Flying on the Edge – Bees use linear features to navigate

Reference: Brebner, J. S., Makinson, J. C., Bates, O. K., Rossi, N., Lim, K. S., Dubois, T., Gomez-Moracho, T., Lihoreaum, M., Chittka, L., & Woodgate, J. L. (2021). Bumble bees strategically use ground level linear features in navigation. Animal Behaviour, 179, 147-160. https://doi.org/10.1016/j.anbehav.2021.07.003

Featured Image Caption: Bumble bees are essential pollinators that use linear features to navigate in agricultural areas (Image Source: “Abejorro europeo (Bombus terrestris), en una verónica (Hebe speciosa).” by Andres Bertens is licensed under CC BY-NC-SA 2.0).

Gridded Roads and Quilted Fields

The first time I flew in an airplane, I remember looking out of the small window and catching a glimpse of the city transitioning gradually into farmland. Before the plane burst through the clouds, I was captivated by how linear we had made the landscape. The roads formed straight lines in a perfect grid with buildings uniformly dotted throughout the square patches of land in the city. Even though the buildings dwindled, the land maintained its quilt-like patches in agricultural areas. Linear features are efficient for many aspects of our lives. For instance, straight roads make for faster travel by creating the shortest distance between two points. Similarly, crop fields have straight edges to optimize the space used for crops.

When we modify the land, we like to utilize straight lines and edges, such as our gridded roads (left) and quilt-like fields (right) (Image Sources: left, “Chicago-from-air-at-night” by dandeluca is licensed under CC BY 2.0; right, “Eastern Colorado from the Air” by Mr.TinDC via flickr).

Despite the benefits of linear features for us, these land modifications impact animals in various ways. For example, straight roads often counteract nature’s curvy features, breaking up patches of habitats. These barriers force animals to risk crossing roads to reach essential resources. On the other hand, our manufactured grids may benefit flying animals, like birds and insects. Bumble bees must find and remember the locations of food sources to make repeated trips to and from the hive. Agricultural land lacks visual cues for navigation, but a recent study found that the bees take advantage of roads and field edges to find food.   

The Path to Success
Bees can be tracked within one kilometer of the hive by attaching a lightweight tracker to their back (Image Source: Meadows R via wikimedia commons).

Bumble bees are essential pollinators, helping plants reproduce by transferring pollen from plant to plant. While pollination is important for maintaining beautiful flowers in our gardens, it is also vital for agricultural crop production. A third of the food produced in the world depends on insect pollinators. To continue this critical role, bumble bees rely on the sun and visual prompts to locate and revisit pollination sites. However, farmland often lacks skyline cues such as buildings, trees, or mountains (depending on the area). Instead, Joanna Brebner and her team of researchers wanted to know if bees could use field edges and paths to navigate to food sources. Perhaps the roads that we use in search of food could help bees perform a similar task.

In Seville, Spain, the researchers set up a beehive on a rice farm pathway. A small, lightweight tracker attached to the bees’ backs tracked the bees within a kilometer of the hive. When the researchers released the bees for the first time at the site, the bees spent a significant amount of time foraging for food along or parallel to pathways on the farm. The researchers then set up two feeders: one at an intersection connected to the hive path and the other on a perpendicular path to the hive (see image below). For the second feeder, the shortest distance from the hive would be to cut across the field rather than following the road. However, bees followed the linear features to the feeders for the first few visits. As they gained experience, they started cutting through the field to get to the second feeder. When the researchers removed the feeders, the bees would return to the feeder location and begin scanning along linear paths when they discovered the food was missing.

The researchers setup a beehive (right) on the path in a rice field and put one feeder down the path from the hive and another on a perpendicular path (left). They determined if the bees took the shortest path (solid, purple line) or used the path to navigate (dashed, black line) (Image Source: “Beekeeper Opening Bee Hive Box” by Alabama Extension is marked with CC0 1.0).
Save the Bees, Protect Our Food

In an agricultural landscape, bumble bees use linear features such as paths, roads, and field edges to find and revisit food. Flowers along these paths may be visited and pollinated more frequently than flowers in the center of the patch. However, the bees stayed within the patch borders when the hive was placed in the center of a field. After repeated visits, bees do not need to depend on linear features and will cut across the field to reach the food. Thus, hive placement in relation to linear features dictates the shape of the first flight spent searching for pollen.

Bumble bees are vital pollinators for our food crop, but populations are declining around the world (Image Source: “Face Full Of Pollen” by Mr & Mrs Apteryx australis is licensed under CC BY-NC-ND 2.0).

The results from this study have implications for hive placement in agricultural areas. Placing beehives on a path or edge may encourage the bees to pollinate along this feature, while a centrally located hive would promote pollination within the field. We can be tactical in our placement of beehives to be sure that the bees have convenient access to food. Further, these findings may be a valuable resource for protecting worldwide bee populations from declining, a significant threat for the future of our food supply.  

The gridded roads and quilted fields that caught my eye from high in the plane provide a road map for foraging bees. These grids could save the bees and protect the future of our food supply.

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Brandi Pessman

I am a third-year Ph.D. student at the University of Nebraska-Lincoln in the School of Biological Sciences. Growing up on a farm in a small town in Illinois, I developed an early love for animals and a fascination with their behaviors. When I was younger, however, it never crossed my mind that I would be using spiders to investigate how human presence affects animal behavior, but I am loving every second of it. Studying the behaviors of animals can tell us a lot about the role that we play in their survival (or death), which is becoming increasingly important as human populations continue to grow. When I am not studying spiders, I enjoy playing with my cat or being outdoors!

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