biology zoology blog benno meyer rochow Not Only Seeds Get Dispersed By Wind

Not Only Seeds Get Dispersed By Wind

Animals get blown off course as well

Everybody knows at least one plant whose seeds are dispersed by the wind: the dandelion. Its seeds and those of thistles as well look like little umbrellas with a tuft of fine and flimsy hairs at the top that catch the wind. Willow trees also produce seeds that are transported by the wind and the wing- or propeller-like seeds of the sycamore (also known as the planetree Platanus occidentalis) are familiar to most people. However, the wind disperses not just seeds (and pollen, of course), but also animals.

I mentioned ones that on newly formed islands like, for instance Surtsey off the coast of Iceland, some of the earliest colonizing animals were spiders, because many species that build webs to trap prey (rather than jumping spiders and other species that catch their prey without the help of a web) have a ballooning dispersal stage, during which the tiny spiderlings can be carried by their silk threads to great heights over long distances. However, insects, especially slender and light ones with relatively small bodies but large wings, are equally good at covering long distances when airborne. It’s the reason why on small oceanic islands one can often find fly and other insect species with reduced wings or no wings at all; obviously, for them it is of paramount importance not to be blown off the island they call home.

And yet it happens. A famous case is that of the small diamond back moth Plutella xylostella, swarms of which were noticed on July 1st 1958 on the eastern coast of Scotland and on July 4th by a weather ship at sea to the southwest of Iceland. It is thought the moths had originally been blown from western Russia via Norway and could even have reached North America a couple of days after they were spotted by the weather ship in the North Atlantic. The hornet distribution right across temperate Eurasia and the eastern United States of America might also have been aided by wind dispersal. Aphids and the Colorado beetle are known to have reached southern Sweden assisted by southerly winds and in the Bible it is stated that “the Lord brought an east wind upon the land all that day and all that night, and when it was morning the east wind had brought the locust” (Exodus 10: 13).

The two French researchers M. Devaud and M. Lebouvier recently described that two live adults of an African dragonfly Pantala flavescens, a species that can fly several thousand kilometres between East Africa and India, had been collected on the sub-Antarctic “Amsterdam Island”. Another insect that made it to the sub-Antarctic Crozet islands assisted by the wind was the nymphalid butterfly Vanessa cardui. These are just two examples, but many more wind-assisted colonizations of islands by insects have been recorded. However, not just insects can be blown off course: birds can be involved, too. A single bird, whether male or female, reaching a faraway island may survive in the new habitat, but it cannot reproduce. Therefore, birds that live and fly as a pair have a much better chance to colonize a new habitat that they happen to reach assisted by the wind than birds that do not form pair bonds. This fact is often used to explain why New Zealand’s three main islands (North Island, South Island, and Stewart Island) have a surprisingly large number of pigeons (5 species of Columbidae) and parrots (13 species of Psittaciformes), i.e. terrestrial species. Their ancestors are likely to have originated from Australia and been blown off course. Many parrot species bond for life or at least form tight bonds during the breeding season as their young are altricial and require the support of both parents. Obviously for immigrant species, a couple is better than a single individual (unless one is dealing with hermaphroditic or parthenogenetic species, but they don’t occur amongst our feathered friends, the birds).

© Dr V.B. Meyer-Rochow and, 2020.
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