One of the earliest lessons children are taught is the need to chew thoroughly each mouthful of food and under no circumstances to swallow it whole. Birds, though, down their meals in single gulps because they have a condition called edentulism. That’s a fancy word for toothlessness.
As a result some species like owls and hawks whose diets consist primarily of small mammals and birds don’t break them up into bite-sized portions but guzzle them in one piece, sometimes even when the prey looks like it’s still alive.
Then, later they regurgitate through their beaks the indigestible bones, fur and feathers in lumps known as pellets. These are often found at nests or wherever the birds roost at night.
Analysing them is a great way to study not just what they have been eating but also which species of voles, shrews and mice are living in the surrounding undergrowth. So it was fascinating at the weekend to watch some barn owl pellets being studied by children at Rodley Nature Reserve during the course of the annual Leeds Birdfair.
This is something I first did with tawny owl pellets around the age of ten. There was a nest in a wood behind our house so I gathered pellets from beneath the tree, soaked them in hot water then used a fork and my mum’s eyebrow tweezers to tease apart the fur in order to separate out the bones and skulls of mammals.
I earned a ticking off for creating this foul broth in our best crystal glass trifle bowl, but these children used proper plastic laboratory trays which very sensibly contained a mildly disinfectant solution.
One of their supervisors, Jeff Knapp, supplied them with pellets collected at Rodley in 2016 and kept stored in a deep freeze.
Studying the skulls which slowly emerged from the mass of black fur in one of the trays, he managed to identify a common shrew and a bank vole.
Jeff told me that in the past he had found field voles in barn owl pellets gathered on the reserve, however the live traps that are used to survey the local small mammals population have never produced a single field vole specimen.
Jeff’s pellet analysis - it is also a popular attraction at the annual Science Fair staged by Leeds Philosophical and Literary Society at the city museum each March - has sometimes found remnants of rats, birds and frogs.
When the process is completed the skulls and bones are sometimes mounted on display cards for the children to see the clear results of their work.
Owl pellets are the most rewarding to analyse because the tiny skulls of their prey are easy to identify.
Kestrel pellets are also interesting, and besides the common small mammals they are usually found to have easily distinguishable fragments of beetles and earthworms.
I once picked up a heron’s pellet and soaked it till it fell apart, but for my troubles all I discovered was a mass of exceedingly anonymous fish bones.