DOI: 10.5061/dryad.djh9w0vxr
title: Mass-migrating bumblebees: an overlooked phenomenon with potential far-reaching implications for bumblebee conservation

description: 1. Bumblebees are one of the most commonly studied pollinators, but they
 are declining in large parts of their distribution. Whether bumblebees can
 cope with anthropogenic disturbances such as climate change and habitat
 loss depends largely on their dispersal capacity. While bumblebee queen
 dispersal is estimated to be only a few kilometres, bird migration sites
 have documented mass-migration events with peak migration of 70 bumblebee
 queens per minute, indicating that bumblebees can migrate over larger
 distances than previously thought. 2. The open-access database
 trektellen.org contains ten daily counts of &gt;1000 migrating queens
 past single points in the Netherlands, and one in the UK (total bumblebee
 records 65,430; range 1-11,142 individuals), mostly in early spring. Such
 mass-migration events are poorly documented in the scientific literature,
 and usually when describing migrations of other insects such as syrphids
 and social wasps. 3. Most common European bumblebee species were
 documented to migrate. Bumblebees were observed flying at sea, coming from
 sea, and flying towards the sea, showing that they can cross large water
 bodies. The wind direction might have helped to concentrate migration at
 landscape bottlenecks. On one day, bumblebee mass-migration was documented
 on two sites located 200 kilometres apart. Together with the concentrated
 and directional flight this suggests that they can migrate for several
 hundreds of kilometres. 4. Because most mass-migration events occur in
 spring, large scale shortage in suitable nesting sites may be the trigger
 for mass-migration (e.g. due to high queen survival or low vole numbers).
 Future studies should test whether this is the case, or whether bumblebees
 show annual seasonal migration. 5. Synthesis and applications. Much
 remains unclear about bumblebee migration, but it may have large
 consequences for the conservation of bumblebees and the ecosystem services
 they provide. For example, bumblebees in highly disturbed areas like
 agricultural landscapes may be continuously supplemented by queens from
 far-away productive natural areas. This suggests that large-scale
 conservation initiatives are required to maintain viable populations of
 common and endangered species. Structured observations and modern-day
 technology, like isotope analyses or radar monitoring, may shed light on
 the drivers and consequences of the overlooked phenomenon of bumblebee
 migration.
description: This is a subset of the original data. All original data can also
 be retrieved through trektellen.org. This data has been collected by
 volunteers that count (mainly bird) migration. The data is owned and
 entered by the volunteers, and has not been curated. New data can be
 entered retrospectively, and old data can be updated. 
description: There are many limitations for this dataset, such as effort,
 observer bias and other contextual variables. Please consult the authors
 if you plan to use this data. Additionally, request an up-to-date file at
 trektellen.org and ask for permission to use that data.