Drought, kiwi and ecological dominoes

By Daniel Collins 27/04/2010

Two weeks ago news hit the TV of the impact the Northland drought is having on kiwi. It had already been picked up far and wide back in February, but as the drought continues, so does the story. The story is this: drought has caused nocturnal kiwi to forage for food during the day.

These normally nocturnal birds forage for insects in the leaf litter on a forest floor. Normally. But the onset of one of the most severe droughts on record has set off the collapse of a line of ecological dominoes. Low rain begets low soil moisture, which begets lower plant growth and harder soils, which beget less food for insects and more inaccessible insects, which means less food for kiwi, which means more excursions by kiwi into the unsafe light of day and potentially higher mortality.

This game of ecological dominoes, triggered by water shortfalls, is seen the world over.

The seasonal swing to dry conditions in the Florida Everglades concentrates fish and other aquatic critters into ever smaller pools of water. These pools become the fast food joints of the bird world, and of bird watchers. The same applies to watering holes from Africa to Australia.

But while this seasonal swing is par for the course in Florida, a sustained climatic shift in the US Southwest that started in the 1970s caused several common animal species to go locally extinct, and some rare species to increase. The middle man in this case was the expansion of shrubs that fared better in the wetter winters. Shrubs have deeper roots than herbaceous plants, giving them a competitive advantage when more water infiltrates deeper into the soil, as would occur during wetter winters.

Back to kiwi, drought is not the number one threat – that dishonour goes to introduced mammals. But I imagine that the threats posed by drought would be substantially alleviated in predator-proof sanctuaries, where daylight foraging is less risky.

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