Do nest sites limit wild honey bee colonies? Decoding swarm waggle dances to assess nest site availability

Abstract

Nest sites are often considered to limit wild honey bee, Apis mellifera, colonies in Europe where wild colony densities are low (mean 0.26/km2). Nest site availability can be challenging to quantify directly, especially in urban areas and farmland where colonies nest in different substrates. Here we assess nest site availability indirectly across large areas (78.5 km2) of mixed habitat (67% farmland, 25% urban and 8% woodland) by decoding 3310 waggle dances produced by scouts on swarms. During summers of 2021 and 2022, 14 artificial swarms were set up in two study areas in East Sussex, England. Swarms advertised three to nine nest locations (mean of 5.5) at distances of 0.1–11.2 km (median 1.2 km) all within 0.4–15.2 daylight hours after dancing commenced (median 2.7). We estimated the total number of nest locations, including those not advertised, by quantifying the overlap in locations advertised by two swarms (a form of mark–recapture), which gave a mean density of approximately three nest sites per km2. The probability of swarms advertising nest sites per km2, calculated using simulations of dance variation, was an average of 42% higher in urban areas (0.018/km2), 78% higher in woodland (0.023/km2) and 12% lower in farmland (0.011/km2) than random expectation. After controlling for distance, swarms were still more likely than expected to advertise nest sites in woodland but only in one study area. Our results indicate that nest sites do not limit wild colonies in the study areas given that our conservative estimate of nest site density (3/km2) exceeds the density of wild colonies on nearby landed estates (2/km2) and other locations in Europe (0.26/km2).