Hooded Warbler
Ecoregional Scale Conservation Planning
spacer
 
   


Made possible through a partnership with the National Wetlands Research Center


Yellow-throated Warbler (Dendroica dominica)
Status:
The yellow-throated warbler is a Neotropical migrant that breeds in the southeastern United States and reaches its highest densities in the Ohio River Valley. The species declined slightly (but insignificantly) in the WGCP over the past 40 years but has increased considerably in the CH (3.8 percent per year since 1967; Table 005 Table 005) . The yellow-throated warbler is not a Bird of Conservation Concern in either BCR but is a planning and responsibility species in the CH (regional combined score = 15; Table 001 Table 001) .
ytwa
Relative abundance of Yellow-throated Warbler, derived from Breeding Bird Survey data, 1994 - 2003.
 
image courtesy of www.whatbird.com
 

Natural History:
The yellow-throated warbler breeds in two distinct habitat types: mature bottomland hardwoods forest and dry, upland oak-pine forest (Hall 1996). The species is more common in the former. Birds exhibit a strong affinity for cypress along the Coastal Plains, but along inland rivers prefer sycamores (Hall 1996, Gabbe and others 2002). Where Spanish moss is found, it is used for both foraging and nesting (Hall 1996). Elsewhere, the warbler forages by creeping along limbs and probing leaf clusters and pinecones. The yellow-throated warbler as both an interior and edge species and may occur in woodlots as small as 6 ha (Blake and Karr 1987). Robbins and others (1989) associated this species with large (>38 cm d.b.h.) tree density, forest in a 2-km buffer, and coniferous canopy cover.

Model Description:

Our model of yellow-throated warbler habitat suitability contains six factors:

  • landform
  • landcover
  • successional age class
  • large (>50 cm d.b.h.) tree density
  • distance to water
  • percent forest in the landscape (1-km radius)

The first suitability function combines landform, landcover, and successional age class into a single matrix (SI1) that defines unique combinations of these classes Table 165 (Table 165) . We directly assigned suitability index scores to these combinations based on habitat association outlined in Hamel (1992) for yellow-throated warblers in the Southeast.

We also incorporated large tree density (SI2) into our model of yellow-throated warbler habitat suitability because of the affinity of this species for nesting and foraging in large trees (Hamel 1992, Robbins and others 1989). Lacking data points from the literature to fit a curve, we assumed habitat suitability scores were logistically related to large tree density up to 50 trees/ha and remained optimal above this threshold (suitability index score = 1.000; Figure 100 Figure 100 ; Table 166 Table 166) .

Yellow-throated warblers nest near water (Hall 1996, Hamel 1992). Thus, we included distance to water (SI3) in the habitat suitability model. We assumed sites closer to water had a higher suitability. Lacking quantitative data on the potential effect of water on habitat suitability, we assumed the yellow-throated warbler had a territory size similar to the Acadian flycatcher but not as dependent on water as this species. Therefore, we assumed all sites <120 m from water to be optimal (suitability index score = 1.000), and we allowed habitat suitability index scores to decline more slowly for the yellow-throated warbler than the Acadian flycatcher Figure 101 (Figure 101 ; Table 167 Table 167) .

Yellow-throated warblers respond to the percent of forest in the landscape (SI4). Thus we fit a logistic function Figure 102 (Figure 102) to a dataset based on the assumptions that landscapes with <30 percent forest were poor habitat (suitability index score ≤ 0.100) and landscapes with >70 percent forest were excellent habitat (suitability index score ≥ 0.900; Table 168 Table 168 ).

To calculate the overall suitability index score, we determined the geometric mean of suitability index scores for forest structure (SI1 and SI2) and landscape composition attributes (SI3 and SI4) separately and then the geometric mean of these means together.

Overall SI = ((SI1 * SI2)0.500 * (SI3 * SI4)0.500)0.500

spacer