The rufous hummingbird (Selasphorus rufus) is a small, yet mighty bird that plays an outsized ecological role in western North America. Weighing just 3-4 grams, these tiny birds migrate incredible distances and have coevolved with various plant species along their migratory routes. Due to their role as pollinators, seed dispersers, and predators, rufous hummingbirds act as a keystone species in many ecosystems. Their presence and activities help maintain biodiversity and ecosystem functioning.
What is a keystone species?
A keystone species is one that has an outsized influence on its environment relative to its abundance. Keystone species exert strong direct and indirect effects on ecosystem structure, function, and processes. Their removal initiates major changes in the ecological community. Four characteristics define keystone species:
They have low functional redundancy
Keystone species perform unique and specific roles that are not duplicated by other organisms in the ecosystem. No other species can fill their niche if they were removed.
They exert large, disproportionate effects
Keystones have effects on their environment that are much larger than would be expected from their biomass alone. They influence ecosystem structure and function in major ways.
They affect many species
By modifying ecosystem structure and resources, keystone species influence the population dynamics of many other species in their communities. Their impacts cascade through the food web.
Their impacts are complex
Keystones have diverse interactions with many species through predation, grazing, pollination, seed dispersal, habitat modification, and competition. Their removal causes unpredictable cascading effects.
Why are rufous hummingbirds considered a keystone species?
Rufous hummingbirds exhibit all four definitive characteristics of a keystone species:
Low functional redundancy
As primary pollinators of many flowering plants along their migration route, rufous hummingbirds cannot be replaced by other pollinators. They are the sole hummingbird species found in many areas and have specialized adaptations for feeding on certain flowers.
Disproportionately large effects
Despite their tiny size, rufous hummingbirds exert huge influence through pollination and predation. Their absence would greatly reduce plant reproduction, seed set, gene flow, and insect populations.
Impact many species
By pollinating wildflowers and facilitating gene flow between fragmented plant populations, rufous hummingbirds affect plant community structure. Their insect predation alters arthropod diversity and abundance.
Complex impacts
As pollinators, predators, competitors, and prey, rufous hummingbirds have intricate direct and indirect interactions with numerous species. Losing them would trigger complex cascading effects through ecosystems.
Pollination services
One of the main reasons rufous hummingbirds are considered a keystone species is due to their essential pollination services. As they feed on nectar from colorful tubular flowers adapted to hummingbird pollination, they transfer pollen between plants and enable fertilization and seed production.
Wildflowers
In western mountains and meadows, rufous hummingbirds pollinate countless wildflower species such as larkspurs, paintbrushes, columbines, honeysuckles, violets, and fireweeds. These plants depend fully or primarily on rufous hummingbirds for reproduction.
Trees and shrubs
While feeding and breeding along the Pacific coast, rufous hummingbirds pollinate important trees like Douglas fir, sitka spruce, and alder. They also pollinate woody shrubs including currants, gooseberries, manzanitas, bush penstemons, and sages.
Desert plants
In the Sonoran and Mojave Deserts, rufous hummingbirds pollinate ocotillos, chuparosas, prickly pears, agaves, and desert willows. These plants rely on rufous hummingbirds to transfer pollen in their harsh desert environments.
Fragmented populations
Rufous hummingbirds promote genetic diversity by moving pollen between fragmented plant populations that are isolated by clearcuts, roads, or human development. This essential gene flow maintains healthy, viable plant populations.
Seed dispersal
In addition to pollination, rufous hummingbirds serve as important seed dispersers for some plant species. As they feed, pollen and seeds stick to their beaks and feathers. When they fly to the next flower, the birds deposit the seeds in new locations away from the parent plant.
Penstemons
Hummingbirds like rufous are the primary seed dispersers for beardtongues (Penstemon spp.). The seeds of these wildflowers likely evolved to stick to hummingbirds’ beaks and heads to facilitate wider dispersal.
Desert plants
Rufous hummingbirds that breed in the Sonoran Desert disperse seeds of desert willow, ocotillo, chuparosa, and prickly pear cacti as they move between flowering plants. This spreads the offspring over a broader area.
Fosters plant diversity
By dispersing seeds beyond parent plants, rufous hummingbirds help create patchy mosaics of vegetation that enhance plant diversity across the landscape. This makes ecosystems more resilient.
Insect population regulation
While rufous hummingbirds famously drink nectar, they get most of their protein from eating small insects and spiders. Their insectivory provides important top-down regulation of invertebrate populations.
Consume many insects
A rufous hummingbird may consume hundreds of tiny insects every day, including mosquitos, gnats, aphids, spiders, caterpillars, ants, beetles, and insect eggs. One study found hummingbirds reduced insect populations by up to 60%.
Affects insect reproduction
By preying on pollinating insects like gnats, rufous hummingbirds reduce their abundance and therefore decrease insect pollination and reproduction in some plants. Hummingbird predation pressures insects to evolve defenses.
Regulates plant pests
When rufous hummingbirds eat plant-damaging insects like aphids and caterpillars, they provide natural biocontrol services that protect vegetation from pest outbreaks. This benefits ecosystem health.
Coevolutionary relationships
Rufous hummingbirds have cultivated intricate coevolutionary relationships with the plants and pollinators they interact with. These relationships demonstrate how the birds are intricately interwoven into the functioning of their environments.
Flower adaptations
Many western wildflowers have adapted specifically to attract rufous hummingbirds. They have tubular red flowers perfectly shaped for the hummingbird’s bill and lots of dilute nectar. Some also have ultraviolet bullseyes to guide the birds.
Timing of flowering
Flowering schedules of many plants along the migration route are synchronized with the passage of rufous hummingbirds in spring and summer to ensure effective pollination. The birds’ presence likely drove this timing adaptation.
Hummingbird adaptations
In turn, rufous hummingbirds have adapted to reach certain flowers. Their bill shape and length, wing-beat frequency, appetite, color vision, sense of smell, and hovering ability have all evolved to facilitate feeding on specialized hummingbird flowers.
A delicate balance
These synchronized adaptations create a delicate ecological balance between rufous hummingbirds and associated plants. If one declines, the other would also suffer detrimental impacts due to their tight coevolutionary relationship.
Competition with other species
Rufous hummingbirds aggressively compete with other species for nectar resources along their migratory route. This competition shapes community structure by determining which species can access essential food resources.
Defends territories
Males establish breeding territories with plentiful nectar supplies and chase away competing hummingbirds and insects. Females also aggressively defend flowering plants they are feeding from.
Impact of competition
By limiting nectar access for less dominant hummingbird species, rufous hummingbirds influence geographic ranges, migration schedules, and population sizes of competitors. They impact community dynamics.
Drives evolution
Competition with rufous hummingbirds for limited nectar supplies applies evolutionary pressure on other hummingbirds and pollinating insects to utilize different resources, adapt morphologically, or change migration timing.
Rufous hummingbirds as prey
While they are influential predators of insects, rufous hummingbirds also serve an important ecological role as prey for other species higher on the food chain. Predation provides an influx of energy and nutrients into ecosystems.
Prey for birds
Rufous hummingbirds are hunted by hawks, falcons, and shrikes. Owls and other birds also opportunistically grab hummingbirds at night. Nestlings and eggs are eaten by jays, crows, and squirrels.
Prey for insects
Preying mantises ambush hummingbirds at flowers. Tiger beetles and robber flies also snatch hummingbirds out of the air. Parasitic botflies and mites infest baby hummingbirds in their nests.
Energy transfer
Consumption of hummingbirds transfers energy up the food chain from nectar sources to top avian and insect predators. This energizes higher trophic levels and fuels ecosystem functioning.
Habitat creation
In constructing their tiny nests, rufous hummingbirds facilitate seed dispersal for certain plants and create habitat conditions suitable for other organisms.
Nest materials
Rufous hummingbirds build soft, stretchy nests using plant down from willows, thistles, and cottonwoods. As they collect this material, they disperse the attached seeds to new sites.
Cavity nesters
The birds nest in older woodpecker cavities and rotted-out holes in dead trees, stumps, and cacti. Their activities maintain these natural cavities used by many other bird and insect species.
Fungi dispersal
Nests built with downy plant material contain fungi and microbes that inoculate the nest site. This changes microbial communities on branches and facilitates fungal dispersal to new substrate.
Ecotourism value
The tiny rufous hummingbird draws birdwatchers from around the world who spend money in local economies. Their charisma makes them an iconic ecotourism species.
Festivals and tours
Hummingbird festivals in California and Arizona attract tourists who hope to see rufous hummingbirds visiting feeders and flowering plants. Guided tours target prime rufous watching spots.
Backyard feeders
People eagerly await return of the rufous hummingbirds each spring when the birds visit backyard nectar feeders throughout western North America. Feeder sales generate millions annually.
Economic benefits
The popularity of hummingbirds drives tourism dollars that support jobs for nature guides, festival organizers, lodge owners, and hospitality staff. Birdwatchers also buy optics, books, feeders, and other hummingbird-related gear.
Vulnerabilities and conservation needs
Despite their keystone ecological importance, rufous hummingbird populations face growing threats during migration and in wintering grounds. Targeted conservation action is needed to ensure their ecological integrity.
Habitat loss
Conversion of meadows and pine-oak forests for agriculture, logging, and development destroys stopover habitat along migration routes and eliminates food resources.
Pesticides
Chemical pesticides reduce insect prey populations. Herbicides also decrease availability of nectar-producing flowers. Both limit critical food resources.
Climate change
Flower timing getting out of sync with migration schedules due to warming temperatures. Increased drought stress also reduces nectar production.
Action needed
Protecting intact habitat corridors free of pesticide use is crucial for migration success. Artificial feeders can supplement food sources. Careful fire management maintains flower availability.
Conclusion
Despite their tiny stature, rufous hummingbirds punch far above their weight class ecologically as illustrated by their keystone species status. Through essential pollination and seed dispersal services, extensive coevolutionary relationships with plants, top-down insect population control, participation in food chains as both predator and prey, facilitation of nesting cavities for other species, and ecotourism value, the rufous hummingbird exerts disproportionately major influences on western ecosystem structure, function, and services. Targeted conservation measures are essential to ensure the continuity of these critical ecological contributions.
