Bee-eaters Put Bumblebees Under Pressure
New study reveals species-specific impacts of European Bee-eater predation on wild bee populations - but genetics may be holding strong
Predators in the Pollinator Patch
The vibrant and charismatic European Bee-eater may be a delight for birders, but for some bumblebee species, its presence is far from welcome. New research from a German team led by Belinda Kahnt has revealed that Bee-eaters significantly reduce both the abundance and body size of certain wild bumblebee species.
The study, published in Oikos, focused on three widespread bumblebee species - Bombus lapidarius, B. pascuorum, and B. terrestris - in areas with and without nesting Bee-eaters in Saxony-Anhalt, Germany.
“Predation is a natural process, but in this case, it’s having measurable, species-specific ecological impacts,” said lead author Belinda Kahnt. “Given that European Bee-eater numbers are increasing due to climate change, this raises important questions for pollinator conservation.”
Winners and Losers Among Bumblebees
In areas with Bee-eaters, B. lapidarius and B. pascuorumwere significantly less abundant. B. terrestris, while not affected in abundance, did show a noticeable reduction in body size. Smaller bees are generally less efficient pollinators, so even subtle morphological shifts could alter pollination dynamics and plant reproduction over time.
The reduction in body size in B. terrestrisand B. pascuorumat Bee-eater sites suggests possible size-selective predation. “Our findings suggest that these birds may preferentially target larger individuals, especially in species where larger body size is more common or more energetically rewarding,” the authors wrote. Interestingly, B. lapidariusshowed no body size shift - possibly due to a narrower size range within the species or because its sheer abundance made it an easy, indiscriminate target.
No Immediate Genetic Fallout
Despite the ecological impacts, the study found no significant decline in effective population size or genetic diversity for either B. pascuorumor B. lapidarius Whole-genome sequencing of over 180 bees revealed that, so far, populations retain healthy levels of heterozygosity and resilience against genetic drift.
This could be due to high gene flow between populations, particularly as bumblebee queens and males are known to disperse widely. It may also reflect the relatively recent arrival of Bee-eaters in the region - sustained predation pressure might yet lead to evolutionary consequences over the coming decades.
Implications for Pollinators in a Changing Climate
European Bee-eaters have expanded their breeding range northwards in recent decades, bolstered by warmer temperatures. In Germany alone, their numbers have grown rapidly, with around 2,300 breeding pairs now present in Saxony-Anhalt. Each bird can consume up to 150 insects a day, and bees form a large part of their diet.
“These birds are natural predators and part of the ecosystem,” said Kahnt. “We are not suggesting they be controlled or culled, but rather that conservationists account for predation when assessing pollinator health - particularly in areas with large Bee-eater colonies.”
Managing for Coexistence
Instead of targeting predators, the authors advocate for habitat management to support bumblebee populations. Measures such as increasing flower abundance, reducing pesticide use, and providing artificial nest sites could help buffer pollinators from natural and human-induced pressures alike.
“The goal is resilience,” said co-author Panagiotis Theodorou. “Understanding both the ecological and genetic dimensions of predation helps us develop better strategies for long-term pollinator survival.”
May 2025
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