The Question: From time-to-time, birds fly into our picture windows and die. On two occasions, once last summer and then again just two days ago, a squirrel or a chipmunk retrieved the carcass and proceeded to devour it. This seems to be unusual behavior, and I wonder what triggers it, or if it happens more often than I am aware?



Submitted by: A. C., Georgia, USA

The Short Answer: Like most people, I once thought of rodents as seed eating herbivores, but it turns out that many, if not most, rodents are really omnivores that will eat insects or meat whenever they can get it. Gray squirrels (Sciurus carolinensis) and eastern chipmunks (Tamias striatus) are known nest raiders that will eat eggs or chicks. They also occasionally kill and eat adult birds. And gray squirrels are commonly seen eating road kills. So the answer to your question is that this carnivorous scavenging by a gray squirrel and a chipmunk is not unusual behavior at all. Great photos, by the way!

More Information: Scientific reports of predation by rodents list gray squirrels as eating other gray squirrels and birds. The list of observed prey for chipmunks also includes birds, as well as other chipmunks, voles, snakes, frogs and salamanders. Surprisingly, even small mice are significant predators of birds, mostly eggs and chicks, but they occasionally kill adult birds as well.

Given that squirrels and chipmunks are such frequent nest raiders, you might think that adult birds would defend their nests against them, but adult birds often simply abandon a nest if a squirrel comes near. This may be because, as mentioned above, squirrels are capable of killing adult birds. Under such circumstances, it might make sense for adult birds to simply give up and save their own lives in the hopes of nesting again in the future – especially under conditions where if the adult bird is killed while defending the nest, the chicks aren’t likely to survive anyway.

So, now you are going to have to view squirrels a little differently. And those cute little chipmunks are actually pretty good hunters. In fact, one study showed animal matter in the stomachs of 75% of chipmunks examined.

And all of this gives a new perspective to the Rodents of Unusual Size (ROUSes) that feature prominently in the satirical fairy tale movie, The Princess Bride. Turns out they are just imitating their relatives of usual size.

Sources:



CALLAHAN. (1993). Squirrels as predators. The Great Basin naturalist, 53(2), 137-144.

LANDRY, SO. (1970). Rodentia as omnivores. The quarterly review of biology, 45(4), 351-&.

Bradley, JE, & Marzluff, JM. (2003). Rodents as nest predators: Influences on predatory behavior and consequences to nesting birds. Auk, The, 120(4), 1180-1187.

Pietz, PJ, & Granfors, DA. (2005). Parental nest defense on videotape: More reality than “myth”. Auk, The, 122(2), 701-705.

Lima, S L. (2009). Predators and the breeding bird: Behavioral and reproductive flexibility under the risk of predation. Biological reviews, 84(3), 485-513.[cite]