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THE WILSON JOURNAL OF ORNITHOLOGY • Vol 123. No. 2. June 2011 
TABLE 1. Primate prey of wild Harpy Eagles. 
Genus 
Species 
References 
Alouatta 
belzebul. seniculus 
Rcttig 1978. Eason 1989, Peres 1990, Sherman 1991. 
Robinson 1994. Ford and Boinski 2007, Piana 2007. 
Ferrari 2009, this study 
Aotus 
sp. 
Piana 2007 
Ateles 
panise us 
Ford and Boinski 2007 
Callicebus 
discolor, hoffniannsi 
Aguiar da Silva 2007, de Luna et al. 2010 
Cebus 
albifrons, apella. nigrivittatus, olivaceous, sp. 
Fowler and Cope 1964. Rettig 1978. Izor 1985', Peres 
1990. Aguiar da Silva 2007. Ford and Boinski 2007. 
Piana 2007. Sevmour et al. 2010 
Chiropotes 
alhinasus, hoffmannsi, satanas, utahicki 
Rettig 1978. Izor 1985". Peres 1990. Martins et al. 2005. 
Aguiar da Silva 2007. Ford and Boinski 2007, this 
study 
Pithecia 
albicans, irrorata, monachus. pithecia 
Rettig 1978. Izor 1985". Peres 1990. Aguiar da Silva 
2(X)7. Ford and Boinski 2007 
Saguinus 
midas 
Ford and Boinski 2007 
Saimiri 
holiviensis, sciureus 
Robinson 1994. Ford and Boinski 2007 
a Only cehid posl-crania were recovered hut four species are likely given the quantify and size ot the remains 
perched individual with the body of what 
appeared to be a black-bearded saki draped over 
the branch below it. The eagle did not flush and 
did not appear to be consuming the saki. 
DISCUSSION 
Harpy Eagles have been reported to prey on a 
number of primates (Table I). We add a new 
species, C. v. chiropotes. to this list. Most Harpy 
Eagle-primate interactions are inferred through 
identification of primate remains at Harpy Eagle 
nests or through observations of Harpy Eagles that 
already have a primate carcass. There are three 
reports that detail the actual interaction between 
an attacking Harpy Eagle and its primate prey. 
Eason (1989) observed a Harpy Eagle attacking a 
group of red howler monkeys at the edge of an 
oxbow lake. The monkeys detected the approach¬ 
ing eagle well before it arrived, alarm called, and 
jumped to a vine tangle as the eagle glided 
towards them with its talons extended; a malt- 
howler then pursued the eagle until it left the area. 
Peres (1990) described a Harpy Eagle that 
attacked and killed a roaring male red howler 
monkey that was vocalizing on the periphery of its 
group. The eagle attacked the howler from "behind 
and it seems the Harpy Eagle was not detected 
until it successfully struck the howler monkey. 
Martins el al. (2005) observed a Harpy Eagle 
dropping the dead body of a male bearded saki 
monkey (Chiropotes utahirki) in mid-flight and 
infer the monkey fought back because, when they 
recovered the carcass, it was clutching feathers in 
each hand. Our observations differ from these 
reports because, of the two cases that provide 
details of the actual attack, in one instance the 
Harpy Eagle was detected early in its approach 
(Eason 1989) and in the other it likely was not 
detected until after its strike (Peres 1990). The 
monkeys in the Lhree cases that we report did not 
appear to detect the Harpy Eagle until the 
individual being attacked saw the raptor al the 
last moment because there were no alarm calls or 
reactions to the eagles until the startle vocaliza¬ 
tion al the instant of the first attempt. The anti- 
predator strategy in the attacks that we describe is 
likely different than in the cases described b> 
Eason (1989) and Martins et al. (2005) due to (he 
different detection times. 
Our observations permit consideration ot the 
potential physiological limitations of Harp) 
Eagles during an attack and the ways primate 
anti-predator behaviors exploit them. Raptors 
have highly focused binocular vision that creates 
‘tunnel vision* and requires them to move their 
heads to track prey (Land 1999). Anatomical 
constraints greatly limit head movements during 
an attack, resulting in a limited ability to make in¬ 
flight focal adjustments (Shifferman and Eilam 
2004). Prey movements at 90 degrees to the attack 
plane can be particularly difficult for a raptor to 
track with predator success rates decreasing to I'T 
for Barn Owls (Tyto alba ) (Shifferman and 
Eilman 2004, Ilany and Eilam 2008). The 
effectiveness of this flight path (Ilany and Eilam 
2008) for escape from fast approaching predators 
