Ruby likely ate a rodent contaminated with poison at the Mt. Auburn Cemetery.

The love story of Ruby and Buzz, two red-tailed hawks, enchanted bird-watchers near Fresh Pond in Cambridge for years. They saw the love birds raise a family together, taking turns hunting and incubating Ruby's eggs, their nest size waxing and waning with the arrival and departure of new chicks.

But their romance came to a tragic end last Friday, when Ruby's body was discovered under her nesting tree near Fresh Pond Mall, an untimely death that veterinarians say was caused by rat poisoning.

Now, the bird-watchers are seeking to find out how Ruby's death could have been prevented and are hoping to change the way their neighborhood handles its rodent problem.

"The irony is that there are a ton of traps with rat poisoning, but, cruelly, they're not controlling the rats; they're killing other animals," said Susan Moses of Cambridge, who has made almost daily visits to the hawks' nest since 2010. "We need different types of rat control with different chemicals that are less toxic."

Ruby probably ate a rodent contaminated with the poison at Mount Auburn Cemetery, a popular hunting area for wildlife in West Cambridge, said Chris Leahy, a field ornithologist at the Massachusetts Audubon Society. The cemetery does not use the poison, but some local businesses are believed to use it.

"I've done work with the cemetery for years, and there have been various birds and mammals that have died from toxic poisoning, so it's an ongoing thing," Leahy said. "It seems to indicate that there's this general rat poisoning in Cambridge, but it could also be that certain businesses with a rat problem near the cemetery are putting out the rodenticide."

Moses, who brought Ruby's body to Tufts Wildlife Clinic last Friday for a necropsy, paid out-of-pocket for additional blood testing to identify what chemical led to Ruby's death. She hopes the results can help her find out what brands of rodenticide are being used in the area and to urge merchants to stop using them.

"Old-fashioned traps are more labor-intensive because somebody has to empty them, but these chemicals are extremely harmful, not just for wildlife, but people's pets and children," Moses said. "Hawks die all the time, but there's a difference when we feel it was caused by human action and could have been prevented."

Photographer George McLean, who has photographed and observed Buzz and Ruby and other local wildlife for years, says it will take action by business owners to fix the problem.

"There are restaurants, grocery stores, [and] bread factories all over the area," McLean said. "The town is getting overwhelmed with rodents, but the creatures who eat the rats die just as easily."

As for Buzz, Ruby's longtime mate, the road to recovery was short. "There is a new female in his life at the moment," Moses said. "Nature has to continue on, but they're all at risk."

Catalina Gaitan can be reached at catalina.gaitan@globe.com. Follow her on Twitter at @catalina_gaitan.

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