Find out what this long-eared owl has eaten by examining its pellets
Image: Chris Gomersall
Most birds produce pellets. The more indigestible material there is in the food, the more pellets are produced. The best known birds that produce pellets are the owls and the daytime-hunting birds of prey (raptors). Owl pellets are the easiest to find and study, because they often collect beneath a favoured feeding post or roost.
Pellets are small, sausage-shaped objects, containing the undigested parts of the birds food which are ejected through the mouth. Pellets do not pass through the intestine of birds and are quite different from droppings. They do not smell, and are not unpleasant to work with. They consist of things like the bones of birds, mammals and fish, teeth, claws and beaks, insect head parts and wing cases, seed husks etc. These are usually enclosed by softer material like fur, feathers and vegetable fibre.
Once you have identified the contents, you can use the results to discover a great deal about the habits of the bird.
When does it hunt?Some mammals are active during the day as well as by night. Others, especially the wood mouse, are strictly nocturnal. You may be able to discover whether a bird hunts by day or by night.
Where does it hunt?Small mammals prefer certain kinds of habitat. The field vole lives in grassland, the bank vole in woods and hedges. Such creatures will give you clues as to where the owl was hunting.
How much does it eat?You can work out the number of animals in each pellet from the number of skulls or jawbones. Some people prefer to count the number of pelvic bones, in case the head of the prey was not swallowed. Remember that an owl probably produces two or
three pellets each 24 hours.
Does its diet change with the season?If you can find enough pellets at different times of the year, you may find some interesting differences.
What part does the owl play in the food chain?Find out what the prey animals eat. Some are vegetarian, like voles. Others eat only animal food, like shrews which feed on insects and other small creatures.
You can construct a diagram of a food chain from your results.
Dissecting owl pellets at an RSPB Wildlife Explorers event
Image: Andy Hay
You will need:
Do not be surprised to find small white live grubs. They are the larvae of clothes moths, and they feed on the fur or feather material of the pellet. Owl pellets must be one of the original homes of clothes moths, long before there were any clothes!
The remains of small creatures such as insects are often found in pellets, and in little owl and kestrel pellets these can be particularly abundant. To find and identify them often requires a dissecting microscope.
The keys in this guide will help you to identify the contents of the pellets.
1. The basic material (Matrix)Fur will lead you to expect mammal remains. It may even keep its colour and help you to recognise the species.
Feathers often break down into a loose powder, but you can still usually find small quills, the central stem of the feathers. They alert you to look for bird remains.
Sand or soil usually indicates earthworms. You will need to use a microscope to find the minute bristles called chaetae which confirm this.
2. BonesSome bones are especially useful for identifying the species of prey. In this guide we use the bones of the head - skull and jawbones - as the means of identifying species. When you have found and cleaned them, try and work out what they are by using the key to skulls. A few other bones are good indicators of species. The most important of these are shown in the key.
Sometimes it is interesting to know the origin of each bone, and what part of the body it is from. We have included a diagram, which illustrates the bones of a typical small mammal, and shows where in the body they are found.
3. Other remainsSome insect remains are fairly easily recognisable, for example the wing cases of beetles. Other hard parts which survive include legs, jaws and even complete heads. Some of these are illustrated in the key.
Have a piece of card handy for each pellet. Write on the top of the card the name of the bird that produced the pellet, and the date and place where it was collected.
Arrange all the articles from the pellet that you have identified onto the card and stick them in place with strong glue.
Beside each of the remains, write the name of the animal from which it came. If you wish, you can include the soft material of the pellet on the card, fully dried and suitably labelled, in a small polythene bag.
Finding pellets requires knowing a little about the habits of the bird. Most pellets are produced at the birds roosting place. But it's not just owls that produce pellets. More...