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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 124. No. 3. September 20/2 
attempted several times to swallow it. In one of 
these attempts, the small chick fell to the ground 
and was rapidly captured by another pelican 
fledgling (75 days of age). This last bird moved 
from the other pelicans with the chick in its heak 
and subsequently placed it into its gular pouch 
(Fig. 2F. G). This fledgling started to swallow the 
small chick with repeated head and neck move¬ 
ments until it was completely ingested (Fig. 2H). 
The pelican then returned to the group of 
aggressors. The cannibalism event was nearly 
45 min. 
DISCUSSION 
Aggression between chicks of the same species 
has been widely reported in the literature, partic¬ 
ularly among nest mates (at limes resulting in 
siblicide and sibling cannibalism) of herons, gulls, 
hawks, and owls (Sianhack and Koenig 1992). Our 
observations report groups of fully grown Peruvian 
Pelican fledglings (60-75 days of age) attacking 
and consuming smaller (5 days of age) pelican 
chicks within neighboring nests. Guerra and 
Cikutovic (1985) observed fully-grown Peruvian 
Pelican fledglings (similar in age to the agressors 
observed in this study) approaching unattended 
conspecific nests and pulling nest material out 
of the nest, but no aggression or canibalism to 
nestlings was evident. 
Harassment and consumption of conspecific 
chicks by fledglings is an unusual behavior, 
different from typical siblicide. Siblicide occurs 
among nest mates and is directed to reduce com¬ 
petition for food delivered by parents (Mock 
1984, Mock and Parker 1997). but aggression to 
and consumption of unrelated conspecil'ies seems 
to be primarily motivated by the nutritional value 
of cannibalism anti has been reported in colonial- 
nesting species, including American White Ibis 
(Eudocimus albus ) (Herring et al. 2005), Austra¬ 
lian Pelican and Australian White Ibis (Thres- 
kiornis molueeus) (Smith and Munro 2008), and 
Black-crowned Night Heron {Nycticorux nyai- 
corcix) (Riehl 2006). Young/fledglings in all 
cases, attacked and consumed small chicks from 
unguarded nests or nestlings on the ground that 
had fallen from nests. 
We identified five common elements in all 
three observed cases of aggression. (I) All 
attacked nestlings were unattended by their 
parents in the nest which allowed aggressors to 
avoid confrontation with guarding adults. This 
suggests aggression and cannibalism of nestlings 
by fledglings were opportunistic behaviors, ex¬ 
hibited only when an unattended nest with chicks 
was discovered. (2) All attacked nestlings ranged 
in age from newly hatched to 5 days of age 
The small nestlings that served as a prey item for 
the aggressors were defenseless and easy 
to swallow. (3) All aggressors were fully-grown 
fledglings, typically 60 days or older. (4) Ag 
gressive fledglings always attacked nestlings in 
groups of 4 to 8 individuals, never alone. (5) All 
cases were observed late in the breeding season 
(Mar-Apr). All victims were from late breeding 
parents and aggressors were from the first-hatched 
birds in the colony. Thus, occurrence of aggres¬ 
sion and cannibalism needs a certain asynchrony 
within the colony and is restricted to short periods 
during the breeding season, mainly when fully- 
grown fledglings coexist with newly hatched 
chicks. 
One explanation for the observed behaviors 
could be related to food deprivation of fledglings. 
Adults of colonial nesting seabirds normally 
leave fledglings unattended and feed them at 
irregular intervals thus exposing them to periods 
of fasting (Stanback and Koenig 1992. Shealer 
2002. Smith and Munro 2008). This situation is 
consistent with our observations; 7,000 pelican 
fledglings wandered across the colony in mid 
April 2011. out of sight of their parents which 
were probably foraging at sea. Fledglings during 
this period are not able to forage for themselves 
and completely rely on their parents for food 
(young Peruvian Pelicans probably do not forage 
for themselves until they are 100— 120 days of 
age. pers. obs.). We have observed fledglings 
begging for food from unrelated conspecific 
adults, most likely in an attempt to obtain food 
!i is thus conceivable that some fledglings were 
seeking food sources and opportunistically took 
advantage of unguarded nests with newly hatched 
chicks and depredated them. Local food shortage 
can also induce cannibalism as fledglings are 
forced to seek alternative food resources tRiehl 
2006). However, we w'ere unable to find any 
evidence of a shortage in the area, nor did vve 
observe any signs of starvation. Cannibalism may 
be also regarded as a feeding opportunity and not 
necessarily a response to food deprivation (Mock 
1984). 
Several authors have suggested there is hor¬ 
monal regulation of aggression in chicks (e.g.. 
Ros et al. 2002, Anderson et al. 2004. Muller et al. 
2008). Chicks exposed very early in their 
