"For a particular bird, you can be pretty sure that the rainy season is going to come at some point, usually when it's supposed to come, but it may be late, or it may be early. The amount of rain may be much higher, or much lower. So there's really no way to predict how much rain, or how much food, you're going to get during a given breeding season."
So for birds that chose to live in the savanna, he added, "it pays to live in family groups. That gives them a better chance to feed their babies."
OK, but what's in it for the cousins, and the siblings, who hang back to help out around the nest? Is this really just altruistic behavior?
Not exactly. Whether starling or human or whatever, what drives the mating instinct is the desire to pass on one's own genes, guaranteeing at least a partial hold on immortality. In an ideal world, Rubenstein said, it's best to go it alone, because your offspring will get half your genes. But if the chances of success are slim, it's better to hang out with the family because you share some genes, so at least some of your genes will be passed on down the line.
"Everyone's looking out for their own best interest," he said. "If you breed on your own you will be producing offspring that are more related to you than if you are helping someone else. But if you can't go it alone, you can pass on at least a share of your genes by helping to raise relatives."
So in the savanna, where rain and food is less predictable, a smart starling chooses to maintain a close relationship with its kinfolk to ensure propagation of the family lineage.
Rubenstein is comfortable with his conclusions, and he said the results were worth all those long and hazardous trips across Africa, but he knows there are still a lot of questions concerning "cooperative breeding." Environmental factors are probably part of the reason why some species work together, while others remain aloof, but the study was based on only 45 species of starlings.
"That's a good group," he said. But there are many birds that don't conform to the patterns seen in Africa, he added.
"It's still not clear why some that live in the same area do (engage in cooperative breeding) and some don't," he said. "There are still a lot of questions."
He expects to expand the research to other animals. Hopefully, he will always be able to outrun the rhinos.
Lee Dye is a former science writer for the Los Angeles Times. He now lives in Juneau, Alaska.