Bees Are Not Optional: USGS Research on Pollinators and a Changing Climate

Farms, cities and wild lands all depend on pollinators — bees, birds, butterflies, bats and even moths. Their work is often invisible, yet it supports diverse wildlife and plant communities and healthy watersheds. Up to 75 percent of crop species important for human food need pollinators to produce.

Pollinators are declining worldwide as land use and climate change. The United States has more than 4,000 pollinating species of insects, birds and mammals, and they are in crisis. Because the country had lagged other regions in assessing them, the Committee on the Status of Pollinators in North America (2007) challenged the U.S. Geological Survey (USGS) and the U.S. Fish and Wildlife Service (USFWS) to draw up conservation plans — including measuring the effects of climate change. The urgency showed in 2017, when USFWS listed the rusty-patched bumble bee as Endangered under the Endangered Species Act (ESA).

Rusty-patched bumble bee (Bombus affinis). Image from the U.S. Fish and Wildlife Service

Who does the work

The USGS Ecosystems Mission Area (EMA) produces biological science for managing and conserving the Nation's living resources, used by the Department of the Interior and by other federal, state, Tribal, nongovernmental and for-profit organizations. Its Climate Adaptation Science Centers, Cooperative Fish and Wildlife Research Units and Ecosystems Science Centers all study climate and pollinators — from when plants bloom to how endangered bumble bees respond to climate and habitat change. Three examples follow.

1. Pollinators on eastern wildlife refuges

Declines driven by climate change, pesticides and habitat loss have prompted petitions to list several pollinators under the ESA. USFWS asked USGS for information on priority, at-risk species to guide how it manages National Wildlife Refuges (NWRs).

• Where: 10 refuges, from Maine to Virginia.
• What is measured: when pollinators use each habitat, how changes in land use and land cover — from local to landscape scale — affect their communities, and how species ranges change with latitude.
• What for: the distribution and ecology of at-risk species and their associates, such as Ashton's cuckoo bumble bee (Bombus ashtoni), to guide management across USFWS's Northeast Region; and whether refuges can act as sources of pollinators for the wider eastern landscape as the climate changes.

Lead USGS scientist: Steve Grodsky, New York Cooperative Fish and Wildlife Research Unit, with Rachel Kelty and USFWS staff.

A female two-spotted bumble bee (Bombus bimaculatus) on wild bergamot (Monarda fistulosa). Image from the U.S. Fish and Wildlife Service

2. The western bumble bee's decline — and its future

A Species Status Assessment summarises what is known about a species and underpins ESA listing decisions. For the one on the western bumble bee (Bombus occidentalis) and McKay's bumble bee (B. mckayi), USFWS turned to USGS. The team:

• measured occupancy trends — where the species is present or absent — across many ecoregions, and designed sampling to fill the gaps;
• worked with agency and university experts on targeted research;
• tested climate, land cover and pesticides as causes of decline.

The result: a mean predicted decline of about 57 percent across the western United States from 1998 to 2020.

The team then projected occupancy to the 2050s under three scenarios built on different greenhouse gas emission levels — from drier and much warmer to wetter with less warming — each paired with land-cover projections ranked from best to worst for the bee. The models also allow for colonies changing size over the summer and for surveys that miss bees that are there. The team produced maps for 1998, 2020 and the 2050s, plus tools to work out how many surveys are needed to detect these species in future. Results for McKay's bumble bee are still to come.

Lead USGS scientists: Tabitha Graves and Will Janousek, Northern Rocky Mountain Science Center, with partners from USFWS, the Canadian Wildlife Service, the U.S. Department of Agriculture, universities and the Xerces Society.

Western bumble bee (Bombus occidentalis)

Hummingbird moth (Macroglossum spp.) on milkweed (Asclepias spp.). Image from the U.S. Fish and Wildlife Service

3. Bees and berries in western Alaska

The Bees and Berries project, a partnership with Alaska Native scientists, educators and students, studies the ecology, diversity and vulnerability of arctic pollinators.

• Berry plants such as cloudberry (Rubus chamaemorus) are essential in subarctic and arctic landscapes and a primary subsistence food for Alaska Native communities — tied to culture, sense of place and the land for more than 3,000 years.
• Little is known about how vulnerable these plants are to environmental change, and even less about their insect pollinators.
• Because pollinators help communities hold together and recover after disturbance, a shift in their numbers or timing — emergence, reproduction and other life events — could cascade into berry harvests, ecosystems and the resilience of the people who rely on them.

The work combines collecting and genetically identifying pollinators, surveys of vegetation and land cover, and traditional knowledge of how plants and pollinators interact.

Hunt's bumble bee (Bombus huntii) on dandelion (Taraxacum officinale). Image from the U.S. Fish and Wildlife Service

Sources

Based on Pollinator Conservation and Climate Science at the U.S. Geological Survey, by Elise Irwin and Jonathan Mawdsley, U.S. Geological Survey Fact Sheet 2023–3026; a work of the United States government in the public domain. The source's map of the western bumble bee's predicted occupancy (from Janousek and others, 2023) is copyrighted by the National Academy of Sciences and is not reproduced.