The 5-letter word for a wading bird that ends with "SAC" is "EGRIS." Egrets are members of the heron family and are known for their long legs and necks, making them excellent waders.
grebe
Ibis?
If the s here indicates a plural, then rails are wading birds that have a 5-letter name ending in s. (The word rail is obviously a 4-letter word.)
avocet
heron
avocet
Rail.
avocet
ibis
Bittern, Limpkin.
Avocet
Avocet