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Diana Guzmán-Colón searches through Río Abajo State Forest in Utuado, Puerto Rico, for the right spot to set a live trap for mongoose.

Imagine if squirrels were fearless and rabid and preyed upon your pets rather than the acorns in your yard. In Puerto Rico, this is quite common. The small Indian mongoose — a sleek, fierce, weasel-like critter — has been troubling the island for decades, yet little is known about this invasive species and how to control it.

Diana Guzmán-Colón PhD’18, a doctoral student in the Department of Forest and Wildlife Ecology and a Puerto Rican native, is no stranger to these animals. Through her work at UW–Madison’s SILVIS Lab, she has chased her childhood curiosity and dedicated the last five years of her life to making sense of these mysterious carnivores.

They may be modest in size, typically measuring about two feet from snout to tail, but small Indian mongooses have a large impact on Puerto Rico. Native to India, they were first introduced to the island in the 1890s by sugar plantation owners to hunt rats. Since then, the mongoose population has exploded while expanding its menu to include native birds, amphibians, and domestic animals like cats, chickens, and small dogs. These attacks frighten and infuriate citizens. Today, the mongoose is so common in Puerto Rico that locals often refer to them as squirrels.

The small Indian mongoose, first introduced to Puerto Rico by sugar plantation owners, has been plaguing the island for decades.

Local and federal agencies have tried to keep the mongoose population in check, but because they are aggressive and often rabid, most strategies have failed. “Mongooses are an extremely resilient invasive species and seem to be unaffected by past control measures,” says Guzmán-Colón.

By tracking the mongoose population, Guzmán-Colón hopes to uncover how the species has spread throughout Puerto Rico, where they thrive, and where they may go next. But how do you keep tabs on an entire community of such elusive little creatures? Guzmán-Colón believes the answer lies in their DNA.

By live-trapping and collecting samples from local mongooses, she will be able to piece together a web of genetic relations similar to a family tree. These relationships can shed light on their population structure and movement patterns throughout the island and indicate where the species is successful. From there, Guzmán-Colón can help identify which mongoose populations should be priorities for management measures.

Since Hurricane Maria ravaged the island in September 2017, Guzmán-Colón has faced a new set of challenges in both her professional and personal life. Thankfully, her family was unharmed, but such an environmental disturbance will certainly affect her research. Still, she remains optimistic.

“The storm was devastating to Puerto Rico, but I try to see this as a rare opportunity for science,” says Guzmán-Colón. “It isn’t every day that researchers are able to observe the reemergence of an entire ecosystem.”

As for the mongooses, Guzmán-Colón sees a possible boom in their population. “Mongooses live in burrows underground, are efficient scavengers, and reproduce quickly. My prediction is that they’ll be unaffected by or benefit from the hurricane.”

All the more reason for further research.