Like many of life's mysteries it is most probably a combination of factors that set off breeding activity. Why do geese fly south, squirrels start hiding nuts, trees stop their summer cycle, all are mysteries that have one thing in common. That common thread is the amount of daylight available in a particular latitude/longitude at a particular time of year. We can gain knowledge about the rut through reading, our own experiences, etc. etc.. Bottomline it is a fairly accurate time period that is affected not only by light but most likely a combination of factors such as temperature, precipitation, food availability etc.. The critters we are after seem to have an innate sense to notice all these changes, process that information and then mysteriously the breeding buttons click on. Could it be that there really is a master plan? Sorry A.C.L.U. I like to observe these mysteries of life and merely use rutting tables, sun light tables etc. as GENERAL GUIDELINES.