A Predator/Prey Conundrum

cropped-20150702_102831.jpgIn my spare time at the moment I’m working on an assemblage report for Haverfordwest Priory in West Wales. Occupation at the site dates to an Augustinian Priory in the Medieval period (around AD 1200) and continues through the dissolution and modern ages. The site has many interesting contexts, one of which dates to the dissolution period of the site, when parts of the Priory were in disuse and neglect.

The Prey

Exhibit A: vole, mouse and shrew jaws. And these were some of the big fragments!
Exhibit A: vole, mouse and shrew jaws. And these were some of the big fragments!
Woodmice, Apodemus sylvaticus. Credit: Mammal.org.uk
Woodmice, Apodemus sylvaticus. Credit: Mammal.org.uk

This particular group of contexts (the “Tower”) contain hundreds of bones belonging to small mammals. Represented were species of frog, rabbits, water voles, field voles, bank voles, wood mice, hazel dormice, house mice, species of rat, water shrew and common shrew. Also identified were the bones of small birds like the starling, blackbird, song thrush, skylark, pied wagtail and passerforms such as the house sparrow. Needless to say, all these tiny tiny bones took a long time to identify using the fabulous reference collection here at the University of Exeter, and I was really interested to look at the context in more detail when I had finished the identification phase and moved on to analysis.

The Predators

Within the same context I also had some really interesting bones of animals higher up the food chain, and I started to think that this assemblage could be the remains of meals eaten by animals using the disused priory tower as a roost/den.

Jackdaw, Corvus monedula. Credit: Brian Hopper.
Jackdaw, Corvus monedula. Credit: Brian Hopper.

Firstly there were many bones of corvid (crow) species in this context. Three corvid species were identified – the jackdaw, in the greatest number, the carrion crow and the raven. The jackdaw and the carrion crow are known to form large groups in the autumn and winter and roost communally (RSPB: Jackdaw). Their diet consists of insects, young birds and eggs, fruit, seeds and scraps/carrion (ibid.), although there are reports of them exploiting mice and frogs (BBC: Corvidae). Like many other birds, crows regurgitate pellets of indigestible material, which include fur and, importantly, bones.

Barn Owl (Tyto alba). Credit: Peter Trimming.
Barn Owl, Tyto alba. Credit: Peter Trimming.

Another potential flying culprit is the barn owl, whose bones were very occasionally found representing just one individual. The Barn Owl’s prey is mostly small mammals – particularly rats, mice, voles and other rodents, and also shrews, bats and rabbits, occasionally eating birds such as starlings and blackbirds (All About Birds: Barn Owl). They also sometimes store prey items at the nest site while they are incubating to feed the young once they hatch. Owls are well known for their regurgitated pellets, which they also use as nesting material, and are known to nest in human structures.

Weasel mandible
Weasel mandible

The final predatory species present in this fascinating context was the weasel. Weasels are a highly active predator in the United Kingdom, preying mainly on mice, voles and shrews but also any other viable prey such as small birds and young rabbits (Notts Wildlife: Weasel). They are known to live in woodlands, hedgerows, dry-stone walls and long grass. Weasels have historically been persecuted by gamekeepers where pheasants and partridges are reared – one probable pheasant bone and two woodcock bones were discovered in this context, but that is not to say that the weasel is entirely responsible!

So – what killed all the cute little furry things?

Well, it could be any of the predators listed above, or a combination, or none of them at all! What can certainly be suggested is that this is not a human accumulation of wild species, which shows the extent to which the Priory buildings were in disuse during this period. The species of prey present also give us a nice snapshot of the surrounding environment, which was marshy and had to be intensively managed before the priory was built – hence the presence of water voles and frogs. My money is on the barn owl for the majority of this accumulation – their prey-base fits the species I have here and their feeding behaviour with the regurgitation of large pellets would lead to the formation of such an assemblage. This was a great and unusual context for me to analyse, I enjoyed it a lot!

Barn Owl (closest match) distal humerus from the tower context.
Barn Owl (closest match) distal humerus from the tower context.

References:

Notts Wildlife: Weasel, last visited 08/12/15 http://www.nottinghamshirewildlife.org/animal-facts/weasel

All About Birds: Barn Owl, last visited 08/12/15 https://www.allaboutbirds.org/guide/Barn_Owl/lifehistory

BBC Corvidae, last visited 08/12/15 http://www.bbc.co.uk/blogs/natureuk/2011/10/autumnwatch-unsprung-round-up.shtml

RSPB Jackdaw, last visited 08/12/15 https://www.rspb.org.uk/discoverandenjoynature/discoverandlearn/birdguide/name/j/jackdaw/

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2 thoughts on “A Predator/Prey Conundrum

  1. Such an interesting post – thanks for sharing this. I wonder – do owl pellets remain in the environment (I’m reluctant to use the term ‘fossilise’ for things from 1200AD) like coprolites do? Or will they always break down and disappear? Could they be an indicator of the number of owls from so long ago?
    Not that I’m a researcher – just an interested amateur.
    Cheers
    Michael

    1. Hi Michael, thanks for your comment! I think that would depend on the preservation characteristics of the soil – in waterlogged environments you probably would get preservation of the individual pellets, but I’m not sure they would preserve in the same way as coprolites as they have a different make up. Hope this helps!

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