閑古鳥が鳴く(かんこどりがなく, kankodori.ga.naku) literarily means ‘a cuckoo sings’, where 閑古鳥 (かんこどり) means ‘cuckoo’ and 鳴(な)く means ‘(an animal) calls/makes a sound’. It is figuratively used when there is no one in a place that is supposed to be lively, such as a restaurant, hotel, and theme park; the empty shops/places are associated with a quiet forest where the desolate sound of a cuckoo resonates. This idiom is particularly used to indicate that a business is not doing well. Because of COVID-19, now ‘cuckoos are singing’ almost everywhere around the globe.
‘A cuckoo is always singing’ in that restaurant. ( = the restaurant is always empty/not doing well)
Because of the effect of the coronavirus, ‘a cuckoo is singing’ in tourist spots. ( = there is no one in tourists spots)
Synonyms: 空（す）いている empty, not crowded, 閑散(かんさん)とした (empty and quite)、ガラガラ (empty and quite)
Synonyms in English: empty, quite, desolate
Related Words and Phrases: 閑古鳥(かんこどり) cuckoo (*「カッコウ」 is a much more common word for ‘cuckoo’), 鳴(な)く‘(an animal) calls/makes a sound’