Book published by Cambridge University Press is first of its kind about primates, examining how they interact in various habitats and how food availability impacts their population

North East Community Action Center's Ralls County Service Coordinator witnesses years of research culminate in the publication of a groundbreaking study about primates and how they interact in various environments around the world.

Dr. LeAndra Bridgeman, a research associate with Washington University in St. Louis, set out on a trip with her cousin and field assistant, Aubrey Tischer, to study Yucatan black howler monkeys in Mexico in 2010.

Bridgeman worked with other experts to explore primates’ behavior in relation to their environment, focusing on aspects like diet and social interaction. Bridgeman and Tischer discovered clues about evolution and helped reinforce a hypothesis about how food availability affects the animals in a study Bridgeman co-authored, known as “Low Levels of Fruit Nitrogen as Drivers for the Evolution of Madagascar’s Primate Communities.”

The study was published by the Cambridge Press in December, and Bridgeman said she is thrilled about the milestone.

“It's exciting to finally get this book published. It's been five years in the making,” she said. “We have collaborators from all over the world — from many, many different countries — collaborating on this book to provide baseline information on primates in this kind of habitat. It's the first book of its kind, and really the first major publication of primates in this type of habitat.”

Bridgeman and fellow team members studied the behaviors of Yucatan black howlers (Alouatta Pigra) living in a swamp filled with mangroves, a tree that grows in brackish water. They found that the howler monkeys were pushed to the isolated island after a nearby lowland rainforest was cut down for cattle pasture land. The primates lived on a diet much different than that of other primate populations around the world — the primates predominately ate leaves, then switched to the copious purple flowers of nearby Gusano trees (Lonchocarpus hondurensis) during dry spells.

Bridgeman said that primates like howler monkeys who eat leafy plants generally choose as many plant species as possible, so they don’t absorb too much of the toxins many plants produce as a defense mechanism. But the howler monkeys on the island eat just 11 species of plants from the available 12 varieties near the island — a far smaller number than what other howler monkey populations eat.

She found their isolated population and habitat ideal for her research, and discovered that the monkeys displayed enhanced social interactions because they didn’t have to travel far to find food.

Although the flooded area is not an ideal environment for the monkeys, Bridgeman found that the population was stable. Howler monkeys primarily eat leaves — Bridgeman said they have an adaptation that allows them to digest leaves that other animals cannot.

She stressed that a variety of environmental factors affect evolution and other traits in animals. For example, destructive hurricanes in 2017 didn’t strike the island in Mexico, but Bridgeman said those extreme conditions could wipe out the leaves the monkeys depend on for survival, creating a substantial risk.

When she receives digital and hard copies of the book, Bridgeman plans to share them on her website,

The book as opened new doors for Bridgeman, who said it has been “inspiring me to look at my other data from my dissertation” to work on two new publications: a look at the ethnobotany of the area — plants that local residents use for medicinal purposes — and a study highlighting the chemical analyses from the local plant varieties.