Field Notes: Singing Titi Monkeys

A typical morning of titi monkey vocalization recording starts off with a 4:30 AM alarm. I roll out of bed, start coffee, and am out in the door in under ten minutes. The 20-minute drive goes by quickly as I mechanically drink my coffee. As I gather my recorder, microphone, and camera, interns begin to show up. At 5:20 AM, my team trudges out to where the coppery titi monkeys Plecturocebus cupreus are slowly waking up with the sunrise. 

A quiet sprinkling of peeps and whistles begins as little voices fill the air. Titi monkeys unwind their tails from their family members and stretch, yawning in a relatable fashion. They glance at us curiously, but after years of observation, they are fully habituated to our presence and pay us little attention. Within a few minutes, the titis begin to pee. Interns swiftly hold collection cups under the animals, attempting to intercept the urine stream before it hits the ground. Bladders relieved, my favorite part of the morning starts.

Check out this amazing footage of wild black-fronted (Callicebus nigrifrons)titi monkeys vocalizing during an encounter with another group.

A few monkeys peep, then a few more, and then finally, a long call, the loudest sound a titi monkey makes, used for long-distance communication [1]. We never know who will start us off, but it’s guaranteed that a full chorus will follow. This first pair of eager singers launches into a full duet, deafening our observant ears and quieting the neighboring groups. The male and female sing equal contributions; as one monkey sings in the lower frequency spectrum, the other sings in a higher frequency range. After around 10 seconds, they switch frequency ranges. This highly coordinated song can continue for upwards of 6 minutes and when this pair of monkeys decide they’re done singing, another will take their place. Depending on who’s nearby, some families will interrupt each other and take over the chorus. My time with the monkeys has led me to believe there is an organized pecking order to who sings when, but for now, that’s just anec-data (a hunch based off observations without empirical analysis).

As the chorus ends, we pack up our equipment to head back to the lab. Our small army of devoted undergraduate interns process urine samples to assess animal health and reproductive status while grooving to today’s pop hits and discussing the titis’ antics from the morning. With 100 animals spread across around 40 families, there’s always an exciting story to share of sibling squabbles, the romance of newer pairs, or the sweet saga of our long-term pairs (some of which have been paired for over 15 years). Titi monkeys are pair-bonding monkeys, which means they find a mate and stick with them for life. Both parents take care of their offspring, but fathers do about 95% of the parenting! This social system is quite rare in mammals, so this colony is important in helping us understand the biology and behavior behind pair bonding.

As processing finishes up, our excellent husbandry staff heads out to feed and care for our colony of titi monkeys [2]. It is with the help of countless animal care, primate medicine, and administrative staff that we are able to provide a healthy, well-suited environment for our captive titi monkeys at the California National Primate Research Center here in Davis, CA. 

A family of titi monkeys at the CNPRC.
Photo credit: Alexander Baxter

While many of our contributors, graduate students, and faculty here on the Ethogram work with wild animals, my study subjects are a bit closer to home. The perks of working with captive animals are many: 

  • we are able to provide excellent medical care for our study subjects, extending their lives beyond their life expectancy in the wild
  • we have full control over their environment and experience, allowing us to provide ample food and the appropriate temperature, humidity, and light schedule to ensure our animals thrive
  • we know every subject, their genealogy (spanning eight generations), and everything they’ve experienced [3]
Here are our coppery titi monkeys in action at the CNPRC. These titis participate in a range of social and biomedical research studies to better understand primate health.

While our titi monkeys at the CNPRC are primarily studied as a monogamous, nonhuman primate model for social behavior and human health, they present a unique opportunity to study species-typical behavior up close [4]. This can lead to some excellent collaborations between field and captive primate researchers, as we can gain detailed baseline knowledge about our animals by combining the strengths of each study arena. In the wild, titi monkeys are quite elusive and hard to find due to their tiny size and neophobia (fear of new things). In captivity, I am able to collect far more detailed acoustic data with greater accuracy and ask more complex questions than I may have been able to in the wild. For example, knowing eight generations of titi monkey genealogy allows me to ask questions about heritability and learning. Similarly, having a large colony of animals allows me to gather a larger sample size (number of animals in a study) than other similar studies.

A young male titi monkey at the CNPRC.
Photo credit: Alexander Baxter

Above all else, a huge perk for me personally is the ability to get to know my subjects on a personal level. My little furry collaborators are an active part of my science. Observing this colony on a day-to-day basis has uncovered some of the most interesting research questions that I get to pursue. Stay tuned in our Newsroom section for the next few years!

Allison Lau is a second year PhD student in the Animal Behavior Graduate group. She studies titi monkey bioacoustics at the California National Primate Research Center.

References:

[1] Robinson, J. G. (1979). An analysis of the organization of vocal communication in the titi monkey Callicebus moloch. Zeitschrift für Tierpsychologie49(4), 381-405.

[2] Tardif, S., Bales, K., Williams, L., Moeller, E. L., Abbott, D., Schultz-Darken, N., … & Ruiz, J. (2006). Preparing New World monkeys for laboratory research. ILAR journal47(4), 307-315.

[3] Kanthaswamy, S., & Bales, K. L. (2018). Evaluating the genetic status of a closed colony of titi monkeys (Callicebus cupreus) using multigenerational pedigrees. Journal of medical primatology47(2), 139-141.

[4] Bales, K. L., del Razo, R. A., Conklin, Q. A., Hartman, S., Mayer, H. S., Rogers, F. D., … & Witczak, L. R. (2017). Focus: comparative medicine: Titi monkeys as a novel non-human primate model for the neurobiology of pair bonding. The Yale journal of biology and medicine90(3), 373.

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