I had the good fortune to observe, from the shelter of a hide in Sierra Morena, a phenomenon worthy of being described… A Great-spotted Cuckoo (Clamator glandarius) recently arrived from its migratory route was filling its crop with the caterpillars that make striking communal nests at the end of winter in the meadows of Andalusia.
ABSTRACT : In its European breeding range, the Great-spotted Cuckoo is known primarily as a specialist predator of Lepidoptera, in particular the urticating caterpillars of the pine processionary moth, Thaumetopoea pityocampa. We observed an individual feeding extensively on larvae of the butterfly Ocnogyna boeticum (Rambur, 1837) in a dehesa ecosystem, with a count of more than 768 caterpillars ingested. PDF
It has given me great satisfaction to publish for the first time in an international ornithological journal, Avoceta -the bulletin of the Centro Italiano Studi Ornitologici-.
Unlike other occasions when I devoted much effort to complex sampling campaigns, the pleasure here is all the greater because this time, the study practically ran itself. From the very first moments, I felt it was worth counting the prey ingested. Moreover, we had booked the hide for the whole day, and we had nothing else to do but calmly observe the bird. A long day, certainly, but just a single day in the field. Perhaps my most profitable day as a naturalist.
I invite you to read the article, which is freely downloadable. Because, beyond the simple counting of caterpillars — which have gone from a life in the open air on their webs to a direct incorporation into the bird’s diet — this mini-study surprised me by the complexity of the questions it raises.
Firstly, the ability to observe a single individual for an entire day and to document its behaviour very thoroughly; the behaviour of the host corvids present (Eurasian magpies and Iberian azure-winged magpies); the synchronisation between the arrival of the migrant — very early — and the hatching of the caterpillars; the possibility that Ocnogyna boeticum constitutes an important part of its diet; and the abundance of both the prey and the bird in other Mediterranean regions, such as Cyprus.
One fine day in 2026, I officially became an ornithologist. The only catch: now I have to follow the path laid out.
Publishing a natural history article based on pure observation means inscribing oneself in the naturalist tradition at a time when this is becoming increasingly difficult to practice on European wildlife. A particular satisfaction.
Acknowledgements: first of all to Daniel and William Dow, with whom we shared a photographic session and who made these observations possible by relying on the G3 guides. It was a pleasure to travel together while maintaining a good atmosphere at all times. To Nick Owens for providing us with information on the diet of the Great Spotted Cuckoo in the United Kingdom. To Guillermo Delgado, manager of Paraje San Ginés and the hide in the Sierra de Andújar, a host always attentive and committed to conservation. To Roberto Ambrosini, editor-in-chief of Avoceta, and to the associate reviewers.
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