The cerulean warbler undertakes an impressively long migration considering its small size, covering approximately 2,500 miles as it flies south between July and September (3) (5). The journey has to be completed once again at the end of winter, with the warbler reaching the breeding grounds in April and May (3). Arriving at the breeding grounds a week earlier than the females, the males use this time to establish and maintain a territory. While this is achieved primarily by singing, aggressive physical attacks can occur (3), with males colliding in mid-air and grappling with bills and feet whilst they spiral towards the ground (2). Cerulean warblers are apparently monogamous and so once the females arrive on the breeding grounds, pairs are formed, and the female sets about building a nest high in the canopy. This is generally a neat cup structure formed from shreds of bark, lichen, moss, and grass, bound together with spider webs and lined with hair and fine moss stems. Finally, the outside of the nest is often decorated with fragments of any grey or white material (2) (3). Usually each pair produces only one brood each year, laying an average of four eggs which are then incubated by the female for 11 to 13 days (3). The young are born with their eyes closed and are incapable of leaving the nest, and so are fed by the parents for the first 10 to 11 days of life (3). Cerulean warblers can first breed at the age of one, and may live for up to six years (2). Cerulean warblers are insectivorous birds, feeding on a variety of insects as they hop along twigs examining the surfaces of leaves and bark for any potential prey (3) (2). They also sometimes consume small amounts of plant material (2).

Named after the beautiful blue colour of its plumage, the cerulean warbler is a small canopy-dwelling wood-warbler. Adult male cerulean warblers have streaky bright sky-blue upperparts, white underparts and a narrow black band that falls, like a necklace, across the throat (2) (3). In contrast, the plumage of adult females is a shade of greenish-blue, becoming bluer at the crown and rump (3). The throat and breast are pale yellow and above the eye sits a prominent pale yellow 'eyebrow' (3). While there is some seasonal variation in the plumage of both sexes (2), two wide white bars across the long, pointed wings and white spots on the short tail remain throughout the year (2) (3). As the cerulean warbler spends much of its time high in the canopy of forests, it can be difficult to spot, and so is best identified by the high-pitched song of the male: an accelerating series of short buzzes ending with a single longer, higher buzz (3).

Dendroica cerulea breeds from Quebec and Ontario (Canada), east to Nebraska and south to northern Texas, Louisiana, Mississippi, Alabama and Georgia (USA)¹. A four year study from 1997-2000 identified several seemingly key sites that support large populations⁴. These included the Cumberland Mountains north-west of Knoxville, Tennessee; the Montezuma wetlands complex and adjacent areas in central New York; the Kaskaskia River Valley and Shawnee National Forest in south eastern Illinois; the Jefferson Proving Ground of southern Indiana: Queens University Biological Station in south eastern Ontario; the Kalamazoo River of south western Michigan; the Eleven Point and Upper Current rivers in Missouri; the Shenendoah National Park and Blue Ridge Highway in western Virginia; and the Delaware River Valley and adjacent highlands of north western New Jersey. These areas may represent primary areas for population monitoring and conservation⁴. It migrates south through the south-eastern USA, the Bahamas, Cuba, Jamaica, the Caribbean slope of Mexico, Belize, Guatemala, Honduras, Costa Rica and Panama, and winters from Colombia and Venezuela south, mainly east of the Andes, to eastern Ecuador, eastern Peru and perhaps northern Bolivia¹. Breeding Bird Survey results show declines equating to 26% per decade over the period 1980-2002, but longer-term declines are even more severe⁷.

Dendroica cerulea breeds principally in the Mississippi and Ohio river valleys, west of the Appalachian Mountains. Its breeding area ranges from central Minnesota, northern Wisconsin, central Michigan, southern Ontario, northern New York, Connecticut, and Rhode Island south to Arkansas, Mississippi, Alabama, and North Carolina. Cerulean Warblers breed very locally in eastern North Dakota, eastern Nebraska, eastern Kansas, eastern Oklahoma, northeast Texas, northern Louisiana, western Massachusetts, northwest Vermont, southwest Quebec, and in the upper peninsula of Michigan. They are seriously declining in the heart of their range, but possibly expanding their breeding range in the north and northeast and onto the Piedmont plateau and Atlantic coastal plain. In winter, D. cerulea is found in northern South America from Colombia and Venezuela south to southern Peru and northern Bolivia. It winters in foothills and middle elevations on the west slope of the Andes Mountains in Colombia and, in greater numbers, on the east slope of the Andes from Venezuela south. Local sightings are reported in southeast Brazil, and very small numbers may winter in Panama and Costa Rica. Migration routes are wide-ranging, but mainly along the Mississippi River, across the Gulf of Mexico, and through Central America (Dunn and Garrett 1997; DeGraaf and Rappole 1995; Scott 1999).

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: southeastern Nebraska across southern Great Lakes region to southern Ontario, southwestern Quebec, and western New England, south to northern Texas, central Georgia and Alabama, western North Carolina, and Maryland (AOU 1983). Most abundant in the Cumberland Plateau and surrounding regions (S. Droege, pers. comm.). NON-BREEDING: primarily in a narrow elevational zone (500-1800 m) on the eastern slopes of the Andes from Colombia and Venezuela through Ecuador to Peru (AOU 1983); relatively few overwinter elsewhere, though a small population exists in the tepui region of Venezuela (Robbins et al. 1992). MIGRATION: in spring through the West Indies, Bahamas, and eastern North America. In fall across northeastern North America to New England and the Maritimes, then over water through Bermuda and the Lesser Antilles to South America (AOU 1983) through Venezuela and Colombia (where a few may winter). Rare transient in Central America (more common farther south); rare or accidental in eastern Mexico and the Caribbean.

The breeding range of the cerulean warbler extends from Quebec and Ontario, Canada, south to northern Texas, Louisiana, Mississippi, Alabama and Georgia in the USA. The cerulean warbler migrates south for winter where it can be found in Colombia and Venezuela, south to eastern Peru and northern Bolivia (3) (4).

Cerulean Warblers, the smallest of the Dendroica (11.5 - 12 cm), are short-tailed and have two wide white wing bars in all plumages. Strongly sexually dimorphic, D. cerulea, however, shows little seasonal variation in plumage. Adult males are blue above and white below with dark back and side streaking and a dark breast band. Adult females have a greenish mantle, a pale yellow breast and throat, a bluish crown, and a pale supercilium. Immature males resemble adult females but show dark streaks and more blue above. Immature females have no blue in their plumage. In the southern United States males weighed an average of 8.35 grams and females 8.04 grams and in the northern Unites States males weighed an average of 9.28 grams and females 8.83 grams. (Dunn and Garrett 1997; Hamel 2000; Scott 1999).

Length: 12 cm

Weight: 10 grams

Habitat and Ecology

Systems

• Terrestrial

Cerulean Warblers are associated in the U.S. and Canada with large, old-growth tracts of deciduous floodplain forest, a habitat that has become extremely rare in the last century. Sensitivity to fragmentation in these areas, along with strict wintering-ground requirements of primary, humid evergreen forest along a narrow band in the Andes foothills, has put the species in jeopardy. Even though they are found breeding in tracts of only 10 ha, studies suggest that large, unfragmented forested areas may be required to support viable breeding populations. A Maryland study concluded that the maximum density of D. cerulea occurs in forests of at least 3000 ha. Researchers have found that Cerulean Warblers are restricted to one of the narrowest bands of elevational zones of any migrant or resident Andean bird and do not accept disturbed habitat (Robbins et al 1992; Oliarnyk 1996; Terborgh 1989).

Terrestrial Biomes: forest ; rainforest

Comments: BREEDING: A tentative description of the characteristics of breeding habitat is a structurally mature hardwood forest in a mesic or wetter situation, with a closed canopy. The size of the trees is of primary importance and their species identity secondary. Landscape situation and context has a strong bearing on whether otherwise suitable breeding habitat will actually contain warblers (Hamel 1992). In eastern Ontario, breeding territories were characterized by well-spaced large trees, with high canopies and dense foliage cover at heights between 12-18 meters (Jones and Robertson 2001). Habitat is frequently described as mature deciduous forest, particularly in floodplains or other mesic conditions (Robbins et al. 1992 in Tennessee and Maryland; Kahl et al. 1985 in Missouri). Territories in central and western Tennessee are found in forest stands with numerous large trees. Within the stands, territories are located in the areas with more large trees than is typical for the stand and are absent from the portions with small trees (Hamel 1988, Robbins et al. 1992). Observations of the utilization of forest vegetation found birds in the tree canopy, almost always above the midpoint of the tree, at an average height of 17 m in a 22-m-tall tree. These results somewhat contradict the statements of Morse (1989, citing Anderson and Shugart 1974), that this warbler utilizes habitat components in proportion to their availability.

Robbins et al. (1989) found occurrences to be associated with large tracts of mature, semi-open deciduous forest in Maryland and adjacent states. Distribution of breeding birds was positively correlated with the natural log of forest area (P < 0.01) and the square root of tree basal area (P < 0.05), and negatively correlated with the arcsine of percent canopy cover by coniferous trees (P < 0.05). In Missouri, Kahl et al. (1985, cited in Robbins et al. 1992), found that habitat around song perches was most consistently characterized by a large number of live stems > 30 cm dbh (range = 50-150 per ha), and a high (always > 18 m), closed canopy (> 85%, never < 65%). Other important features included an intermediate number of woody stems < 2.5 cm dbh (1,030-2,800 per ha, never < 1,030), and few dead stems 2.5-9.9 cm dbh (always < 175 per ha).

In North Carolina, a disjunct population occurs in the old-growth, mature floodplain forest communities of well-drained natural levees within 330 m of the Roanoke River (Lynch 1981, cited in Robbins et al. 1992). The dominant canopy species are sycamore (Platanus occidentalis), green ash (Fraxinus pennsylvanica), and sugarberry (Celtis laevigata). These communities are characterized by a closed canopy ranging in height from 24-30 m, a distinct shrub layer, and complete ground cover.

In the Cumberland Mountains of eastern Tennessee, a dense population occurs at Frozen Head State Natural Area (C.P. Nicholson, pers. comm.). This area's second-growth forest is in advanced growth, with a high, closed canopy of large trees similar to those described above, in mesic cove and slope topography. Forest composition is of a diverse assemblage of hardwood trees. In North Carolina, also found in mature cove hardwood forests on relatively steep slopes with little understory (H. LeGrand, pers. comm.).

Placement of the nest has been described differently by various authors. Nests in tall tree, about 4.5-27 m up (typically high in tree), well out on large branch, often [apparently] near forest opening. More information is needed on nest site preferences, especially the relationship (if any) to canopy gaps (Hamel 1992). Previous summaries of breeding habitat from studies in the 1980s indicate that the forest in which the birds breed is one with a closed canopy. Bent (1953) states that "...the nest is usually placed...over an opening [sic]." A nest discovered in central Tennessee in 1950 was built in an elm at the edge of an opening beside a farmhouse (K.A. Goodpasture, pers. comm.). Bent (1953) describes a nest site that was five meters out on a limb of a tulip-tree (Liriodendron tulipifera), and 14.8 m up "....with no other limb between it and the ground." Harrison (1984) presents a photograph of breeding habitat which shows a discontinuous canopy edge at a forest road.

Several important questions arise from these conflicting indications of nesting habitat. Do cerulean warblers usually nest in continuous, unbroken forest? Do they build their nests in the canopy of the forest where little other vegetation occurs between the nest and the groundcover? Do they typically build their nests in association with canopy gaps in otherwise unbroken forest? Are they indifferent to nest situation, using closed canopy forest, canopy gaps, and the edge between forest and other land uses in proportion to their availability? The literature is insufficiently clear to distinguish these alternatives. Observer bias is certainly possible in reporting nest locations when nest searches were haphazard, as was almost certainly the case in the existing literature. In such a case, nests built in locations that are easy to find would appear with greater relative frequency in the literature than in the field. One further possibility is that current observations may not reflect the preferences of the birds as they existed in the past. Instead, the current situation may be only a remnant of the actual capability of the birds; a remnant produced by the action of limiting factors (Hamel 1992).

NON-BREEDING: Concentrated on the eastern slopes of the Andes Mountains in western South America. Elevational range is limited to the lower slopes between 500-1,500 m, in precisely the elevation at which human habitat encroachment is proceeding most rapidly (Skutch, cited in Bent 1953; J. Fitzpatrick and S. Robinson, pers. comms.). The winter habitat is mature deciduous forest, also with large trees, although quantitative measurements are so far lacking. This recent information is different than that quoted by Bent (1953, referring to Taczanowski) that the birds range between 10,000-13,000 ft (3,000-4,000 m) in the Peruvian Andes. Terborgh (1989) associates cerulean warblers with montane forests of middle elevations in the Northern Andes. He further indicates that this warbler does not accept disturbed habitats. In migration, occurs in various forest, woodland, second growth, and scrub habitats; forest canopy, gaps and edges, semi-open areas, usually high in trees (Stiles and Skutch 1989). In winter, occurs in forest and woodland borders on mountain slopes, primarily in tall, primary, evergreen forest (Robbins et al. 1992) (deciduous, according to Hamel 1992).

During the breeding season the cerulean warbler inhabits mature deciduous forest, generally with open understorey, between 30 and 1,000 metres above sea level (2) (3). Over winter, the cerulean warbler can be found in broad-leaved, evergreen forests and woodland on the east slopes of the Andes and in the montane forests of Venezuela, at elevations of about 500 to 1,500 metres (2). It shows a preference for mature primary forest, although this warbler has also been found in mature coffee plantations (5).

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.

They arrive in North America in April and leave in September for wintering grounds in northern South America. Birds leave the breeding grounds early, perhaps in early July. Records exist of arrival in Ecuador as early as mid-October (Bent 1953).

Cerulean Warblers' primary foraging strategy is to glean insects from leaves in the upper canopy of deciduous trees (sometimes greater than 45m high), working from the proximal to the distal end of twigs. Less frequently, the birds will sally and hover-glean to capture insects. Analysis of stomach contents has shown the major food items to be Homoptera, Lepidoptera (primarily larval), Coleoptera and smaller amounts of Hymenoptera, Diptera, Hemiptera, Araneae, and other arthropods (Hamel 2000; Sample et al. 1993; Ehrlich et al 1988).

Comments: Cerulean warblers are insectivores, foraging in and about the foliage of deciduous trees for small arthropods which they capture by gleaning and by sallying (Hamel 1992, Terres 1980, Bent 1953). A sample of four stomachs taken in Alabama in April 1912 (Howell 1924) contained Hymenoptera (42%); Coleoptera, including weevils (23%); and Lepidoptera (35%). These are the only quantitative data on the diet. Warren (1890) mentions a stomach (presumably from a bird taken in Pennsylvania) that contained fragments of spiders and small beetles. In Nebraska, S. Aughey in June 1865 watched an adult bring locusts to its young (C. Robbins, pers. comm.). No plant materials have yet been reported in the diet. Current information is insufficient to establish a distinguishing characteristic of the diet.

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: 81 to >300

2500 to >1,000,000 individuals

In various areas, the highest breeding density was 82-290 pairs per sq km (Robbins et al. 1992). Little work has been done on wintering ecology. J. Fitzpatrick and S. Robinson (pers. comm.) have observed that birds participate in canopy-foraging flocks of forest insectivores, with only one or two warblers in a particular flock. This implies that the foraging flock is a resource that is actively defended by the individual warbler against conspecifics. Though empirical data to support this hypothesis are lacking, this behavioral tendency could be of critical importance. Single flock membership implies a finite limit to the total population; a limit determined by available space. However, these recent findings are in contrast to the earlier reports of movements of large flocks of warblers (Bent 1953).

Average lifespan

Status: wild: 59 months.

Maximum longevity: 6 years (wild)

The Cerulean Warbler breeds in wooded swamps, mesic uplands, and wet bottomlands. The female builds a nest from bark fibers, lichen, moss, and fine grasses in any of a variety of tall deciduous trees (at 5 to 30m) and far out on a limb. The breeding season begins mid-May to early June and usually ends in July. Four eggs (17 X 13 mm) are laid (range usually 3-5) in a single clutch. Eggs are smooth, slightly glossy, and vary from creamy-white to grayish-white to pale greenish-white. Speckles, spots, or blotches are reddish-brown, purplish-brown, or paler brownish-gray, often concentrated on the larger end. After an 11 to 13 day female incubation period, the nestlings hatch slightly downy and altricial. Nestling period has been shown to be between 10 and 11 days. Both parents feed the young and remove fecal sacs. Birds reach sexual maturity and breed when 1 year old. Cowbird parasitism has been observed at multiple breeding sites (Baicich 1997; Robbins et al. 1992; Oliarnyk 1996).

Apparently a monogamous, single brooded species. The compact nest is built by the female on the lateral limbs of a tree and placed at a considerable distance (e.g., 2-7 m: Harrison 1984) from the bole of the tree, usually saddled on a large, lateral branch, attached perhaps to a small protruding twig. The nest is rather shallow for a warbler (Bent 1953). Variation in site selection is considerable, particularly with respect to the distance from the bole. All authors agree that nests are not built near the ground. Heights from 5-20 m are reported by Bent (1953), Harrison (1984), and Hands et al. (1989), and the typical height is probably above the middle of this range.

The female lays three to five, usually four, eggs. Incubation is believed to be about 12 days (Harrison 1975), and nest life of the young is nine to ten days (n = 1: Southern 1962). The young are fed by both parents, and subsequent to fledging, they move first to lower-level vegetation where their parents feed them, and then gradually farther afield as they approach independence.

The following is a representative barcode sequence, the centroid of all available sequences for this species. 

 
There are 3 barcode sequences available from BOLD and GenBank.  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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Barcode of Life Data Systems (BOLDS) Stats
Public Records: 3
Species: 3
Species With Barcodes: 1

Year Assessed

Assessor/s

Reviewer/s

Contributor/s

Justification

History

• 2004
  Vulnerable

Dendroica cerulea is listed as Threatened in 2 states and is considered in need of some less restrictive protection in 13 states and 1 Canadian province. In Michigan, it is a species of special concern. It is not currently protected under the federal Endangered Species Act, but efforts are underway to petition for its listing. As with most migratory birds, it is protected from hunting and harassment under the Migratory Bird Treaty Act of 1916. The species has shown the greatest decline of any species of warbler (3.4%/year) from 1966 to 1987. Recommendations have been made that the federal and state governments within its range protect large tracts of public land for habitat and restore second growth forests (Hamel 2000; Robbins et al. 1992).

US Migratory Bird Act: protected

US Federal List: no special status

CITES: no special status

State of Michigan List: special concern

IUCN Red List of Threatened Species: vulnerable

Canada

Rounded National Status Rank: N3B - Vulnerable

United States

Rounded National Status Rank: N4B - Apparently Secure

Rounded Global Status Rank: G4 - Apparently Secure

Reasons: Large breeding range in eastern North America, but declining, even with population expansion in some areas; decline apparently is due primarily to habitat loss and fragmentation, with the greatest effect perhaps occurring in the winter range in South America.

Classified as Vulnerable (VU) on the IUCN Red List 2007 (1).

Population

Population Trend

Global Short Term Trend: Decline of 10-30%

Comments: North American Breeding Bird Survey (BBS) data indicate a significant population decline in eastern North America, 1966-1994; decline was 49.5% between 1966 and 1993, a nonsignificant 17.2% between 1984 and 1993 (Price et al. 1995). The decline has been most pronounced in the core of the breeding range (Robbins et al. 1992). Population size has declined across range in eastern U.S., but species has expanded range, particularly in the Northeastern U.S. and Ontario, perhaps in response to forest maturation (Hamel 1992, Oliarnyk and Robertson 1996). See Hands et al. (1989) for information on status in the north-central U.S. See McCracken (1993) for information on status in Canada (fairly stable).

Major Threats

Degree of Threat: C : Not very threatened throughout its range, communities often provide natural resources that when exploited alter the composition and structure over the short-term, or communities are self-protecting because they are unsuitable for other uses

Comments: The fact that the rangewide decline in numbers is most severe in the center of their range, where the highest numbers of individuals are recorded on the BBS, is a cause for concern. Threats and limiting factors most frequently mentioned are destruction of both breeding and wintering habitat. In each case, human agency is associated with the destruction as the primary threat. The traits of the species as a single brooded, forest nesting neotropical migrant are believed to be the features that put the species at risk for population decline resulting from habitat destruction. Habitat destruction may operate at three different scales by three different mechanisms. First, as potential habitats are destroyed, the gross area of habitat is reduced and the carrying capacity of the breeding or wintering range is reduced in proportion to the reduction in area. While this threat is straightforward and undeniable, it has not proceeded to the point that it alone is threatening the population with extinction rangewide. Second, the manner in which the reduction in gross area occurs can affect the actual carrying capacity of the remaining habitat. Evidently, patches of habitat below a certain size are simply not capable of supporting breeding birds (Robbins et al. 1989). Whether this is also true in the wintering range is unknown. Third, some evidence indicates that certain tree species of apparent importance to the birds may be experiencing rangewide declines in vigor as a result of as yet undetermined factors (Robbins et al. 1992). Hands et al. (1989) list contaminants, predation, competition, diseases/parasites, weather, and human disturbance as additional potential limiting factors. Hands et al. (1989) comment that red squirrels (TAMIASCIURUS HUDSONIUS) may depredate the nests, and note the red-eyed vireo (Vireo olivaceus), northern parula (Parula americana), and yellow-throated warbler (Dendroica dominica) as possible competitors. Robbins et al. (1992) indicate that nest parasitism by brown-headed cowbirds (Molothrus ater) is a likely factor in the decline. Nest parasitism by cowbirds is at least part of the mechanism by which the forest fragmentation effect is manifested (Hamel 1992). No specific causal connection of the decline to any particular factor has been investigated or demonstrated. Several factors are involved in synergy and protection efforts will be required before the complex of causes can be proved beyond a doubt. Fragmentation is not the cause of the reduction in populations of the birds in small tracts, but rather the precursor that permits the operation of that causal factor. Expanding range of the shiny cowbird (Molothrus bonariensis) poses a potential threat (Robbins et al. 1992). Warbler disturbance by humans is primarily by destroying and degrading mature forests. This suggests that management plans should include education programs for land owners and managers of the habitat needs of the warbler. Emphasis in these programs should be on the need for protection of large tracts of mature, deciduous, primarily lowland forests (Hands et al. 1989).

Once a common species in the forest canopies of eastern North America, the cerulean warbler has since undergone a long-term, steep decline, and is now only frequently sighted in core parts of its breeding range (5). The primary force behind these dwindling populations is habitat loss and degradation, in both the warbler's breeding and non-breeding habitats (4) (5). While the breeding habitat is subject to forest loss, fragmentation, and a loss of suitable vegetation structure within mature deciduous forests, the winter forest habitat is suffering from clearance for the production of coffee, tea, coca and hill rice, and pasture for livestock. Around 60 percent of the cerulean warbler's wintering habitat may have already been lost to these activities (5). In addition, the cerulean warbler faces the potential threats of, amongst others, an increased frequency of catastrophic weather events, and a shift in the location of suitable forest types as a result of climate change (5).

Conservation Actions

Restoration Potential: Restoration to areas from which old forest habitat has been removed will require substantial periods of time. Reverting farmland and early-successional forests can be regenerated to suitable mature hardwood forest within 80 years. Recovery of habitats will require an unavoidably long-term commitment (Hamel 1992).

Preserve Selection and Design Considerations: Breeding populations in small forest tracts throughout the range are declining rapidly to extirpation. Populations in Wisconsin showed increasing size dependency in a study in which the largest habitat "island" was 40 ha (Gustafson 1985). Robbins et al. (1989) indicate that the probability of occurrence in Maryland study sites reached 50% of its greatest value when tract sizes were 700 ha or greater. Primary breeding habitat is large tracts of floodplain forest of tall, mature deciduous trees; rarely nests in forest tracts smaller than 250 ha (Robbins et al. 1992). In a study in western Tennessee bottomland hardwood forests, birds were not found in tracts less than 1,600 ha in extent (Robbins et al. 1992).

The implications of these results are that protection of land will only be possible in large tracts. These tracts must be at least 4,000 ha in extent and they should be arranged in such a way that a minimal perimeter distance occurs per unit area (Hamel 1992). No proof exists that the provision of such tracts, composed of suitable breeding habitats, will provide a secure future for the warbler as a breeder in the North American avifauna. However, there is ample evidence that failing to provide such tracts will result in a decidedly insecure future.

The location of breeding and wintering habitats of individual populations is unknown. Consequently, protection of breeding habitat for a particular population may afford no long-term security if its wintering ground is also not secure. Similarly, protection of a particular winter location may not afford security for the birds that winter there unless their breeding grounds are also secure. Establishment of a network of large preserves with extensive tracts of old forest, representing the breadth of both the breeding and wintering grounds, will most likely provide a potentially secure future.

Reserves are not necessarily incompatible with a variety of other low intensity land uses, including forest management, as long as the openings created by forest harvest activities are small. The definition of small is speculative, but probably is of the order of magnitude of a treefall gap rather than of an 8-ha clearcut patch. Thoughtful guidance for preserve design considerations is provided by Harris (1984) and Maser (1988).

A summary of recommendations for preserve design on the breeding grounds is (Hamel 1992): 1) Provide a network of large (at least 4,000 ha) compactly shaped reserves, each capable of providing habitat for 1,500 breeding pairs. 2) Distribute these reserves in such a way that they represent the breadth of the species' range in the middle Mississippi Valley, including particularly Ohio, Pennsylvania, West Virginia, Kentucky, Tennessee, Arkansas, Missouri, and Indiana. 3) Provide habitat in these and in other reserves such that compact, continuous, centrally located tracts of old forest are permitted to become established and persist on good soils in these and in other forest tracts.

On the wintering grounds, preserve design should include the following recommendations: 1) Establish a similar network of preserves in primary forest. Such preserves will also likely be of considerable size, a size as yet undeterminable. 2) Distribute the preserves so that they encompass the breadth of the winter range.

Management Requirements: The management potential for populations of this species is unknown. Populations in large tracts in good habitat are apparently stable, suggesting that factors responsible for the decline are not operating uniformly everywhere. The persistent increase in the known range, particularly in the Northeast, suggests that management potential is good (Hamel 1992). If the cerulean warbler is a management priority, then habitat management consists of restricting timber harvest, preventing chemical contamination, and maintaining natural hydrology. Reforestation and protection of young trees on large, lowland tracts should provide future habitat (Hands et al. 1989). Young hardwoods adjacent to mature stands should also be protected from harvesting to ensure the availability of future habitat. Possible protection techniques include conservation easements on, and purchases of, large forest tracts. Lowland hardwood forests can be protected through enforcement of existing wetland-protection regulations (Robbins et al. 1992).

The fact that many known populations are already restricted to public land indicates that public land managers at the state and federal levels are primarily responsible for the bird's future. The tract size proposed by Hands et al. (1989) of 1,730 ac (700 ha) is a minimal estimate. Different studies in different areas have uniformly indicated that forest fragmentation is a significant issue in the protection. That the minimal tract size has varied from region to region in the range indicates that the land use context in different regions has a strong bearing on the operation of the forest fragmentation phenomenon as it affects warblers (Hamel 1992).

Current major land management activities that can be carried out include: 1) the provision of large tracts of old forest, in rich situations rather than in marginal soil types, at several locations throughout the range, and 2) forest management activities that are sensitive to the fragmentation of existing tracts. Forest management that mimics the gap phase succession of eastern deciduous forests will more likely provide a continuous supply of habitat than will even-aged management in large blocks (Hamel 1992).

Management Research Needs: Few specific, quantitative data exist on the vegetation parameters associated with breeding and wintering habitats. Few quantitative data also exist on the population structure, demography, productivity, and habitat utilization. Research needs are thus a substantial portion of the management and monitoring recommendations outlined above. Hands et al. (1989) present a list of information needs indicating for each stage of the annual cycle and each life stage, whether information is lacking on the biology. Robbins et al. (1992) point out that because the species is a canopy dweller whose nests are difficult for humans to access, a life history study has not been done to produce summary values of biological traits. Such a study should be supported and it should include aspects of the monitoring and land management information needs outlined above, as well as traditional data on life history.

Cerulean warblers represent a kind of rarity that may become much more common in the future in North America: landscape-scale rarity on both the breeding and winter grounds. This warbler thus has considerable value as a model for the study of landscape scale change on the increase, decline, and redistribution of habitat and population. A number of studies have addressed various aspects of the fragmentation of forests. Study of this warbler in forest tracts under different landscape contexts, from primarily agricultural to primarily forested ones, will help elucidate the different features operative in the forest fragmentation effect, from the behavioral predisposition, through the operation of edge effects on prey populations, predator populations, populations of potential competitors, and the effects of nest parasitism.

Research on the behavior, biology, and control of brown-headed cowbirds will be an important part of the understanding of the distribution of breeding populations, and of many other host species as well. It is a reasonable hypothesis that the operation of forest fragmentation is a reflection of the penetration of cowbirds into tracts and the extinction of host populations resulting from the reduction of host reproduction below maintenance levels by such parasitism. Research on this topic will be a very useful benefit of study of cerulean warbler populations.

Regardless of monitoring, research, and management on the breeding grounds, the future will not be secure until clear understanding of the winter biology, population distribution, and habitat utilization of the species has been determined, and appropriate protection strategies developed and implemented. In this way, cerulean warblers are also a model species for the need for international cooperation in conservation (Hamel 1992).

Global Protection: Unknown whether any occurrences are appropriately protected and managed

In 2001, the Cerulean Warbler Technical Group (CWTG) was formed (5), and together with various partners, initiated a number of conservation measures for this threatened bird. This has included undertaking research projects on the cerulean warbler's biology and ecology, conducting surveys, and beginning dialogues with representatives of the forestry and mining industries regarding development of recommended practices for Cerulean warbler conservation (5). The CWTG has identified many more actions that are required to ensure the long-term survival of this species, outlined in a Conservation Action Plan, particularly the need to prevent the further loss of large areas of forest (5).

Unknown.

This species is surely important for the ecosystem services it provides, including insect control. It is of great interest to scientists as an indicator of overall ecosystem health of both eastern North American and tropical South American forests. Birders, interested in seeing this rare bird, provide tourist dollars to communities in which it occurs. Parks or wilderness areas created to protect the species' habitat would have residual economic benefits.

Stewardship Overview: Inhabits mature deciduous forests on both the breeding grounds in North America and the non-breeding range in the Andes. Breeding areas in the Northeast are often in floodplains or other mesic conditions and are typified by large, mature trees and closed or semi-open forest canopies. Nests are located on the lateral limbs of a tree at considerable distances from both the ground and the bole. Common vegetation characteristics of nest sites are unknown and use of openings and edge requires further study. Populations have declined across the range in the eastern U.S., although the range has expanded, particularly in the Northeast, perhaps in response to large-scale forest maturation. More detailed population information is needed to accurately determine trends, causal factors, and distribution at the landscape scale. Occupied forests should be surveyed specifically for the species as well as other neotropical migrants. Large tracts of mature forest (at least 4,000 ha) should be managed by regulating timber harvest and allowing immature stands to reach maturity.