San José, Costa Rica, since 1956

Arenal Howlers Have Friend in Area Resident, Zoologist

Early one morning last September, a Ministry of Environment and Energy (MINAE) vehicle crawled up the long, steep drive to zoologist Gloria Dempsey’s mountainside home near Lake Arenal, in north-central Costa Rica. Two MINAE employees approached the wide veranda, one carrying what seemed to be two small animals. He handed them both to Dempsey. One was a baby howler monkey hardly bigger than her hand. The other was a stuffed teddy bear the men had provided to comfort the animal, whose mother had been killed in the night by dogs. The tiny monkey, cold, its eyes closed tightly, clutched its surrogate mother.

What happened to little Sami, as Dempsey named the infant animal, represents, she says, one of the three main hazards facing Costa Rica’s monkeys today. Besides death at the hands of domestic animals, monkeys are often struck by cars or electrocuted when traveling on power lines.

In a recent mass e-mail, Dempsey wrote, “It has been the tragic circumstance of Sami and many others like him that has prompted me to look for solutions to the problem of destruction of natural corridors to monkey feeding trees.” The destruction of the corridors forces the monkeys to descend to the ground or use power lines to move from one group of trees to another on their feeding circuits.

Meanwhile, Sami has survived. In September, Dempsey estimated Sami’s age at about 5 weeks.

“Baby howler monkeys are born silver and slowly turn a gold color, and by the time they are 3 months old, they are black, like their parents,” she explained. “Sami was partly silver and gold.”

Dempsey first put the baby monkey in a plastic animal carrier with a heating pad and began to give him warm milk with an eyedropper, she recalls.

“In a few hours he opened his eyes and had warmed up, and then I began regular feedings every two to three hours around the clock – middle of the night, too,” she said, adding that she started out feeding Sami cow’s milk and then switched to Nursoy, a soy-based baby milk replacement.

Animal Lover

Dempsey and husband Jim Nadolski moved to Costa Rica in September 2000, and built a spacious veranda-skirted house on a mountainside property overlooking LakeArenal and the hilltop town of Nuevo Arenal.

“Being a zoologist by profession and having a deep love and appreciation for all animals, I came here for the thrill of living with and studying these wonderful wild animals,” she said. “In the six years I have lived in Arenal, I have seen many changes on the face of the land.Many more families have moved here and more of the natural habitat is now disturbed.Much of the natural forest habitat was long ago destroyed by local people to raise cattle.”

However, Gloria has noticed a new threat to the habitat she is trying to save.

“Now what I am seeing is people coming in and purchasing huge tracts of land to develop it into small parcelas, with huge amounts of construction causing major destruction to critical feeding areas of many wild animals, including howler monkeys,” she noted.

Predominantly leaf eaters, howler monkeys have a very specialized diet, and thus tend to travel around on a specific circuit as they follow new leaf growth on their preferred food trees, Dempsey explains. They normally forage from tree to tree, and when they have exhausted the new growth in one area, they head to another, using the trees as their “highways.”

In many instances, Dempsey says, the monkeys’ feeding areas are becoming isolated and fragmented, so they can’t safely travel in the canopy from one area to another, but have to come down to the ground to cross roads, where many are killed by cars.

Others that stay aloft to avoid dogs are electrocuted on power lines, Dempsey says.

These problems have inspired action in other parts of Costa Rica. In the Manuel Antonio area, on the central Pacific coast, the Association for the Conservation of the Mono Tití ( has programs under way to map corridors, plant trees, and insulate electrical wires to save the endangered squirrel monkey (mono tití) and other animals. In Playa Nosara, on the northern Pacific coast, the community is raising money to reduce howler monkey deaths by insulating power lines; in at least one area, people are providing rope lines between trees, hoping that monkeys and sloths will use the ropes instead of the electrical wires.

Professional Help

When Dempsey moved to Arenal, the community, upon learning about her background, spontaneously drafted her into caring for injured animals, both wild and domestic: a black Labrador bitten by a viper; a sloth with feet burned by electrical wires; five baby oropendolas whose storm-tossed hanging nests fell from a communal tree; a young howler monkey brain-damaged when hit by a car. This first monkey, Chito, injured in 2003, stayed with Dempsey for five months until she discovered the baby howler monkey rescue and release program at

Zoo Ave

in La Garita, northwest of San José.

“We think Chito may have been about 7 months old,”Dempsey said.“He was hit by a car on the left side of his head, which initially affected his left arm and leg. But over the course of months, he (regained) full use of all his limbs.”

Having already discovered

Zoo Ave

, Gloria was able to turn Sami over to the facility within a few weeks.

“When I contacted them about this little one, they told me they had two others twice his size and would gladly take him,” she recalled. “So when he was stable and eating and gaining well, I took him to be with the other two to begin to bond with them and in the future form their own little troupe to return to the wild. The earlier little howlers are placed together, the better their chances of bonding with each other and relying less on humans for successful survival in the wild.”

When not tending injured animals, Gloria is very much involved in other projects.

During her university teaching career, she worked with cobra venom, researching its possible medicinal uses. In Costa Rica, her interest in poisonous snakes has turned to teaching people to differentiate between the country’s many nonpoisonous and 19 types of poisonous snakes, and to kill neither, ignoring the harmless ones and relocating the poisonous. To this end, she is working on a book of snake photos, on which she is making progress “bit by bit,”while also helping with spay-neuter clinics and trying to obtain better emergency help for domestic animals in the field.

“What seems to happen with me is that each day one project takes more urgent priority over the others, which get put on the back burner,” the busy zoologist said. “And then something brand new comes up with even more urgency, so I always try to prioritize those things that are more life-threatening at the time.”

Advice from a Zoologist

Dempsey has the following advice for property owners who want to help the monkeys: Take time to walk your property and make note of the route the monkeys take as they go from one feeding area to another. Study also the route they must take to get onto your property. As you are walking the area, make note of the trees the monkeys feed from. Also make note of any break between the trees on the route the monkeys travel during their foraging. In any area where the monkeys must go down to the ground to cross to another area, there is potential danger to them, and you have a great opportunity to plant a tree or trees to fill that gap.

If you aren’t familiar with the species of trees, consult someone who is. You can make the task ultra simple by choosing from ficus, inga (guava) and cecropia trees, which are the three genera of trees that make up the major bulk of the monkeys’ preferred diet. In a pinch, almost any tree that grows fast and produces strong branches to support the monkeys’ weight can be used to fill a gap in a corridor of their arboreal highway, but choosing from feeding trees adds the bonus of providing food for the monkeys as well.

Then, speak to your neighbors and teach them to do the same thing. Together, you can try to plan to plant trees to enable the monkeys to cross any roads safely as they go from one property to another.

Based on research done by Ronald Sánchez at the University of Costa Rica (UCR) in 1991, Dempsey has compiled a list of the indigenous trees that best provide the leaves, flowers, fruit and seed pods on which the monkeys feed. The list may be obtained by emailing Dempsey at

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