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Pollinators, like bumblebees, are essential for agriculture, yet they’re declining due to landscape simplification and habitat loss. In this blog post, Riho Marja and colleagues tell us more about their study.
Riho Marja and his team explored the effect of field size on Bumble bee populations in Austria and Hungary. They explored this by setting up 56 commercial bumblebee colonies in Eastern Austria and Western Hungary. Two regions earlier divided by the Iron Curtain and now significantly different field sizes—Austria with very small and narrow fields (around 2 ha), and Hungary with large area fields (around 17 ha). At each site, colonies were placed next to either mass-flowering oilseed rape or near winter cereal fields, and either close to or far from semi-natural habitats like forest patches, hedgerows, river margins, or low intensively managed grasslands.
The goal was to find out how local (crop type) and landscape-scale features (field size and proximity to semi-natural habitat) affect colony success, specifically colony traffic rate (a proxy for activity), growth, and reproduction. We also examined collected pollen diversity and tested bumblebee navigation by relocating workers and recording how quickly they returned home colony with small radio frequency identification tags.
What we found
- Proximity to semi-natural habitats and oilseed rape fields increased bumblebee activity and colony performance. Colonies next to oilseed rape and near semi-natural habitats had higher traffic rates, grew faster, and produced more queen brood cells.
- Semi-natural habitats improved bumblebee orientation. Bumblebees returned to their colonies faster when they were close to semi-natural habitats, especially when flower diversity was high. In contrast, colonies far from these habitats showed slower return times, likely due to fewer visual navigation cues.
- Small field size improves navigational efficiency. Bumblebees returned faster even when flower species richness was low. This seems counterintuitive, but we believe that dense networks of field edges in these areas make orientation easier—even without a high diversity of flowers.
- Bumblebees didn’t just use for the most abundant flowers. Interestingly, bumblebees often preferred pollen from wild bushes or trees and herbs in semi-natural habitats over the more abundant and flowering oilseed rape. While oilseed rape supported colony growth, the majority (more than 80% of cases) of pollen came from wild plants like Acer and Prunus species.
Why it matters for land managers and policymakers
This study shows that small fields are very importantm but aren’t a only solution to support pollinators. Their benefits for pollinators depend also on nearby semi-natural habitats, which offer diverse and season-long food resources and help bumblebees navigate.
In large-scale farming areas, restoring or maintaining semi-natural habitats becomes even more critical. Without them, even mass-flowering crops like oilseed rape can’t fully compensate for the lack of food resources throughout the season.
So, for effective pollinator conservation and sustainable agriculture, we recommend:
- Retaining or restoring semi-natural habitats, especially in large-scale agricultural regions.
- Maintaining or creating small field sizes where possible.
- Enhancing flower diversity, not just abundance. Diverse pollen sources are key to colony health and reproduction.
Final thoughts
Our findings suggest that smart landscape design—not just crop choice—is crucial for supporting pollinators. Semi-natural habitats and small-scale farming systems complement each other in creating a pollinator-friendly environment.
For the farmers we recommend: combine small field structures with patches of semi-natural habitat to support healthy pollinator populations and the ecosystem services they provide.
Read the full article ‘Pollinator benefits of small-scale landscapes depend also on semi-natural habitat‘ in Journal of Applied Ecology.
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