Preferences for Different Types of Offal by Black Kites Milvus migrans from Urban Garbage Dumps of Kolkata, India

Abstract

Facultative scavengers often forage on organic wastes from urban dumps. Despite being a major scavenging raptor in many urban areas, studies on Indian subspecies of Black Kites Milvus migrans govinda are very few. We studied the pattern of offal preference by Black Kites foraging in the dumping sites adjoining two major markets of Kolkata, India through cafeteria experiments, where successful foraging events and abundance of foraging Black Kites were recorded. We also carried out questionnaire surveys among 156 meat and fish sellers of 32 markets of this area to assess their offal disposal practice and understand their attitude towards Black Kites. During questionnaire surveys majority of the respondents (77.92%), indicated that Black Kites consume various kinds of offal, particularly chicken offal from garbage dumps of Kolkata. 51.92% respondents opined that Black Kite population has declined in Kolkata, and 41.03% of them believe such decline is due to food scarcity. Still many respondents (64.74%) sell their offal, which reflect their indifferent attitude towards this scavenging raptor. During ‘cafeteria experiments, we noticed that foraging kites pick up small pieces of offal from the garbage dumps, particularly chicken, mutton and fish offal (in 15.45 ± 7.749, 9.7 ± 4.542 and 9.95 ± 4.951 successful foraging events/h respectively). Energy content (cal/g) of sun-dried samples of each type of offal substances revealed that the energy (calorie) of swine offal was highest followed by beef offal, mutton offal, chicken offal and fish offal. In spite of being energetically rich, beef and swine offal were less selected by Black Kites possibly because they are visibly larger than other offal, thus requires greater handling time and invites higher risk of kleptoparasitism. Successful foraging events were significantly influenced by offal type, but not by months, study sites or by the relative abundance of foraging Black Kites.