Hummingbirds are well known for their ability to hover in place and sip nectar from flowers using their long bills. This behaviour leads many people to assume that hummingbirds play an important role as pollinators. But do hummingbirds actually pollinate flowers and spread pollen from plant to plant? The answer is more complex than you might think.
The basics of hummingbird pollination
Hummingbirds do pollinate some species of plants. When a hummingbird visits a flower, pollen from the flower’s stamen (male reproductive organ) sticks to the hummingbird’s head and bill. When the hummingbird flies to the next flower, some of this pollen rubs off onto the pistol (female reproductive organ) of the new flower, fertilizing it. This allows the plant to develop seeds and fruit and is the basic mechanism of pollination.
Some plants have evolved very specialized relationships with hummingbirds and rely on them almost exclusively for pollination. These plants have tubular or cup-shaped flowers that perfectly match the long, slender bills of hummingbirds. Bright red flowers that provide lots of nectar are particularly attractive to hummingbirds. Examples of plants pollinated mainly by hummingbirds include certain species of columbine, trumpet creeper, penstemon, fuchsia, and coral bells.
Factors that limit hummingbird pollination
While hummingbirds certainly do pollinate some types of plants, there are some factors that limit their overall effectiveness as pollinators:
- Very territorial – Hummingbirds are very territorial and tend to return to the same patch of flowers every day rather than ranging widely. This means they often transfer pollen between the same plants rather than between different populations.
- Don’t brush against stamens and pistils – Hummingbirds can sip nectar from flowers without contacting the reproductive parts of the plant, so pollen transfer does not always occur.
- Grooming – Hummingbirds groom themselves frequently, removing pollen buildup on their feathers. Excessive preening limits the amount of pollen they carry between flowers.
- Low pollen amounts – The small size of hummingbirds limits the amount of pollen they can transport compared to larger pollinators like bees.
- Nectar robbing – Hummingbirds will often pierce flowers at the base to rob nectar without contacting stamens or pistils.
These behaviours mean that even when hummingbirds visit lots of different flowers, they often pollinate those flowers inefficiently compared to insect pollinators like bees. There are always exceptions, but most flowering plants rely more heavily on bees, beetles, flies, butterflies, and other insects for thorough pollination.
Research on hummingbird pollination
Scientists have conducted research to try to quantify the importance of hummingbirds as pollinators. Here are some key studies looking at hummingbird pollination:
- A study in a California flower meadow found that hummingbirds accounted for only about 15% of flower visits, while insects accounted for 85%.
- Experiments with artificial flowers found that hummingbirds successfully transferred little pollen between flowers compared to bee visits.
- Monitoring of hummingbird movements showed they moved frequently between the same clusters of flowers rather than ranging farther afield.
- Analysis of pollen loads on captured hummingbirds revealed relatively few pollen grains compared to bee pollen baskets.
- Field studies of pollination networks found hummingbirds tended to play peripheral roles compared to highly connected insect pollinators.
Based on this type of research, most biologists conclude that while hummingbirds certainly pollinate, they are relatively inefficient pollinators compared to bees, flies, butterflies and other pollen-transporting insects.
Comparative pollination by hummingbirds and bees
It’s informative to directly compare the pollination efficacy of hummingbirds versus bees, the two major nectar-feeding pollinators:
| Hummingbirds | Bees | |
|---|---|---|
| Body Design | Needle-like bill good for sipping but not catching pollen | Fuzzy body and branched hairs excellent for catching pollen |
| Foraging Range | Small territories, frequent same flowers | Search widely, regularly find new flowers |
| Flower Handling | Hover at flower opening, may avoid contact | Crawl inside, rub against anthers and stigma |
| Grooming | Frequent preening and bathing | Pack pollen into baskets on legs |
| Pollen Transfer | Small amounts on bill and head | Large amounts on body hairs |
As the table illustrates, bees are much better adapted for transferring pollen between flowers. Bees actively gather pollen to take back to their nest, have hairy bodies that latch onto pollen grains, and regularly fly long distances between patches of flowers. Hummingbirds may transport some pollen, but their nectar-sipping behaviour limits widespread pollination.
Adaptive significance for plants
If hummingbirds are not the most efficient pollinators, why have some plants evolved to rely on them? Here are a few potential advantages:
- Hummingbirds visit flowers in rain or cold when insects are inactive.
- Their preference for red flowers may help plants target specific pollinators.
- Hummingbirds can pollinate flower shapes bees can’t easily access.
- Their territorial behaviour means frequent visits to the same plants.
- Hummingbird-pollinated plants don’t have to produce as much pollen.
So while hummingbird pollination may not be hugely productive, it confers some advantages that help certain plant species get by with a less efficient but dependable pollinator.
Conclusion: a minor pollination role
To summarize, while hummingbirds certainly pollinate some species of plants, especially those with specialized red tubular flowers, they are generally not the most effective or important pollinators in most ecosystems. Bees and other pollen-covered insects tend to do the bulk of pollination work. Hummingbird-dominated pollination systems are more the exception than the rule. However, hummingbird pollination can still be evolutionarily beneficial for some plants in certain situations.
