Riddle me this: IOC lists "buttonquail". Then, it proceeds to list "stone-curlew". Why would stone-curlew not be stonecurlew, if buttonquail is without a hyphen?
From the IOC Website (
http://www.worldbirdnames.org/english-names/spelling-rules/compound-names/):
Compound single words are used...
"IF the second word is a kind of bird (e.g., Nighthawk, Bushtit, Waterthrush, Meadowlark), but the taxon is not a member of the bird family named.
For example, a Meadowlark is not a Lark; a Cuckooshrike is not a Shrike. Thus the name should not be spelled as two words without a hyphen (e.g., Meadow Lark), or spelled with a hyphen followed by a capital letter (e.g., Cuckoo-Shrike). Rather, a single word is used except where it would be hard to pronounce or look odd (e.g., Silky-flycatcher,
Stone-curlew, Flycatcher-shrike). Conversely, if the second word is a type of bird and the taxon is deemed to be a member of that bird family, the name would be spelled with two words, either without a hyphen or with a hyphen followed by a capital letter (e.g., Bush Lark, Eagle-Owl). Converting these to single words states, in effect, that the taxon is not in that family but is rather something different. Exceptions have been made in a few cases where long and widespread usage dictates a single word, such as Goldfinch, Skylark, Woodlark, and Sparrowhawk. These and other cases are under review for potential revision."