Persistence of Lexicon in Signing Chimpanzees


  • Emily Patton (School of Graduate Studies)
  • Courtney Garzone (School of Graduate Studies)
  • Jenna Skinner (School of Graduate Studies)
  • Emilie Rich (University of Montreal)

Mentor: Mary Lee Jensvold


Chimpanzees Tatu and Loulis use signs of American Sign Language (ASL) to communicate (1,2,3,4,5). They lived with other chimpanzees at the Chimpanzee and Human Communication Institute (CHCI) from 1980 to 2013 and then they moved to Fauna Foundation (FF). At CHCI all caregivers and chimpanzees used ASL. At FF only some caregivers and none of the chimpanzees used ASL. Tatu and Loulis continued to sign at FF (5). Caregivers at both CHCI and FF kept daily records of the chimpanzees’ use of signs in sign checklists. The current study is an analysis of 2018 and 2019 sign checklists. Tatu’s mean number of signs used per day (M=12) in this sample was lower than in the previous years at FF (M = 14) and Loulis’ was the same at both samples (M=4). Tatu’s lowest range of signs used per day in the previous years was 1–32 in 2016 and this sample was comparable in 2018 but lower in 2019. Loulis’ range was lower in this sample than his lowest range in previous years (1-8 in 2015). The total number of vocabulary items per year was similar to previous years at FF, with a slight increase for both chimpanzees as compared to 2015 and 2016. High frequency signs were nearly identical to previous years at FF. While Tatu’s and Loulis’ vocabulary use changed slightly in their transition from CHCI to FF, it remained consistent during their time at FF. ASL lexicon and use in chimpanzees is a robust behavior that persists throughout environments.

1. Bodamar, M. D., & Gardner, R. A. (2002). How cross-fostered chimpanzees (Pan troglodytes) initiate and maintain conversations. Journal of Comparative Psychology, 116(1), 12-26.
2. Gardner, R.A. & Gardner, B.T. (1989). A cross-fostering laboratory. In R. A. Gardner, B. T. Gardner, & T. E. Van Cantfort (Eds.) Teaching sign language to chimpanzees (pp. 1-28). Albany, NY: State University of New York Press.
3. Jensvold, M. L. A., & Gardner, R. A. (2000). Interactive use of sign language by cross-fostered chimpanzees (Pan troglodytes). Journal of Comparative Psychology, 114(4), 335-346.
4. Leeds, C. A., & Jensvold, M. L. A. (2013). The communicative functions of five signing chimpanzees (Pan troglodytes). Pragmatics & Cognition, 21(1), 224-247.
5. Leitten, L., Jensvold, M. L. A., Fouts, R. S., & Wallin, J. M. (2012). Contingency in requests of signing chimpanzees. Interaction Studies, 13(2), 147-264.
6. Jensvold, M. L. & Dombrausky, K. (2019). Sign language in chimpanzees across environments. In M. L. Jensvold (Ed.), Chimpanzee behaviour: Recent understandings from captivity and the forest (141-169). New York, NY: Nova Science.


3 thoughts on “Persistence of Lexicon in Signing Chimpanzees”

  1. Nice to see our former chimpanzee companions still signing at their “new” home (it’s been a few years), and that you can compare their use of ASL now with before they moved.

  2. Danielle Kuchler

    Great poster! It was interesting to learn that when Loulis was young, he was able to acquire his signs from other chimpanzees. Has this been witnessed at the Fauna Foundation? Have any of the resident chimpanzees picked up any ASL from Tatu and Loulis?

    1. Hi, Danielle! Thanks for the question. Loulis was probably so well equipped to acquire signs because he was an infant when he was first immersed in the group of signing chimpanzees. Just like humans are best at language acquisition in our earliest years, wild chimpanzees are primed to pick up on communication methods of their group in early years. All of the chimpanzees at Fauna Foundation were over 20 and some of them were pushing 50 when they met Tatu and Loulis. They showed interest in Tatu and Loulis’ signs, but the staff there did not see them use any of the signs consistently enough to qualify them as “acquired.”
      I wonder what Tatu and Loulis thought of the chimpanzees at Fauna when they first moved there! I don’t think they’d ever met other chimpanzees who didn’t use ASL before that. But they had been around humans who didn’t use ASL, so maybe it wasn’t too surprising 🙂

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