http://www.in.gov/dnr/fishwild/3375.htm
POPULATION UPS AND DOWNS
Cottontail numbers, like most animal populations, run in cycles of highs and lows. The population builds up to a very high level, then disease, strife and poor reproduction down to a low level. This low may continue for two or three years before a slow increase begins to bring numbers back to another high. Peak populations usually occur at intervals of about 10 years. Within this 10 year cycle, there may be local areas having highs and lows opposite to the overall state cycle. Also, some areas may hold a continued high or low for several years and not seem to go through the cycle change. Optimum food and cover and balance between the number produced and the number harvested by hunter, predator or disease may hold the population stable. Drastic changes in numbers grow to a high in August. The with peak of reproduction past, the rabbits begin to disappear. By the first of November, their numbers may be cut one-third or more, with another third lost by the beginning of the next breeding season. Thus, while some rabbits may live four or five years, the average life expectancy for young rabbits that survive to leave the nest is only about 11 months.
I have read 7 and read 10. It is generally stated the cycle is between peaks in population. so 5 on the way up and five on the way down...or 3.5 &3.5 depending on the article...lol.
I think there may be cycles but cover, food and mortality would be causing it. I hunted an overgorwn apple orchard as a kid and you couldn't bring enough shells with you. it was great until the hardwood saplings came and grew. then the canopy started to close. I was back home a couple years ago and went there. no underbrush at all and no rabbits. The habitat totally changed.