summer bird
Refers to birds that are present in a region during the summer, often migratory species that breed in Japan during the warmer months.
Swallows are summer birds in Japan.
この森では夏鳥のさえずりが聞こえる。
In this forest, you can hear the songs of summer birds.
Compound of 夏 (natsu, 'summer') and 鳥 (tori, 'bird'), with rendaku voicing of とり to どり.