September 15, 2000.
White Faced Storm Petrel:Part II
White-faced storm petrels are found over vast areas of the Atlantic and Pacific, but their appearance over these expanses is seasonal. In both these oceans they nest on very few islands. In the Pacific they may be encountered anywhere across the entire sea, south of the equator, from the Galapagos to Australia. But they nest only in the western portion of this range. That means that wnen the nesting season of the petrel that visited the Odyssey in the middle of the night approaches, it will have to fly nearly 6000 miles back to the islands off Australia or New Zealand on which it will find its mate, dig a burrow in soft earth, lay eggs, incubate them, and raise its young through a season that December.
Some ornithologists believe that storm petrels are the most abundant birds on earth. Strange that such solitary animals should be the most numerous. One might have expected some densely flocking species to hold that record. But if a thinly scattered species like storm petrels exceeds in number even the flocks of passenger pigeons that once darkened the sky on their Mississippi flyway for a week at a time, what this should really teach us about is just how vast the ocean really is.
Here on the Odyssey we think of that as we inch our way over this vast ocean.
Another interesting aspect of this species is that it feeds on the same prey on which baleen whales depend-euphausiid shrimp (krill) and copepods. This means that the competitors of storm petrels are whales, and vice versa. I suppose that if you could tell a baleen whale that such a tiny puff of feathers attached to a few grams of muscle posed a potential threat to it that the whale might laugh loud and long. But that would simply mean that the whale would be being as shortsighted as we were back when we thought that our puny efforts on an all-but-infinite sea could never have a significant effect.
The lesson is that large numbers of small effects add up to major and sometimes devastating effects. It is the same with the effects that petrels have on whales. Were there enough safe nesting islands for the petrels, one might suppose that they might out-compete the whales and bring them to extinction by starving them out. However, since that has not happened there must be some mechanism that prevents it. Usually, when two species compete openly for food, each has a somewhat different strategy in the ways in which it exploits the common food resource. For example: some bird species feed on seeds that fall to the ground while their competitors land on weed heads and take the same seeds directly from the plant (something you can see at any bird feeder where the sparrows on the ground eat seeds that have been spilled by the finches on the feeder above them). Each misses out on the seeds that the other is getting. In this case the mechanism to avoid total competition seems to be that the whales feed on copepods and krill when they are deep and therefore out of range of the petrels, which is why the petrels have never outcompeted the whales.
So why haven't the baleen whales brought the storm petrels to extinction? Probably because the petrels can subsist on far more thinly scattered food than whales can. The tendency of the krill and copepods to spread out, which works so well to save these plankton species for many months from the whales, fails to protect them from storm petrels.
© 2000 - Roger Payne