Scientific Name: Dendroica cerulea
Nest Type: Cup
Nest Location: Deciduous trees; 30-60'
Clutch Size: 3-5; avg. 4
Food: Insects
Foraging Guild: Foliage gleaner, hawks
The Cerulean Warbler is a locally common breeding bird in the mature deciduous forests of eastern North America. Its range extends from Minnesota south to
northeastern Texas, east to northern Alabama, and north to southern Ontario. It also breeds east of the Appalachian Mountains in central Virginia, Maryland and
eastern Pennsylvania (Peterson 1980). In Minnesota, the species is confined to the southeastern portion of the state primarily along the Mississippi, Minnesota, and
St. Croix River Valleys. It has been reported as far north as Mahnomen County and as far west as Brown County (Janssen 1987).
The Cerulean Warbler is a long distance migrant, wintering from Venezuela and Columbia south to eastern Peru and northern Bolivia (Ehrlich et al. 1988). It
generally arrives on its breeding grounds in Minnesota during early May and leaves for the tropics again by late August (Janssen 1987).
The preferred habitat of the Cerulean Warbler is mature, deciduous floodplain forests (Graber et al. 1983, Brewer et al 1991). In Missouri, (Kahl et al. 1985) found
Cerulean Warblers on moist, wooded slopes and stream valleys in uplands as well as in bottomland hardwood forests. In this study, vegetation samples at 77 song
perches were characteristic of mature forest with a high, dense canopy and well-developed but not dense subcanopy and shrub layers. Moisture gradient was not
significantly correlated with abundance of Cerulean Warblers (Kahl et al. 1985). Bond (1957) also recorded Cerulean Warblers on upland sites in southern
Wisconsin, and stated that this species should not be considered "a strictly bottomland bird." However, Bond (1957) found the Cerulean Warbler "strikingly more
common with increasing mesic conditions." It was present on xeric sample plots only if the forest tract was larger than 40 ac (16 ha) (Bond 1957). In southern
Illinois, populations of Cerulean Warblers in upland forests were about half as dense as those in bottomland forests (Graber et al. 1983). Based on these data, the
Cerulean Warbler is classified as dependent on mature, hardwood forest types.
The Cerulean Warbler forages and nests in the upper canopy of the tallest trees. The nest is placed on a horizontal limb often as high as 20 m (60 ft) above the
ground (Harrison 1975, Roberts 1932). Little is known of its specific diet, but it is presumed to be largely or entirely insectivorous (Ehrlich et al. 1988).
The Cerulean Warbler is fairly common within its preferred habitat and is thought to be expanding its range in the south and northeast (Ehrlich et al. 1988). It is
sensitive, however, to fragmentation of its breeding habitat, and the extent of mature deciduous forest may be a major determinant for the Cerulean Warbler in
Minnesota. Several studies provide evidence suggesting that the Cerulean Warbler is an area-sensitive species. Bond (1957) found these warblers much more
common in medium (40-80 ac) and large (>80 ac) forest tracts in southern Wisconsin than in small tracts (<40 ac). In east-central Illinois, Blake and Karr (1984)
did not detect Cerulean Warblers on study plots of less than 65 ha (160 ac). Research by Robbins et al. (1989) in the middle-Atlantic states suggests that this
species is rarely found in forest tracts of less than 138 ha (340 ac) and tracts of greater than 3000 ha (7400 ac) may be necessary to insure its continued presence.
Data collected in the USFWS Breeding Bird Survey indicate that although the Cerulean Warbler apparently increased in Wisconsin, overall, it decreased by 3.1%
per year in the north central US from 1966 to 1987 (Hands et al. 1989). Sauer and Droege (1992) recently reported a decrease of about 4 % in the eastern United
States for data gathered through 1988. No trend data are available for the species in Minnesota because it was too infrequently observed on roadside counts
(Janssen 1990, Collins et al. 1992). The Minnesota Department of Natural Resources has listed it as a species of special concern.
Graber et al. (1983) attributed the apparent decline of this species in Illinois to a loss of bottomland forest habitat. Due to its sensitivity to fragmentation, the
Cerulean Warbler is classified as a forest interior species. Overall, the best documentation of this area sensitivity and the issues associated with the species are
described by Robbins et al. (1992).