Tui and the Flowers of Native Flaxes
The Tui (Prosthemadera novaeseelandiae), unlike the majority of our native land birds, has adapted well to changes brought about by humans in New Zealand. Even although nearly all prime lowland forest on the main islands has been cleared, the widespread planting of both native and many different species of introduced flowering plants in both urban and rural areas seems to have provided Tui with a regular year-round food supply. Indeed, the variety of native and introduced nectar-bearing plants which has become available to Tui in many urban areas, perhaps in the North Island particularly, has undoubtedly materially contributed to those birds being year-round breeding residents in some of those habitats.
Tui are predominantly nectar feeders, but they also eat many different kinds of fruits, and a wide variety of invertebrates particularly during summer. Tui play an important ecological role as pollinators of several native (and probably also some introduced) plants, and they are also one of the main dispersers of the seeds of plants with medium-sized fruits. The tongue of the Tui is highly specialized and admirably suited to its nectar-feeding habit. The extremity is brush-like and composed of four finely attenuated arms, each arm being provided with very fine bristles. Also, the main body of the tongue is deeply canalled, thus enabling nectar collected to flow more easily towards the gullet. In addition, the curvature of the bill of the Tui closely conforms to the curvature of the filaments of some of the flowers at which it feeds, including those of the two native flaxes, Phormium tenax and Phormium cookianum, and their many cultivated varieties, which are widely grown in urban parks and gardens.
Flax flowers are a profuse and favoured source of nectar for Tui during early summer, generally from November into January. There seems to be no doubt that those flowers are adapted to cross-pollination by Tui. They are curved along the lower surface, and their opening is almost invariably facing upwards. The curvature of the pistil and stamens conforms to the lower curvature of the flower, which in turn matches the curvature of the Tui’s bill. When a Tui obtains nectar from deep within a flax flower, usually by probing it from above, its crown and lores come in contact with the flower’s anthers and thus receive a liberal coating of pollen which clings readily to the bird’s plumage and is transported to the next flowers it visits. Tui sporting foreheads covered with pollen obtained while feeding at flax flowers are often seen at that time.
The accompanying photographs of Tui in Phormium cookianum bushes were taken at Pukekura Park in New Plymouth in November 2002.
Reproduced, with permission, from Miranda Naturalists’ Trust News No. 48 (February 2003).