Police are appealing for witnesses to a "sickening" attack in the Brisbane CBD where an ibis was strangled to death and used to threaten passers-by on Saturday morning.

Detectives said a man captured and killed the bird about 5.30am on George Street before approaching members of the public as they walked past and threatening them with the dead bird.

Ibis are a common sight around South Bank and the Brisbane CBD. Credit:Bradley Kanaris

Police attended and spoke to a man at the scene but are appealing for anyone who witnessed the incident or may have footage to contact them.

RSPCA Queensland spokesman Michael Beatty said after hearing the news "you just shake your head".