Waggle dances reveal bees' favorite environments

Honey bee foragers perform waggle dances upon returning to the hive to advertise rich sources of nectar and pollen to other foragers.  The performance of a waggle is itself significant, since bees will only dance for a food source if it exceeds a certain quality threshold, which fluctuates depending on the other forage available and the needs of the colony.  These dances are even more informative, however, in that they communicate the location of a food source to other bees – and to researchers.  Given that the duration of a single waggle run indicates the distance between the hive and the food source, and the angle of the waggle run with respect to vertical corresponds to the angle between the food source and the sun, a few studies (by Seeley, a notable bee researcher, and others) in the past have used waggle dances to map out the most profitable sources of forage surrounding a bee hive.  However, a recent study by Margaret Couvillon and co-workers, published in Current Biology, is the first to use a long-term assessment of waggle dances to determine which environments are most hospitable to honey bees.

Couvillon and co-workers kept three colonies of bees in a laboratory at the University of Sussex, England, with both rural and urban surroundings.  This gave the bees a variety of environments in which to forage, including urban areas, nature reserves, non-regulated rural areas, and rural areas under varying levels of agri-environment schemes (AESs), which offer financial incentives to "make existing agricultural land more wildlife friendly" (Couvillon).  The foraging behavior of bees, as Couvillon notes, is one measure of the effectiveness of AESs, since domestic bees forage from plants that wild pollinators also visit.  Over two years, the researchers observed and decoded over 5,000 waggle dances, which they mapped onto the surrounding landscape to locate the most preferred food sources for their colonies.  Distance from the hive is an important factor in how bees determine resource quality (which, in turn, affects whether or not they dance), so the researchers corrected for the effect of proximity in order to analyze the inherent value of each type of environment for foraging.

Density and distribution of profitable forage sites surrounding the hives (white star), before (A) and after (B) correcting for the effect of distance.  In (A), we see that most of the dances occurred for resources relatively close to the hive, but in (B) we see that there was an inherently high-value resource located to the southeast of the hive.  (image source: Couvillon 2014)

The researchers found that the most profitable sources of forage for bees were within nature reserves.  With the area surrounding the hive divided into square blocks (as seen above), the highest-ranked block (not affected by distance) contained a nature reserve a medium distance away from the hive (the red blotch to the southeast), while the second highest-ranked block also contained a nature reserve, but was at the outer edge of the range described by 99% of the observed dances (the orange-yellow area to the northwest).  This indicates that the nature reserves, which are often full of wildflowers, were valuable enough to the bees to merit even long trips away from the hive.  Interestingly, bees also showed a preference for a certain type of AES that requires "the creation and maintenance of long-term set-asides and temporary grasslands" (Couvillon), which likely contain wildflowers.  With distance effects removed, the bees also showed a slight bias against urban areas and a significant bias against a type of AES under which fields of nectar-rich flowers are regularly mowed; the authors suggested that mowing these fields removes the value that they would otherwise have for pollinating insects.

It is well-accepted that bees thrive with diverse sources of food, especially pollen, which provides amino acids and other nutrients for developing bees that vary greatly between flower species.  Therefore, it is not surprising that bees would prefer to forage in natural environments that contain a variety of wildflowers over agricultural or other planted areas.  Given that the health of domestic bees is declining, and wild land is becoming increasingly scarce in the United States and Europe, this is a sobering realization.  However, learning where bees prefer to forage in particular environments will help in designing more precise policies to protect and even improve the health of domestic bee colonies.  For example, this study revealed that grassland is attractive to bees, but regular mowing destroys its value.  The results of this study, that bees prefer areas with an abundance wildflowers, suggest that allowing wildflowers to grow among crops could make the colonies that pollinate those crops stronger and perhaps less susceptible to illness.  Furthermore, the bees' preference for diverse patches of flowers suggest another advantage of polyculture (growing multiple crops in the same area at the same time), beyond plant and soil health.  The method that Couvillon and co-workers developed to assess the value of various environments to a bee colony, simply by tracking the dances performed by bees in the hive, can be used anywhere to provide localized information about which agricultural and ecological conservation schemes are most beneficial to honey bees and other pollinating insects.

I also consulted the perspective article written by Stephan Härtel and Ingolf Steffan-Dewenter before writing this summary.