Spotted Wood Owl: Pellets
Posted by BESG on 21 August 07, Tuesday
Contributed by - see article -
A number of Spotted Wood Owl’s (Strix seloputo) pellets were collected on the evening of 12th August 2007 under the roost of a juvenile (left). These pellets were 4-5 cm x 3-4 cm, light brownish and white, the former representing mostly the fur of the owl’s victim and the latter various types of bones (below top and bottom). The pellets had a distinct odour, an indication that decomposition had set in.
As most birders know, raptors and owls cast pellets of indigestible food parts, mainly fur, feathers, teeth, claws and bones. Many other birds like shrikes, herons, kingfishers and bee-eaters, similarly cast pellets of insect exoskeletons and bones of fishes and amphibians,
In the case of owls, the small animals they eat are swallowed whole. These end up in the gizzard where the digestive fluids act on the soft tissues. The hard, undigested materials, often more or less intact, are regurgitated as a compact pellet, looking wet and slimy as the exterior is covered with a liquid that acts as a lubricant
Owl pellets vary in size and shape, depending of the species of owl and the animals they eat. Normally, a pellet forms a few hours after a meal. It then travels from the gizzard into a space above known as the proventriculus. This pellet has to be ejected before the owl can swallow new food. Apparently, different species have their own schedules of pellet casting i.e. so many hours after a meal.
Before an owl ejects a pellet, it acts as if it is coughing or retching.
The image below (scale in mm) displays the different bones that were found in a number of pellets collected below the roost of the juvenile Spotted Wood Owl. They were sorted out only after they were baked at 150 degrees celsius for 50 minutes wrapped in a piece of aluminium foil. Why? Owl pellets are known to contain bacteria and viruses that can cause various diseases. As such, they should be handled with extreme care.
The skull and jawbones with teeth intact can be identified if their dental formulae are worked out. But we need an experienced mammalogist to do this. For the moment it is enough to know that the owl’s food includes different vertebrates.
Images by YC except owl by Johnny Wee.
Reference:
Long, Kim (1998). Owls: A wildlife handbook. Boulder: Johnson Books.
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