Midwest to the Pacific: Hosto explores fruit bats

Erin Hosto has spent her life in the Midwest–from growing up in La Moille, Illinois, to attending Cornell College in Mount Vernon, Iowa.

Erin in the rainforest
Erin Hosto

The college senior, however, left the familiar Midwest setting behind during her college career to explore a destination on the other side of the world–the Mariana Islands in the Pacific. It’s a place where bats are not the small mammals that eat insects, rather a much larger species with wingspans of three feet that eat fruit on trees.

Hosto, a double major in biology and environmental studies, explored the rainforests for her senior capstone project during Block 5 of last year with Associate Professor of Biology Tammy Mildenstein, who has studied fruit-eating megabats for about 25 years.

“The fieldwork itself was a bit intense, but a lot of fun,” Hosto said. “The island we were on, Rota, is mostly rainforest on top of steep cliffs of fossilized coral called karst, which is a fragile yet sharp rock.” 

Because Hosto was only taking One Course At A Time, she could spend the entire 3 ½ weeks of the block immersed in her research. A big part of that was collecting data.

“We found trees where bats had roosted via radio collar tracking data,” Hosto said. “When we found the tree, we would identify it, then measure its diameter. We would then form a 10-meter radius circle around this tree and identify and measure the diameter of the other trees within this circle. We did this to understand what trees the bat was selecting to forage.”

Now Hosto is analyzing the data and writing her final report. Her research will help provide information on actions that could be taken to save the Mariana fruit bat, which faces extinction because of habitat loss, hunting, invasive species, predation, and typhoons. 

“The goal of my study is to ascertain this species’ optimal habitat for reforestation,” Hosto said. “Lots of collaboration has been involved in this research, such as reaching out to locals or specialists from Guam and Rota to help me better understand some of our data.”

Erin Hosto with a bat pup
Hosto with a fruit bat pup

Now she’s spending hours examining every measurement and data point on several Excel spreadsheets to summarize her findings. Hosto and Mildenstein hope this research helps people understand the importance of species diversity preservation. 

“I think there are a lot of reasons why biodiversity is important,” Mildenstein said.  “The most cited reason is that maintaining biodiversity supports the ecosystem, making it robust and more likely to persist through environmental disturbance, both natural and man-made.”

The research data will provide further insight for those who are working to save the species through reforestation efforts. Their findings show that fruit bats have a wide diet, using many different tree species’ flowers and fruits as food.

“These bats require a range of fruit and flower-bearing trees across a few miles of habitat to forage, and they seem to select larger trees located in the forest rather than in the plains regions, which are mostly populated by coconut trees and species of tree called Pandanus,” Hosto said. 

Erin in the rainforestMildenstein says they’ve discovered two key results that suggest the bats are limited and very dependent on the diversity of native trees in their diet.

“First, these trees are pretty spread out and second the trees are only fruiting and flowering during a narrow season,” Mildenstein said. “So, by having a wide diet, fruit bats are assured there is likely something fruiting and flowering somewhere all year long. They just need to find the food that is available to them.”

Studying these bats is Hosto’s third research project with Cornell College

She participated in the Cornell Summer Research Institute in 2018 when she studied monarch butterflies with Mildenstein. Then, in the summer of 2019, she was a Cornell Fellow where she spent eight weeks at the Baruch Marine Field Lab in South Carolina.

 “I think Cornell provides several fantastic research opportunities across disciplines,” Hosto said. “My time doing research here has been among my favorite opportunities, and it has pointed me in the research direction post-college. Along with providing students with opportunities in labs and field stations around the country, I’ve found these opportunities also provide a valuable opportunity to make connections with professionals in a specific field.”

Hosto plans to get a master’s degree in conservation ecology to continue doing similar types of research.