God Created Cohorts:  Bird and Mammal Plant Pollinators by Ginger Allen

The great variety in color, shape, pattern, and scent we observe in flowers is a direct result of the intimate association of the flowers with their animal partner pollinators or cohorts. With a symbiotic (dependent) mutualistic relationship (mutually beneficial), the plant expends less energy in pollen production and more energy in producing showy flowers, nectar, and/or odors. By attracting a specific pollinator on a regular basis, this specialized flower has an advantage of wasting less pollen versus flowers that attract indiscriminate pollinators. The pollinator gains an advantage of having its own private food source, thereby exerting less energy in food competitions between other pollinating species. The plant must supply a reward (nectar and pollen), an attractant (brightly colored flowers or odor), and a mechanism for pollen transfer (flower tubes, strong landing pads, etc.). Animal-pollinated plants have large, irregular shaped pollen grains covered with hooks, spines, or craters. A rough texture and sticky surface ensure that the pollen grains will stick to the visiting animal’s hair, feathers, or appendages. The pollen stays on the animal until it visits another flower where the pollen is rubbed off onto the other flower’s stigma, resulting in fertilization. Fertilization and continued production of new plants is the flower’s reward.

The plant and pollinator have adapted together under God’s original design. Some species have unique and harmonious relationships, which could not have arisen randomly. Insect and plant symbiotic relationships were discussed in a previous article (God Created Cohorts: Insect Plant Pollinators¹). This article will discuss unique pollinating relationships between plants birds and mammals.

Excluding insects, bats, and birds are the main animal pollinators. There are a few plants that have entered into pollination partnerships with such diverse creatures as mice, possums, some primates, and even snails or earthworms. Animals use flowers as sources of food for themselves and their offspring. Animal-pollinated flowers produce nectar, a sugar-based substance containing vitamins, amino acids, and other nutrients. The amount of nectar a flower typically produces relates to the physical needs of its pollinators.

Mammal Pollinators: Bats

The diets of bats vary from species to species, but you can group bats by three main types of feeding preference. Many species are generalists and display opportunistic feeding behavior, feeding on whatever is available. Insectivorous bats feed primarily on night-flying insects. Frugivorous bats eat fruit and nectivorous bats feed on nectar from plants. Bats rely on sight and smell (perfumed flowers & nectar) to locate their food sources, and since they feed in the evening hours, night blooming flowers are a main nectar source. Many of the nectar-eating bats have long thin tongues like hummingbirds that can reach deep into the flower for the nectar. Nectar feeding bats also have short ears and long slender noses for reaching into flowers and big eyes for excellent vision. In contrast to the fluttering zig-zagging flight of insect-catching bats, the flight of the nectar bats is strong and direct. Being strong fliers they can hover while they drink the nectar and not disturb the flower too much. Pollen grains cling to the bat’s fur and are carried to the next plant ensuring fertilization of their food source. Bananas, mangoes, dates, figs, peaches, cashews, guava, avocados, and agaves rely on bats for pollination.²

Nectar-drinking bats in the tropics play indispensable roles in maintaining forest diversity and in assisting forest regeneration through seed dispersal and pollination. There are a large number of plant species which grow in tropical forests, however most individual species are low in number and scattered throughout the forest. This scenario represents a dilemma for pollination. How do you transfer pollen effectively from the flowers of one tree to another when the distance between these individuals may be over 300 feet. The answer to this pollination problem is solved by flying insects, birds, and bats.³ Experiments concluded that bats can transfer nearly four times as much pollen as hummingbirds. Below are a few examples of interesting bat pollinators.

The Tube-Lipped Nectar Bat (Anoura fistulata) was discovered in the forests of the Andes of Ecuador in 2005. Researchers report that this nectar bat can launch its tongue one and a half times its body length, longer than any other mammal and second only to chameleons among vertebrates. Also, this bat extends its tongue twice as far as its other scientific family members. The bat adapted⁶ a longer tongue to feed on a tubular flower (Centropogon nigricans) where the nectar is located at the end of an equally long funnel. Just like humans, the bats tongue begins at the base of the mouth, so the only way to stretch tongue length would be to grow an equally long snout. But that’s not what happened with this bat. The base of the long tongue is pushed back into the rib cage, and is stored between the heart and sternum. That gives the Tube-lipped nectar bat sole pollinating rights to the flower.⁷

To ensure a bat’s head will be dusted with pollen, a flower must be wide enough to fully accommodate its snout. Geoffroy’s tailless bats (Anoura geoffroy, Figure 1) have a long tongue and elongated muzzle which allows them to visit wide tube flowers. Tropical Burmeistera flowers are intensely dependent on bats for survival. Flowers of Burmeistera have a tubular base that expands into a bell shape. Researchers studied flowers of nine species of Latin American Bell flowers (Burmeistera species) that were dull green in color, with varying amounts of purple, and emitted odors ranging from faint (B. succulenta) to very strong (B. borjensis and B. multiflora). All nine study species had flowers that opened in the early evening, and they are primarily bat-pollinated (Anoura geoffroyi and A. caudifera). The bat-pollinated flower species were duller in color, had a wider opening, shorter flower tube and more rigid flower stems than other flower species (B. rubrosepala) that are hummingbird pollinated.⁸ Since the bats are sometimes found in areas without Burmeistera plants and forage on nectar from other flowers, the bat is not dependent on the Burmeistera for survival.

In the United States, only three species of nectivorous Long-tongued bats (Leptonycteris nivalis, L. curasoae, and Choeronycteris Mexicana, Figure 2) are found in the northern limit of their range. Arizona is host to two nectivorous bats (L. curasoae and C. mexicana) which are critical to the pollination of columnar cacti (saguaro and organ pipe) and agave desert plants. Pollination of agave and various cacti would drop approximately 97% without nectivorous bats. Lesser long-nosed bats Leptonycteris curasoae) are food specialists, feeding on cactus (Organ pipe, Cardon and saguaro) and Agave flowers (Agave palmeri). Lesser long-nosed bats ensure that the desert ecosystem remains healthy and cactus populations continue to survive, by pollinating their flowers and dispersing their seeds.¹⁰ Greater long-nosed bats (Leptonycteris nivalis) synchronize their migration from Mexico and arrival in Texas to coincide with the summer blooming cycle of agave plants upon which they rely for pollen and nectar. Is it not clear how important partnerships are for the survival of plants and animals?

Another fascinating relationship involves flying foxes. Flying foxes are large bats weighing up to 2 pounds, with a wing span that may exceed three feet. They consume fruit and nectar and are important pollinators and seed dispersers of native trees. The Grey-headed Flying-fox (Pteropus poliocephalus, Figure 3) is a native species that is endemic to Australia. It flies up to 25 miles to forage in flowering gum trees such as the spotted gum (Corymbia maculate), eucalyptus, paperbarks, and banksias. It is estimated that a single flying fox can dispense up to 60,000 seeds in one night. This is a very important mechanism for rainforest re-vegetation.¹¹ Not all bats are “scary and blood-thirsty,” as some believe. They serve interesting and important roles in God’s natural world.

Hummingbirds

Hummingbirds play an important role in the pollination of numerous species of shrubs and vines, some of which are specifically adapted to hummingbird pollination. Throughout the Americas it is estimated that 8,000 plant species have flowers whose principal pollinator is a hummingbird. Generally, the plant and hummingbird relationships are facultative and not fully dependent on each other for survival. The plant has a beneficial relationship with its pollinator, but because there are many species of hummingbirds and many varieties of flowers to pollinate, a unique and dependent partnership is absent. Of course there are always exceptions to the rule. In Peru there is one rare species of bird, the Sword-billed hummingbird (Enisfera ensifera, Figure 4), which has a beak long enough (4 inches) to pollinate the Long-tubed tasconia (Passiflora mixta).¹²

As we discussed earlier, flower structure design may facilitate pollination by a primary pollinator and restrict other ineffective pollinators. After hummingbirds are acquired as reliable partner pollinators, continuing selection may favor other traits that make the flowers even more specialized for hummingbird pollination. Flowers manifest variation in corolla length, corolla width, and flower color.An example of this is red coloration in hummingbird-pollinated flowers. The red coloration may develop primarily to discourage visitation by bees and therefore preserve pollen for hummingbird visits.¹³ Scientists have learned that bees require more time to find red flowers than blue ones.¹⁴ Therefore, the bees will stay at a blue patch of flowers rather than exerting time and energy searching for red flowers.

Bees use scent to locate flowers, can carry more pollen than hummingbirds, and tend to deposit most grains in the first few flowers visited. Hummingbirds use sight to locate flowers, deposit pollen grains more evenly across a group of flowers and, because of their higher metabolic rates, ingest more nectar than bees. Consequently, hummingbird-pollinated plants usually have little or no fragrance and produce greater amounts of nectar than bee-pollinated plants. Consider, if you were a flower designer, how would you design flowers to attract pollinators?

The majority of hummingbird flowers grow horizontally, permitting the hummingbird to enter from the side, but with some, like fuchsia, its flowers hang down and must be approached from below. In some hummingbird pollinated flowers (Aphelandra species, Penstemon barbatus)¹⁶ the size of the opening of the flower is just a fraction wider than the hummingbird’s head. The flower anthers and stigmas are positioned at the right length so that pollen is deposited on the hummingbird’s forehead (Figure 5). Usually hummingbirds can insert their bills and access nectar without even moving the flower. Just like the bat, the hummingbird picks up the pollen then transfers it to the next flower. Hummingbirds are physically designed to drink nectar from tubular-shaped blossoms. Bill designs influence the types of flowers that are utilized by each species of hummingbird. Long bills fit into long floral tubes. Short-billed hummingbirds visit short-tubed flowers. These different partnerships allow long-billed and short-billed pollinators to coexist with minimal competition. Bill shape can also be categorized as straight or curved downward (decurved, Figure 6). Bill curvature generally corresponds to straight or strongly curved floral tubes. Another unique design is the hummingbird tongue. The tongue has grooves on the sides that collect nectar.

In order to consume enough nectar to survive, hummingbirds must visit hundreds of flowers daily. They are excellent fliers in terms of maneuverability and can fly up to 60 miles per hour, with their long, blade-like wings. Unlike other birds, this bird’s wing connects to the body at the shoulder joint. This adaptation allows the wing to rotate almost 180°, enabling the bird to fly forward, vertically, laterally, backward (the only bird able to do so), and upside down. The backward flight is possible because the muscles that lift the wing are as well-developed as the down-stroke muscle. Only hummingbirds have wing muscle strength on the up-stroke. This bird can also hover. Hummingbird wings are larger in proportion to their body weight than that of non-hovering birds of similar size. Hovering permits a hummingbird to spend a minimal quantity of time at each flower, moving on without having to land and take off. Some hummingbird species are capable of visiting and sampling 20 flowers per minute. However, hovering is the most energetically expensive form of flight. What unique features God has designed in this tiniest of birds.¹⁸

Throughout the world, very few flowers are pollinated exclusively by one animal species. Hummingbird-adapted flowers can be visited by insects, and insect-pollinated flowers are visited by hummingbirds. For instance, long-tongued bees and butterflies often share flowers with hummingbirds. One-to-one partnerships are rare but there are some interesting relationships.

In Western North America, hummingbird-pollinated flowering time comes in seasonal waves from Mexico to Alaska. These plants provide nutrition for hummingbirds migrating north to breed. Within a mountain range, hummingbird plant flowering often progresses as a wave from low elevation to high, creating a vertical food resource up the mountain. Hummingbird plants are concentrated along the north-south mountain ranges on the western side of the American continent, and these are the same corridors used by hummingbirds as they migrate north and south each year. At the end of the Northern migratory route, few hummingbird-pollinated plant species occur (five in southern Alaska), but in the mountain region, at the end of the southern migration route (Sierra Madres in Mexico, Central America; Andes in Peru), the number of hummingbird-pollinated species increases dramatically. It is no coincidence that Central America and the Andes Mountain region have the highest hummingbird diversity on the planet, for here is where most of the important nectar plants thrive.¹⁹ Table 1 lists the Western breeding hummingbirds of the United States and their nectar plant partners.

Of special note: Rufous hummingbirds (Figure 7) have been called the most important hummingbird pollinator in Western North America. This is because they migrate from Alaska to Mexico, pollinating plants their entire journey.

The Ruby-throated Hummingbird (Archilochus colubris) is eastern North America’s only breeding hummingbird. Most of these hummingbirds winter in Mexico & Central America, but a few overwinter in Florida. The Ruby-throated hummingbird’s long, thin bill is perfectly adapted to the deep tubular flower of plants like the trumpet creeper. Table 2 contains a general, but not exhaustive, list of Eastern North American plant species used for nectar by this bird.

Other Bird Flower Pollinators

Hawaiian honey creepers obtain nectar from and pollinate flowers which are usually large, colorful, and red. These flowers have a characteristically twisted corolla which fits the curved beak of the bird. Plants pollinated by crested honeycreepers (Palmeria dolei) (Figure 8) are the Ohi’a lehua (Metrosideros polymorpha), many native hibiscus, and native Lobelia flowers (such as Trematolobelia macrostachys).²⁴

Sunbirds are small, largely nectarivorous perching birds with long, slender, sharply pointed, decurved bills. The sunbirds are thought to pollinate several tree species of the Nigerian forest. The importance of sunbirds as pollinators is largely unknown and is being studied. Sunbirds do hover, although for shorter time spans than hummingbirds. Usually these birds will perch to obtain nectar.

The Crimson Sunbird (Aethopyga siparaja, Figure 9), has been known to stab the bottom of the flower base and steal nectar without pollinating the plant. Not a very desirable behavior for a pollinator to undertake. The Malachite sunbird (Nectarinia famosa) is the largest of the group and naturally visits large red flowers of aloes, proteas, Candelabra Flower (Brunsvigia orientalis), and Wilde Dagga (Leonotis species).²⁵

Sugarbirds are a small group of perching birds that reside exclusively in Africa. They are specialist nectar feeders with a long down-curved bill and long tail feathers. They primarily feed on Protea plants. The Cape sugarbird (Promerops cafer, Figure 10) also pollinates the black protea (Protea lepidocarpodendron) shrub. The black protea flowers stigma stays closed until the flowers’ pollen is removed by the sugarbird.²⁶

The brush-tongued parrot (Trichoglossus haematodus) of Australia and New Guinea has a specialized and unique tongue for feeding on nectar. Tiny hair-like structures line the end of the tongue in the shape of a U. When one of these parrots extends its tongue during feeding the hairs stand on end, like bristles on a brush, and allow nectar and pollen to be easily soaked up.²⁷

Terrestrial and Arboreal Mammal Pollinators

It is estimated that over 50 species of land mammals actively visit and pollinate native flowers. These include several species of possums, arboreal mammals such as marsupials, small primates, and some rodents.²⁸ Flowers pollinated by primates tend to be unscented and very large in order to accommodate their heavier body weight. Flowers pollinated by marsupials usually grow higher in the tree canopy while flowers pollinated by rodents tend to be located at ground level.²⁹ Below are some examples of fascinating relationships from various regions.

The Red-Bellied Lemur (Eulemur rubriventer, Figure 12) is an endemic primate of Madagascar. The red-bellied lemur is mainly a fruit eater, but also feeds on leaves, nectar, and flowers. This animal will lick the nectar out of flowers leaving them unharmed. Red-bellied lemurs visit and presumably pollinate the flowers of the traveler’s palm (Ravenala madagascariensis) and possibly Brexia and Parkia plants.

The Sugar glider (Petaurus breviceps, Figure 13) is a small gliding marsupial from Australia. These mammals leap from tree branches and glide much like the North American flying squirrels. There are seven species of sugar gliders that live in trees and eat insects small vertebrates and eucalyptus sap. The yellow-bellied glider, Petaurus australis, feeds on the nectar of Banksia and Eucalyptus.

The honey possum (Tarsipes rostratus), in the same order as the sugar glider (Diprotodontia), is a tiny mammal with a body length of 3 to 4 inches. It is not, however, a close relative of the sugar glider and is one of the few truly nectarivorous mammals. The animal’s long, pointed snout and long, extensible, and brush-tipped tongue allow it to gather pollen and nectar of native Australian Banksia and Adenanthos plants.

In the temperate forest of South America, the seeds of the mistletoe (Tristerix corymbosus) are dispersed solely by another marsupial known as Monito del monte (Dromiciops gliroides, Figure 14). The current scientific order (Microbiotheria) of this mouse-like marsupial contains one family and one species. However, some scientists are working on the theory that Monito is more closely related to the Australian marsupials.³⁰ The important point is that this created “kind” of animal has a unique role in its environment. In the temperate forests of Patagonia, Monito, is the sole seed dispersal agent of the parasitic mistletoe which grows on the bark of tall trees. Nearly 100 families of birds and mammals rely on mistletoe for fruit, nectar, and nesting material. The seeds of mistletoe do not survive intact when other animal species eat them. Only the Monito passes the seeds undamaged through its digestive tract and deposits them directly onto the bark of host trees.³¹ This mutual partnership is key to the biodiversity of the whole forest.

In South Africa, flowers of Massonia lilies (Massonia depressa) are visited at night by at least four rodent species: two gerbils, the hairy-footed gerbil (Gerbillurus paeba) and Cape Short-eared Gerbil (Desmodillus auricularis); plus 2 muridae species, the Namaqua Rock Rat (Aethomys namaquensis) and Cape Spiny Mouse (Acomys subspinosus). The flowers of this lily are situated at ground level and are not brightly colored. The nectar is gathered from a well-structured bowl-shaped open chamber. Large volumes of nectar were found in individual Massonia flowers during the night.³²

Several species of gerbils, mice, rats, and shrews also visit flower heads of some South African sugarbush (Protea amplexicaulis, Protea humiflora, Protea nana). Flower heads are usually hidden inside the sugarbush at ground level where they are accessible to rodents. Rodents are attracted by a strong musty odor and are rewarded with copious amounts of a thick sugar nectar. In order to prevent birds and insects from stealing this nectar, rodent-pollinated Proteas have inconspicuous brown or black bracts (modified leaves). The insides of the bracts may be pale white and the tips of the flowers may be shiny red. These features guide the rodent to the nectar in the dark. The nectar is contained within a tube, and the distance to the nectar equals the length of the rodents snout, about 0.5 inches. Pollen is deposited on the head of the rodent.³³ The nectar of rodent-pollinated Protea species has a higher sugar concentration than that of bird-pollinated species.³⁴ Rodent pollinators of Protea nana include; Namaqua Rock Mouse (Aethomys namaquensis), Striped mouse (Rhabdomys pumilio, Figure 15), and Verreaux’s White-footed Rat (Myomyscus verreauxi).

From all of the examples discussed we have learned how different flowering plant species possess or developed a variety of strategies to achieve the pollination of their flowers to ensure a new generation of plants. Some plants rely on the wind to move pollen, but most depend on the contact of an insect, bird, or animal. Flower structure, scent, and growth form vary between plant species. This allows different plants to attract different pollinators. The pollinators in turn have various features, or mechanisms, by which they obtain and carry the pollen to the next plant (Figure 16). In some cases, the link between the plant species and its pollinator has become so close that each is dependent on the other for its continued existence. This is a clear reminder of another relationship: the one between man and God the Creator.