Wednesday, October 21, 2009
Hey, Mr. Warbler Guy: Is a Yellow-Breasted Chat truly a wood-warbler? C’mon, they don’t look like one, act like one, or sound like one.
Answer: Good question, Rob, in Cordelia, CA.
At seven inches from bill tip to tail tip, the Yellow-Breasted Chat (YBCH) is EASILY our largest North American wood-warbler family member. All the other warblers in our area range from 4.25 to 5.5 inches in length. Equally vexing, unlike YBCH, most other wood-warblers have an insect-catching small bill. Consequently, seeing a YBCH’s oversized one — it looks more like a tanager’s in shape and size — leaves you scratching your head.
So does hearing its Northern Mockingbird/Brown Thrasher-like song. Even the YBCH’s skulking, secretive behavior is somewhat strange for a wood-warbler, given many (especially among the 27 Dendroica genus members in North America north of Mexico) are extroverts in fast-forward mode during the breeding season while displaying “hover and glean” foraging behavior in search of insects amidst the tips of branches.
So why is a YBCH considered a wood-warbler? Primarily because researchers use more than birds’ songs, their behavior, their skeletal structure, and their general appearance to define a species (as well as the genera, families and orders of birds that constitute the 9,800 or so species in the world). They also employ blood analysis (i.e., DNA/DNA hybridization techniques) techniques. All of these aforementioned distinguishing techniques form the “Phylogenetic Species Concept” that is broadly accepted by most taxonomical scientists (but only SOME biologists) as an accurate way to determine a species.
Of course, molecular analysis of blood is a somewhat recent development technique for distinguishing birds at the species level. Hearken to pre-DNA analysis, and you stumble upon the studies of one E. Eisenmann. In1962, he called into question the then generally accepted placement of the YBCH in the wood-warblers by pointing out how it is missing jaw muscle, thereby suggesting an affinity with tanagers (Thraupidae family). Eisenmann also argued that the YBCH’s hyoid apparatus (a specialized system of bones and muscles within the avian tongue) differs from that of design present in many songbirds. No matter. Eisenmann lost his tug of war with other experts. Various conscientious objectors in the birding community have similarly raised their voice (and ire) to question the inclusion of YBCH in the wood-warbler family.
Adding fuel to the debate is the American Ornithological Union's checklist of birds where an you an asterisk appears after YBCH's name, denoting that this species is "probably misplaced in the current phylogenetic listing, but data indicating proper placement are not yet available" (see http://www.aou.org/checklist/north/full.php).
Nonetheless, YBCH holds tight. It officially remains a wood-warbler.