Most of the time studies seem to be short, a couple years. Long term studies are what is needed because no one year is "normal" or "average".

I read a summary of the studies that were done on a single island in the Galapagos, looking at evolution among two or three species of Darwin's Finches. Essentially, one conclusion is that of they hadn't studied the island continuously for the 20-30 years they would have come up with incorrect conclusions. It took that length of time to actually see what was going on with all of the environmental changes going on, too. It was the Grant's, a husband and wife team, that did these studies.