PHILADELPHIA — Some humans consider mulberry trees little more than oversize weeds, but Stella the giraffe loves them. Her long, gray tongue snakes around the leaves and plucks them from their branches with elegant efficiency.
Stella’s mother, Abby, strolls over for her share, and the Philadelphia Zoo’s two female giraffes quickly strip the handful of branches, consuming approximately a pound of leaves in mere minutes. Fortunately, the zoo has plenty of the snack, thanks in part to an unusual source: the local power company.
Utility companies routinely trim trees to keep branches from damaging power lines and causing outages, and usually the clippings end up in landfills or are ground into mulch. But in recent years, a growing number of regional energy providers have begun donating the collected roughage to zoos, whose hungry animals are happy to gobble up the green, leafy tree branches known as “browse.”
Browse partnerships between zoos and power companies are one example of the creative and sometimes unexpected ways zoos work with local organizations to meet animals’ particular — and often enormous — dietary needs. Grocery store chains and restaurants sell or donate greens, fruits and vegetables to zoos, and local landowners, botanic gardens and nurseries also provide plant material. But utility companies are in the singular position of needing to regularly cut back branches that they cannot use themselves.
From August through October, PECO Energy Co., Pennsylvania’s largest electric and natural gas utility, delivered three pickup trucks full of browse — totaling between 100 and 200 pounds — every week to the Philadelphia Zoo. The zoo gets browse from several sources, but PECO is its first corporate supplier, and its tree-trimming contractor assigned a dedicated crew manager to coordinate the special deliveries. The cargo was mostly mulberry clippings, with acacia, honey locust and willow mixed in when available.
“The great part about the PECO partnership is the sheer volume of browse it provides,” said Barbara Toddes, the zoo’s director of animal nutrition. “It’s a tremendous amount.”
Zoos require a lot of browse because it’s such an important part of many animals’ diets. Of the Philadelphia Zoo’s 330 species, 40 eat it — from giraffes and giant tortoises to gorillas and little rodents called degus. Browse has it all: fiber, protein, vitamins, minerals and a little fat. It’s also lower in sugar and higher in protein and fiber than some other plant material, Toddes said. Chewing on the bark is even good for animals’ teeth.
What’s more, browse provides captive animals with important enrichment and exercise, she said, by giving them new material to play with and forcing them to strip branches of leaves, twigs and bark. In the wild, giraffes graze on the tops of trees. So zoo staff hang bundles of browse up high to simulate their native environment, which gives visitors a better idea of the animals’ natural behavior.
“I want the public seeing giraffes eating browse,” Toddes said.
Zoos typically grow browse themselves or buy it from farms. The Philadelphia Zoo has its own farm, and it also purchases browse from a Florida farm that grows browse for zoo animals. The zoo freezes and stores the greens during the winter months.
The first such program in the United States was launched in 2010, when the Brookfield Zoo, near Chicago, partnered with its local utility provider, Commonwealth Edison Co. Brookfield’s browse partnership is now the nation’s largest in terms of the amount the zoo receives from a utility partner, said Mike Maslanka, chair of the Association of Zoos and Aquariums’ Nutrition Science Advisory Group and head of the nutrition science department at the National Zoo in Washington.
The Philadelphia Zoo-PECO partnership isn’t far behind in its browse collection, he said.
“Giving browse to an herbivore is like giving a carcass to a carnivore,” said Maslanka, whose home zoo gets browse from its own farm, nurseries and local property owners. “The positive impact of zoo browse partnerships is beyond what a lot of people can imagine.”
For the utilities, the biggest challenge is avoiding browse that may be contaminated with pesticides. That’s one reason mulberry is the tree most commonly harvested in these programs: It’s relatively pest-resistant and unlikely to be sprayed, particularly if it’s not close to residential areas.
The Brookfield and Philadelphia zoos’ partners, ComEd and PECO, are both owned by Exelon Corp., a Chicago-based power company that operates in 48 states and Canada. Another Exelon company, Baltimore Gas and Electric Co., will be launching its own browse program with the Maryland Zoo Baltimore in 2018, according to an Exelon spokesman.
The St. Louis Zoo launched its own partnership with a regional power company in May. In the past, the zoo grew some browse on site and obtained some from the Missouri Botanical Garden, but it struggled to harvest as much browse as it wanted, said animal nutritionist Debra Schmidt. From May through October, Ameren Missouri, the power company, made three browse deliveries every Thursday. Next year, the arrangement will expand to twice-weekly deliveries so the animals can munch on the stuff every day.
“Browse is so important for so many species,” Schmidt said.
Zoos also turn to gardens for browse donations. The Sacramento Zoo, for example, accepts several kinds of tree and shrub trimmings from area residents’ properties, provided they’re whole, fresh, leafy and pesticide-free. The Dallas Zoo has a similar program.
But local electric companies could become a growing source of this salad for zoo residents. In September, ComEd gave a presentation on its work with Brookfield at a national conference for utility vegetation management professionals as part of a session on the perennial challenge of disposing of brush and wood. The talk was “a big hit,” said Emily Kramer, who runs the company’s vegetation management division. “We have been thrilled with the program’s results and are excited to share our findings with other utilities.”