The White-eye and the Bluebell in Mauritius

Ria Winters - AFC
August 27, 2011 share
Artists for Conservation

Mauritius may be just a small island in the Indian Ocean and the former home of the Dodo, but it still has an amazing array of endemic species, most of them unfortunately endangered. Like in most isolated places, Mauritian plants and animals have evolved in such a way that they have become dependant on one another.

This is the story of a very rare songbird and an even rarer plant.

The Olive white-eye (Zosterops chloronothos) is a member of the large family of Zosteropidae, small passerines native to tropical islands of the Indian Ocean and the Western Pacific.

Mauritius is the home of two of those: the Grey white-eye which is the only common endemic on the island and the Olive white-eye, of which only approximately 125 pairs remain. The Olive white-eye mostly lives on nectar - this is where evolution played its part: to get to the nectar it has developed a slender, slightly curved bill for probing into the flowers.

Because Mauritius has been robbed of most of its forests, few indigenous areas have survived, with the result that many of Mauritius' 300 endemic flowering plants are now surviving in just one spot. Some of them are so rare that until recently their existence was unknown. This was the case with a member of the bellflower family; in 1976 a new species was found on an inaccessible cliff in the southwest of the island. It wasn't just another bluebell: it looked remarkably different from other Campanulaceae because it secreted red nectar!

Coloured nectar is a rare feature in plants. Together with two other bell-shaped plants (Trochetia blackburniana and Trochetia boutoniana, both with red flowers growing on shrubs), Mauritius has three plant species with red nectar which may be the highest percentage in the world of plants on such a compact area with this unusual feature.

Tests have shown that the endemic day geckos - who feed off nectar - prefer coloured nectar to colourless nectar and indeed, the geckos feed on the coloured nectar of the red bell-shaped Trochetias that are still common in Mauritius.

The new blue bellflower was described in 1980 as Nesocodon mauritianus. So far I have not come across a common English name but in French (the spoken language of Mauritius) it is called "La Clochette Bleue".

A team of researchers has been studying these flowers to determine why red nectar evolved and who the pollinators are. They spent days watching the cliff-face home of the last 130-or-so known plants of the species hoping to spot the native pollinator, but they failed - probably because pollinators and plants got separated during the last few hundred years of habitat destruction. (The plant could probably survive by rooting.)

They theorize that red nectar may have coevolved with a pollinating bird species that is now extinct. But because the day geckos feed on coloured nectar too, as well as the specialized nectar-feeding Olive White-eye, it is likely that they too are candidates for being pollinators of the Nesocodon bluebell.

Unfortunately the day geckos don't live near the cliff and the Olive White-eye is too rare and lives too far from the Nesocodon pocket.

My watercolour shows the two together: Nesocodon mauritianus with the red nectar and the Olive White-eye as its pollinator. It is a vision of the past and hopefully of the future.

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