The crop is basically a food storage device. Birds have such a fast metabolism that they would have to eat every few hours if they didn't have a crop. The crop is essentially a bag of skin, or membrane, surrounded by muscles. About 2/3 of the way up the crop is the opening to the stomach, the esophagus. When the stomach is ready for more food, the crop muscles contract, pushing food into the opening. If the muscles are weakened, or the crop is stretched out, the muscles can't contract it all the way and the food in the bottom of the crop can't get to the stomach.

Guidelines for handfeeding:

- The crop should be filled until it feels like a soft water balloon, i.e. it should still have "give" to it, not be taut or hard. This prevents crop stretching.

- The crop should be allowed to empty completely at least once every 24 hours. This is because, due to the location of the esophageal opening, the crop empties from top to bottom. Therefore, if you put fresh food on top of old food, the fresh food will move out first, leaving the old food in the crop longer. If this happens repeatedly, the food at the bottom of the crop will spoil, causing "sour crop."

- The food should be fed at a temperature of around 104 - 105 degrees, not below 100 deg. and not above 110 deg. Above 110 can burn the delicate crop membrane, and food that is too cold will not move out of the crop well. The baby must also be kept warm, especially when it is not well-feathered; if it gets too cold, food will not move out of the crop well. (The necessary temperature decreases as the baby gets older - Day One hatchlings should be at about 95 degrees, after 10 days or so 90 is good, then 85 at about 3 weeks, then 80 when baby is about half-feathered, then to room temperature.)

- Hand-feeding formula is a perfect breeding ground for bacteria and other organisms; therefore, formula should be mixed up fresh every time, not stored.

- Humidity is essential. Baby birds need lots of fluid; if the environment is too dry, the baby's body will leach fluid out of the crop, leaving the food in the crop too dry to be pushed into the esophagus easily. (If you don't have a commercial brooder, a soaking wet sponge in a bowl will provide humidity without giving the baby something to drown in. :) )

Sour Crop, Candida, and Crop Stasis

Crop stretching, chilling, overfeeding, food sitting in the crop too long, and "dry" food in the crop all lead to one thing: "sour crop." Sour crop basically means that the food in the crop has soured, or spoiled. Most often the yeast organism, Candida, which is normally present in small amounts, will take advantage of the situation to grow out of control, causing a Candida infection of the crop. Another possibility is bacterial infection of the crop due to the growth of bacteria in the spoiled food. Either way, this baby will need to be taken to the vet to have the crop flushed out and medication begun.

In severe cases, infection in the crop can lead to "crop stasis," where the food will not move out of the crop at all and just sits there. This baby will die of starvation if the condition is not corrected. It is also possible to have crop stasis because of an infection further on in the digestive tract which has stopped the digestion of food, and it "backs up" to the crop; the food in the crop literally has nowhere to go.

Additional Notes:

The older the baby, the less likely it is to have these problems, and the less important temperature becomes. Obviously the solid food and water that weaned babies consume is not warmed! It is also, therefore, more critical to keep younger babies warm than older ones. Fully feathered babies (check the area on the body that is covered by the wing tips when folded - that feathers in last) can usually be moved to a cage without supplemental heat and be just fine.

In the normal course of hand-feeding a baby, the process goes so smoothly that you are hardly aware of it. You feed the baby, the crop empties, you feed the baby again, and so on… Then the baby begins to eat on its own and you adjust your schedule to feed only when the crop does not already have a significant amount of food in it. Finally, the crop is half full or full of food most of the time, and the baby is eating well enough that you can stop the feedings and call it weaned.

My personal experiences, conversations with others, and things I have read all tell me that cockatiels for some reason are particularly prone to crop problems, especially Candida infections. It is, in my experience, seldom seen in other babies, and something you should be aware of if you are hand-feeding a baby but not -worry- about unduly. (If, on the other hand, you happen to be feeding baby cockatiels, this information should prompt you to be very careful to prevent crop troubles, and very watchful of your babies' crop condition at all times.)