During the breeding season (spring-summer), the chestnut-sided warbled can be found in northern hardwood and mixed forests of southern Canada and north-eastern United States. It spends the winter in Central America.

Biogeographic Regions: nearctic (Native ); neotropical (Native )

occurs (regularly, as a native taxon) in multiple nations

Canada

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Breeding

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Breeding

Global Range: (20,000-2,500,000 square km (about 8000-1,000,000 square miles)) BREEDING: northeastern British Columbia, east-central Alberta across southern Canada to Nova Scotia, south to northern North Dakota, eastern Nebraska, central Iowa, northern Illinois, central Ohio, Appalachians to northwestern Georgia, Maryland, and Delaware; disjunctly Colorado and in Ozark Plateau of Missouri and Arkansas (Richardson and Brauning 1995, AOU 1998). NON-BREEDING: primarily from Oaxaca, southern Veracruz, Chiapas, and Guatemala south to eastern Panama, casually to Trinidad, Colombia, western Ecuador, and western Venezuela; Netherlands Antilles (Stiles and Skutch 1989, Ridgely and Tudor 1989, AOU 1998). Most common in Costa Rica (Richardson and Brauning 1995).

In non-breeding plumage, chestnut-sided warblers can be identified by their plain white underparts, greenish yellow upperparts, bold white wingbars, and white eye ring. In the summer, breeding plumage, chestnut-sided warblers have a yellowish forehead, black eye-stripe, plain white underparts, and a chestnut streak along its sides. The chestnut streak is longer and brighter in males and older birds. It may be missing completly in immature females and first year males.

Other Physical Features: endothermic ; homoiothermic; bilateral symmetry

Sexual Dimorphism: sexes colored or patterned differently; male more colorful

Average mass: 9 g.

Length: 13 cm

Weight: 10 grams

• Terrestrial

Before the 1800s, the chestnut-sided warbler was not well known. Because of its highly specialized habitat and foraging techniques, it was believed to be limited to former natural disaster areas such as sites of forest fires. With the clearing of primeval forests and the subsequent growth of shrubby habitats, the chestnut-sided warbler is one of the most abundant breeding warblers in second growth deciduous woodlands.

Terrestrial Biomes: forest

Comments: BREEDING: In new, second-growth thickets of alder (Alnus spp.) and other deciduous bushes growing in scrubby clearings and brushy areas or along the margins of streams, in orchards, pasturelands, forest edges, cut-over forests, roadsides, in open deciduous woodlands and in powerline corridors (AOU 1983, Askins 2000, Dunn and Garrett 1997, Richardson and Brauning 1995). Becomes most common in deciduous second growth or large forest clearings (Richardson and Brauning 1995). Avoids deep woods.

Makes extensive use of scrubby patches, particularly those with Rubus spp. present (Richardson and Brauning 1995). At high elevations, mountain laurel thickets are used (Dunn and Garrett 1997). Both wet and dry habitats used. Usually avoids conifer-dominated habitats and mature deciduous forests; however, populations from Manitoba west to Alberta occur in mature deciduous woodland with an understory of dogwoods and cranberries. Rarely found in urban settings and in areas of intensive agricultural use; has decreased where such development has replace fragmented or brushy habitats (Garret and Dunn 1997, see Robbins 1990, Burleigh 1958).

In the boreal forest of central Saskatchewan, found almost exclusively in stands of pure aspen (Hobson and Bayne 2000). In north-central Minnesota, found in habitat described as open fields with shrubs (Collins et al. 1982) or open habitat (Collins 1981). In the Appalachian Mountains, inhabits high-altitude stunted oak (Quercus) forests (Burleigh 1958). In portions of Appalachian region, found in thickets of young chestnuts, which die before reaching maturity (Richardson and Brauning 1995).

NON-BREEDING: Disturbed areas and clearings within tropical forests, forest borders, second-growth and even shaded gardens and coffee plantations (AOU 1988, Dunn and Garrett 1997, Pashley 1989). Also in moist submontane forest, to an elevation of 1300m (Curson et al. 1994).

In the Canal Zone of Panama, found in equal densities in old and young forest (Greenberg 1984), but prefers mature and late-second growth. Found in mesic and wet sites during wet and dry season, leaving the scrubby areas in the dry season (Morton 1980). Found in mid- to upper canopy of dense, moist forest, but not in the outer canopy of old forests that have a broader, branching structure (Greenberg 1984). In Costa Rica, also inhabits coffee plantations and riparian vegetation (Stiles and Skutch 1989). In Mexico, occupies, humid to semi-humid evergreen forest and edge, plantations, at mid- to upper levels (Howell and Webb 1995).

MIGRATION: Migrating birds can be found in a variety of shrubby habitats and in open woodlands, occasionally deep forests (Obserholser 1974, Bohlen 1989, Richardson and Brauning 1995).

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.

A long-distance nocturnal neotropical migrant. Fall migration begins from mid-August to late September. Route is broad, extending throughout the eastern United States, east of the Rocky Mountains. Birds move across the central Gulf of Mexico (Rappole et al. 1979) through eastern Mexico and Belize and arrive in Costa Rica by mid-September (Stiles and Skutch 1989). In spring, moves north via the western Gulf of Mexico or along the western Gulf Coast from Central America, beginning to arrive on its northern breeding grounds in mid-May (Rappole et al. 1979).

The chestnut-sided warbler is predominately insectivorous, but will eat some fruit. Each bird forages alone. It searches on the underside of leaves for insects. It hops from branch to branch with its tail cocked.

Comments: Insectivorous. Eats primarily the larvae and some adults of Lepidoptera and Diptera, some spiders, and some seeds and fruit as well (Richardson and Brauning 1995, Dunn and Garrett 1997). Usually forages alone. Gleans the undersurfaces of leaves at the low to medium levels in shrubs and the lower branches of small trees, but may feed in the upper canopy (Curson et al. 1994). Sometimes takes food from the ground or flycatches. On the breeding ground, males forage most often in hardwoods. Females forage most frequently in aspens in mixed hardwood dry-mesic forest in Wisconsin (Sodhi and Paszkovski 1995). In the Canal Zone, Panama, makes frequent use of plant species with planar leaf arrangements (Greenberg 1984).

Highly specialized in its habitat and foraging niche, which probably limited its distribution prior the 1800s (AOU 1998). Was largely dependent on natural disturbance, occupying sites of former forest fires and windstorm blowdowns, stream-bank areas where flooding periodically created early-successional habitat, and early-successional growth around Beaver (Castor canadensis) ponds (Richardson and Brauning 1995, Askins 2000).

Territorial during breeding season; male chases intruders from territory. Solitary and territorial in winter, but single birds frequently join mixed foraging flocks as they pass through their territory (Curson et al. 1994, Howell and Webb 1995). Variously reported as highly intraspecifically territorial or variable; maintains small territory around antwren territory (Greenberg 1984).

Average lifespan

Status: wild: 83 months.

The chestnut-sided warbler is believed to be monogamous. They can reproduce in their first year. After returning from winter migration and before the females arrive, males establish territory by continuous singing and aggression. Once females arrive, males act very aggressively at first. After copulation, the male follows the female, apparently guarding her. A female constructs a nest entirely on her own in deciduous trees or shrubs. She also incubates the eggs alone. Eggs are laid mid-May to mid-July. On average, there are about four eggs per brood and only one brood is reared per season. Both parents care for the young. At first they feed the young by regurgitation, then as the young become older they are fed small insects. Both parents help in removing waste from the nest.

When they first hatch, the young are altricial. They experience rapid growth in the first week and are capable of flight on the ninth day. They usually leave the nest on the tenth or eleventh day and move to low open thickets where they wait to be fed. They continue to beg for food until they are about one month old.

Average time to hatching: 12 days.

Average eggs per season: 4.

Apparently monogamous.

Nesting in shrubby habitat close to the ground, sometimes deciduous trees. In Ontario, most commonly in hazel (47%), Rubus (28%), maples (17%), and alder (7.6%). In a small crotch or within a group of thin vertical stems (Peck and James 1987). Average nest height 0.6 m, rarely up to 2 m (Kendeigh 1945, Baicich and Harrison 1997).

Nest built by female. A compact cup of fine grasses, bark fibers, shredded weed stems, and plant down. Lined with fine grasses and hair. Typically 3-5 eggs (usually 4), laid mostly in late May and June. Eggs white, creamy or pale greenish. Incubation 11-12 days be female only (Baicich and Harrison 1997). Female broods; male visits nest and feeds. Young leave nest at 10-12 days and move to low thickets where they are fed and tended by parents young (Richardson and Brauning 1995). Rarely two broods per season (Andrle and Carroll 1998).

Studies have been done on the effect of pesticides on the chestnut-sided warbler. They show that the birds still forage in treated areas, but return in fewer numbers in following years. It has been suggested that because the chestnut-sided warbler forages on the undersides of leaves, it may be less affected than other species in treated areas. It has been reported that a large number of chestnut-sided warblers are killed in collisions with stationary objects. Many are found dead at the base of TV towers, smokestacks, and large buildings during migration.

US Migratory Bird Act: protected

US Federal List: no special status

CITES: no special status

State of Michigan List: no special status

IUCN Red List of Threatened Species: least concern

Canada

Rounded National Status Rank: N5B - Secure

United States

Rounded National Status Rank: N5B - Secure

Rounded Global Status Rank: G5 - Secure

Reasons: Still widespread and fairly common, but declining.

Global Short Term Trend: Decline of 10-30%

Comments: Populations and breeding range increased during the 1800s in response to activities that allowed regrowth of forests; local increases also occurred with forest loss from chestnut blight and where open farmland and pastures grew back to scrub and second growth (Dunn and Garrett 1997). Populations remain high in comparison to pre-colonial estimates. However, populations underwent an overall slow decline from the early 1960s to the early 1990s (Sauer and Droege 1992); more recent analysis of Breeding Bird Survey data indicate a decline that is not statistically significant -- 0.7 per cent annual decline, 1966-1999; 0.5 per cent annual decline, 1980-1999 (Sauer et al. 2000). No common trend pattern across the range -- statistically significant declines have occurred 1966-1999 in the Adirondacks, northern New England and Nova Scotia; statistically significant increases have been recorded in the St. Lawrence River Plains and the Great Lakes Transition zones (Sauer et al. 2000). Local population fluctuations are due to regional habitat change (Richardson and Brauning 1995). Similarly, populations on non-breeding grounds appear to be exhibiting local declines where the availability of shrub/scrub/edge habitats are decreasing and fragmentation and urbanization are increasing. Common in forest borders and woodland in lowlands and foothills on both slopes in western and central Panama, but becoming decidedly less numerous in eastern Panama (Ridgely and Gwynne 1989).

Comments: HABITAT LOSS/DEGRADATION: Because this species responds favorably to certain human-induced habitat changes, highest densities are found in areas logged or disturbed and subsequently allowed to regenerate. As agricultural use and urban sprawl increase this species is expected to decrease (see Janssen 1987, Robbins 1991). Widespread logging and urbanization are associated with absence (Janssen 1987). PESTICIDES AND CONTAMINANTS: Use of insecticides and bt (Bacillus thuringiensis), a biological control agent, may cause decreased productivity or abandonment of some areas (Richardson and Brauning 1995). COLLISIONS: 349 of 17,967 birds killed at a single Ontario tower identified as Chestnut-sided Warbler (Weir 1989). Large numbers reported killed in Illinois and Georgia (Graber et al. 1983, Johnston and Haines 1957). PARASITISM: A significant percentage of nests are parasitized by cowbirds throughout range (Peck and James 1987). Reed (1992) ranked this species as having a probability of extinction of 6 on a scale of 1-10 (highest probability = 1), due to its lack of specificity of habitat, its apparently large population size and its relatively narrow geographic distribution. Stotz et al. (1996) describes this species as a relatively low conservation priority in the neotropics.

Restoration Potential: Not currently in need of restoration.

Preserve Selection and Design Considerations: Specific habitat requirements are not well documented. Data suggest that larger areas of forest are required; negatively correlated with urbanization and extensive logging. Research suggests maintaining a shifting mosaic of early successional habitat within a largely unfragmented forest landscape.

Management Requirements: The primary management concern is the provision of adequate habitat, which is ephemeral and often declines as a result of natural vegetation succession. In the absence of naturally occurring fires and other disturbance, active management (prescribed burning, clearcutting) effectively provides early-successional habitat. Management practices that closely mimic the natural disturbance regimes of forests will best manage for the resident bird community and provide adequate habitat throughout breeding range (see Schulte and Niemi 1998). Before colonization, depended largely upon natural disturbances such as wildfires, floods, localized insect outbreaks and the activity of animals such as beaver and moose to provide early-successional habitat. Where feasible, these natural disturbances should be permitted (Askins 2000).

Single areas generally cannot provide continuously favorable habitat, so successful management in a region will require the provision of a mosaic of sites in different stages of vegetation succession. Where appropriate, clearcuts can be used to maintain a wide range of successional stages, especially when the rotation time between harvests is long enough to permit the forest to mature (Askins 2000). Selective cutting does not appear to create the habitats needed by many early successional species. Found in greater numbers in logged vs. burned areas in northeastern Minnesota, but with a high relative abundance in both treatments. Logged sites were dominated by red maple (Acer rubrum; 47%) lesser amounts of conifers (33%) and aspen (11%) (Schulte and Niemi 1998). Management must maintain appropriate mixtures of different tree species at the stand and landscape level (see Hobson and Bayne 2000).

Vegetation along powerline corridors is a significant source of habitat. Powerline corridors can negatively impact forest bird species that require large expanses of uninterrupted forest, but also sustain important populations of shrubland birds. Right-of-ways should be managed by selective tree removal that produces a thick shrubland, resistant to the invasion of trees. Other options such as mowing or "bush-hogging" that mechanically chop up woody vegetation, should be avoided as should broadcast spraying of insecticides (Askins 2000). Habitat management must also take into account neighboring land uses as this species avoids town and areas of intensive agriculture throughout its range, and has decreased where such development has replaced or fragmented brushy habitats. (Dunn and Garrett 1997).

NON-BREEDING: Maintaining large tracts of undisturbed habitat is also a priority on the wintering grounds. While it has low vulnerability to tropical deforestation, is a somewhat area-sensitive species uncommon in small forests. Management for this and other neotropical migrants that utilize shrub/scrub habitat throughout Central America (see Blake and Loiselle 1992, Slud 1964, Stiles 1980) will concentrate on maintaining patches of early-successional habitat and controlling fragmentation and urbanization.

There are indications that fragmentation of tropical forests may lead to increased mortality for migrants occupying those patches. Until further research proves otherwise, limiting fragmentation and increasing forest connectivity should be guidelines for forest management in the tropics as well as in the temperate forests of North America (Petit et al. 1996).

Management Programs: No known management programs directed at this species (Richardson and Brauning 1995).

Monitoring Programs: The BBS is the only systematic survey that gathers data throughout the breeding range of most neotropical migrants (Sauer et al. 1997). Chestnut-sided Warbler is monitored by this survey, but is not a special target species. Partners-in-Flight is increasing efforts to monitor all neotropical migrants throughout North and South America. Their goals are to improve understanding of neotropical migrants, identify species most at risk, and develop habitat protection plans.

The Forest Bird Monitoring Program (FBMP) has been on-going in Ontario, Canada, since 1987. In 1993, 125 sites (600 listening stations) were surveyed for a number of species, including the Chestnut-sided Warbler. Contact: Mike Cadman, Canadian Wildlife Service, 75 Farquhar St, Guelph, ON N1H 3N4; 519-826-2094 (phone), 519-826-2113 (fax); Mike.Cadman@ec.gc.ca (Last update: 12/21/1999). Results available online: http://www.cws-scf.ec.gc.ca/canbird/news/bt98/ins9_e.html

The Vermont Forest Bird Monitoring Program, based on the Ontario FBMP, has recorded breeding bird information on a number of tracts of relatively undisturbed, interior forest habitat since 1989. Information on Chestnut-sided Warbler and other species are available. Contact: Steve Faccio, Vermont Institute of Natural Science, R.R. #2, Box 532, Woodstock, VT 05091; 802-457-2779; treefrog@sover.net (Last update: 12/21/1999). On-line at: http://vmc.snr.uvm.edu/bird.html#results.

Birdcast is a pilot radar ornithology project that focuses on the mid-Atlantic region and is designed to monitor the migration of neotropical migratory birds and hopes to improve identification of important migratory habitat. Birdcast is a cooperative project of the National Audubon Society, the Cornell Lab of Ornithology, Clemson's Radar Ornithology Laboratory, and the Academy of Natural Science, with support from the Environmental Protection Agency. Information available online: http://birdsource.cornell.edu/BirdCast/

Management Research Needs: Stotz et al. (1996) describe this species as a medium research priority in the neotropics. Richardson and Brauning (1995) suggest the following research needs relevant to management:

1) Determine incidence of second and subsequent broods and lifetime reproductive success.

2) Determine rates of return to natal sites.

3) Study is needed of isolated populations (e.g., in Alberta and Colorado) to determine basic biology and genetics and how closely these birds relate to those in the main populations' range. In addition, the location of these wintering birds and how they mix with the main population is worthy of study.

4) Studies of territoriality across the wintering range, with special emphasis on relationship to habitat type (wet and dry seasons), are needed.

The effect of habitat fragmentation and loss of connectivity in tropical environments is poorly understood. Further investigation of this question is of immediate concern because of the rapidly increasing human populations throughout Central and South America.

Biological Research Needs: Better determination of the relation of song types and their variation to behavior is needed (Richardson and Brauning 1995).

The chestnut-sided warbler eats potentially harmful insects. This may benefit farmers as a natural way to control insect populations.

Stewardship Overview: Because this species often inhabits habitats that are human-modified and created, habitat protection through acquisition is not a suitable or feasible method of protection of itself. Overall, populations appear healthy at present, but are declining locally in response to increasing forest fragmentation and urbanization. Maintaining larger patches of habitat and using forest management practices that closely mimic natural disturbance regimes in forests will provide adequate habitat for Chestnut-sided Warbler and other shrubland birds. Existing management practices at sites such as utility right-of-ways can easily be modified to provide higher quality habitat.