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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 123, No. 1, March 2011 
marshlands, and mangrove swamps (Payne 1997, 
Sick 1997). Greater Anis are gregarious and live 
in groups of four to >100 individuals (Hilty and 
Brown 1986) foraging on arthropods and small 
vertebrates from mid-canopy to the ground. They 
occasionally venture into the forest, usually to 
follow army ant columns (Willis 1983, Hilty and 
Brown 1986). I describe the first record of a 
commensal foraging association involving a flock 
of Greater Anis and freshwater fish, based on an 
opportunistic observation along a man-made 
waterway in the northern region of the Pantanal, 
Brazil. 
STUDY AREA 
The Pantanal of Mato Grosso is the plain 
formed by the upper reaches of the Paraguay 
River and its tributaries in western Brazil, in the 
states of Mato Grosso and Mato Grosso do Sul 
with a small portion in Bolivia and Paraguay. The 
plain slopes gently in the region creating a 
complex system of river flooding and ebbing 
with slow run-off (Antas 2004). This annual cycle 
of flooding and ebbing in the Pantanal has caused 
local residents to depend upon boats for transport 
during the rainy season, as well as in flood and 
ebb periods when roads are impassible. Boat 
transport during the latter two periods, when 
travel by road is difficult, has been enhanced by 
digging ditches parallel to roads to retain 
sufficient volume of water for use of boats, 
extending their use before and after the peak of 
the rainy season. These ditches have been dug to 
facilitate transportation of materials and people to 
and from the (RPPN) ‘Private Natural Heritage 
Reserve' SESC Pantanal. The RPPN SESC 
Pantanal is in the northern Pantanal (16° 41' 11 " 
S, 56 10'32" W) in the municipality of Barao 
de Melga^o, State of Mato Grosso and covers an 
area of 106,782 ha. Digging of one of the ditches 
egan in 2002 and it is cleared every year during 
the dry season to remove the accumulation of 
vegetal material. The ditch is ~2 m wide with a 
depth of between 0.5 to 1 5 m 
OBSERVATIONS 
At-0800 hrs on 3 February 2007, a group of 
mne Greater Anis was observed moving along a 
ditch tor about 20 min. The anis were foraging 
close to the water’s edge, catching insects amid 
the nverbank vegetation. Throughout this obser¬ 
vation, the group stayed within ~l-2 m of each 
other, moving at a constant pace (~1 m every 
10 sec). From a vantage point, 30 m distant, I 
observed the anis were catching insects that 
flushed from vegetation emerging from the water 
that was being disturbed by fish that were darting 
back and forth along the edge of the ditch. The 
water surface remained calm and without current, 
allowing partial view of fish that were closer to 
the water surface. At times I noticed the fish 
performed more abrupt movements, such as a 
fight, when I could see many insects flushed by 
the movement of vegetation. All anis in the group 
foraged along the ditch, including five young 
(short tail, opaque plumage, bill not yet hooked, 
dark irises). The birds eventually dispersed, 
probably due to an approaching boat. 
DISCUSSION 
This is the first account of which I am aware 
involving birds and freshwater fish in a commen¬ 
sal foraging association. However, there are 
reports in the literature of commensal foraging 
behavior that involve Greater Anis associating 
with army ants (Willis 1983), as well as groups of 
monkeys (Cebus spp.) and Hoatzins ( Opisthoco- 
mus hoaziri) (Sigrist 2006). Fish may congregate 
in the shaded waters of riverside galleries to take 
advantage of the remains of fruit and insects that 
fall on to the water surface (Sigrist 2006), thus 
providing opportunities for birds to forage on the 
insects flushed by the activities of fish at the 
surface. It has been shown for some species of 
birds that visual orientation is of great importance 
in catching prey (Eriksson 1985). However, it is 
unlikely in the present account that the birds 
focused their foraging based on the presence of 
fish, due to the turbidity of the water. It is more 
likely the birds detected the movement of the 
vegetation and the resulting movement by poten¬ 
tial prey. The frequency of this type of opportu¬ 
nistic behavior by Greater Anis, and birds in 
general, may be low in relation to broader 
foraging tactics. The paucity of reports involving 
birds and freshwater fish suggest it may be 
sporadic. However, I believe this event can occur 
more frequently in the late ebb, when the flooded 
area decreases and concentration of fish increases. 
Further observation of the feeding behavior and 
foraging tactics of Greater Anis is necessary. 
ACKNOWLEDGMENTS 
I am grateful to P. T. Z. Antas for important 
contributions, and the Superintendent of RPPN SESC 
Pantanal for financial and logistical support. 
