flycatcher vs whistler

flycatcher and whistler both are nouns.

Word	Noun	Adjective	Verb	Adverb
flycatcher	Yes	No	No	No
whistler	Yes	No	No	No

As nouns, whistler is a hyponym of flycatcher; that is, whistler is a word with a more specific, narrower meaning than flycatcher:

flycatcher: any of a large group of small songbirds that feed on insects taken on the wing
whistler: Australian and southeastern Asian birds with a melodious whistling call

Other hyponyms of flycatcher include Muscicapa grisola, Muscicapa striata, spotted flycatcher, thickhead.

flycatcher (noun)	whistler (noun)
any of a large group of small songbirds that feed on insects taken on the wing	Australian and southeastern Asian birds with a melodious whistling call
large American birds that characteristically catch insects on the wing	large-headed swift-flying diving duck of Arctic regions
	large North American mountain marmot
	someone who makes a loud high sound