(Originally posted in September 1997 with the comment “This will no doubt become topical again some time”.)
In recent times there have been many news reports concerning the problems of rabbits for farmers in the south island and the release of rabbits contaminated with the RCD rabbit virus. I am writing because I have some information which might be of relevance to the problem, and without which some mistaken conclusions might be reached.
There is a cycle of 9.6 years in snowshoe rabbit populations in the northern hemisphere. Many other animals show this same variation, including Canadian Lynx, hawk, owl, partridge, tent caterpillars, chinch bug, ticks, coyote, fisher, martin, mink, muskrat, four varieties of fox, timber wolf, goshawk, skunk and salmon. In most cases the variations in animal populations and reproduction rates vary by enormous factors over the 9.6 year cycle. For example the Canadian Lynx population increases by about 1000% in 5 years and just as rapidly declines to its original level. A graph of the Canadian Lynx population, as measured by the number trapped for fur, and covering a 200 year period is enclosed. Humans too are slightly affected by the 9.6 year cycle with a variation in heart attacks.
These matters have all been reported extensively by Edward Dewey and others at the cycles foundation over a long period. Other variations over a cycle of 9.6 years include wheat production, tree ring widths, financial crises, storm track shifts, magnetic measurements, lake varve thicknesses, atmospheric ozone content, atmospheric pressure and the runoffs of certain rivers.
I recently came across an old book with some further interesting material related to the matter. Ellsworth Huntington reported in the 1940s that ozone concentration in the lower atmosphere also varies over the same cycle and that some solar variations are suspected to be responsible. It is also known that litter sizes and breeding frequency increase considerably as the growth phase of the cycle gets under way.
Huntington makes it clear that we do not fully understand these things but offers clues for further research.
Some research on the various creatures affected by the cycle has been carried out because several others are pests as well as rabbits.
Although there is no certainty on the cause, the suspected culprits of weather variations and such factors are not the primary cause of variations.
The question of relevance to farmers is whether epidemics of rabbits can be predicted and, that being so, whether anything can be done about it.
The other important question is what would the natural cycle be doing at the moment without the RCD rabbit virus. All of the animals whose populations vary on a 9.6 year cycle reach peaks at nearly the same time. This is called cycle synchrony by Edward Dewey and is common to other cycles also. There are other cycles of different periods in other animal populations and in many other variables.
Extending forward the dates of the peaks of the various animal populations from the historical records of the 9.6 year cycle leads me to conclude that they would mostly reach a peak around early 1996. On that basis, assuming that our southern hemisphere animals follow the same cycle then it is quite understandable that there has been a serious problem for farmers over the last several years. However, even without the release of RCD rabbit virus we could expect a reduction in rabbit populations to already have begun and for rabbit populations to decline significantly through 1997 to 1999 and reach a low around the end of the year 2000.
It concerns me that even if the rabbit population just follows its normal decline this may be interpreted as being a result of using RCD and so RCD may acquire a reputation whether or not it deserves it. For that reason I wanted to make the facts about animal population cycles known so that when MAF and others are reaching their conclusions at some time in the future they will put this information into the equation also.
(originally posted 31/01/07 on Wobbly Universe blog by Ray Tomes and then I commented later)
This is unbelieveable! It was 9.4 years ago that I wrote this article at the peak of the last rabbit cycle in NZ. Only yesterday I posted it to my blog, realising that the cycle of 9.6 years was due. Today on the TV news there is a report of massive numbers of rabbits in Southland.
I should add that I wrote this article originally and sent to TV presenter Paul Holmes who did not reply. Visit my Just Thinking blog (under links to the right) [Now defunct] for other ignored correspondence with the media.
Then again I sent a message that was ignored:
I just sent the following email to TV3 presenter John Campbell:
I love your show and your enthusiasm. Great!
About nine and a half years ago I sent a fax to Paul Holmes about the Rabbit infestation and the fact that a cycle in rabbit population of 9.6 years was known in the Northern hemisphere. It got ignored (it is normal it seems, my letters to the NZ Herald and NZ Listener also all get ignored).
You might like to look at the info about this on my blogg at http://ray.tomes.biz/b2/index.php/a/2007/01/31/rabbits_diseases_and_cycles
The amusing thing was that 9.4 years after I wrote the article, and 1 day after I posted it to my blog there was a TV News item that the rabbits were back.