A Butterfly Tsunami

In conversation with Justice Ulric Cross a while ago he observed to me with a question the disappearance of so many butterflies that were so common in open spaces such as the Queen’s Park Savannah. I had to agree with him that indeed many of the animals that were so common to that part of the capital and elsewhere in open spaces a few decades ago had simply vanished. It was not only the butterflies but the candle flies as we called them, now known to this generation as fireflies. This conversation triggered the memory of Senior Counsel Martin Daly in a debate on the problem of the illegal paving of the Savannah, recalling his days as a child collecting tadpoles in minute puddles of water here and there in the Savannah, to be ridiculed by a government minister. In fact he was not in error, for one species of slender-toed frogs actually did breed in open savanna and as far as I can tell have now simply disappeared.

Sometimes however a few casual observations suggest to me that something out of the ordinary was happening. Many people will long remember the dry season of 2010 that was followed by an unusually wet rainy season with the first rains causing flash flooding in many places. I cannot of course claim that what I have seen about my immediate space is applicable to the entire country but I did notice the appearance of many butterflies about the garden, common enough species in my childhood in and about Port of Spain, but rarely seen in my garden until July of this year—postmen, coffees, tomatoes or coolies, tigers, flambeaus, doctors, king pages, crackers, shoemakers, sweet oils or sulphurs, gold rims, mort bleus, Martiniquan soldiers, an emperor and even a cravat.

But when I wrote these words—October 23—I had concluded that something really must have happened. It started gradually on October 21 with an observation of a relatively large number of sulphurs flying across the park opposite me, building up on October 22, and into a veritable tsunami on October 23, all flying south down the Maraval Valley. It is a common enough species in suburbia and open spaces and periodically there is a population explosion and startling dispersal/migration from source. These butterflies, in English vernacular, are generally referred to as sulphurs, with some species given some forename characterising them.

To get some idea of the scale of the migration I counted electronically the numbers crossing line of sight to a palmiste tree at the far end of the park some 100 metres away over a ten-minute period, estimating that they were passing in the same southward direction at the rate of about 2,000 per hour over a period of about five hours. As the floor of the valley at this point is perhaps about 500 metres wide the flood must at its peak have been in the order of 10,000 per hour. By mid-afternoon they had completely disappeared. Just imagine this over perhaps 10 hours over three days and you get some idea of the scale of the event. Columnist Paolo Kernahan confirmed seeing a similar migration while in the field at Cumaca at the other end of the Northern Range, while others observed the phenomenon at Asa Wright Nature Centre and Maracas valley.

Lepidopteran migrations and dispersal flights are a well known phenomenon, the most striking being that of the monarch butterfly of North America that goes on an annual intergenerational migration to a specific location in Mexico where they festoon trees in their millions and incidentally become a tourist attraction. But this is an annual event. In the mid-1990s we had a massive migration of white tailed pages (actually a day flying migratory moth, with black forewings, iridescent green hind wings with a pair of white “tails”) through much of western Trinidad and even Port of Spain.

Amongst many invertebrate animals, when things are favourable there is often a population explosion followed by an out migration from the focus. In the case of the white tailed pages each year a scattered few may be seen flying eastward across the Gulf of Paria and crossing roads on particularly the southwestern peninsula, but that event was across the full expanse. It is possible that it was simply a good year of the moths which as larvae simply stripped their food resource base and emergent adults reacted by outmigration.

So back to our sulphurs. The last similar mass migration was about 25 years ago. Possibly the harsh dry season may have reduced their predators and parasites, or, possibly their host plants may have benefited from the extensive bush fires that reduced the numbers of plant competitors, thus favouring their food supply and consequently their breeding success. Perhaps if Justice Cross and Senior Counsel Daly read these words they may be reminded that much of the foundation of 19th century geology and biology was built by individuals originally trained in law, a field that requires critical thinking—before that term became a university bureaucrat’s buzzword!

SOURCE

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