The trophic strategy of the European honey-buzzard Pernis apivorus during breeding: extravagant specialization or ingenious solution?

This article provides insight into the trophic strategy of a little-known top predator and allows for a better understanding of the selective pressures that shape its diet. We studied the diet of European honey-buzzards, a raptor specialized in consuming social wasp brood. The ratio of predator to prey biomasses is one of the highest among raptors. Considering the prey size and ingestion rate hypothesis, we investigated the honey-buzzard's preferences for native and exotic eusocial vespid species. We also described other prey items in the diet and how diet changes throughout the breeding season. We installed trail cameras in 24 honey-buzzard nests in north-western Spain in 2018–2021. We estimated the proportion and daily rate of delivery of native common-wasps, invasive Asian-hornets, reptiles, and birds and the honey-buzzard's preferences for vespid species. We performed LMMs, GLMMs, and CLMMs to analyse relationships between response variables and predictors. Honey-buzzards mainly consumed vespids (82% of prey). Common-wasps and Asian-hornets were almost the only two vespids consumed. The invasive hornet was the second most consumed prey, but common-wasps were preferred. Vespids became more important as the age and number of nestlings increased. Our results suggest that this diet is the adaptive result of the conflict between being a median-sized insect-eating nidicolous raptor and collecting enough morsels for the growth of its nestlings. This would allow them to deliver a relatively large amount of biomass to the nest with a high ingestion rate. We discussed implications of our findings for the management of the invasive wasp.