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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 123. No. 2. June 2011 
new attempted capture several meters distant. 
Apparently, captured crabs were left mostly 
intact: the one we examined before waves washed 
it away had the telson removed and no eggs were 
present. Thus, it appeared the ravens were 
capturing female sand crabs to eat the egg clusters 
carried by them; some of the crabs may have been 
fatally wounded during capture, but none of the 
captured crabs was eaten. 
DISCUSSION 
Several aspects of our observation of raven 
predation on sand crabs are worth noting. First, the 
ravens must have been using subtle cues to locate 
the sand crabs, because the crabs were completely 
buried in the sand, and repeated wave action made 
the beach surface smooth. Surface movements by 
crabs to new locations on the beach occur rapidly 
(in < 10 sec) ami only when they are submerged in 
waves (MacGinitie 1938, Efford 1965). conditions 
apparently avoided by the ravens. At most, only the 
small eyestalks and first pair of antennae (used for 
respiration) project above die sand (Ricketts ct al. 
1968) and form a small opening in the sand. These 
small appendages also redirect receding water, 
leaving a small v-shaped pattern in the sand. 
Human observers can see both cues, and the ravens 
may have learned to associate them with the 
presence of hidden sand crabs. 
Second, adult female sand crabs are not 
uniformly distributed over the beach, but are 
more abundant lower on the beach than males and 
are most aggregated on a daily basis during low 
tides (Ricketts et al. 1968, Perry 1980); peak 
aggregations occur during two seasons, one of 
which is in late summer. The conditions under 
which we made our observations (low tide in mid- 
August) were particularly favorable for finding 
female sand crabs. 
Third, exploitation by ravens of sand crabs on 
the northern Oregon coast is a behavior probably 
learned during the last 20 years. The North 
American range of Emerita analoga , the only 
member of the genus found on western U.S. 
beaches, includes the Pacific Coast from Baja 
California, Mexico to Kodiak Island, Alaska 
(Efford 1976); populations inhabiting beaches 
north of California are patchily distributed and 
largely dependent on recruitment by zoeal larvae 
traveling from California as planktonic drift in the 
Davidson Current (Efford 1970, Sorte et al. 2001). 
Recruitment of sand crabs on the Oregon coast is 
particularly successful during El Nino years, but 
the ability of northern Oregon populations to 
persist in non-EI Nino years is questionable (Sorte 
et al. 2001). Sand crabs first appeared on northern 
Oregon beaches in 1992. were noted annually 
during the next decade (Sorte et al. 2001), and 
continue to occur there during at least some years. 
How ravens learned to exploit female sand crabs 
for their eggs is not known. Ravens could have 
discovered that females carry eggs masses in 
autumn by examining injured or dead gravid 
females stranded on the beach, as we did. Learning 
where to look for gravid female crabs when they 
are buried in sand seems initially more challenging. 
One possible method is by observing and copying 
the behavior of another predator of sand Crabs 
Western Gulls (Larus occidentalin) are resident 
year-round on the Oregon coast, capture and 
consume a variety of live and dead animal matter 
that also appear in the diets of ravens, including 
intertidal invertebrates (Pierotti and Annett 1995), 
and would seem an ideal species for ravens to copy 
We have seen Western Gulls on Netarts Spit 
capture small invertebrates they stirred up ham the 
wet sands of the swash zone through the process of 
foot paddling (Hendricks and Hendricks 2006), 
including earlier on the day we saw the ravens 
reported here. Western Gulls frequently hunt sand 
crabs on California beaches in spring and autumn 
(Smith 2007) and it is possible they do the same 
along the Oregon coast, although we have yet to 
see them capture sand crabs on Oregon beaches 
Ravens could also have learned to exploit live sand 
crabs by watching Sanderlings {Calidris alba) and 
other shorebirds during autumn as they hunt and 
consume smaller juvenile and male crabs (carapace 
length typically < 1.5 cm) and the egg clusters of 
lemale crabs loo large to be eaten whole (MacGi¬ 
nitie 1938, Maron and Myers 1985, Kvitek and 
Bretz 2005, Smith 2007). 
ACKNOWLEDGMENTS 
Our manuscript benefited from the suggestions of three 
anonymous reviewers and the blue pencil of the editor "e 
thank Stuart and Midge for not Hushing the ravens as they 
crabbed. 
LITERATURE CITED 
Bent, A. C. 1946. Life histories of North American jays- 
crows, and titmice. U.S. National Museum Bulletin- 
Number 191. 
Boarman, W. I. and B. Heinrich. 1999. Common Ra' cn 
(Corvus corax). The birds of North America. 
Number 476. 
