The use of hyphens in the spelling of compound bird names is a contentious issue among ornithologists.  More broadly, grammarians now view past enthusiasms for  hyphens as excessive and unnecessary — see Death-Knell. Or Death Knell by Charles McGrath.

On hyphens and phylogeny  provides some historical perspective and the IOC position regarding the following rules for the use and spelling of two-word compound English names of birds:

• Two words should be used to spell all names not falling within the rules for single-word names.
• A hyphen should not be used as a general rule, and both words should begin with capital letters (e.g., Black Tyrant, Screech Owl, Green Pigeon, Storm Petrel, Wood Partridge). This rule is contrary to the broadly used names of Sibley and Monroe (1990) and currently of the AOU. We attempted to use hyphens to denote group names, despite reservations of several committees, but finally rejected the practice for two primary reasons:
  • In standard English, hyphens should not be used to link a noun with an adjective that modifies it to create a new noun. Rather, compound nouns are formed (Yellowstone) or the two words remain separate but are used as one (French Poodle).
  • The goal of creating group names by adding hyphens is intrinsically unstable, confusing, and impractical. It requires that we add a hyphen when one species, such as Warbling Vireo, is split into a group of two species (Eastern Warbling-Vireo and Western Warbling-Vireo), and that we remove the hyphen when two such species are lumped. Hyphens then must be added or subtracted in concert with changes in species taxonomy, which only a small group of specialists will be able to track in something approaching real time.
• Where both nouns are the names of birds or bird families a hyphen should be inserted to signify that the taxon belongs to the family of the second word, not the first (e.g., Eagle-Owl, Nightingale-Thrush). This conforms to correct English use of hyphens.
• If a name is of a taxon that is not a member of the stated bird family, the letter after the hyphen should be lowercase to clarify that status (e.g., Flycatcher-shrike). This is a companion to the rule, described above,  that hyphenates single-word names to avoid confusion, as in Silky-flycatcher or Stone-curlew.