Hi Trinko,
Assuming you always have three birds per list
birdData =
{{"bird", 0.95, "sparrow", 0.8, "flying bird", 0.9},
{"duck", 0.95, "flying bird", 0.8, "goose", 0.9},
{"duck", 0.95, "flying bird", 0.8, "swan", 0.9}};
birdData[[All, {1, 3, 5}]] // Flatten // DeleteDuplicates
(* {"bird", "sparrow", "flying bird", "duck", "goose", "swan"} *)
birdData[[All, {1, 3, 5}]] // Flatten // Counts
(* <|"bird" -> 1, "sparrow" -> 1, "flying bird" -> 3, "duck" -> 2, "goose" -> 1, "swan" -> 1|> *)
If there are a varying number of birds per list the part specification needs to pick every odd element e.g.
birdData[[All, 1 ;; -1 ;; 2]]