What Is a Bird's Crop?
(noun) The crop is a muscular pouch that is an extension of a bird’s esophagus used to store excess food prior to digestion. While most birds do have a crop, it is not always visible and should not be confused for similar parts of the bill, mouth, or throat.
(rhymes with stop, flop, top, and mop)
About the Crop
The crop is not generally considered part of overall physical or chemical digestion, but rather is a simple storage area that enables birds to take in a lot of food in a short period of time. This allows birds to eat more food than necessary in a single sitting, reserving excess food for a later time when food may be scarce. This can also make feeding safer since birds can quickly ingest large quantities of food then move to a safer, more sheltered location to slowly digest.
When a bird has a full crop after a large meal, the throat can look grossly distended as if the bird is choking, has an internal injury, or might have a cancerous growth, but there is no distress. If a bird were choking, it would likely be fluttering its wings, hunching its back and trying to dislodge whatever was in its throat, but birds with a full crop are more likely to sit quietly and calmly as they digest. Birds with a full crop will often be reluctant to move even if closely approached, but may move to a safe perch to digest.
Parent birds store partially digested food in their crop before regurgitating it to feed nestlings. Some birds, such as pigeons and flamingos, produce crop milk as a nutritious supplement for very young chicks. This "milk" is not a diary product, but is partially digested food that will be easier for young birds to digest.
What a Crop Isn't
A bird's crop should not be confused with other anatomical features that may seem similar but actually have very different structures and purposes. Body parts that are commonly confused with a bird's crop include:
- Gular Sac: The gular sac is a bare-skinned, fleshy, expandable pouch below a bird's bill, such as with pelicans and frigatebirds. While these pouches are instrumental in hunting, they are not deliberately used to store food. While a bird's crop is part of its internal anatomy and is hidden by feathers, a gular pouch is often brightly colored and visible most of the time.
- Air Sac: An air sac is a small pouch used to create audible booms or similar noises, typically as part of courtship displays. Air sacs are prominent in many types of terrestrial game birds, such as sage-grouse. They are usually only visible when in use for courtship, and are part of the respiratory system rather than the digestive system. Air sacs are unrelated to food entirely.
- Gorget: The gorget is a colorful patch of plumage on the throat, often iridescent. The gorget is most familiar with male hummingbirds, and they may flash or flare the feathers to make the coloration more brilliant during courtship displays, territorial disputes, or aggressive behavior. The gorget is made up of external feathers only and is not involved with feeding or digestion.
- Malar Stripe: A malar stripe is a distinct marking on the side of a bird's throat, similar to a mustache marking, and may vary in length, width, color, and overall shape. While this type of marking can be useful for bird identification, it is an external patch of color only and is unrelated to how the bird eats or digests its food.
- Gape: The gape is the corners of a bird's bill where the upper and lower mandibles meet. In younger birds it is often more brightly colored and may appear swollen to help attract parents' attention and encourage more feeding. Food may occasionally be stuck on or spill out of the gape, but this structure is not in the throat and is not deliberately used for storage like the crop.
Birds With Crops
While most birds do have a crop, it is not always easily visible depending on the bird's posture, size, and feeding behavior. The crop is generally more prominent on larger birds with irregular feeding habits, such as birds of prey that must hunt for a meal and take heavy advantage of food when it is available. Birds that do have more visible crops include vultures, hawks, falcons, eagles, gulls, and many types of quail.
Crops are not unique to birds and are also found in many species of insects, snails, and leeches.
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