Bispectral index reveals death-feigning behavior in a red kite

Abstract

Red kites (Milvus milvus) are raptors known to feign death in the presence of humans. An adult wild red kite (Milvus milvus), ASA II, underwent coelioscopy. Butorphanol was administered before induction of anesthesia which was maintained with 1.5% isoflurane in oxygen. Intraoperatively, heart rate and respiratory rate ranged from 240 to 260 bpm and from 16 to 28 brpm, respectively. Pupil and corneal reflexes were always present. Body temperature was maintained at 40.4°C. Suppression ratio was 0 during the whole anesthesia. Bispectral index was 44 immediately after intubation, ranged from 44 to 57 during maintenance of anesthesia and at the moment of extubation it was 59. The index rose up to 85 within a minute while the kite remained immobile under the suspicion of feigning death in sternal recumbence. The bird was perched keeping immediately the upright position. This fact confirmed the correspondence of the BIS value (85) with a fully conscious patient. Whereas behavioral or cardio-respiratory variables remained unchanged, the degree of hypnosis was uncovered by BIS, which anticipated a possible sudden awakening episode of the kite.