The Pollination Story, Part 4; the birds arrive, dream customers

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Undoubtedly birds had long taken sporadic advantage of the nectar and pollen on offer from insect-attracting flowers, though the quantities available would scarcely have made it worth their while. However given their advantages over insects as potential pollen couriers - the ability to cover much greater distances carrying much more pollen, and bigger brains to recognise more complex cues and differences in flowers - it was inevitable that some plants would adapt their strategies and make bigger investments to employ them.

Brown Honeyeater Lichmera indistincta on Melaleuca viridifloris, Barkly Tableland, Northern Territory
(above and below).

 

The development of bilateral symmetry (see the link above) could progress further, to produce flowers that only a bird could probe.

Eastern Spinebill females Acanthorhynchus tenuisostris  on Pityrodia sp.,
National Botanic Gardens, Canberra.

The characters of a bird-pollinated flower will be different from those of an insect-specialising one. They are likely to be red, pink or orange - this is more to hide them from insects, which see best at the yellow-blue (and beyond) end of the spectrum, as birds can see these colours perfectly well too. They will be tube-shaped or have large protruding stamens, and must have strong stems and flower stalks. The corolla - the collective petals - must be strong enough to bear their weight, but without offering a landing platform that insects can use. Anthers and stigmas must be distant from the nectary, so that the bird's forehead is contacting them while the tongue is collecting nectar. And because birds need bigger rewards, the flowers not only produce more nectar,  but are often clumped or in spikes to increase their attractiveness.

Dusky Honeyeater Myzomela obscura, on Grevillea sp., Darwin.
Such flowers tick all the boxes to attract bird pollinators.

It would of course be no good for the plant to give a bird all the nectar it wants - the whole point is to send it off, with a pollen shipment, to another flower. In fact most bird-pollinated plants seem to produce approximately 5-20% of a bird's daily needs. A bird can dip into over 50 eucalypt flowers per minute, compared with a bee's maximum of about six. 

Important work done by David Paton of Adelaide University back in the 1970s, on New Holland Honeyeaters Phylidonyris novaehollandiae in the heathlands of central Victoria, showed the importance of nectar to such species.

New Holland Honeyeater with Calothamnus sp., Cape le Grande NP, Western Australia.
Note the pollen on its forehead.

Paton discovered that the birds relied on nectar as their key energy source; their abundance, breeding success and physical condition all depended on nectar abundance and distribution. They needed small flying insects as a protein source, but could get all they needed in ten minutes, even if at an energy loss. Their energy requirements however demanded several hours of foraging a day. Very good news for the plants!

Australia seems to have an inordinately large number of bird-pollinated plans compared with other areas. Over a thousand Australian plant species are known to be visited by over 100 bird species; in Europe and North Africa there appear to be none at all, and in North America just a handful. The honeyeaters, the largest Australian bird family with some 70 species (some 10% of the bird fauna), are predominant.

Eastern Little (or Brush) Wattlebird Anthochaera chrysoptera, on Banksia serrata,
south coast New South Wales.

Western Little Wattlebird Anthochaera lunulata on Banksia speciosa,Esperance, Western Australia.

Scarlet Honeyeater Myzomela sanguinolenta on bottlebrush, Callistemon sp.
Cape Hillsborough NP, Queensland.

Other groups are also significant however, notably the lorikeets, small brightly coloured nomadic parrots which often descend in flocks.

Musk Lorikeet Glossopsitta concinna, on Eucalyptus leucoxylon, Coles Bay, Tasmania.

Rainbow Lorikeet Trichoglossus haematodus, Rosedale, New South Wales.

Many other Australian groups take nectar to a significant degree, though are not as single-minded as honeyeaters and lorikeets; they include silvereyes, woodswallows, other parrots, thornbills and pardalotes. 

Silvereye Zosterops lateralis on Callistemon, Canberra.
(From the balcony outside my study window in fact!)

In Africa the obvious nectar specialists are the glittering sunbirds, 130 species of nectar-lovers (some of which are Asian, with one in northern Australia). They resemble some of the smaller long-billed Australian honeyeaters to a surprising degree - but we ought not to be surprised, given their very similar lifestyles.

Scarlet-chested Sunbird Chalcomitra senegalensis, Entebbe Botanic Gardens, Uganda.
This species ranges across most of Africa.

And of course in the Americas, especially the Neotropics, are the superb hummingbirds, nearly 350 species of superb aerialists, the ultimate hoverers. Some of them are specialists in just one plant species, or a few closely-related ones, to a degree not found elsewhere. This of course is a plant's dream.

Sapphire-vented Puffleg Eriocnemis luciani, El Cajas NP, high Andes, southern Ecuador.
This one is almost cheating by perching to feed! I can (after many attempts) offer you
a couple of examples of hummers feeding more typically, hanging implausibly in the air in front of the flower.

Green Violetear Colibri thalassinus on Nicotiana flowers, near Cusco, Peruvian Andes.

Bearded Mountaineer Oreonympha nobilis, also near Cusco, and also on Nicotiana.
This one is much less common, being limited to the southern Peruvian Andes above about 3000 metres.

While less bird species than insects are involved in pollination on the part of both plants and animals, in the southern hemisphere in particular they are a key part of the fabric. Keep an eye out for them - it really is a great story!

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