Rufous hummingbirds (Selasphorus rufus) are one of the most widespread hummingbird species in North America. However, in recent decades their populations have shown concerning declines, especially in certain parts of their breeding range. Understanding the reasons behind these declines is an important step towards developing conservation strategies to protect these tiny, fascinating birds.
Range and Population Trends
The breeding range of the Rufous hummingbird extends from southeastern Alaska south along the Pacific Coast to northern California. They spend the winter in Mexico and the Gulf Coast states. Their migration route covers an incredible distance – some Rufous hummingbirds may travel over 5,000 miles round trip each year! This is one of the longest migration routes of any North American bird relative to its body size.
Breeding Bird Survey data indicates that Rufous hummingbird populations declined by about 3% per year between 1966 and 2015. The most significant declines have occurred along the northern Pacific Coast, with little change in the Rocky Mountains and inland northwest. For example, surveys in northwest Oregon showed Rufous hummingbird declines of 9% annually from 1978 to 2007. Their numbers in northern California and southwestern Oregon dropped by over 60% in just two decades. They have virtually disappeared from some areas where they were once common.
Possible Causes of Decline
Scientists are investigating a number of potential reasons for the loss of Rufous hummingbirds from parts of their breeding habitat:
Habitat Loss
Habitat loss and degradation may be contributing to the declines in hummingbird populations. Rufous hummingbirds rely on moist mountain meadows, forest openings, and scrubby areas that provide the flowers they feed on. These habitats are being lost to logging, agricultural expansion, development, and other human land uses. For example, it’s estimated that temperate forest coverage in the Pacific Northwest declined by about 29% between the 1970s and 2007. Rufous hummingbirds that breed in this region may be negatively impacted by reductions in suitable habitat.
Climate Change
Some research indicates that climate change may also play a role in Rufous hummingbird declines. Changing weather patterns and increased drought may be affecting food availability or nesting success. One study predicted that an additional 4°C of warming could eliminate most of the current Rufous hummingbird breeding range in British Columbia. Their range is expected to retract northwards as the climate warms.
Pesticides
Pesticide use could potentially impact hummingbirds through direct toxicity or by reducing insect populations that the birds rely on for food. One study found that Rufous hummingbirds nesting along creeks with higher pesticide levels tended to have lower nesting success. However, more research is needed to fully understand the role of pesticides in hummingbird population declines.
Disease
Emerging diseases are a threat to many wildlife species, including hummingbirds. West Nile virus arrived in North America in 1999 and is now widespread across the continent. While we don’t know the full impact on hummingbird populations, evidence suggests this exotic disease has caused mortality in some species. Avian malaria is another introduced disease that may pose a risk.
How Climate Change May Impact Rufous Hummingbirds
Let’s take a closer look at one of the potential factors in Rufous hummingbird declines – climate change. Here are some of the ways a warming climate may negatively affect these tiny birds:
Timing of Flowering Plants and Emerging Insects
Hummingbirds time their migration and nesting to coincide with peaks in flower and insect availability. However, climate change may be disrupting this timing. For example, higher spring temperatures cause certain flowers and trees to bloom earlier, whereas hummingbirds may not be advancing their arrival by the same degree. This can limit food availability during critical nesting periods. Unmatched timing could become more common as climate variability increases.
Heat Stress
Rufous hummingbirds have high metabolisms and can be sensitive to heat stress. As daily temperatures rise and heat waves become more frequent, hummingbirds may suffer impacts including reduced feeding and nest abandonment. One study in the Mojave Desert found that heat caused a 40% decline in a hummingbird population over 7 years.
Drought
Lower rainfall and moisture deficits can affect flowering plants and decrease nectar production. Drought may also reduce insect populations that hummingbirds rely on for food. These impacts can be especially detrimental during the breeding season when energy demands are high.
Extreme Weather
Severe storms, cold snaps, hail, frost, and other extreme weather events may threaten hummingbirds directly or damage flower and insect food sources. For example, late spring frosts can wipe out a whole season’s worth of nectar-bearing flowers.
Wildfires
Increased wildfire frequency and intensity due to climate change can alter hummingbird habitat and reduce food availability. Fires may also directly kill birds if they occur during nesting season.
Disease Risk
Mosquito-borne diseases like West Nile virus and avian malaria spread faster and pose a greater threat to birds during hotter conditions. Drought and wildfires can also increase disease risk. As climate disruption accelerates, disease-related mortality may rise.
Range Shifts
Climate changes are expected to push Rufous hummingbird breeding habitat northwards and to higher elevations. However, the birds may not be able to fully compensate for these shifts, resulting in population declines, especially at the southern edges of their range.
While climate change poses many threats to hummingbirds, its impacts will vary across different parts of their range. More research is needed to fully understand these complex effects.
Conservation Strategies
Protecting remaining habitat, reducing pesticide use, controlling invasive species, and limiting climate change are some approaches that could benefit Rufous hummingbird populations. Here are a few specific conservation strategies:
Protect and Restore Habitat
Preserving meadows, scrublands, riparian areas, and open forests that provide key food sources through land conservation programs. Also improving habitat connectivity to support migrating hummingbirds. Restoration projects to increase native flowering plants and nest sites will further help provide good habitat.
Reduce Pesticide Impacts
Using integrated pest management, reducing overall pesticide application, and avoiding pesticide use near hummingbird habitat and food sources. Organic farming practices can benefit hummingbirds by increasing insects.
Providing more hummingbird-friendly urban gardens and landscapes with native plants and flowers free of pesticides and herbicides. Educating home gardeners on avoiding chemicals toxic to birds.
Monitor Disease
Conducting surveillance for avian diseases and parasites. Research to better understand disease impacts on hummingbirds and develop mitigation strategies.
Hummingbird Feeders
Supplementing wild food sources by providing clean hummingbird feeders, especially during migration and in urban areas low on flowers. Educating the public on proper feeder use and maintenance.
Citizen Science
Engaging birdwatchers and the public in monitoring programs such as the Breeding Bird Survey. Reporting hummingbird sightings to eBird. Involving community scientists in habitat projects and data collection efforts.
A combination of scientific research, habitat conservation, wildlife policy improvements, and public education will give Rufous hummingbirds the best chance of reversing population declines.
Conclusion
The reasons for declining Rufous hummingbird populations are likely complex, but research points to habitat loss, climate change, pesticides, and disease as probable contributing factors. Protecting habitat, reducing pesticide risks, anticipating climate impacts, monitoring disease, and engaging citizens in conservation efforts are important steps to stabilize populations. More studies are still needed to deepen our understanding of the threats facing these tiny migratory birds and refine conservation strategies to support their future.
