Birds are attracted to nectar for a few key reasons. Nectar is an important source of food and energy for many species of birds. It contains natural sugars that provide calories for flight and activity. Nectar is also readily available from flowers, allowing birds easy access to this nutritious substance. Additionally, some species of birds have evolved specialized beaks and tongues to more efficiently feed on nectar. Understanding why birds are drawn to nectar can provide insight into avian ecology and evolution.
Nectar as an Energy Source
Nectar is essentially a sugar-rich liquid produced by plants. It is secreted by glands called nectaries, located within flowers. The main components of nectar are sucrose, glucose, and fructose, which are all simple sugars. This makes nectar an excellent source of carbohydrates and energy for birds.
Many species of birds have very high metabolic rates and expend a lot of energy flying and going about their daily activities. The natural sugars in nectar allow birds to refuel and maintain their high energy lifestyles. A hummingbird may visit up to 2,000 flowers per day to get enough nectar to meet its energy needs.
Calories in Nectar
Nectar is an energy dense food source. One study found that the nectar from a popular hummingbird feeding plant (scarlet gilia) contains about 15% sugars, which provides about 60 calories per tablespoon of nectar. In comparison, the same volume of a typical hummingbird nectar mix (1 part sugar to 4 parts water) contains about 20 calories.
So wild nectar offers more calories per lick for busy birds. It’s estimated that hummingbirds get 25-50% or more of their daily energy requirement from nectar alone.
Availability of Nectar
In addition to being an excellent source of energy, another appeal of nectar for birds is its wide availability in the environment.
Nectar-producing flowers grow in abundance across most environments, from backyards to rainforests. Different species of flowering plants produce nectar suited to attract specific pollinators. So there is an ample supply of nectar across regions and seasons to fuel bird populations.
Some common nectar-producing flowers that attract hummingbirds, honeyeaters, and sunbirds include:
- Fuchsia
- Trumpet vine
- Cardinal flower
- Salvia
- Apache plume
- Aloe
- Eucalyptus
- Banksia
- Melaleuca
These plants can be found in most habitats, which means birds don’t have to travel far or compete intensely to find nectar sources. The abundance of nectar-filled flowers supports specialized nectarivorous birds as well as generalists that supplement their diet with nectar.
Adaptations for Feeding on Nectar
Some groups of birds have evolved specialized physical and behavioral adaptations that allow them to more effectively feed on nectar. Two examples are hummingbirds and sunbirds.
Hummingbird Adaptations
Hummingbirds have the following anatomical and behavioral adaptations for nectar-feeding:
- Long, slender bills to reach inside tubular flowers
- Forked tongues with hair-like filaments used to lap up nectar
- A rapid lapping tongue, licking nectar up to 13 times per second
- High metabolism and rapid heart rate to power sustained hovering and licking
- Ability to remember which flowers they have emptied to avoid wasting energy
- Aggressive behavior to dominate nectar-rich feeding sites
These adaptations allow hummingbirds to specialize on nectivory. Their hovering behavior, bill shape, and tongue structure particularly suit them for accessing a wide variety of ornate, tubular flowers.
Sunbird Adaptations
Sunbirds in Africa and Asia have some similar adaptations as hummingbirds for nectar-feeding:
- Long, thin, downward-curved bills to probe flowers
- Tubular tongues with brushy tips that soak up nectar
- Ability to hover briefly while feeding
- High capacity to digest and metabolize sugar-rich diets
- Bold behavior and aggression around flowers
Sunbirds don’t hover as expertly as hummingbirds, but they still have tongues and beaks specialized for slurping up nectar. Their adaptations allow them to exploit nectar sources in tropical ecosystems alongside honeyeaters.
Role of Nectar in Avian Ecology
Nectar-feeding is an important ecological strategy that influences avian community structure across biomes. Species that rely on nectar fill an important niche and have complex relationships with plants.
Coevolution of Nectar-Eating Birds and Flowers
Species like hummingbirds and sunbirds have coevolved alongside flowering plants. This means the nectar-feeders and nectar-producers have adapted in ways that benefit each other over time.
For example, tubular red flowers matched to hummingbird bills and vision developed to ensure pollination while providing food. In return, the hummingbirds became reliable pollinators as they visited the energetically beneficial flowers. This ongoing specialization between nectarivores and flowers shapes entire ecosystems.
Impact on Pollination
Nectar-feeding birds are essential pollinators for many plant species. As they forage for nectar, pollen sticks to their bills and heads which is then transferred to other blossoms. Hummingbirds are the primary pollinators of orchids and wildflowers across the Americas. Sunbirds and honeyeaters fill a similar crucial ecological role in Africa, Asia, and Australia.
These nectarivores support plant reproduction and biodiversity through their role in pollination. Nectar provides food to fuel their movements, which benefits flowering species.
Competition for Nectar Resources
There is intense competition among nectar-feeding birds for prime flowers and feeding territories. Birds aggressively defend flowering patches and will attempt to chase off other nectar-eaters. Dominant hummingbird species may monopolize and control feeders or clusters of flowers.
Nectar-eaters must efficiently forage across many blossoms and remember which ones they have emptied. This reduces wasted visits and unnecessary territorial battles. The difficulty of securing enough nectar sources has led to specialized behaviors and adaptations to maximize energy intake.
Conclusion
Nectar is an attractive food source for birds because it provides efficient energy, is abundantly available in the environment, and can be accessed with specialized adaptations. Groups like hummingbirds and sunbirds have evolved to efficiently feed on nectar. In doing so, they have become essential pollinators that maintain mutually beneficial relationships with plants. The ecology of nectar-feeding illustrates the complex dynamics between flowers and their avian partners.