Environmentalists from Cornell University (USA) have put forward an interesting hypothesis, believing that through their life cycle cicadas manage the dynamics of populations of birds that eat them. And then you can immediately assume that the output of the larvae to the surface coincides with the peak number of birds, that is, the most that neither is a common and banal environmental law. But the fact of the matter is that, as the researchers wrote in the journal American Naturalist, the metamorphosis of the cicadas have the minimum number of birds.
In the past, studies have been conducted that show that birds can destroy the entire population of cicadas, if they do not appear above ground at the time. To be certain of the connection between population watch the birds and cicadas, the researchers used data on the dynamics of bird populations, collected over the past fifty years. Ecologists interested above all the species that have for a particular tendency of cicadas, like American Yellow-billed cuckoos, sparrows and red-woodpeckers. It turned out that in the moment of the number of cicadas all these birds reaches a minimum, then rises and starts to decline. It looks as if the cicadas specifically waiting for the right situation — when predators will terrorize them the least.
But can a single output cicadas lead to such debt, "echo", which lasted more than ten years? The researchers argue that it can. According to them, the cicadas have a very large proportion of the biomass — and it suddenly appears, so to speak, in the public domain. The consequences of stuffing cicadas in the food chain can be seen for quite some time, although the environmentalists recognize that there need additional experiments to confirm this hypothesis.
And just as more research is needed to answer another question: why 13 and 17 years old? Where they have a craving for a prime number? How birds can so accurately to reduce their number is on the 13th or 17th year after the cicadas? And cicadas understand that here on this 13th year is not the time, because we want to wait another four years? .. It is unlikely that there are any mystical numerological laws, but biologists still have to smash his head.