Species-Specific Management (SSM)

Cerulean Warbler

The warbler,Dendroica cerulea, is a bird of the tall canopies of old forests throughout much of the Eastern half of the US.

There has been reported the gradual decline throughout their range of about 4% per year since 1966, a total decline of over 70%, of the warbler. It is likely that the forests of the permanent sampling points near roads are disappearing, but the bird numbers have conspicuously decreased during the survey. The apparent population decline represents the largest among any warbler species and among neotropical migratory birds.

There is now a Cerulean Warbler Atlas Project, in progress since 1997. Partners in Flight has ranked the Cerulean as an overall "high priority species" throughout most of its range. A recent Partners in Flight prioritization scheme gave the Cerulean an overall score of 25 out of 30, and identified the Cerulean to be in need of management and/or monitoring attention. This score was based on several measurable criteria including: Relative Abundance, Breeding Distribution, Winter Distribution, Threats to Breeding Range, Threats to Non-breeding Range and Population Trend. In the Southern Appalachians, once estimated to contain 51% of the breeding population of Ceruleans in the United States, Cerulean populations have declined by about 90% in the last three decades.

The Cerulean warbler is a neotropical migratory songbird that nests throughout the eastern United States. Its breeding range extends from the Mississippi River to the eastern coastal states and from the Gulf Coast states northward to southern Ontario. It breeds and nests in the southern Appalachian forest starting about late April. Cerulean warblers, like other songbirds, play an important and commercially-valuable ecological role through consuming insects, dispersing seeds, and pollinating flowers.

Cerulean warblers nest in the interior of contiguous forest tracts and need large areas of mature, undisturbed forest to reproduce successfully.The primary explanations for the Cerulean's decline are:

• the loss of old, dense-canopy hardwoods
• changing land use in floodplains and riparian areas (reduced forests)
• shortened timber rotations (larger areas in young-age forests)
• wide dispersal of remaining old-age forests due to logging, agriculture, and other human development,
• sampling errors (low and rapidly-changing old forests found among the permanent sampling sites Breeding Bird Survey (BBS))
• nest losses to cowbirds at forest edges
• the loss of the bird's winter habitat in the Andes to similar human activities.

Cerulean warblers are said to merit listing, protection, conservation, and recovery under the Endangered Species Act.

Biology

The Cerulean warbler is a member of the subfamily Parulinae, family Emberizidae (or simply family Parulidae, depending upon classification methodology) and order Passeriformes. Alexander Wilson originally described the Cerulean Warbler, now classified as Dendroica cerulea, in 1810 as two separate species: the female Sylvia rara Wilson and the male Sylvia cerulea Wilson. No subspecies have been described.

The warbler has a short tail and relatively long, pointed wings. Its striking plumage gives rise to its name, and along with its distinctive call, makes it one of the most noticeable of the warblers. The adult male has light blue-gray plumage above with streaked (black-gray with white) underparts and sides. The adult female is more subdued in color than the male, with the head and upper back a dull, blue-gray or bluish-green, becoming olive-green on the lower back.

It is a bird of the "deep woodlands", forest interiors or cores, expanses of mature bottomland hardwoods, "original southern Appalachian forests" and large (perhaps > 2000 ha) unfragmented forests. Males defend areas of about 1 hectare, thus dispersed populations require large areas.

In the southern Appalachians of Tennessee, Kentucky, and West Virginia, the core of its breeding range, the Cerulean occupies mature, upland, mesic forests. In the Northeast, the Cerulean may be found in mature deciduous forests on dry slopes and ridges or near stream bottoms, along lake and river shores, or on river islands. Robbins et al found the following to be significant predictors for the Cerulean:

forest area, square root of tree basal area, percentage ground cover

(There was a negative correlation with canopy cover by conifers. )

Likewise, a study in the Clinch Ranger District of the George Washington and Jefferson National Forests found the following important breeding habitat characteristics for the Cerulean:

1. stand age (mean age = 98.6 years; not an obligate - found in forests of 46 to 160 years)
2. overstory tree height (mean height = 97.8 feet or 30 meters)
3. overstory canopy closure and presence of canopy gaps (mean crown closure = 67.7%, 13 of 16 stands had gaps within 49 feet of nest tree)
4. understory tree height (mean height =39 feet or 12 meters)
5. number foliage layers (mean number of layers =2.4)
6. understory canopy closure (mean understory crown closure = 45.9%)
7. site index (mean = 83.5)
8. tree diameter class distribution (mean DBH = 13 inches)
9. understory vegetation (no evergreen in understory)

Ceruleans build their nests near the tops (77% height of tree) of the tallest trees or trees with the largest basal area available. The nest is usually about 30 to 60 feet above the ground. Cerulean nests also tend to be near small canopy openings, such as that created by the fall of a single tree. They nest in areas with an intermediate to closed subcanopy, a distinct shrub layer, or dense ground cover. They nest in a variety of tree species including black cherry, oaks, maples, elms and the American chestnut (older records). The combination of a nearly closed canopy, small canopy gaps and an understory indicate that the Cerulean needs vertical canopy diversity of the mature, uneven-aged forest.

In the fall, Cerulean warblers migrate through the southeastern United States, through central America to forested mountain slope winter habitat in the Andes Mountains of Venezuela, Columbia, Ecuador and Peru. This winter habitat consists of a relatively narrow elevation zone in the Andes, between 600 and 1300 meters above sea level. These areas are being denuded and replanted with coca plants for the illicit cocaine trade.

Management

The objective is likely to be stabilizing or increasing the population. To do so:

1. Improve monitoring including area proportional sampling and logistic regression analyses of probable bird presence using GIS and report findings
2. Favor old age forests (inventory and report lands unsuitable for logging, thus held and aging for the warbler)
3. Reduce cowbirds or their effects
4. Maintain canopy; increase height diversity
5. Reduce gap size or eliminate all but natural gaps (thereby reducing edge and cowbird nest parasitism threat)
6. Prevent insecticide uses over the forests
7. Reduce loss of riparian and flood-plain forests
8. Improve use of areas where the birds occur
9. Study "preservation of large unfragmented tracts >50,000 acres"
10. Improve and protect "staging areas" (including observations) in Texas, Louisiana, and Florida panhandle for the annual migration to South America
11. Work with programs to influence areas being used and management of South America wintering areas including ranging
12. Conduct educational tours and work to add the bird to citizens' life-lists.

Reference Notes

Neotropical birds

Butler, Amos W. 1884. The Cerulean Warbler. Ornithologist and Ovologist 9 : 27-8

Robinson, S.1997. The Case of the Missing Songbirds, Consequences: Vol. 3, No. 1,

Swanson, R.1998. Down But Not Out (Cerulean Warbler), in Birder's World, June

Robbins, C., Fitzpatrick, J., and Hamel, P., 1992. A Warbler In Trouble: Dendroica cerulea, in Hagen, et al., Ecology and Conservation of Neotropical Migrant Landbirds (Smithsonian Inst. Pr.);

Oliarnyk, C. and Robertson, R., 1996. Breeding Behavior and Reproductive Success of Cerulean Warblers in Southeastern Ontario, Wilson Bull. 108(4),

Simons, T., et al.1999, The Role of Indicator Species: Neotropical Migratory Songbirds, in Ecosystem Management for Sustainability,

Robbins, C., Sauer, J., and Peterjohn, B.1992, Population Trends and Management Opportunities for Neotropical Migrants,

Villard, M. and Maurer, B. 1996. Geostatistics As A Tool For Examining Hypothesized Declines In Migratory Songbirds. Ecology 77(1)

Buehler, D. and Nicholson, C. 1998. Ecology of the Cerulean Warbler in the Cumberland Mountains and the Southern Appalachian, at 1 (Annual Rpt.);

Franzreb, K. and Rosenburg, K.1997. Are Forest Songbirds Declining? Status Assessment From the Southern Appalachians and Northeastern Forests, in Trans. 62nd No. Am. Wildl. and Natur. Resour. Conf. .

Stine, P.1959, Changes in the Breeding Birds of Bird Haven Sanctuary Over a Period of Forty-five Years. Wilson Bulletin. 71: 372-380

Mayfield, H 1977., Brown-headed Cowbird: Agent of Extermination? American Birds. 31(2): 107-113

Robbins, C., Dawson, D., and Dowell, B.1989. Habitat Area Requirements of Breeding Forest Birds of the Middle Atlantic States, Wildlife Monograph 103

Askins, R., Philbrick, M. and Sugeno, D 1987. Relationship Between the Regional Abundance of Forest and the Composition of Forest Bird Communities, Biological Conservation Vol. 39

Connor, R. and Dickson, J.1997. Relationships Between Bird Communities and Forest Age, Structure, Species Composition and Fragmentation in the West Gulf Plain, Texas J. Sci. 49(3)

Penhollow, M. and Stauffer, D. 2000. Large-scale Habitat Relationships of Neotropical Migrant Birds in Virginia. J. of Wildlife Management. 64(2): 362-373

Martin, Thomas E. and Deborah M. Finch (eds.) (1995). Ecology and Management of Neotropical Migratory Birds. Oxford University Press, Oxford

Finch, D. 1991. Population Ecology, Habitat Requirements and Conservation of Neotropical Migratory Birds. USDA Forest Service. Rocky Mountain Forest and Range Experiment Station. Fort Collins, Colorado

Rodewald, P. and Smith, K. 1998. Short-Term Effects of Understory and Overstory Management on Breeding Birds in Arkansas Oak-Hickory Forests, Journal of Wildlife Management 62(4): 1411-1417

Wilcove, D.1984. Nest Predation In Forest Tracts and the Decline in Migratory Songbirds, Ecology 66(4)

USFS 1998. An Interim Management Strategy for Dendroica cerulea. Clinch Ranger District. George Washington and Jefferson National Forests. USDA-Forest Service

Robinson, S., et al.1995, Ecology and Behavior of Cowbirds and Their Impact on Host Populations, in Martin, T. et al., Ecology and Management of Neotropical Migratory Birds , Oxford: Oxford Univ. Press

Brittingham, M. and Temple, S. 1983., Have Cowbirds Caused Forest Songbirds To Decline?, Bioscience Vol. 33

Robinson, S., et al. 1995. Regional Forest Fragmentation and the Nesting Success of Migratory Birds, in Science 267:1987-1990

Submitted by Robert H. Giles, Jr., March, 8, 2001

A contribution from a project funded in part by US Forest Service, Dr. Mike Rauscher, the Southern Appalachian Forest Hypertext Encyclopedia project, 2002

This Web site is maintained by R. H. Giles, Jr.
Last revision July 10, 2002.