Comparative Owl Nutrition

At the start of a birds digestive tract there is a beak and tongue used for food manipulation (Duke 1997). Continuing on there is the oesophagus, which is larger in diameter and longer compared to other animals in order to accomodate unchewed food items (Duke 1997).

 

Birds also uniquely possess a crop and gizzard in their digestive tract. Where the crop is a site of food storage and the gizzard is a muscular stomach that mechanically breaks down the ingested food (Duke 1997). However, owls do not posses a crop, so food moves immediately into the glandular stomach or proventriculus after exiting the oesophagus (Duke 1997). After a short stay, it then reaches the muscular stomach or gizzard, where gastric secretions further break down the ingesta (Duke 1997).

 

The gizzard also functions as a filter for the organic material that is difficult to break down, like teeth, bones, fur, etc (Tabaka et al. 1996). These hard to digest parts of prey are then compacted into a pellet and regurgitated out from the owl's beak (Tabaka et al. 1996). 

 

Chemical digestion and nutrient absorption then occurs in the duodenum and ileum of the small intestine, being shorter in carnivorous birds - like The Great Horned Owl and Burrowing Owl (Duke 1997). 

 

Not all avian species have a caeca, but they are present in owls. The caeca is important for water balance, fermentation of fibre and creating amino acids through recycling nitrogenous waste (Duke 1997). 

 

After passing through the large intestine, organic material reaches the relatively short rectum where water is absorbed, and  urine and fecal matter is eliminated through the cloaca (Duke 1997).

It is assumed that the gastrointestinal tract of the burrowing owl would look the same as shown in Figure 1, but would probably be much smaller as Athene cunicularia is smaller than Bubo virginianus. The Burrowing Owl is also a carnivore, so the proportion of features within the tract would also be similar.