Reproductive Biology and Endocrinology | Field Projects International

Reproductive Biology and Endocrinology

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Detailed Description

Reproductive variation is the currency of evolution, with individuals who produce more offspring having higher chances of passing on particular characteristics. But what determines who gets to reproduce, and why do we see reproduction regularly skewed toward particular individuals? In tamarins and other callitrichine primates, these questions are particularly perplexing. While multiple females may live in a group, reproductive success is generally limited to a single primary breeding female. This female gives birth to twins that are cared for by other members of the group. However, the other females in the group almost never reproduce. Captive studies suggest that this suppression of reproduction occurs via physiological means, where non-primary females experience delayed development or temporary pauses in ovarian cycling. These responses occur in response to the sight or scent of the primary breeding female or in groups where the only available breeding males are closely related. In the wild, though, we get a more complicated story. Group members are more widely dispersed and their home ranges overlap extensively with other groups, and contrary to what’s been found in captivity, the few studies on wild female reproductive physiology show that non-primary breeders are experiencing regular ovarian cycles. Nevertheless, they still do not reproduce, and the single primary breeding female remains.

What is happening in these natural systems? Through what behavioral or physiological mechanisms does this extreme variation in female reproductive success persist, and why? Answering these questions is key to understanding not only the basic dynamics of callitrichine reproduction, but the fundamental element driving callitrichine evolution. To this end, this project will use behavioral observations and hormone profiles from female tamarins in conjunction with data collected by the Wildlife Handling and Sensory Ecology teams to investigate female reproductive physiology, relationship dynamics between females within and between groups, and genetic relatedness between individuals in the same and neighboring groups.

What will you do?

As a research assistant for this project, you will be involved in collecting behavioral data, collecting fecal and urine samples, and extracting steroid hormones from those samples for later hormone analyses. Data collection for this project will involve long days (12+ hours!) following tamarins through the forest, with two days per week reserved for data cleaning and rest. A typical day will involve you and a research partner waking up between 4 and 5 am, walking out through the still-dark forest to find the group for that day’s follows, and waiting patiently until the tamarins decide to wake up. Once they do, you’ll look for your first “focal animal” (the animal you’ll be following) of the day. As they duck and weave expertly through the trees, you’ll be following on foot while recording their every move (did they interact in some way with another individual? What did they do? Was that a copulation?!) and hoping dearly that they’ll defecate or urinate and that you or your partner be able to find it. You’ll continue like that through the rest of the day, following one individual in the group, then another, and another, until the group decides it is time for bed (typically around 5 pm). You’ll then go back to the station to eat, enter your data for that day, and extract the hormones from any fecal samples you’ve collected – and finally, sleep! Before doing it all again the next day.

Collecting data on wild primates is no walk in the park, and we want to emphasize that it will absolutely be physically and mentally tiring. Keeping track of miniature monkeys while trying to find your footing in a rainforest can be quite trying, and there will be days that you feel discouraged. But- it can also be one of the most rewarding experiences you’ll have in your life. As the days go on, you’ll get to know individual tamarins and their particular habits and personalities, and while some days you may feel the forest is deliberately out to get you, you’ll also have the opportunity to see just how amazing the Amazon can be.

Skills and Training

By the end of this program, you will have gained a number of skills essential to the study of animal behavior (especially primates!) and non-invasive hormone monitoring. These include the ability to:

  • Conduct full-day behavioral follows of wild primates using focal- and scan-sampling methods as well as ad-libitum data
  • Collect and process fecal and urine samples as well as perform hormone extractions in a field laboratory
  • Use radio telemetry equipment to locate groups
  • Clean and organize data using a relational database system
  • Comfortably and safely work and move on and off trail systems in a Neotropical rainforest

Research assistants will also have the opportunity to contribute to publications that result from this research. As with other FPI projects, we do not give co-authorship for collecting data alone, but we do welcome students interested in data analyses for potential future publications.


We are currently recruiting participants with the following requirements.  If you are uncertain if you are eligible, contact us to confirm.

  • Participants must be at least 18 years of age by the time the training program begins
  • Participants must demonstrate a grounding or strong interest in zoology, biology, or anthropology
  • Previous field experience is not required
  • Participants must justify why this program is important to them, and what they hope to gain from it
  • Participants must provide a letter of recommendation from a source that can substantiate the participant’s experience and skills
  • Participants must be in good physical condition, with the capability to walk 4 miles a day
  • Participants will not be discriminated against for medical conditions they might have if we determine that being on this project will not pose an immediate risk to their health
  • Participants must sign waivers of liability for this project and for the field station before their participation in the project is finalized
  • Participants must be willing to maintain long hours in the field, and return to complete data entry in the evenings
  • Participants must be able to adapt to flexible schedules that are dependent on the weather
  • Participants must exhibit a willingness to adjust their schedule to primate daily activity patterns. This can require waking up early, sometimes by 4 or 5 am, and going to bed early, 8 or 9 pm.
Quick Info

Program dates: May 31 – September 26, 2020
Start dates: May 31, June 7, June 21, July 5, July 19, August 2, August 16
Minimum stay required: 6 weeks (in special cases we will consider 5 weeks)
Application deadline: May 1, 2020
COVID-19 Status: Click here for up-to-date information
Program fee: $3000 for 6 weeks; $450 each additional week

Primary Investigators

This project began in 2009, and the primary investigators working on it are Rachel Voyt, Mrinalini and Gideon Erkenswick Watsa. Reproductive biology data collection will be in its eleventh year in 2020, with research assistant alumni working on data analyses of these projects year-round.  

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