VOICES Voices Icon Ideas and Insight From Explorers


Four infants met their surrogate parents in Shanghai Wild Animal Park, China

Posted by Hilda Tresz of Phoenix Zoo

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.

 Four infants met their surrogate parents in Shanghai Wild Animal Park, China

April 22-28, 2016

The purpose of the visit was to integrate four infants, a female solitary chimpanzee and a pair of chimpanzees into a group and to give recommendations regarding basic husbandry routine and enrichment for all species.


Screen Shot 2017-02-15 at 11.25.10 AM

SWAP has beautiful, large exhibits, full of tall furniture, climbing structures and natural surface with grass. The inside cages need a little bit of improvement with furniture and substrate, though.

Fig 9. Introduction, Photo by Hilda TreszIntroduction, Photo by Hilda Tresz

Fig 10. Introduction continues Photo by Chloe RossmanIntroduction continues Photo by Chloe Rossman

Fig 11. Chimp with substrate Photo by Chloe RossmanChimpanzee with substrate Photo by Chloe Rossman

Fig 12. Introduction cont. 2 Photo by Chloe RossmanIntroduction cont.Photo by Chloe Rossman

Animals received hay as substrate prior to the introductions. Chopped food was hidden in their night houses in order to bring the animals off of the hard surface and provide plenty of foraging enrichment. Chimpanzees won’t touch their food when they are upset. Thus, observing the animals as they started to forage gave the consultant a chance to see exactly when the animals began to calm down during the introduction.


There were seven chimpanzees kept in 3 different enclosures Shanghai Wildlife Park (SWP).

Lili was kept in solitary confinement for approximately nine years due to previous aggression between her and Zhenzhen. While the four infants were kept together, they were housed separately from the adults because of the belief that the male would kill them if introduced.

The introduction was accomplished in four days. First, Lili was introduced to the four infants. It is not well known, but formerly-bonded infants can and will protect each other if needed (even against adults). As expected, the infants stood up for themselves during Lili’s mild attacks, but soon the group settled down and began socializing (playing, tickling, grooming, etc.). This group of five chimpanzees was housed together for an extra day to allow Lili the opportunity to feel more comfortable and gain more allies before moving to the adults. During this period, Xiaoxiao and Zhenzhen were let inside the tunnel system – a design allowing the shifting of animals from all directions to any enclosure.

Fig 13. Tunnel system, Photo by Hilda TreszTunnel system, Photo by Hilda Tresz

In this tunnel system, the pair could observe the five chimpanzees together. The group was separated overnight or when being fed.

By the morning of the third day, the Lili/infant group appeared to be relaxed and comfortable together; the chimpanzees did not fight when let together after separation, were playing together, grooming each other and/or resting comfortably with each other. At this time, the male adult, Xiaoxiao, was introduced. As is typical for males, Xiaoxiao displayed for a couple of minutes, running around, kicking and banging on doors and mesh before settling down. His aggressive display made the rest of the group nervous (running around and screaming) and the other chimpanzees, again, stood up for each other and even chased Xiaoxiao to a corner where he cried and solicited for reassurance with an extended hand. At no point did Xiaoxiao threaten aggression, despite the fact that he could have easily killed and/or seriously injured any or all of the infants at any time; he chose to exhibit the submissive behaviors described above. Although we cannot completely understand the motivations for his behavior, one can speculate that he was most interested in keeping the peace, knowing that he was responsible for frightening the group. This incident provides another example that male chimpanzees – at least in managed settings – are most often gentle giants and have no interest in exercising their strength on weaker members. On the fourth day, the second female was integrated into the group without any incidents. Shanghai Wildlife Park continues to report the group is doing well together.

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.


  1. Becky Roudebush
    San diego
    March 5, 11:11 pm

    I’m a recent trip to Nayarit Mexico, I visited the El Tigre Golf club. There were many large cats, tigers, cougars and lions, captive in small cages. They were clearly frustrated and in need of a different habitat. These animals need help or the El Tigre Golf club needs to be educated on how these animals should be cared for. I hope Teresa is able to help the animals have a better life. Please contact me if you have questions. Thank you,