SHORT COMMUNICATIONS 
407 
specific sites on 233 occasions. Mobbing was 
usually by flocks comprising 10-25 (15.9 ± 4.1 
SD) crows and included calling incessantly (n = 
176: 100%) and dive-bombing (n = 633 separate 
attacks by 103 flocks, i.e.. in 59% of mobbing 
events) the Osprey. The observed Western Osprey 
stopped feeding on the fish and observed the 
crows on all occasions. Western Osprey appar¬ 
ently tried to avoid being hit by either facing 
the attacking crows (n =118; 67%) or crouching 
(n = 58: 33%). Mobbing of the Western Osprey 
lasted between 75 and 305 sec (187.5 ± 76.2 SD) 
after which the House Crows returned to the trees 
on the shore if the kleptoparasitism attempt w'as 
unsuccessful. The Western Osprey abandoned the 
fish and flew from the immediate area on only 
seven (4%) occasions. On these occasions the 
crows retrieved the fish, flew with it to the sandy 
portion of shoreline, and fed on it. The size of the 
House Crow flock significantly affected klcpto- 
parasitizing success (/-test, P ~ 0,0014) while 
duration of mobbing did not (P 0.19). However, 
because neither Western Osprey nor House Crows 
were marked for individual identification, we do 
not know how many times the same individuals 
were involved in these intra-specific interactions. 
DISCUSSION 
Morand-Ferron et al. (2007) emphasized the 
central role of cognitive abilities in avian kleptopar¬ 
asitism and offered a novel perception of avian food 
stealing which, in the past, was primarily seen in 
terms of ‘brains’ rather than'brawn’. Our results do 
not concur with their suggestions and the House 
Crow resorts to ‘brawn’ and not ‘brain* in their 
attempts to access a high quality food source. They 
appear to recognize the freshly-caught fish as a rich 
resource (which may reflect advanced cognitive 
ability ), but did not display any innovative tactics to 
steal the fish. This is further substantiated when we 
consider that usually when a Western Osprey was 
observed to catch a fish and perched to feed, it w'as 
mobbed by House Crows. The Osprey perched 
>200 m from the areas where crows breed or roost 
in most cases. They were mobbed only when they 
had caught a fish and w'hile perched relatively far 
from breeding or roosting areas of die crows sug¬ 
gesting that crows recognized the value of fish as a 
rich food resource, and the purpose of the mobbing 
was to kleptoparasitize the Western Osprey to gain 
food. 
The reliance upon a brawn-based strategy is 
surprising because corvids are considered to be 
intelligent and fast-learning, and display advanced 
manipulative and cognitive abilities (reviewed by 
Emery and Clayton 2004). Ravens, for example, 
are known to cooperatively hunt and kleptopar- 
asilizc (e.g„ Yosef and Yosef 2010, Yosef et al. 
2011). associate with predators to obtain food 
(Stahlcckor et al. 2002), raid caches of arctic fox 
(Alnpex hitfopus; Careau et al. 2007), scavenge, 
supply disinformation to inter- and con-specifics 
(Bugnyar and Heinrich 2003, 2005), exploit novel 
and hidden food resources (Hendricks and Hen¬ 
dricks 2011), or nest based on predation experi¬ 
ence of past seasons (Tryjanowski et al. 2004). 
The uniformity in the behavior of the crow 
flocks, and their lack of a strategy to kleptopar- 
asiti/e Osprey, leads us to assume crows recognize 
the Western Osprey, a raptor, as a potential pre¬ 
dator and attack it to dissuade it from approaching 
their frequented areas and kleptoparasitism result¬ 
ed accidently wherein a mobbed individual aban¬ 
doned its prey. House Crows do not maintain 
individual territories but are gregarious and engage 
in group defense over large urban areas (RY. pers. 
ohs.). However, it has not been ascertained in any 
study if local populations intermingle and if they 
have an encompassing strategy or restrict them¬ 
selves to specific neighborhoods. We assume it is 
the first because every evening we observed indi¬ 
viduals flocking to a central fresh water drinking 
site from all over the city. They also concentrated 
at specific roost sites in different areas. Hence, we 
were unable to ascertain whether the individuals 
involved in each engagement were the same. 
Ospreys are known to be kleptoparasitized by 
other species (e.g.. Bald Eagle [Haliaeetus leucoce- 
phalus], Prevost 1979; Parasitic Jaegers \Stercorarius 
parasiticus ], Belisle and Giroux 1995; Great Blue 
Herons [A idea herodias 1, Squires 1998; Northern 
Crested Caracara [Caracura cheriway\, McNair et al. 
2000), hut no previous study has shown cooperative 
kleptoparasitism of Ospreys by House Crows. Future 
studies should investigate whether this behavior is 
common where the two species occur together or is 
restricted to our study area. This is of conservation 
importance because the Western Osprey is a native 
species with low breeding densities (Ferguson-Lees 
and Christie 2001), while crows are bioinvaders and 
as yet unable to routinely successfully kleptoparasi- 
tize Western Osprey by mobbing. 
ACKNOWLEDGMENTS 
We thank G. G. Frye, J.-F. Giroux, and the editor for 
improving an earlier draft of the paper. 
