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Fickle bills of fare.

IN SOME parts of the world, nectar-bearing flowers and the `nectarivorous' birds that feed on them have a highly specialised relationship. For example, some flower shapes are accessible only by bird species with particular bill structures. Scientists have found that in the monsoonal north-west of Australia, however, the bird-flower relationship is more generalised.

Donald Franklin and Dr Richard Noske from the CRC for the Sustainable Development of Tropical Savannas, and the Northern Territory University, looked at the bill length and body weight of certain nectarivorous birds (including lorikeets and honeyeaters), and the flower structure of plant species on which the birds fed, to see if bird and flower morphology (structure) were linked.

They found that the most abundant and popular nectar sources included flowers from the families Myrtaceae (eucalypts and bloodwoods), Proteaceae (grevillea and banksia) and Loranthaceae (mistletoe). Eight flower shapes and three groups of birds were identified, depending on the flower shapes they used. But the scientists found a limited relationship between the size and bill-shape of the birds, and flower structure. Instead, the birds tended to use whatever flowers were available in their habitats. Variation between bird species in patterns of use of different floral structures primarily reflected the habitats occupied, rather than a shared or co-evolved morphology.

A combination of factors probably contributed to this generalised relationship: the abundance of mass-flowering myrtaceous trees, aridity during past glacials which may have removed specialists from the system, and the sharing of nectar sources with bats.

Fruit and blossom bats may have been a selective force in the evolution of vertebrate pollination relationships in the Australian tropics, and their prevalence may have mitigated against the evolution of highly specific bird-pollination relationships.

Franklin DC and Noske RA (2000) Nectar sources used by birds in monsoonal northwestern Australia: a regional survey. Australian Journal of Botany, 48:461-474.
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Title Annotation:research on nectar sources used by birds in Australia
Author:Pyper, Wendy
Article Type:Brief Article
Geographic Code:8AUST
Date:Oct 1, 2000
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