Spoiler alert: They’re not, as so many people believe, true scavengers. Meaning, they’re not mostly eating carrion. I know what you’re thinking: MIND BLOWN. Also you might be thinking PBS lied to you, and you’d technically be correct. So why is this myth so pervasive that even PBS fell victim to its ubiquity?
An American crow picks at the torn up belly of a rat in a Bellevue neighborhood. After a few minutes, it had its fill and moved on to other feeding opportunities, leaving most of the rat untouched.
Well, a huge part of the problem is that like so many words in science, their use in general discourse has parted from their scientific meaning. Typically we use this word to describe say, grad students at the end of the party stuffing their pockets with the leftovers but, biologically speaking, scavengers are organisms who are specialized to consume, or obtain most of their food, from the decaying tissue of animals or herbaceous matter. Now don’t get me wrong, the title of ‘scavenger’ can get a bit blurry as Bernd Heinrich argues in his book, Life Everlasting. Ravens for instance, switch primarily to scavenging during lean winter months. For most American crows, however, the identity of ‘scavenger’ simply will not do.
Which is really too bad, since the title of scavenger is bestowed with honor given how they make our living on planet earth possible. I’m not being hyperbolic when I say thanking the undertakers of our ecosystem should be part of everyone’s pre-meal ritual, but perhaps that argument should be saved for another post.
As for crows, carrion makes up only a very small part of their diet. In Seattle, roadkill accounts for <5% of crow food, and in wildland areas carrion accounts for even less1. Crow beaks aren’t even strong enough to break through the skin of a grey squirrel, though they will usually give it a try.
So what are they eating? Mostly human refuse (no surprise) and invertebrates. In fact human garbage (meat, grain products and veggies) account for about 65% of their diet in urban areas, whereas in wildland areas it’s roughly split between garbage and inverts (35% and 35% respectively)1.
Crows spend much of their time patrolling lawns looking for invertebrates
These data correct another common misconception about crows: they’re not mostly eating the eggs and nestlings of other birds. In fact, crows only account for 1 of 20 observed nest predators in WA and have been found to have a nonsignificant, negative relationship between abundance and rate of predation in experiments using artificial ground nests, shrub nests, and canopy nests1.
So there you have it, American crows are neither true scavengers nor meaningful nest predators. They’re primarily omnivores with an emphasis on human refuse and invertebrates. So the next time you see one patrolling your grassy lawn remember; they’re busy trying to bring home the bacon. Er, bugs. Well, probably bugs, but preferably bacon provided you were crazy enough to throw some out.
Literature cited
- Marzluff, J.M., McGowen, K.J., Roarke, D. and Knight, R.L. 2001. Causes and consequences of expanding American crow populations. in Avian ecology and conservation in an urbanizing world (J.M. Marzluff, R. Bowmanm and R Donelly, eds). Kluwer academic Press, norwell, Ma.
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