Steve's Herpetological Blog

An insight into the life of Steve, his research and the many books he reads


#SciFri: The wonders of dissecting owl pellets

Did you know that many birds such as owls produce pellets? Pellets are formed of all of the indigestible material they’ve consumed such as bones, teeth, feathers and fur. This is then compacted in the gizzard and regurgitated as a pellet, which can then be found by inquisitive minds to investigate. Owl pellets are not droppings – they haven’t been through the digestive tract, and in general do not smell (though this depends on the environment they’ve been deposited in, and what bacteria has colonised them). Pellets are usually found near roosts, and by taking a detailed look inside, you can determine what the owl (or other bird) has been eating. How cool is that?

So where did I acquire these magical pellets that contain all the secrets about the diet of the owls that regurgitated them? As it so happens, I collected them from a site in Norfolk during the summer months. You’re more likely to find owl pellets in areas where they are known to roost, as they’ll eat their prey here and then the magic happens! Once you’ve collected your pellets, you then want to think about storage. I’m lucky in that I have a dedicated freezer to all of my lab samples and this is where I chose to store my pellets until it was time to investigate what was inside. Upon collection, I put the pellets in a plastic bag, which was then sealed in a plastic container prior to freezing. If you don’t have access to a specialised freezer, don’t worry as it isn’t the end of the world. This step is taken to help make the pellets safer before investigation, but they still need to be soaked in a solution of water and anti-bacterial spray before you can tease them apart. Please do not store pellets in your domestic freezer as they may contaminate your food.

One of the owl pellets we dissected after being soaked. We aimed to remove as much of the excess moisture as possible before moving onto the next step

One morning in November, I was joined by my friend Vanessa to investigate the pellets that I had been hoarding since July. Here is her take on the events of that grey and gloomy day that was brightened by our curiosity!

Vanessa searching for small mammal bones in her first owl pellet dissection

Having never seen one in real life before, I had always imagined an owl pellet would be the size of a malteser. But when Steve extracted a barn owl pellet from the plastic bag, it was in fact oval-shaped and relatively large – more like the size of a damson. The first thing we did was to soak it in a Tupperware container of water mixed with disinfectant, for about twenty minutes. This loosened up the pellet, making it easier to dissect. Then we gathered some tweezers and toothpicks, I pulled on some gloves, and placed the pellet on a piece of kitchen roll. With the tweezers I began prodding the pellet gently, teasing it apart where it was naturally weakest. It turned out to be easy to accidentally break the fragile bones, by pulling the pellet apart too forcefully. The fur of the animals ingested by the owl, is what makes up much of the pellet, and is packed densely around the animal bones. Before long, we were extracting all sorts of bones from the matted fur. We were finding narrow, tiny bones like digits, tail bones, and miniscule vertebrae, all the way through to long, sturdy bones like femurs, pelvic bones, and humerae. We found a vast number of rib bones, as a small rodent like a mouse typically has 12 pairs of them!

A selection of the bones drying on some kitchen roll after being cleaned. All of these bones (and more) were found in a single pellet.

Skulls were also hidden in amongst the pellet. Freeing these skull parts from the pellet was fascinating: sometimes half of an intact skull would emerge, complete with teeth in the mandible. We were lucky enough to have a microscope to hand, so, after gently washing the skull piece in the water/disinfectant mix, we could take a look at the structure of the teeth in detail. Some teeth had a jagged, sharp zig-zag pattern (when seen from above), while others had a pattern of softer, wavy-looking cusps. After consulting the RSPB’s Owl Pellets guide, we could identify the species of small critter who the teeth and skull belonged to. What surprised me was that in just one pellet, we discovered the bones of three individual rodents  – a bank vole, a field vole, and some kind of mouse. It was hard to imagine that three skeletons had been bundled up and squashed together in this single owl pellet. Despite it being a fairly lengthy, delicate process, the dissection was highly interesting and absorbing. Whether you’re scientifically or forensically-inclined, or an eager naturalist with toothpicks to spare, I’d definitely recommend giving it a go, and seeing what you can uncover.

The bones we extracted from two owl pellets categorised by bone types (mostly). Can you spot the teeth we previously found at Reculver?

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