van den Hout P.J. (2006) Dense foraging flotillas of Eurasian Coots Fulica atra explained by predation by Ganges Soft-shell Turtle Aspideretus gangeticus. ARDEA 94 (2): 271-274

Overwintering Coots Fulica atra atra were observed in January 2006, in Keoladeo National Park, India. Here they fed on aquatic plants, which they exploited in strictly-maintained dense flotillas; these flocks behaved like a super-organism. This observation adds to a description of Ali & Ripley (1969), who do not explicitly discuss the cause of raft formation by Coots, but only mention the occurrence of Coot predation by Greater Spotted Eagle Aquila clanga. Having observed a Coot being drowned by a Ganges Soft-shell Turtle Aspideretus gangeticus, I suggest that predation risk by these turtles should be taken into account as a possible cause for this herding behaviour. When on the water, Coot flocks now and then suddenly scattered; this suggested disturbance by a hidden aquatic predator, all the more because no raptor attacks were witnessed on these occasions. Coots visited the water exclusively for foraging, and, in contrast to their usual behaviour, roosted on islands. This indicates that they considered the water as a dangerous environment, despite the fact that on land the risk of predation by eagles may be greater. My observations suggest that, by foraging in very dense groups, Coots and other waterbirds exploited the rich food resources in Keoladeo whilst minimising the risk of predation