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Co-operative feeding by Black Egrets, Little Egrets and African Spoonbills in Ndumo Game Reserve, South Africa

At about 12h00 on 15 December 2003, while driving in Ndumo Game Reserve, I saw a large number of birds moving around in the shallows in the north-eastern end of Nyamithi pan. I moved closer and observed the birds for some time with binoculars from a distance of about 100m. There were several hundred birds, principally White-faced Duck Dendrocygna viduata and many waders including Black-winged Stilts Himantopus himantopus, avocets Recurvirostra avosetta and plovers Charadrius spp. wading in the shallow water. One discrete but multispecies group caught my attention, as they appeared to be moving as a cohesive and co-ordinated unit. The group consisted of 27 Black Egrets Egretta ardesiaca, 126 Little Egrets Egretta garzetta and 13 African Spoonbills Platalea alba. The birds were closely grouped and alternately walking and feeding together. The ‘vanguard’ and ‘tail’ consisted of Little Egrets, with groups of Black Egrets and African Spoonbills occupying the central part of the group. The water was shallow (c. 15cm) but fairly clear and the birds left a trail of muddy water indicating their path. There was active feeding by all three species intermittently throughout the group and occasionally small fish could be seen jumping out of the water around the periphery of the group of birds. The birds remained together for at least 15min, when observations ceased. The Little Egrets fed and moved throughout the group but most active feeding took place towards the front and around the periphery. The Black Egrets, using their typical ‘umbrella’ fishing method, mostly fed simultaneously in fairly loose groups in the clearer water around the margins of the group. The African Spoonbills mainly fed in the muddy water to the middle and rear of the party using sideways slashing movements with their bills. From the observations it appeared that each species was benefitting from the communal activity. The Little Egrets were principally catching fish in the clearer waters in front of the group as they escaped disturbance. The African Spoonbills were feeding in the relatively turbid waters created by the mass activity, while the Black Egrets, using their wing-shading technique, offered apparent sanctuary to fish escaping the group of birds. Black Egrets are occasional but erratic visitors in small numbers to Ndumo Game Reserve (Taylor et al. 1999). This aggregation of Black Egrets was thus noteworthy in terms of numbers alone. Black Egrets sometimes feed communally, occasionally in large groups (Brown et al. 1982, Del Hoyo et al. 1992) and have been reported feeding with Little Egrets (Del Hoyo et al. 1992). Little Egrets typically are solitary (Brown et al. 1982, Del Hoyo et al. 1992, Maclean 1993) though have been reported feeding with other species (Fraser 1974, Brown et al. 1982). African Spoonbills, which generally use tactile cues to detect prey, often feed in groups (Brown et al. 1982, Del Hoyo et al. 1992, Maclean 1993, Newman 1983, Sinclair et al. 1997) but there weren’t any reports of such extensive and co-ordinated co-operative feeding between these different species in any of the references mentioned above. The months before the sighting had been particularly dry and many of the Pongolo floodplain pans, which normally contain water at this time of year, were empty. By December Nyamithi pan is usually fairly full and the extensive mudflats at the north-eastern end of the pan are usually covered with water. Waterbird numbers (based on routine Coordinated Waterbird Counts) are usually low during such conditions (Taylor et al. 1999). Good rains fell shortly after the sighting and many of the waterbirds subsequently dispersed. Prior to 2003 a road embankment just downstream of Nyamithi pan had acted as a partial barrage, maintaining the pan at a fairly high level throughout the year. Early in 2003 a weir through the road crossing, which had become clogged with debris, was cleared and the pan was able to drain more rapidly. The rapid draining of the pan led to the more rapid development of mudflats suitable for the feeding behavior of the species seen. This management action possibly facilitated increased numbers of waders in the pan and also the activity reported in this note.