The Los Arboles Spider Monkey Project in 2020

Well, 2020… what a year! It seems the monkeys also heard about the threat of Covid-19 and made a break for it. This has been the year with the fewest monkey follows by the research team to date. It was especially tough in the second part of the year. In LAT our research team follows two monkey groups. The group that spends most of their time on the eastern side of LAT we baptized the “Tulum” group and the group that spends the majority of their time on the western side is called the “Coba” group. In the past, we were able to find and follow the monkeys of the Coba group 17-18 days per month, which means that we followed the monkeys pretty much any day we went to look for them. This is because our team works 5 days a week, including two days a month checking trees to estimate how much food is available for the monkeys (more on that below). In the last 5 months of 2020, however, we managed to follow the monkeys less than 8 days per month on average, with only 3 days in August and 2 days in September!!!

Where were the monkeys during this time? We guess outside LAT. The good news we will have more people to look for them in 2021 as one PhD student will start his PhD in LAT, a volunteer will support the project from the end of February onwards and another PhD student and a Master student will likely spend time in LAT. With a larger team we will also be able to track the monkeys outside LAT!

You might be wondering can monkeys be affected by Covid-19? As humans, spider monkeys, and howler monkeys are all primates, it may be possible for spider and howler monkeys to contract Covid-19, but we do not know yet, as very few studies have been done so far. However, several primate species have tested positive for the virus, most recently the gorillas of San Diego Zoo. It is therefore important to keep avoiding all physical contact with the monkeys and not to feed them. Our research team always maintains a safe distance of 10 meters (about 10 yards) from the monkeys to avoid any chance of transmission of the virus.

WHAT HAVE WE BEEN UP TO THIS PAST YEAR IN LOS ARBOLES?

DRONE RESEARCH

In February 2020, we continued with the next phase of our drone research in Los Arboles. Drone pilot Coral Rangel Rivera used a drone with a high-definition red-green-blue camera (the Mavic 2 Pro) to try and detect monkeys from the sky. This drone is much cheaper and easier to use than the equipment we used in the previous study, making it an attractive option to use to find monkeys in new areas. However, before we can do that, we needed to test whether you can actually see monkeys in the videos and the best way to do that is in a place where we know monkeys occur. Hence, we came to Los Arboles! Coral’s flights in Los Arboles were a success and she spotted several spider monkeys in the drone video footage. Just this week we finished the scientific article in which we present the results of this study. Let’s hope it gets published in the next few months.

Spider monkey spotted in the drone video.

GETTING TO KNOW THE MONKEYS

We also continued to identify monkeys individually. Romina focused on the Coba group (the group that uses the western side of LAT) during the first part of 2020 and when Michelle and Samantha joined the team, they helped finalize the identification of all group members. The Coba group consists of 43 monkeys!! In July Romina shifted her attention to the Tulum group (which uses the eastern side of LAT) and by the end of the year she already identified 22 monkeys, and will continue to follow this group so that hopefully by the end of 2021 we recognize all the individuals. We’ll keep you updated! More exciting news is that in 2020 new monkeys were born: 3 in the Coba group and 3 in the Tulum group. This is great news, not only because we all love babies, but also because it means that these groups are reproducing, which is a good sign!

TROPICAL STORMS, HURRICANES, AND BAD WEATHER!

How did the spider monkeys cope with the heavy winds and rain this fall during the hurricane season? A study in Punta Laguna conducted by Filippo and Colleen after two consecutive hurricanes in 2005 found that spider monkeys change their diet and behavior to deal with the limited supply of fruits. For instance, the monkeys change their highly frugivorous diet (a diet based largely on fruits) to one that includes a lot of leaves.

Research assistants Samantha and Michelle did not sit still after the tropical storms hit Los Arboles, helping to clear the paths of branches.

WHICH TREES PROVIDE FRUIT WHEN?

On top of following the monkeys through the forest, the team monitors 135 trees in Los Arboles Tulum. Spider monkeys eat the fruits, flowers and leaves of a huge number of different species, so we selected 4-10 individuals of 16 species that we know are very important in their diet. Our team visits each tree every two weeks throughout the year and notes down whether the tree has fruits and/or flowers. With this information we can see if the amount of food available to the monkeys and the tree species providing food sources to the monkeys change over time. For example, a tree species may fruit in January of 2020 but in 2021 does not provide fruit until March. How will the monkeys cope with that? Do they need to spend more time in other areas to look for food? Answering these questions takes time! This is therefore a long-term project, but we wanted to share some of the results from 2020 for those as passionate about trees as we are!

Flowers of the Chechen tree, scientific name: *Metopium brownei*. Spider monkeys eat the fruits of this tree.

Fruits of the Zapote tree, scientific name: *Manilkara zapota*. Spider monkeys eat both ripe and unripe fruits of this tree.

Below are graphs that show the percentage of trees of 4 species that were bearing fruit over the course of 2020. The trees we show here are Ramon (Brosimum alicastrum), Zapote (Manilkara zapota), Chechen (Brosimum alicastrum), and Guaya (Talisia olivaeformis). What we see is that all these tree species seem to fruit around more or less the same time of year (June-July) but that both Zapote and Ramon also produce fruits at the end of December/start of January. We will keep monitoring these trees to see if the same pattern appears next year!

Some trees you might not be as familiar with but that are highly important in the spider monkey diet in Los Arboles Tulum.

Leaves, fruits and seeds of the Silil tree (*Diospyros tetrasperma*). The pulp of these fruits is very sweet!

The tree, flowers and fruits of Pa’sak (*Simarouba amara*). These trees produce grape-like fruits that change from green to red to a dark blue/purple as they mature.

Leaves and fruits of *Coccoloba spicata*. The Mayan name of this tree is Boob, pronounced “bob”. This tree has very large leaves but very small fruits that are very popular not only with the monkeys but many bird species too.

GOING INTO OUR FIFTH YEAR 2021

We have started our fifth year of following and studying the spider monkeys in Los Arboles Tulum. In 2017 we were just getting started, focused on figuring out where the monkeys were sleeping. Since then, we have learnt so much about the areas used by the spider monkeys in Los Arboles Tulum. Here are some maps of where the monkeys went during the months of January and February 2017, 2018, 2019 and 2020. In different years we dedicated different amounts of effort to the two monkey groups, which is why some areas look like they are used in some years but potentially not in others. As of the summer of 2020, we started to study the two groups at the same time! This is hugely exciting and we will continue to do so into 2021!