Thursday, 28 May 2015

Owl Pellet Detectives

Yesterday we found three owl pellets whilst on a treasure hunt in the woods - a pretty good treasure find! With a bit of help from an RSPB guide , we decided to dissect them and see if we could work out which owl had made them and what they'd eaten.

An owl pellet contains all the undigested parts of the birds diet, such as bones, fur, teeth, insect wing cases and claws. After the soft bits have been digested, what remains is prevented from travelling further through the gut, compacted into a pellet and regurgitated by the bird.

We found them in the centre of Brush Hill, next to one of the ponds that was created during the winter. There are tall trees for roosting sites around the pond, including a few very tall conifers.

The pellets were grey, about 5cm long and you could easily see the fur and bits of bone in them. They didn't smell!

We soaked them in water and a splash of disinfectant for half an hour, then carefully dissected them using bamboo skewers. We searched through and pulled out all the bits of bone that we could find.

The basic material of the pellets (the matrix) was made of a mass of grey fur, presumably from rodents. The bones were in fairly small pieces, with no complete skulls, jaws or leg bones.

We found a couple of curved rodent teeth. There were a few slightly larger pieces of bone, which may have been part of a skull and possibly a part of a pelvis (but definitely not sure on these).

Rodent teeth

Top bone may be part of a skull and the bottom bone may be part of a pelvis
A tiny centipede crawled out of a mass of fur as well!

So what made our pellets?

The RSPB guide provides the following info:
  • Barn owls - roost in buildings or old oak or ash trees. Pellets are 3-7cm long and usually black. Often contain intact bones.
  • Tawny owls - roost in tree trunks, often tall conifers. Pellets are 2-5cm long and usually grey and obviously furry. The bones are usually more damaged by digestion than a barn owls.
  • Little owls - roost on old oak and ash trees. Pellets are 1.5-4cm long and often contain insect wing cases.
  • Kestrels - Pellets are 2-4cm long, pale grey and have a 'felty' texture. They digest more of the bones, so less bone fragments are likely to be found.
  • Sparrowhawks - Pellets are 2.5-3.5cm long and usually contain feathers (rarely contain bones)
We found 5cm long, grey, furry pellets, underneath tall conifers in woodland. When we dissected them, the bones were broken up and it appeared the bird had been eating rodents. Looks like we found Tawny Owl pellets!

We have a lot of Red Kites here, so I wonder what their pellets look like? I couldn't find anything out about them, so there's always a possibility that they could be from a Red Kite!

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