Hooded Warbler
Ecoregional Scale Conservation Planning

Made possible through a partnership with the National Wetlands Research Center

Blue-winged Warbler (Vermivora pinus)

The blue-winged warbler is a Neotropical migrant found from southern New England west to the Lake States and south through the southern Appalachians and Ozarks. Across most of its range, blue-winged warbler numbers have been stable and have even increased in some areas (possibly to the detriment of the golden-winged warbler with which it sometimes interbreeds; Gill 1980). Once limited to a mostly Midwestern range, this species expanded its range into southern New England as forests were cleared and farms abandoned. As the forest has matured in this region, though, the species has experienced declines (3.3 and 5.3 percent annually from 1966–2004 in the increasingly residential Connecticut and New Jersey, respectively). A similar phenomenon has occurred in the Southeast and BBS data indicate a 3.7 percent decline in USFWS Region 4 during this same time period (Sauer and others 2005). The species is designated a Bird of Conservation Concern in the CH but not in the WGCP Table 001 (Table 001) , where it rarely breeds. The species has a regional combined score of 19 in the CH and is a bird requiring management attention in the region Table 001 (Table 001) .

Relative abundance of Blue-winged Warbler, derived from Breeding Bird Survey data, 1994 - 2003.
image courtesy of www.whatbird.com

Natural History:

The blue-winged warbler is an early successional species (Gill and others 2001) that benefited from European settlement by expanding its range following the initial clearing of forests for agriculture and the subsequent abandonment of farms. Breeding habitat includes early- to mid-successional forest containing dense low growth (e.g., shrubs, young trees, thickets). The species utilizes a variety of landform conditions from wetland edges to dry uplands; however, mated males have more xeric territories than unmated males. Territories range from 0.2-5 ha, with boundaries often aligned along edges. Nests are typically within 30 m of a forest edge in grassy areas with high numbers of small (<10 cm d.b.h.) trees. Blue-winged warbler density is inversely related to successional age class, fragmentation, and the abundance of golden-winged warblers and brown-headed cowbirds.

Model Description:

The blue-winged warbler model contains five parameters:

  • landform
  • landcover
  • successional age class
  • forest patch size
  • canopy cover

The first suitability function combines landform, landcover, and successional age class into a single matrix (SI1) to define unique combinations of these classes Table 037 (Table 037) . We directly assigned suitability index scores to these combinations based on habitat associations reported in Hamel (1992) for blue-winged warblers. We modified Hamel’s data to maximize suitability index scores in the transitional-shrubland landcover class in the xeric landform.

We also included early successional forest patch size (SI2) in our model based on data from Rodewald and Vitz (2005) on the relative abundance of blue-winged warblers in small and large clearcuts Table 038 (Table 038; Figure 018 Figure 018) . We defined early successional forest by age class and included only grass-forb, shrub-seedling, and sapling age classes in the patch size calculations.

We used an inverse logistic function Figure 019 (Figure 019) to quantify the relationship between canopy cover (SI3) and suitability index scores to reflect the lower densities of blue-winged warblers in forests with increasingly closed canopies. We defined this function by fitting a curve to data from Annand and Thompson (1997) on the relative density of blue-winged warblers in forest stands with different canopy cover estimates Table 039 (Table 039) .

To calculate the overall suitability index score for blue-winged warblers, we determined the geometric mean of SI scores for forest structure attributes (SI1 and SI3) and then calculated the geometric mean of this value and early successional patch size (SI2).

Overall SI = ((SI1 * SI3)0.500 * SI2)0.500