Barn Owls Eating Cockchafers

I recently found a Barn Owl nest site in North Yorkshire, with an associated roost in an old abandoned, stone building. The nest appeared to have not been used this season, although birds were still evidently roosting in the building on occasion, as told by dropping and pellets. As is often the case at nest sites there was a huge collection of pellets. As I walked past one in particular caught my eye, upon picking it up I found it was absolutely packed with Cockchafer remains, as indeed were several others around it. This was quite interesting given I rarely ever find invertebrate remains in Barn Owl pellets.

Barn Owl pellet full of Cockchafers

Cockchafers are large beetle which fly on an evening, in late spring and are often associated with grassland habitats. The larvae develop underground where they feed on the roots of broad-leaved plants and grasses. This is a common species, which can become very numerous around emergence times and is nocturnal behaviour makes its a great food resource for species like Noctule Bat and Little Owl, which were both also observed using this same site, and both undoubtedly making use of the Cockchafer feast.

Despite never seeing Cockchafers in Barn Owl pellets before, this is a very adaptable owl species found throughout the world in a wide range of habitats. Not surprising its diet varies considerably throughout its range, as well as throughout the year when fluctuations in prey may influence hunting strategy. Even in Europe the diet contrasts with birds in he north favouring microtine rodents, birds in the south being more skewed towards a diet of reptiles, in particular geckos. There's even birds on islands in SW Europe which specialise in catching Storm Petrels. Therefore eating a large very numerous beetle shouldn't be that unusual one might think.

Birds of the Western Palearctic lists a large number of prey items recorded from Barn Owl pellets, throughout Europe and this includes beetles in the Scarabidae (the family in which Cockchafers belong). It also states that "invertebrates form only readily available prey group which appears to be avoided" and that "Pellets do not allow precise quantification, but, in Europe, more insect remains found in south. In Britain and Ireland, invertebrates negligible in both pellets and guts: mostly beetles—342 among 47 865 vertebrates in pellets".

Diet studies in the UK (below) adapted from the Birds of the Western Palearctic show invertebrate prey to be extremely low in the diet of British birds. This study included 47 865 prey items of which only 342 were invertebrates.

*larger mammals include species like brown rat, water vole, weasel

I couldn't find any reference to Barn Owls feeding on Cockchafer online, or on the Barn Owl trust website so I will keep digging. A friend at the Lower Derwent Valley near York had mentioned only previously seeing this behaviour once and that they considered it to be an unusual occurrence. Were these birds just taking advantage of a highly abundant food source or has the poor cold spring weather made hunting poor or reduced prey densities and Cockchafers in pellets are a sign of birds struggling to find alternative more favourable food. I will keep digging..