Kestrel Diners
Four Fine Falco Fledglings, Long Mead Barn.
'If you build it they will come...'
This is our experience of putting up nest boxes at Long Mead. So when we built our thatched barn and installed a kestrel nest box under the eaves we were not surprised to find that a kestrel pair took up a long lease on it for their family home. In lieu of rent they leave us food pellets outside the front door most mornings, knowing they are worth their weight in silver for our research projects.
We have been collecting pellets of the kestrels and a pair of barn owls, who are not (yet) nesting in the barn, but visit regularly to leave us their pellets.
Barn owl pellets (L), Kestrel pellets (R), collected at Long Mead Barn.
The pellets are regurgitated lumps of undigested food, so can provide direct information about a bird’s diet - if someone is expert enough to analyses the contents. Fortunately, a dream team - Linda Losito, a beetle expert, and Bob Cowley, a small mammal expert - took on the challenge of analysing a year’s-worth of pellets we had diligently collected from Long Mead Barn. Why a beetle expert when everyone knows that a hovering kestrel is looking for a small furry animal for its dinner? The clue lies in the name of the journal that published their intriguing results: The British Journal of Entomology and Natural History.
Typically, the pellets of the kestrel and the barn owl have a dark uniform appearance (see photo above). Bob was able to identify from the bones in the kestrel pellets that their main diet consisted of field voles, with side helpings of bank voles, wood mice, common shrews and pygmy shrews. In mid-summer months, however, we noticed that the pellets we collected had a glistening, glittery appearance, which was clearly not due to any small mammal. What glittered were the undigested carapaces of many beetles, and here beetle-expert Linda was able to identify the individual species, 29 in all, mainly members of the family called Carabidae, which are ground-living beetles, thus indicating that the kestrels not only catch prey by their impressive hovering technique, but they also forage on the ground.
Interestingly Linda also found evidence that in July our kestrels went hawking and caught insects on the wing, mostly brown chafers. Presumably other winged species like dragonflies might also be caught, but if they are well-digested they would not leave their signature in the pellet. Clearly, kestrels are not fussy eaters and will opportunistically eat whatever animal comes their way. Insects might be tiny compared to voles, mice and shrews, but they are rich in protein and other important nutrients like minerals and vitamins. And there are lots of them on the meadows.
The fact that we collected the pellets month-on-month meant that Linda and Bob could plot how the kestrel’s diet changed over the year. In autumn, winter and spring, the main prey items were small mammals and they found only three species of insects. Then as summer progressed, beetles became more and more predominant in the catch, reaching a peak in July, when the remains of only one mammal was found. Interestingly, none the barn owl pellets collected over the same period had beetle remains.
Nocturnal visitors to Long Mead Barn actively participate in NRN research projects by donating their food pellets for science.
One implication of their painstaking analyses is particularly relevant to NRN activities: their evidence that insects are such a crucial part of the kestrel’s diet, particularly during the time they are raising a brood, means our work to create habitats, like meadows, hedgerows and woodlands where a diversity of insects can flourish, has huge value for birdlife. As a corollary we should, 'do no harm' and redouble our efforts to stop using insecticides in our gardens and on our pets and wherever possible buy food sourced from organic or regenerative farms and market gardens, which use no pesticides (recommended reading: The Silent Earth by Dave Goulson of Sussex University about his research on the devastating impact of insecticides and other pesticides and herbicides used in farming).
Postscript:
Linda and Bob have not rested on their well-deserved laurels, but continue to analyse pellets from Long Mead barn and identify the beetles that live on ancient floodplain meadows and the meadows we are restoring. One notable recent finding was that the barn owls had captured harvest mice, our smallest mammal (7g!) and relatively rare in Oxfordshire (Facebook link below). Another of their remarkable feats was identifying the remains of a Natterer’s bat that had been ringed by Dr. Danielle Linton in Wytham woods in July 2014. This particular individual had not been seen since 2016, but its skeleton (with identifying ring!) was deposited in a pellet at Long Mead in late summer 2024; presumably it had been caught by a barn owl.
We eagerly await further revelations about our resident and visiting Long Mead birds of prey.
All credit and thanks to Linda and Bob for contributing their time and painstaking work to the Long Mead research efforts.
KACM
References
Losito L, Cowley B, (2025) The importance of beetles in the diet of kestrel (Falco tinnuculus) and little owl (Athene Noctua). Brit. J. Ent. Nat. Hist. 38: 21 – 25.
https://www.facebook.com/bob.cowley.oxford/posts/pfbid02Kenzy5uKNvb6cJy4dNSetYiQNLbz4aCG5jgVneT5vfT4zaeygKYhU1cqhm6HGdGkl?rdid=cEjThctxufH6lC9Q
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