Here are results from the first three years of the California Bumble Bee Atlas!
Where we found the bees
In 2024, we made observations of 7,630 bumble bees, bringing our 3-year total to 18,337 bumble bee observations. Together, volunteers and project staff completed 794 effort-limited ('point') surveys, bringing our project total to 1,930 surveys. To-date, 579 people have submitted data to the California Bumble Bee Atlas! Here's a map of all observations you submitted to Bumble Bee Watch 2022-2024:
In 2024, we made observations of 7,630 bumble bees, bringing our 3-year total to 18,337 bumble bee observations. Together, volunteers and project staff completed 794 effort-limited ('point') surveys, bringing our project total to 1,930 surveys. To-date, 579 people have submitted data to the California Bumble Bee Atlas! Here's a map of all observations you submitted to Bumble Bee Watch 2022-2024:
Progress on grid cell map
A goal of the project is to complete multiple point surveys in each of 266 grid cells distributed across the state. To accomplish this, we asked volunteers to "adopt" a grid cell, then complete two or more surveys in that cell during the field season. After three years of work, how are we doing with this goal? As the map below illustrates, we have made a lot of progress, with 62% of grid cells completed (i.e., having had two or more surveys; green in the map below). That said, we still have a lot of cells that need surveys! In 2025, we'll be encouraging you to complete field surveys in some of these cells that have not yet had two surveys--especially those in the Central Valley and northern California. While we also have a lot of cells in the low deserts that have not been surveyed, we're somewhat less concerned with these, given that many parts of the Mojave and Sonoran deserts are too hot and dry to support bumble bees.
One note, we don't mind if multiple volunteers adopt the same cell, and this has resulted in very thorough surveying of some cells, with a high score of 77 surveys in one Bay Area grid cell!
A goal of the project is to complete multiple point surveys in each of 266 grid cells distributed across the state. To accomplish this, we asked volunteers to "adopt" a grid cell, then complete two or more surveys in that cell during the field season. After three years of work, how are we doing with this goal? As the map below illustrates, we have made a lot of progress, with 62% of grid cells completed (i.e., having had two or more surveys; green in the map below). That said, we still have a lot of cells that need surveys! In 2025, we'll be encouraging you to complete field surveys in some of these cells that have not yet had two surveys--especially those in the Central Valley and northern California. While we also have a lot of cells in the low deserts that have not been surveyed, we're somewhat less concerned with these, given that many parts of the Mojave and Sonoran deserts are too hot and dry to support bumble bees.
One note, we don't mind if multiple volunteers adopt the same cell, and this has resulted in very thorough surveying of some cells, with a high score of 77 surveys in one Bay Area grid cell!
Bumble bee species frequencies in our surveys
One way of understanding the California Bumble Bee Atlas results is to compare species by frequency (or relative abundance) in the data. The graph below shows the percent of identifiable records in the CABBA dataset that are accounted for by each species in 2022 (blue triangles), 2023 (gold squares), and 2024 (green circles). As you can see, B. vosnesenskii is by far the most common bumble bee species in California, while others, such as B. occidentalis, are much less common. One thing that's interesting to note is that some species have steadily increased or decreased in commonness across the three years of the project. Some of these changes may be driven by environmental factors such as precipitation (e.g., we have speculated that B. crotchii is more common following wet winters such as those preceding the 2023 and 2024 field seasons), while others may reflect changing patterns of survey effort in each year. As we go forward, we'll be making an effort to understand what is driving apparent demographic changes in California's native bumble bees.
One way of understanding the California Bumble Bee Atlas results is to compare species by frequency (or relative abundance) in the data. The graph below shows the percent of identifiable records in the CABBA dataset that are accounted for by each species in 2022 (blue triangles), 2023 (gold squares), and 2024 (green circles). As you can see, B. vosnesenskii is by far the most common bumble bee species in California, while others, such as B. occidentalis, are much less common. One thing that's interesting to note is that some species have steadily increased or decreased in commonness across the three years of the project. Some of these changes may be driven by environmental factors such as precipitation (e.g., we have speculated that B. crotchii is more common following wet winters such as those preceding the 2023 and 2024 field seasons), while others may reflect changing patterns of survey effort in each year. As we go forward, we'll be making an effort to understand what is driving apparent demographic changes in California's native bumble bees.
Seasonal phenology (timing)
What has the project revealed in terms of bees' seasonal activity periods? Consistent with what is known generally about these animals, we have documented a lot of variation between years. The graphs below show the relative commonness of Vosnesensky bumble bee (B. vosnesenskii) and Crotch's bumble bee (B. crotchii) across the summer in each of three years. For Vosnesensky, it looks like queens and workers (combined as "Female" here) vary as much as 2-3 weeks in the timing of their activity, while the pattern of male observations is more consistent. By contrast, for Crotch's, we have documented quite a lot of variation in both female and male activity between years. We don't know exactly why bumble bees vary so much in the timing of their life history, but in California, temperature and precipitation seem to play a big role. This variation means that in some years, queens may become active either before or after critical food plants bloom. This 'phenological mismatch' has recently been the focus of some climate-change-related bumble bee research.
(How to read these graphs: these curves are called kernel density plots, and give an index of how abundant the species/sex is at each point along the horizontal time axis. We don't need to worry about the units on the vertical axis, but the shapes of the curves can tell us a lot about bee phenology. As always, we should expect that these patterns may be affected by human bias, such as timing of our surveys.)
What has the project revealed in terms of bees' seasonal activity periods? Consistent with what is known generally about these animals, we have documented a lot of variation between years. The graphs below show the relative commonness of Vosnesensky bumble bee (B. vosnesenskii) and Crotch's bumble bee (B. crotchii) across the summer in each of three years. For Vosnesensky, it looks like queens and workers (combined as "Female" here) vary as much as 2-3 weeks in the timing of their activity, while the pattern of male observations is more consistent. By contrast, for Crotch's, we have documented quite a lot of variation in both female and male activity between years. We don't know exactly why bumble bees vary so much in the timing of their life history, but in California, temperature and precipitation seem to play a big role. This variation means that in some years, queens may become active either before or after critical food plants bloom. This 'phenological mismatch' has recently been the focus of some climate-change-related bumble bee research.
(How to read these graphs: these curves are called kernel density plots, and give an index of how abundant the species/sex is at each point along the horizontal time axis. We don't need to worry about the units on the vertical axis, but the shapes of the curves can tell us a lot about bee phenology. As always, we should expect that these patterns may be affected by human bias, such as timing of our surveys.)
Credits: bumble bee species thumbnail graphics on this page from Williams et al. 2014, Bumble Bees of North America: an Identification Guide.