What’s in a pellet?

November 7th 2021

What’s in a pellet?

During the last week in October 2021 Murray Anderson from Achnacarnin posted, on Facebook, a photo of a Tawny Owl, Strix aluco, pellet that looked very interesting. The main thing that caught my eye was the short length of complete spinal bones. So, I offered Murray a mission to re-find and rescue the pellet. That would then allow me to dissect it and see what the owl had been feeding on.

Not only did Murray find the pellet he also hand delivered it. The packaging was a small cellophane bag used by a local business to sell their delicious chocolate products; sadly, it now only contained the pellet!

Why pellets?

Why do owls produce pellets? Being birds of prey, owls hunt for things such as small mammals, birds, frogs, insects, etc. As with other birds owls cannot chew their food so the prey item is generally swallowed whole – bones, fur, teeth, the lot. Owls digestive juices are less acidic than in other birds of prey so the fur and other larger, harder parts are not broken down and so aren’t digested.

These indigestible parts are held in the bird’s gizzard before later being regurgitated as a pellet. That’s what I now had in front of me so there was only one thing to do, dissect it.

Dissection

Owl pellets are not faecal material and they don’t smell, other than slightly ‘musty’.

However, if you fancy trying this at home then please take care with hygiene – wear ‘rubber’ gloves and don’t touch your mouth or eyes while dissecting. Wash your hands thoroughly before you do anything else. Clean all surfaces used once you are finished.

After soaking the pellet in warm water in a margarine tub for about 30 minutes to soften the fur wooden cocktail sticks and tweezers were used to gently tease the pellet apart.

Take your time and you should recover most of the bones contained in the pellet and then you can work out what the owl had for supper!

The best bones to help identify the prey are the skull and lower jaws. The size and shape of these along with the layout and style of the teeth are perfect.

There are lots of sites on the internet to help with identification, but I use a brilliant leaflet produced by the Field Studies Council – ‘Guide to British owls and owl pellets’. Last time I looked it was only £3.30, a great present!? Anyway, here’s the link https://www.field-studies-council.org/?s=owls.

After an hour or so I’d extracted all the bones I could find in the pellet. The fur was put outside to decay and return its nutrients to the soil.

The result

A quick look at the skull bones told me that the pellet contained the remains of only one prey animal, a Field Vole, Microtus agrestis. That was what was expected as it has been a really good ‘vole year’. Many of Assynt’s owls have had above average breeding success this year and most of that is probably down to the abundance of prey items like this vole.

So, here are two photos. One shows the pellet as received, and the other shows the bones recovered from it. There was not a complete skeleton in the pellet, some bones may have been in another pellet. Also I don’t guarantee the anatomical accuracy of the ‘reconstruction’!

For an idea of scale the skull measures 20mm front to back and 14mm across.

You’ll get hooked. Enjoy.

D. Haines

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