Museum Volunteer Ian Harvey writes:
We’re all familiar with owls and for many people, they’re their favourite animal. And we know owls from literature; the owl and the pussycat, owl in Winnie the Pooh and the owls in the Harry Potter books.
Owls are birds of prey or raptors meaning they feed on other animals. They have certain features making them great hunters; excellent eyesight even at night, sharp claws of talons and a sharp, hooked beak.
In Britain we have 6 species of owl. The most common three are:
Two less common owls in Britain are:
The final owl occasionally visits the north of Scotland: the snowy owl.
People think that all owls fly at night but that’s not true. Little owls can often be seen during the day as can the short-eared owl (but mainly only in Winter when they visit Britain to areas ideal for hunting). Barn owls are often seen at dawn and dusk as ghostly, pale figures flying over fields hunting their prey. Tawny and long-eared owls tend to rest up during the day and come out at night. If you hear the classic “twit twoo” call, it’s a tawny owl.
The owl’s diet
What do our owls feed on? Mainly animals smaller than themselves. This includes:
Rodents, such as field voles, bank voles, water voles, field mice, house mice, harvest mice and rats;
And others, including frogs, beetles and birds.
How do owls feed?
Most raptors hold their prey in their talons and rip off the meat with their sharp beaks but owl’s typically do it differently, they swallow their prey whole (but bigger prey will be torn into bits!) They let their intestine do all the work.
When the prey is swallowed, it’s moved down the esophagus (the food pipe) by muscular contractions called peristalsis into the proventriculus or glandular stomach. This produces enzymes, acids, and mucus that begin the process of digestion.
The food then passes to the second part of stomach, called the ventriculus, or gizzard. There are no digestive glands in the gizzard, it serves as a filter, holding back insoluble, undigested items such as bones, fur, teeth and feathers.
The soluble parts of the food are ground by muscular contractions, and allowed to pass through to the rest of the digestive system, the small and large intestine. The liver and pancreas secrete digestive enzymes into the small intestine where the food is absorbed into body. At the end of the digestive tract (after the large intestine) is the cloaca which opens to the outside by means of the vent. That’s the poo!
Several hours after eating, the indigestible parts (fur, bones, teeth & feathers that are still in the gizzard) are compressed into a pellet. This pellet travels up from the gizzard back to the proventriculus. It will remain there for up to 10 hours before being regurgitated. Because the stored pellet partially blocks the owl’s digestive system, new prey can’t be swallowed until the pellet is ejected (vomited). When the owl eats more than one prey item within several hours, the various remains are consolidated into one pellet and a pellet can contain the remains of one or over ten animals. Think of a rat as a banquet, voles and mice as decent meals and shrews as snacks. A pellet is likely to contain the remains of a single rat, two or three voles or mice, maybe six or more shrews and often a mix.
The owl pellet
Collecting, dissecting and analysing an owl pellet tells us so much about what an owl has eaten. It contains the bones from its prey. We can identify many bones which we human mammals have but in miniature; pelvis, femur, tibia and fibula, ribs, scapula, clavicle, radius and ulna, vertebrae and most tellingly, jaws and skulls.
Looking carefully at the jaws, teeth and skull help us to identify not only the type of prey, but the species. We can see if it’s bank, field or water vole, whether it’s common, pygmy or water shrew and if it’s field, wood or house mouse. Or it may be a rat!
There is nothing like dissecting an owl pellet to embark on a forensic journey of discovery!And there is more analysis possible. Expert, microscopic analysis of the hairs in a pellet can determine prey species. And getting very scientifically sophisticated, using DNA sequencing of pellet contents enables us to see what soft-bodied animals have been eaten, animals without bones such as slugs and worms. This type of analysis is important especially for the little owl pellets but clearly you can’t do this at home.
What do you need to dissect an owl pellet?
Most obviously an owl pellet but where do you get one? They can be purchased online or you can find them yourself. The easiest to find are barn owl pellets as barn owls tend to roost in regular places so if you know where a barn owl either roosts or nests, search on the floor below. A word of warning! Barn owls are protected in law so you must NOT disturb them.
You’ll need a bowl or tray. You probably don’t fancy dissecting a pellet on a dinner plate so a disposable paper plate or bowl is recommended. To pull the pellet apart, the best tools are a pair of tweezers and fingers. If you don’t fancy touching the pellet, wear thin, disposable gloves and always wash your hands thoroughly after the dissection.
Some people like to dissect their pellet dry, others prefer to soak them first, it’s just a matter of personal preference. And, of course you need patience and care!
To get the best from your experience, you need to have a guide to refer to identify the bones. The Field Studies Council publish the excellent “Guide to British Owls and Owl Pellets” which is fairly inexpensive (around £5 or you might get a second hand one for less). Alternatively, there are good guidance sheets for download, an excellent site is the RSPB.
As a substitute for doing a real, live, hands on owl pellet dissection, you might like to visit kidwings.com where you get lots more information about owl pellets and can have a go at a virtual dissection.
Not just for kids!
Owl pellet dissection is for everyone to enjoy whatever their age and it’s a great activity for a family to share. There is nothing more rewarding than seeing youngsters, parents and grandparents getting excited together as a pellet slowly reveals its treasures!