008). "Prescribed Burning to Restore Mixed-Oak Communities in Southern Ohio: Effects on Breeding- Bird Populations". Conservation Biology 15 (5): 1423–1434. doi:10.1111/j.1523-1739.2001.00181.x. Retrieved 26 February 2014.
- Pitts, Irvin. "The Status and Breeding Habits of the Worm-eating Warbler in South Carolina". Carolinabirdclub.org. Retrieved 26 February 2014.
- Moore, F.; P. Kerlinger (1987). "Stopover and fat deposition by North American wood warblers (Parulinae) following spring migration over the Gulf of Mexico". Oecologia 74: 47–54. doi:10.1007/bf00377344. Retrieved 26 February 2014.
- Vitz, Andrew C.; Lise A. Hanners; Stephen R. Patton (2013). "Worm-eating Warbler (Helmitheros vermivorum)". The Birds of North America Online. doi:10.2173/bna.367. Retrieved 26 February 2014.
- Robbins, C.S.; J R Sauer; R. S. Greenberg; S. Droege (1989). "Population declines in North American birds that migrate to the neotropics". Proceedings of the National Academy of Sciences 86 (19): 7658–7662. Bibcode:1989PNAS...86.7658R. doi:10.1073/pnas.86.19.7658.
- Greenburg, Russell (1987). "Seasonal foraging specialization in the Worm-eating Warbler". Condor 89 (1): 158–168. doi:10.2307/1368770. JSTOR 1368770.
- Moulding, Jonathon (1976). "Effects of a low-persistence insecticide on forest bird populations". The Auk 93 (4): 692–708. JSTOR 4084999.
Names and Taxonomy
Comments: See Banks and Browning (1995) for a brief discussion of nomenclature.