The last two times Riverbanks Zoo and Garden's attendance had large spikes, major new additions were the obvious reasons - the aquarium-reptile complex in 1989 and the gorilla exhibit in 2001.
So how to explain topping the 1 million mark in 2009, when the biggest addition was a baby giraffe?
The only thing to point to is the economy.
"People continue to visit not only because of our exceptional animal and plant collections, but also because the zoo and garden is a fun, affordable place to spend time with family and friends," said Tommy Stringfellow, director of marketing for Riverbanks.
Daily admission is $9.75 for adults, $7.25 for ages 3-12 and free for children 2 and younger. That's comparable to a movie, and a zoo visit can last anywhere from a couple of hours to all day.
The best deal is a family Riverbanks Society membership, which allows unlimited visits for $69 a year.
The 2009 attendance total was 1,006,170, falling short of the record 1,019,834 set in 1990 when the aquarium-reptile complex was new. The zoo also edged past 1 million in the fiscal year (July 1-June 30) of 2001-2002 as locals flocked to the Gorilla Base Camp exhibit.
Since the opening of the Aquarium and Reptile Complex, the zoo's annual attendance has averaged 800,000 to 850,000. Zoo leaders began to notice a jump in visitors as the economy sank in 2008. In the fiscal year that ended in June, attendance was 955,542.
And while other zoos have noticed similar increases, Riverbanks takes pride that its attendance topped the 2008-09 fiscal year numbers at zoos in larger Southern cities such as Zoo Atlanta (711,574 visitors), the Audubon Zoo in New Orleans (683,807) and Jacksonville Zoo (687,300).