Circumstances: On Thursday, 28 Nov. 2002, Andrew Block found a Dendroica warbler tentatively identified as a Hermit Warbler (D. occidentalis) near the Boardwalk Restaurant at Jones Beach State Park, Nassau County, New York. Although cautious about the identification, he quickly posted news on the internet and returned the following day accompanied by a number of local birders. The bird was still present and the identification more firmly established. Excellent digiscoped pictures were posted by Seth Ausubel <http://home.nyc.rr.com/sausubel/page2.html> that night and Shai Mitra posted a commentary on the identification, focusing on the important problem of distinguishing a 'pure-blooded' Hermit Warbler from a Hermit x Townsend's hybrid - more on this topic below. Either way, this is a special bird for the state and was certain to trigger a reasonable-sized twitch.
On the morning of Saturday 30 Nov.2002, I joined thirty or so birders in the restaurant parking lot and we watched the warbler for an hour or two. It fed actively in some small junipers to the east of the restaurant as well as in the chrysanthemum plantings. For some of this time it associated loosely with a Ruby-crowned Kinglet and a Palm Warbler. I was able to take some photographs and several other birders took video. Although the mood was upbeat, most birders were open to the possibility of a hybrid and willing to await expert commentary on photographs.
Note on photography: The following photographs were taken with a Canon 400mm/F5.6 lens and EOS D-60 body. Digital film sensitivity was set to ISO 800 equivalent to cope with the dull conditions. Images were cropped in Photoshop 5.0 and sharpened slightly.
Figure 1. The 'Hermit Warbler' perches momentarily on a stone wall bordering the chrysanthemum plantings. The yellowish head, prominent white wing bar and greenish back suggest a first basic female Black-throated Green Warbler, however, the yellow is brighter and more extensive. In addition, BTGW of any age would show a yellow wash on the vent.
Figure 2. Portrait view showing the bright yellow head, silvery white underparts and prominent wing bars. The flanks are only weakly streaked, strongest at the top of the wing. The upper breast shows a subtle yellow wash. The auriculars (cheek) and lores are slightly greener than the borders of the face, but nowhere near as strong as a typical Townsend's Warbler.
Figure 3. View from of the back showing the gray-green (olive?) mantle and broad black streaks.
Figure 4. Another back view showing details of the remiges and rectrices.
Figure 5. Head on view showing the incomplete black bib and faint yellow wash below it. The yellow extends above the eyes, fading to yellow-olive on the crown. Neat dark flecks extend along the crown and merge with the darker nape. Several commentators have zeroed in on this feature as evidence of hybridization.
Figure 6. Higher zoom of the image shown in Fig. 1. The upper wing bar formed by the median coverts is brilliant white and more striking than the lower wing bar (greater wing coverts).
Figure 7. View of nape and mantle. Narrow streaks are visible on the white lower flanks. There is no evidence of yellow on the flanks or vent.
Not shown here, the bird had prominent white outer rectrices (tail feathers).
Identification - Hermit Warbler or Hermit x Townsend's (Heto) Warbler?
Black-throated Green Warbler (D. virens), Golden-cheeked Warbler (D. chrysoparia), Townsend's Warbler (D. townsendi) and Hermit Warbler (D. occidentalis) are closely related taxa and together form a superspecies (Curson et al.'s 'Black-throated, yellow-faced Denroica' group). In Washington (Cascade Mountains) and Oregon, Hermit Warblers hybridize regularly with Townsend's Warbler (Jewett 1944; Morrison and Hardy 1983; Dunn and Garrett 1997; Rohwer and Wood 1998). Such hybrids are sometimes referred to as 'Heto Warblers' (Eckert 2001). There is at least one example of vagrancy by hybrids into eastern North America, a bird that reached Newfoundland (Mactavish 1996).
A detailed study of birds from hybrid zones by Sievert Rohwer and Chris Wood (1998) indicates a high degree of individual variation, presumably reflecting different degrees backcrossing. Parameters they followed include:
(1) Extent of gray color
tone to the back.
(2) Extent and intensity of yellow coloration below black bib patch.
(3) Extent and location of black streaking on its mid-flanks.
(4) Extent and location of black streaking on its lower-flanks.
(5) Details of bib corners.
(6) Yellow on crown.
Unfortunately published photographs and field studies dwell on adults in breeding plumage, particularly males that are responding to tapes or mounted specimens (e.g. the superb collection of photos in Eckert 2001).
Curson, J., Quinn, D. and Beadle, D. (1994) Warblers of the Americas. Houghton Mifflin Co., Boston.
Dunn, J. L. and Garrett, K. L. (1997) A Field Guide to Warblers of North America. Houghton Mifflin Co., Boston.
Eckert, T. (2001) A HETO Warbler showcase: Hermit/Townsend's Warbler hybrids. Birding 33(4): 342-350.
Jackson, W. M., Wood, C. S. and Rohwer, S. (1992) Age-specific plumage characters and annual molt schedules of Hermit Warblers and Townsend's Warblers. Condor 94: 490-501.
Jaramillo, A. (1995) Townsend's and Hermit Warblers in eastern Canada. Birders Journal 4: 232-236.
Jewett, S. G. (1944) Hybridization of Hermit and Townsend's Warblers. Condor 46: 23-4.
Mactavish, B. (1996) Hybrid Hermit x Townsend's Warbler in Newfoundland. Birders Journal 5: 33-34.
Morrison, M. L. and Hardy, J. W. (1983) Hybridization between Hermit and Townsend's Warblers. Murrelet 64: 65-72.
Rohwer, S. and Wood, C. (1998) Three hybrid zones between Hermit and Townsend Warblers in Washington and Oregon. Auk 115: 284-310.
Many thanks to Andrew Block for first discovering the bird and spreading the news in a timely fashion. Seth Ausubel, Ned Brinkley, Tom Burke, David Fix, Julian Hough, Paul Lehman, Kevin McGowan, Todd McGrath, Hugh McGuinness, Shai Mitra, Steve Mlodinow, Evan Obercian, Gerard Phillips, Peter Pyle, Sievert Rohwer, Andrew Spencer and Rex Stanford provided useful comments, photographs and/or information.