A preference for local foods: bumble bee foraging decisions in a Rocky Mountain meadow

Pollinators must make decisions about where to forage in landscapes where floral resources are patchy at many spatial scales. The resulting foraging decisions can influence plant pollination and reproductive success. Despite this importance, we still have a poor understanding of how pollinators use patches which vary in floral abundance and isolation, particularly at an individual pollinator level. We marked and resighted known individual bumble bees (Bombus spp.) visiting 12 flowering Delphinium barbeyi patches that varied in size (small and large: 4 and 400 m², respectively) and isolation (near and far: 5 and 50 m distance, respectively) in a subalpine meadow in the Colorado Rocky Mountains. At the patch level, large and near patches received more bumble bee visits per flower than small and far patches. At an individual bee level, most marked individuals foraged only in one patch. Bombus nevadensis, B. flavifrons and B. appositus were the most common bumble bees seen, yet we saw very few marked B. nevadensis again, suggesting that this larger bee is less site faithful and may have a larger foraging range than the other two common smaller bumble bees. We show that individual bumble bees commonly forage very locally in a meadow and that they prefer to forage in large and near patches, which may have implications for the pollination of D. barbeyi.