Bird Watcher's General Store

A Bird's Crop is Storage Space for Extra Food
05/08/12


Dear Bird Folks,

Recently on your Facebook page you posted a photo (taken by Liz Hogan) of a falcon with a bulging neck. Your comment was that the bird had a full “crop.” I would like to know what the actual function of the crop is. Do all birds have them or just falcons?

Paula, Lewisburg, PA

Look around, Paula,

I wasn’t familiar with Lewisburg, PA so I checked it out on a map. Have you noticed the name of the towns around you? You have some odd neighbors. Near you there’s a town called “Old Furnace” (sounds like a hip place). There’s also “Larryville” (gee, I wonder who it’s named after). Then there is a village called “Oriole” (I’m okay with that one). Finally, right there, deep in the woods of central Pennsylvania is a town called (get ready) “Jersey Shore.” Really. While I’ve never seen the TV show of the same name, I didn’t picture the setting for Jersey Shore to be in PA, sitting between Old Furnace and Larryville. Shows you what I know.

I’m glad you reminded me about our Facebook page; now I can copy what I posted. It will save me a lot of work. Thanks. Here’s what it said. When we finish a large meal (think Thanksgiving), some of us have eaten so much we have to unbutton our pants. But when a bird overeats it has to unbutton the collar on its shirt. The crop is located in the neck area and when it becomes packed with food it bulges out, making the bird look like it has a bad case of goiter. Why does a bird pack its crop with food instead of just eating it? Birds typically fill their crops when they are too full to eat any more. It’s their version of a doggy bag; only in this case, the dog never gets anything. (It’s important to note that a bird’s crop shouldn’t be confused with food that farmers grow. That word is spelled “crop.” It also shouldn’t be mixed up with what riders use on horses. That’s spelled “crop.” Try to remember that.)

The Declaration of Independence states that “all men are created equal,” but the same thing can’t be said for birds. Some birds have evolved into great swimmers (loons), or fast flyers (falcons) and some birds can’t even fly at all (penguins and Big Bird). The same is true for their crops. Some birds have large, well-developed crops while others have crops that are barely noticeable, which leaves them with a serious case of crop envy. The Blue Jay doesn’t have a true crop, but it does have an expandable esophagus and that allows it to transport extra food. In the fall you may have noticed that Blue Jays are super piggy at your feeder. They aren’t actually eating all of those extra seeds, but instead are stuffing them into their stretchy throats. This allows the birds to transport the seeds to hidden locations and store them away for the winter. Insect-eating birds, like swallows and warblers, typically feed nonstop all day long, so they don’t really need a place to carry or store extra food. Food opportunities aren’t as abundant for birds of prey, so when they score a meal they need to take full advantage of it. If a hawk catches, say, a rabbit, it will eat its fill and then eat some more. The hawk can’t leave anything for later because there won’t be anything left of the rabbit when it returns, especially if there are any Brits around. So the hawk, just like that Facebook falcon, will stuff its crop with as much of the remaining rabbit as possible. It will then fly off to someplace quiet to do some serious digesting and to avoid being seen with that unsightly bulge in its neck.

Ground dwelling birds such as Wild Turkeys, quail and pheasants have well developed crops. Since these birds would rather walk or run than fly, they can afford to be weighed down with extra food. It’s not unusual for a turkey’s crop to be stuffed with dozens of acorns. (Being stuffed with acorns is okay, but if the birds somehow become stuffed with chestnuts, bread and assorted spices, it can lead to serious trouble.) A friend of mine who raises chickens tells me that when he feels his chickens at night he knows exactly what they have been eating during the day. If the birds have been eating vegetable matter, their crops are hard and solid. But if the chickens have been eating commercial food pellets, their necks feel like beanbags. I wanted to ask my friend why he was “feeling his chickens at night,” but I was afraid of the answer.

In addition to storage, pigeons and doves use their crops to produce something called “pigeon milk,” which they feed to their nestlings. Other birds use their crops to soften and pre-digest their food. And some grouse use their crops to produce sounds during courtship. Crop sounds during courtship, eh? Hmm. Maybe I should try that.

I hope this answers your questions about crops, Paula. Usually in May I like to write about more festive topics such as the return of hummingbirds and colorful spring migrants. A falcon’s crop doesn’t really fit into the “festive” category. But I did it for you. Consider it a Mother’s Day present. Speaking of Mother’s Day, I have to buy my own mother a gift. I think it’s too late to buy her flowers. Hey, maybe I’ll give her the most recent Jersey Shore DVD. I’m sure she’ll just love Snooki.




Artwork by Catherine Clark


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