My data collection has been going well so far. I have dissected 30 pellets and aim to dissect another 30 by halfway through next week.
Here are some pictures of what I have been doing:
An owl pellet from Forwood farm:
Part of the jaw and skull of a Field vole:
The lower jaw of a Brown Rat I found in a pellet from Willow Works, in Beckingham (It was HUGE): 
And a clothes moth grub (I keep finding these guys, and adult clothes moths in the Willow works pellets):
Content of pellets from breeding and roost sites in Southern England (from this study)
“Bird remains were not identified to species, and a figure of 20 g has been used for the liveweight equivalent of a bird. Average weights per species used in calculation are as follows: mole 70 g; common shrew 8 g; pygmy shrew 4 g; ‘bat’ 6 g; bank vole 16 g; field vole 21 g; water vole 100 g; wood mouse 18 g; harvest mouse 5 g; house mouse 12 g; brown rat 60 g; ‘bird’ 20 g.
Between 1983 and 1985 members of the Banbury Ornithological Society took part in the so-called Domesday Project, where the twelve 10 km squares identified as the Society’s study area were surveyed to determine land use. Over the study area, 53% was arable, 35% permanent pasture and 8% ley (rotational grassland)”
This table shows the results of dissecting 23058 pellets, which I could compare to outcomes of similar studies and see if I can build up a picture of what to expect from the pellets I dissect.
The study also states that there was a negative relationship between the Field Vole and Wood Mouse, indicating that the Wood Mouse may replace the Field Vole in the diet of the Barn Owl when the vole is less available. This suggest that the availability of field voles may be less important for breeding success than is stated by the Shawyer book.
Prey Items and Diet Variation
Barn Owls swallow prey whole and are incapable of digesting much bone, which is why the contents of their pellets can prove very revealing. They tend to prey on small mammals such as voles, mice and shrews, with Field Voles being the most nutritionally important prey item in mainland Britain. Shrew are not as nutritious in terms of weight.
The amount of prey consumed must be especially high before breeding and throughout the nesting period, when prey items consumed for a pair of owls increases from around ten to forty per day. The breeding biology of the Barn Owl is largely adapted to the vole’s availability. The population of the vole peaks around Autumn, which is when inexperienced young owls are first hunting. By comparison, the Wood Mouse population tends to peak early-winter, while shrew numbers peak mid-summer.
In the Spring shrews become more vocal and male voles become more active, while rats often move to farm buildings in late-Autumn. These changes are typically reflected by changes in the Barn Owl’s diet, as they make these prey items easier to find.
The number of mice taken over the summer may fall as they have more cover to hide in. Moles only tend to be taken between May and August, during which time they are closer to the surface. Starlings and House Sparrows feature more commonly in the Barn Owl’s diet during Winter.
Barn Owls do not appear to select voles, mice and shrews of any particular age or sex.
Pellets
Pellet length can provide an indication of the amount of live prey taken (Although Michael Toms has found a more reliable way to determine this -Look this up? Is it relevant to my investigation?) . Immature owls may digest bones more thoroughly than adults.
Pellets can provide the following information:
This bears no relevance to my investigation as I will not personally be collecting the pellets I will be using, but I found the following warning amusing:
Barn Owls seem very active in their bombing, usually selecting an escape path overhead and…