Birds do not chew or digest food the same way as humans or other familiar mammals do. Understanding birds' different digestive organs and their eating process can help birders be more knowledgeable about the best foods for birds and why a healthy diet is important for every bird.
Bird Eating Behavior
Observing when and how birds eat is the first step to learning more about their eating habits and digestion. Birds are most active foraging in the morning and evening as they refuel after a long night and stock up for the next night, but they will eat at any time of day. To understand bird digestion, watch birds eating different foods and observe their behavior before, during, and after a meal.
- How active are feeding areas at different times of the day?
- Which foods are the most popular and which are least popular?
- Do birds take small bites, break food apart, or eat it whole?
- How quickly does a bird take multiple bites?
- Does the bird stay at the feeder or fly away between bites?
- Does the bird hide any food or consume it all at once?
- After eating, is the bird active immediately or does it rest?
Careful observation will show how birds treat their food as they eat and how their bodies react while digesting.
How Birds Digest Their Food
Digestion is a multistep process that begins with finding food and ends when indigestible waste is expelled from the bird's body.
- Finding Food: Birds have different diet types and preferences so they find foods in different ways. They are all opportunistic feeders and will often sample many different foods. More aggressive species will guard favored food sources, and some birds store food for future meals. Once a bird has found food, the eating and digesting process can begin.
- Chewing and Swallowing: Birds have specialized bills to help them take bites, but they do not chew as humans do. Instead, birds will either swallow food whole or if it is too large or awkward to directly swallow, they will break it into smaller pieces. Some birds may rip or shred food such as fruit or prey, or they will use their bills to break up harder chunks of nuts or large seeds. In some cases, birds will beat their food against a rock or branch to help break it into pieces, and birds may even use their talons to hold food as they break it up. To swallow, birds tip their heads back to move the bite to the back of the throat, and their tongues help maneuver the food into a good swallowing position. Saliva also makes food easier to swallow.
- The Digestive Tract: Several organs make up a bird's digestive tract. From the bill, food moves down a tube called the esophagus and into the crop, which stores excess food so the bird can digest it slowly. The food then moves to the proventriculus, which is the first part of the stomach, where it is softened by gastric acid, mucus, and other digestive juices. The second part of the stomach, the gizzard, grinds the food into smaller pieces, often with the aid of grit such as sand or small stones the bird has swallowed earlier. If the food is particularly tough, it may move between the proventriculus and the gizzard several times for more efficient digestion. Once the food is sufficiently broken down, it moves into the small intestine, where the liver and pancreas help with absorbing nutrients. Next is the large intestine, which is very short for most birds. Where the small and large intestines join are the ceca, two pouches that help absorb any remaining water from the food and finish the digestive process.
- Waste: After digestion, any remaining material, both liquid and solid, passes through the cloaca to be expelled from the bird's body. For many birds, waste products can also be expelled from the gizzard in the form of pellets. Fur, bones, tough husks, and other materials that cannot pass through the bird's intestines are compacted into a small, oblong ball of material (the pellet) and regurgitated through the bill.
The time it takes a bird to digest a meal depends on several factors, including the type of food and the bird species eating it. While the general digestive tract is the same for all birds, the size and shape of different organs, particularly the crop and gizzard, also vary for different bird species.
Much like a cow, the hoatzin's unique digestive system relies on bacterial fermentation. It's the only bird in the world that uses a foregut compartment called a "rumen" instead of a stomach to process their food.
Helping Bird Digestion
A bird's digestive tract is designed to efficiently extract as much nutrition as possible from everything and anything a bird eats, but some foods are more easily digested than others. The most nutritious foods are the ones birds need most, and birders should avoid offering junk foods such as bread, excessive scraps, or spoiled food. To help birds enjoy a nutritious diet they can easily digest:
- Offer many different foods to give birds a greater variety of healthy choices, including both feeders and natural foods from trees and shrubs.
- Offer foods in different sizes, such as whole black oil sunflower seeds and peanuts alongside hulled seeds, hearts, or chips and peanut butter for different birds to sample.
- Clean bird feeders regularly and check to be sure no seed is spoiled, discarding any wet, moldy, or mildewed seeds and removing spent seed hulls.
Understanding bird digestion is a great step toward offering only the best foods for birds to eat and keeping them healthy and well-fed.
"Digestion". Bird Digestion - Fernbank Science Center, http://www.fernbank.edu/birding/digestion.htm.