A nocturnal call of the black ibis (Pseudibis papillosa)

During the night of 12 May 2013, in Udaipur city (24°31'30"N 73°40'38"E), we heard a harsh sound that could not be associated with any animal. The following morning we observed a pair of black ibis (Pseudibis papillosa) with one juvenile on top of an Azadirachta indica (Meliaceae) tree which was the tallest among all nearby trees. The birds were on a platform-type nest made of small sticks. We heard the same call the following night. While tracking the direction of the sound in the moonlit night, we found that the black ibis was making such a call on the same tree. After two consecutive days of hearing the same strange call we decided to record it and see if the call would recur. We heard the same type of call for the next 13 days. Black ibis made this call between 24:00 h and 01:30 h each night. During these 13 days, we recorded all calls (of two birds) with the help of a Canon SX40 video camera and later conducted sound analysis to understand the structure of this unusual call. The video file was converted into WAVE audio file using Total Video Converter 3.02 software and analyzed with the help of Raven Pro 1.4 software.