VOICES Voices Icon Ideas and Insight From Explorers


Dehiwala Zoo making positive changes- Tony and Sanju chimps get a family!

BACKGROUND: In 2012, in partnership with The Jane Goodall Institute, the Phoenix Zoo created a unique position to promote international animal welfare. Hilda Tresz, the Behavioral Enrichment and International Animal Welfare Coordinator, is responsible for developing and overseeing the Zoo’s Behavioral Enrichment program, but also extends her work beyond the Zoo through an international role of helping zoos improve animal care. The following stories will describe the significance and logistics of this position through Hilda’s travels across the globe.

In some foreign zoos with limited knowledge and funding, animals are often housed alone in sterile environments, on bare concrete floors and with no “furniture” (climbing structures, resting platforms, visual barriers and the like). Many times they are malnourished, injured and/or have a variety of behavioral problems. To complicate matters further, when she visits one of these zoos, she typically have only one week to make improvements. In the remaining time, it is her responsibility to assess, negotiate and improvise to make immediate changes with limited available resources.

She must quickly determine how to effectively implement all necessary changes. Every zoo and every country is different when it comes to available resources. Initial doubts and fears of proposed changes by zoo staff are often evident; she must develop a working relationship with unfamiliar people in an unfamiliar setting. Suggestions that would seem to be common practices for those working in an Association of Zoos and Aquariums (AZA) facility in the United States are viewed as novel recommendations by many visited institutions.


Aug 30, 2016 – Sep 8, 2016

I visited to Sri Lanka to introduce two solitary male chimpanzees to four females and to provide suggestions for improvements to the basic husbandry, enrichment, training or behavioral issues for all species in the collection.


Top row: Fig. 1. 1.0 Tony, 17-years-old Fig 2. 1.0 Sanju 11-years-old Bottom row: Fig 3. 0.1 Malee 28-years-old, Fig 4. her daughter Masha 8-years-old
Top row: Fig. 1. 1.0 Tony, 17-years-old; Fig 2. 1.0 Sanju 11-years-old
Bottom row: Fig 3. 0.1 Malee 28-years-old; Fig 4. her daughter Masha 8-years-old
Fig 5. 0.1 Kiri Menika 38-years-old
Fig 6. 0.1 Pinky 21-years-old

There were many obstacles to this introduction.

Behavioral problems

Since the males were raised and kept alone, they had both developed some odd behaviors and tried to communicate with humans. Tony was making noises with his lips (similar to sucking on one’s teeth), perhaps to entertain himself, and Sanju made praying and kissing movements as soon as a human being approached. None of these are natural chimpanzee behaviors.

Fig 6. Sanju kissing face, photo by Shamal Samaranayake

Malee was an overly aggressive female (even during the “howdy” period), sometimes biting the bars with such force that I was concerned about her breaking her teeth.

Creating groups with only certain animal members and avoiding inbreeding

The zoo asked to create two smaller groups in order to be able to ship one group out to their Safari Park later. Kiri Menika was old, and I felt she should not be transferred to a completely new place at her age.

Malee was the mother of Tony, and Pinky was the mother of Sanju. Further, the zoo had not put the females under contraception yet. Therefore, in order to create two healthy groups without inbreeding, Malee had to be introduced to Sanju and Tony would be introduced to Pinky. Lacking flexibility within introduction groups made the integrations even more challenging.

Tony was also older than Sanju and the favorite chimpanzee of the visitors, so he needed to stay. Thus, the only option for group configuration was:

Tony with old Kiri Menika and Pinky

Sanju had to go with Malee and Masha

Tony and Pinky were introduced without incident and their closeness grew daily, while Kiri Menika appeared indifferent.

Introducing Sanju and Malee, on the other hand, was more involved due to aggression from Malee (e.g., screaming, biting the mesh when housed next to Sanju). Because of this aggression, Malee was separated from her daughter, Masha, so Masha could get acquainted with young Sanju in hope that if Malee saw her daughter relaxed and playing, maybe aggression towards Sanju would cease. Malee became even more upset when separated from her daughter, but the step was necessary. Every time Sanju approached Masha, she ran to the mesh to her mother, naturally making the situation even worse. Sanju and Masha were together for tense three days, warming up to each other a bit but, never overcoming the tension. When, all three were introduced. Malee spent the next five days periodically attacking Sanju. Although it appeared to be quite vicious and the zoo management wanted to separate them, Malee was merely displaying without causing any real threat of physical harm towards Sanju. Malee was regularly chasing, hitting and biting, but was extremely careful of not penetrating the skin, and Sanju had a similar response verifying the decision to keep them together and not separate unless a serious injury was to occur. The chimpanzees have been together ever since without further issues. Email communications since have reported that the chimpanzees make small interactions, but spend most of the time apart. While the situation is not yet perfect, it is definitely better than solitary confinement. With time, hopefully they build a relationship with each other with demonstrated positive behaviors among them.

Sanju, Malee and Masha housed together. They maintain considerable spatial distance among them, but we anticipate and hope that their behavior will change in the future.

Fig 8. Tony, Pinky and Kiri Menika together in the large exhibit.

It was suggested, that the two groups need to be alternated monthly providing all animals an opportunity to live in the larger exhibit.

Roots and Shoots program

Dr. Jane Goodall also would like to establish a Roots and Shoots program in Sri Lanka which would also tie school programs with the Jane Goodall institute. Schools can be part of many enrichment and junior research programs. http://www.janegoodall.org/what-we-do/roots-and-shoots/

An enrichment program was initiated instantly with the help of two students Hasitha Bandara and Jayaruwan Sulakshana from Open University of Sri Lanka who also work as temporary research assistants in the zoo. They are also members of Sri Lanka Young Zoologist Association. The students are continuously working on creating monthly enrichment schedules using the Phoenix Zoo’s templates and they email me frequently about the changes.

Fig. 9
Fig. 10
Fig. 11


“Today we did some enrichment for orangutans, chimpanzees, Bengal tigers, fishing cats and jungle cats.

 We gave cardboard boxes for chimpanzees and orangutans, filled with grass and their food. The baby orangutan played with the cardboard boxes and by the way he didn’t care about the food. The mother orangutan also played with boxes but not much. She covered her body with cardboard box laid on in it. The male one didn’t enjoy it. 

In chimpanzee enclosures, Kiri Menika and Pinky took the boxes, tore them and eat food but Tony didn’t care about the boxes. In Sanjus’ cage, we couldn’t go inside the cage because they didn’t move to the inner cages. We kept the boxes on the top of the cage so they had to pull and tore the boxes to get food.

We threw empty cardboard boxes to fishing cat enclosure but they didn’t do anything, they just sniffed them and went away. We gave pineapple tops for jungle cats. They also didn’t care about them. We left the boxes and pineapple in the enclosures because we hope they will do something with them tonight.

For tigers, we gave cardboard tubes which were kept in the zebra enclosure last night. They played with them and really enjoyed it a lot”.

Reading reports like this makes all the work worthwhile!


Photo by Victoria Kostenko
Photo by Victoria Kostenko
Hilda Tresz with Dr. Jane Goodall
Hilda Tresz with Dr. Jane Goodall

Born and raised in Budapest, Hungary, Hilda Tresz now resides in Mesa, Arizona, where she has lived since 1989. After graduating high school, she began working as a zookeeper and has been working with animals ever since as a caregiver, enrichment specialist, trainer, educator and behavioral manager, focusing on chimpanzees and general behavioral management for all species for over 28 years. She holds a triple-major degree in Biology, Geography and Education.

Hilda Tresz changes the lives of animals, the people that work with them, and institutions that house them. She is currently the Behavioral Enrichment and International Animal Welfare Coordinator at the Phoenix Zoo; as well a mentor for the Jane Goodall Institute. She has worked with numerous international zoos (in India, Israel, Qatar, Egypt, UAE, Mexico, Paraguay, Argentina, Chile, China, and other countries) to enhance the psychological wellbeing of chimpanzees and other species.

Many international institutions in developing countries have become overwhelmed with the financial and physical demands that are required to care for these animals; too often, many of these animals are left in barren, isolated situations with meager subsidies. Hilda finds solutions by collaborating with these institutions, and their staff to create productive, healthy, mentally stimulating conditions for their animals with little to no funding. She utilizes past experiences to educate her temporary teammates about animal diet and natural behavior to enhance their understanding and encourage ongoing improvement of their husbandry techniques. Because of her passion to leave no chimp isolated, no elephant chained, or no tiger malnourished, she embraces those who may not know and teaches them that they are the voices for those who cannot speak, the guardians for those who cannot step away, and the saviors for those who cannot save themselves.