Of the 42 dominant species of waterbirds at Lake Turkana, Kenya, 14 fo
raged uniformly throughout the day and night, five foraged mostly duri
ng the night, five foraged during both the night and day but with diur
nal peaks, 17 were exclusively diurnal and only one was exclusively no
cturnal. Species with uniform feeding activity usually captured small
prey, using tactile or visual plus tactile cues; most diurnal species
captured large prey, using visual cues. However, some species which fe
d mostly at night, or uniformly, relied exclusively on visual cues. We
found support from only one species that moonlight influenced foragin
g activities. Palaearctic immigrants spent significantly more time for
aging than partial migrants and residents; they were also smaller and
mainly microphagous. Only gulls and terns were restricted to diurnal f
eeding, presumably by their need to see and capture prey while flying.
The other groups were formed by species which foraged uniformly over
24 h or partially by day or night. These patterns indicate that in mos
t waterbirds feeding activities are not basically tied to any phase of
the diel cycle. Since most waterbirds display some degree of nocturna
l activity, time budget studies based only on diurnal observations are
likely to be misleading.