WATER DEPTH SELECTION, DAILY FEEDING ROUTINES AND DIETS OF WATERBIRDSIN COASTAL LAGOONS IN GHANA

Water depth requirements, diet, feeding styles and diurnal activity pa tterns are described for waterbirds using two brackish water lagoon sy stems in coastal Ghana, the Songor and Keta Lagoons, We project the ha bitat and activity data on a guild structure defined on the basis of i ndividual feeding style and the sensory mechanism used to detect food, A total of 3199 flocks containing 118,648 individuals of 36 different waterbird species were examined during October-November 1994. Feeding habitats varied from dry mudflats to wet mud and shallow water of not more than 20 cm, The depth of water selected by waterbirds for foragi ng (but not for roosting) was correlated with tarsus length, Foraging birds exhibited a wide range of feeding styles using visual and/or tac tile means for detecting prey: pecking, probing, stabbing, sweeping an d ploughing, sometimes feeding singly, communally or socially in loose or dense flocks, Prey items taken ranged from seeds of Widgeongrass R uppia maritima to invertebrates (mainly polychaetes, molluscs and crab s) and fish, mainly juvenile Tilapia. The daytime was spent on two mai n activities, feeding and roosting, with a small fraction of the time (average of 10% for 25 species) spent on comfort activities. The water birds exhibited either a circadian (most waders, except Common Sandpip ers Actitis hypoleucos and Turnstones Arenaria interpres) or a diurnal foraging activity pattern (herons and terns), with no purely nocturna l species, Some species fed throughout the day, others showed peak for aging at various times of the day The proportion of time spent foragin g was related to guild (highest in visual and tactile surface-foraging waders) and was negatively correlated with the size of the species. W e conclude that the observed patterns in the use of the 24-h day by wa terbirds for foraging are not species specific but vary depending on c onditions on the feeding grounds, Nocturnal foraging is a normal and a regular strategy used by waterbirds to obtain enough food to fulfill their energetic requirements, so that irrespective of the sensory mech anism used to detect prey and the conditions prevailing on the feeding grounds, waterbirds forage day and night as dictated by their energet ic needs, Water depth appears to be the key environmental factor contr olling the availability of food for the waterbirds in the Ghanaian lag oons.