In our first field season we noticed that some seeds traveled so far that they must have moved out of the home range of an agouti. This led us to wonder whether the massive seed re-caching behaviors we observed were the result of one agouti caching its seeds many times or agouti thieves moving seeds from one territory to the next.

To solve this question we needed to be able to identify individual agoutis, which otherwise all look alike. After substantial live-trapping effort we were able to catch >20 agoutis in one portion of the island (in and around the 25 ha plot). We individually marked each agouti we caught with a distinctive radio-collar, ear-tag and/or freeze brand. Then, we put a motion-sensitive camera next to a buried seed where we knew the “owner” and recorded every agouti (or other species) that walked by. This allowed us to determine whether the cached seeds were being dug up and moved by their owners, or by thieves. We are still crunching the numbers from these experiments but in the process discovered a cool video that shows just how crafty agouti thieves can be.

Many rodents bury seeds in times of plenty to save them for lean times, and these hidden food caches are critical to their survival. Rodents will go to great lengths to protect their seeds from potential thieves. For example, Michael Steele and colleagues found that if a squirrel wanted to bury a seed but was being watched, it would often behave “deceptively” by making fake caches and making caches behind trees so the observer could not see the cache being made. While I would have loved to do some similar experiments with the agoutis, it would have been hard to observe the agoutis without scaring them away. However, if you run enough camera traps for enough time you eventually record some surprising clips.

In this case, I didn’t notice what was going on the first time I saw this video, and only recently realized how it shows the subtle dynamics between different agoutis sharing an area. The seed that this camera was monitoring was previously cached by an agouti named Tracy, who can be identified by a small diagonal white freezebrand mark on her body. In the video you can see Tracy come to uncover her seed four months after she originally placed it there (we had a camera there the whole time). Given the high rates of cache movement, Tracy was lucky her seed lasted that long and her strategy of saving food underground for the low food season seems to be a good one. Unfortunately for her, as soon as she begins digging up her cached seed she gets chased away by another more dominant agouti who steals her seed. Even sadder is the fact that Tracy came back to the old cache location a few seconds later to see if it was still there (it wasn’t). While this isn’t fair to Tracy, the other dominant agouti got a free meal on the cheap. The degree to which our agoutis used this kleptoparastic strategy is unclear, but given the behaviors seen in this video, we think it might be a good idea if agoutis used the same sorts of deceptive behavior found in squirrels.


If you get excited about sensor networks, yagi antenna, live data streams, and agoutis, then you’ll love our new paper in the Computer Journal describing the technical details of the Automated Radio Telemetry System (ARTS) that helped us track animals and seeds in Panama.

 

Photo: ARTS tower rises above the tropical rainforest canopy of BCI to help researchers track the movement and activity of animals and seeds, sending data back to the lab in real-time.

ARTS tower

With our kitchens and restaurants it’s been easy for us humans to settle into a comfortable eating routine of a morning breakfast, mid-day lunch, and evening dinner.  Animals, on the other hand, have to hunt down their meals out in the wild.  For agoutis, and other ground-dwelling frugivores, this means walking around waiting for fruit to fall out of trees and land on the ground.  That leads to a simple question – when do fruits fall out of trees?

As far as I can tell, this question has never been studied – who wants to sit around and watch fruits slowly fall down all day, and night?  Yet this is a basic bit of natural history information that could be quite important when considering the survival strategies of agoutis, in particular, and daily rhythms in the forest, in general.

Camera traps are a perfect tool for this question, and our student Vivian Mass set some aimed at the fruits of Astrocaryum palm trees.  For this to work she had to find another tree at just the right distance away from the targeted palm-fruits and then get a camera trap up there, which she did with the help of ladders and some canopy access climbing by Daniel and Alejandro.  This was a bit of a side project from Vivian’s main thesis, and the data remained unanalyzed until this spring when high school student Tessa (Taz) Holliday joined our team as an intern from the Emma Willard School.

Taz looked through each picture and noted if any fruits had fallen off since the last picture.  In some cases it was obvious – a big howler monkey was on the tree picking fruits, eating the fleshy part, and then dropping the nut down to the ground, where agoutis and other terrestrial critters could find them.  In other cases fruits would fall off without any animal intervention, just because they were ripe.  In total Taz noted 450 seed fall events from 8 different Astrocaryum trees, with slightly less than half being dropped by animals.

Looking at the fruit fall over the entire fruiting period (figure 1) it was obvious that arboreal animals had a huge effect on when a fruit would fall.  A few trees that had no arboreal animals visit would drop a few fruits a day for 2-3 weeks.  Once an animal visited they would drop all, or nearly all, of the fruits in one sitting.

Fig 1. Timing of fruit-fall over four weeks for 6 Asrocaryum trees.

These arboreal animals also had an impact on what time of day the fruits hit the ground. The monkey- and parrot-fed fruits fell in the day while the kinkajou-fed fruits fell at night (figure 2).  Overall, this led to more fruits falling during the afternoon than you might otherwise expect (figure 3b), although with only 4 trees in this analysis (the time lapse photos didn’t work for 4 trees), we should be careful in what we conclude from it.

Fig 2. Time of day that fruits fell out of 4 Astrocaryum trees

Even more surprising was considering what time the fruits fell when no animals knocked them off. This is tree-behavior, when do they ‘want’ their fruits to fall to the ground.  Surprisingly, this showed a strong trend to more fruits in the late night (midnight-5am, figure 3a).  We know from our agouti tracking that this is the most dangerous time for agoutis to be out foraging, we have found quite a few agoutis killed by ocelots in this time period.  Are the trees trying to temp the agoutis out for an early breakfast?

Fig 3. Expected and observed times of day that fruits fell out of trees, with and without arboreal animals (significantly different than random p<0.0001)

Lets call this the “Machiavellian plant behavior hypothesis”.  Long-lived agoutis might be bad for trees because they remember where they buried all the seeds and come back and eat them year after year.  However, if dropping seeds more at night led to a higher turnover of agoutis nearby due to ocelot predation, it might also lead to a better chance that their cached seeds survived, since the “new agouti on the block” wouldn’t know where the “recently deceased” buried the seeds. This Machiavellian plant behavior seems a long shot, but this preliminary result that Taz teased out of data collected earlier by Vivian suggests it might be worth following up on.

On Barro Colorado Island we have the rich agoutis and the poor agoutis. The rich agoutis live in fancy neighborhoods with lots of palm trees, which make nuts for them to eat. The poor agoutis live in areas with few palm trees, the agouti ghettos, with less food. Rich or poor, all agoutis bury seeds in scattered underground caches as an insurance policy for the end of the rainy season, when there is almost no freshly produced fruit. Of course, the trees would rather the agoutis don’t come back later and eat the seeds, giving the seeds a chance to germinate and grow into a new generation of trees. These buried seeds are more likely to be dug up in the agouti ghettos, where seeds are more valuable because they are so scarce.

One of the ways that a cached seed might avoid being eaten by an agouti is if the agouti which buried the seed dies. This leads to the question: do predators like ocelots help palm trees by killing agoutis before they have a chance to go back and dig up palm seeds?   Related to this, is the question: are agoutis living where food is scarce more likely to get killed because they must work harder for their food, thus take more risks?

These are the questions asked by Willem-Jan Emsens, a Masters student at Wageningen University. He studied activity patterns, refuge use, and space use of agoutis in relation to predation risk. He compared rich and poor agoutis: animals that differed strongly in the amount of Astrocaryum fruits they had in their home range. As any loyal reader of the Agouti Enterprise knows, Astrocaryum fruits are the most important food resource to agoutis.

Willem-Jan used the Automated Radio Tracking System (ARTS) to track the animals 24/7 and determine the home range size of the radio-collared agoutis. This showed that poor agoutis had larger home ranges than rich agoutis. Not surprisingly, poor agoutis seem to need a larger area to find enough food. Therefore, they may take more risks of getting caught by an ocelot.

Willem-Jan also took his radio-tracking receiver and tromped around BCI at night, when agoutis are sleeping, to find out exactly where agoutis had their refuges. He found agoutis used three types of sleeping sites: dense vegetation, burrows, and hollow logs. Each agouti had a 2-8 different places they could sleep on different nights.

Agouti RefugeTypes

Agouti RefugeTypes

Once he identified the sleeping sites, Willem-Jan put camera traps at burrow entrances to see exactly when they came and went. Agoutis never left their refuge before sunrise, but were more variable in the time they went to bed. Most agoutis retired to bed around sunset, but 13% came back at night. The cameras also caught some amazing footage of ocelots coming to these sleeping sights and looking for agoutis. You can actually see the ocelots looking into logs, presumably scaring the crap out of an agouti, but then leaving empty handed. Ocelots were the only predators that visited the refuges, and they visited refuges more often than random locations. It seems that ocelots knew where the agoutis were sleeping dropped by hoping to catch one near the entrance to their burrow.

Some of the agoutis that Willem-Jan was studying were killed by ocelots. By analyzing the ARTS data, he was able to determine the exact time the agouti was killed. Willem-Jan found that agoutis are most susceptible to predation around dusk and dawn, which is also when they overlap most in activity with the nocturnal ocelots. This may also be tied to their entrances and exits from dens. If ocelots know these locations, they might wait nearby to catch a commuting agouti.

One of the surprising results came from comparing the location of the refuges with the overall space use of agoutis. We presumed that agoutis would act like many other burrowing animals, using the refuge as a ‘central place’ and conducting feeding bouts more near the hiding hole than far from it. But this was not the case. Maybe the fear of a lurking ocelot is enough to make an agouti keep its kitchen and bedroom in different parts of its home range.

Finally, combining his work with data collected by an earlier student on the project, Lennart Suselbeek, we were able to compare the risks taken by the rich and poor agoutis. The ghetto agoutis had to be more active to find food in their enlarged home ranges, and accomplished this by getting up earlier and going to bed later. This is risky behavior when your neighborhood is patrolled by nocturnal ocelots. All of this makes the agoutis nervous, but is quite fine with the Astrocaryum trees, who root for the agoutis to burry their seeds and then the ocelot to make them disappear.

The Smithsonian has officially gone wild.  They (we) have created a site with over 200,000 pictures of wild animals taken with camera traps in the wilds of China, Peru, Kenya, Sarawak, Thailand, Adirondacks, Appalachian trail and…. Panama.

Images from Vivan Maas’s thesis on what eats palm fruit, and Helen Esser’s on what animals live on canal islands, were included in the site.  We would have included more from our research on BCI, we have a lot more, but didn’t want to overload folks with agoutis.  Even with these two sub-projects, we contributed over 88,000 agouti pictures to the collection.

This project was a collaboration between different scientists working at the Smithsonian, including our Agouti experts.  In fact, they built the site of the database started on BCI by Bart Kranstauber and used by our team ever since.

The site just launches last week, and the visitation has been off the charts.  We were even featured in an NBC news story last night.

People love the site, the crowd is going wild.  They are going to want more pictures.  Good thing Helen is coming back for her PhD research!

 

Our work was featured in a video produced by Untamed Science for the 2009 Miller and Levine high school biology textbook.   Check it out in your text book or at one of these two links below.

Untamed Science Video on Remote Sensing

Facebook Version


 

Imagine you’re a tree.  You’re rooted to the ground and can’t move.  You have a crown full of seeds ready to usher in the next generation of your species, but all you can do is drop them straight down, where they are doomed by the shade of your own crown, not to mention the predators and parasites attracted to this bounty of seeds. Meanwhile, all these animals are scurrying and flying around you, flaunting their mobility.  You’ve got a serious case of movement envy.  You need to move your seeds as far away as possible to give them a chance to survive and germinate. You need mobility assistance.  Maybe the animals can help.

Animals do help.  Many trees have co-evolved relationships with animals and offer them some reward for moving their seeds around – a bit of nutritious fruit-bribe surrounding the seeds.  But some animals are not helpful, eating the fruit without moving the seed away from the mother tree, or even consuming the seed along with the fruit.  Trees don’t appreciate these cheaters, but evolution’s rule book allows it.  The trees can fight back by co-evolving with certain species of animals that are the most beneficial to them, and putting up defenses against the others.  When evaluating these relationships biologists consider the ‘disperser effectiveness’ as the value of an animal species as a disperser for a given tree species.

Palm trees have been bribing animals and fighting cheaters for millennia, evolving a variety of sweet fruit lures surrounding hard nuts.  The trees “want” a cooperative animal to eat the fruit and move the seed away from the mother tree.  Our earlier work using cameras to monitor animals feeding under fruiting Astrocaryum palms trees found Agoutis, Spiny Rats, Red-tailed Squirrels, and Collard Peccaries to make up 99% of the visitors. The next question was to evaluate the disperser effectiveness for this group.  Lieneke Bakker took this challenge on as her MS thesis project at Wageningen University.

Lieneke used small radio-transmitters to follow the movement and fate of Astrocaryum seeds, and used camera traps to determine which species of animal was doing the moving.  She considered a number of factors to evaluate the effectiveness of each species as a disperser including: how often they moved seeds, how far they moved them, rather or not they buried them and, if so, how long the seeds survived.

Agoutis moved by far the most seeds in Lieneke’s experiments, followed by squirrels and then rats.  Peccaries did not move any seeds, probably because Lieneke cleaned the fruit off the seeds for her experiments, and peccaries only eat the fruit part, being unable to crack the hard seed.    All three rodents moved seeds about the same distance (average 9-15m), but they treated them much different, with agoutis and rats burying most of their seeds in underground caches, and squirrels taking about half of them up into the trees to eat or store them.  Finally, the rat-buried seeds were typically dug back up after just 1-2 days, while the squirrel or agouti buried seeds remained underground for three weeks, or more.

Lieneke defended her Masters Thesis this month, concluding that agoutis are by far the most effective initial disperser of Astrocaryum seeds, moving more of them, burying more of them, and leaving them in their underground caches longer than the other rodent species.  Add to this Veronica’s earlier results showing that once a seed is dug up from an agouti burrow it might get re-buried into another underground cache (i.e. secondary dispersal), and Agoutis come out as the main mobility assistant for Astrocaryum trees.

Congratulations to Lieneke on an outstanding Masters thesis.

November in Panama: cooler weather, heavy rainy season, low fruit production, and stressed animals. This is also the time of the year when agoutis go back and eat their cached seeds. This year, the agoutis depleted most of their caches by the end of November. The bulk of seeds were eaten in July, August, and September. This also means that we don’t have many seeds left in the ground. After continuously following 222 seeds over the past six months, we now only have 18 seeds remaining. It also means that we don’t have much remaining work for the project’s chief field assistant; Sumana Serchan. In November, Sumana packed up the lab, helped clean up two years of accumulated mess, did one last big census of caches (from both 2009 and 2010) and left BCI. While Sumana will surely be missed on BCI, I’m sure her friends and family in Vermont are happy to see her back home. The entire agouti seed dispersal project crew thanks Sumana for her hard work and dedication! While the project doesn’t have any full time members living on BCI (for the first time since October 2008), that doesn’t mean the project has stopped entirely. We still have a few seeds left to monitor! Seed checking duties are now being taken over by Jose Alejandro Silva Ramirez (or Alejo for short) who has worked with us tracking agoutis and Dipteryx seeds in 2009. Alejo was also a superstar tamandua catcher while working with Danielle Brown on her dissertation thesis project. We promise Alejo that monitoring and tracking the remaining seed caches will not involve any animals attempting to gouge him with sharp claws. Anyway, we welcome Alejo, and are excited to see what, if anything, happens to the remaining seeds over the coming months.

 

Sumana in the field

 

 

 

Alejo with tamandua

  • Here is the STRI Newsletter piece on the ARTS lab closing down.

    Animal trackers move on from towers to satellites and cameras

    The Automated Radio Telemetry System (ARTS) on STRI’s Barro Colorado Island (BCI) is taking down its towers used to track animals with radio-transmitters and switching to GPS and camera trap systems that produce more data with less infrastructure.

    Experiences with ARTS over the last eight years on BCI have led to the development of new technologies, including the miniaturization of GPS tracking devices, revolutionary camera trap monitoring techniques, a Smithsonian repository of camera trap images, and a global archive of animal tracking data www.Movebank.org

    BCI is famous as a training ground for pioneer ecological research systems that allow scientists to ask new questions. In 2003, researchers Roland Kays (New York State Museum) and Martin Wikelski (Princeton University, now at the Max Plank Institute) founded an experimental Automated Radio Telemetry System (ARTS) to track the activity and movement of animals wearing small radio-transmitters. According to Kays, “at that time tracking options were limited because GPS devices were so large they were carried by surveyors in backpacks and camera traps were limited to rolls of 36-exposure film.”

    With support from the National Geographic Society and the Levinson and National Science Foundations, Kays and Wikelski brought a team of specialists to BCI to erect a network of seven towers that streamed live data on the location and activity of animals that had been fitted with small, inexpensive radio transmitters. Since then, the ARTS has been used to track 374 individuals from 38 species, including 17 mammal species, 12 birds, seven reptiles or amphibians, and two species of plant seeds. The unique data gathered by ARTS have allowed researchers to tackle previously intractable questions about the ecology and behavior of species ranging from palms and bees to monkeys, by providing a means to “see” cryptic events and track animal movements and activities over large distances and long time periods.

    However, ARTS-based tracking is limited to BCI because of its extensive infrastructure requirements, and thus researchers have also been looking past radio transmitters to new, more flexible technologies. GPS devices have been improved and miniaturized over the past three years, spurred on in part by former ARTS engineer Franz Kuemmeth (founder of E-obs GPS tracking company) and ARTS biologists, who rapidly adopted the new technology to track animals on BCI…and off. New sensors are also being developed to work in concert with GPS tags to provide detailed information about animal behavior and physiology.

    ARTS researchers also developed new methods for monitoring animal movement with camera traps. This approach was initially developed to monitor animals moving palm seeds that were being tracked by the ARTS, but is now being implemented at SIGEO sites around the globe. The BCI camera trap data are also being shared with the public through a new ‘SI Wild’ website that combines the images from ten Smithsonian camera trap studies around the world and will launch in 2011.

    Many of the most important moments in an animal’s life are hard to study because they are rare or difficult to observe. Due to the shy nature of most species, tracking animals is necessarily a high-tech enterprise. The development ARTS and related technologies on BCI over the last eight years offers another example of how STRI-supported science can help develop new fields; in this case, one where detailed data on animal movement, physiology, and behavior can be integrated to address the next generation of scientific and conservation questions.

    14 December  2010

    STRI Tupper Conference Room, Panama

    When is an animal born?  Where does it go when it leaves home? How does it die?  Many of the most important moments in an animal’s life are hard to study because they are rare or difficult to observe. Over the past 7 years, the Automated Radio Telemetry System (ARTS) on Barro Colorado Island has helped STRI scientists address many of these important questions by allowing them to “see” cryptic events and track animal movements and activities over large distances and long time-periods. Recent technological advances have now made is possible to collect ARTS-style data using satellite technology, and the ARTS initiative will soon be disassembling the original radio-telemetry based system on BCI and transitioning to GPS based tracking.  Please join us December 14th, 2010 in the STRI conference room at Tupper, to hear about how the ARTS system has improved our understanding of the behavior and ecology of  tropical vertebrates and learn about the exciting new directions we are taking with our animal tracking research.

    ARTS Science Symposium: where have we been, where are we going?

    12:30-12:55 Rodent thieves: multi-stage dispersal leads to long distance seed dispersal.

    Ben Hirsch, Smithsonian Tropical Research Institute & New York State Museum

    12:55-13:20 From the pond to the forest: a glimpse into the movements and activity of the veined tree frog on BCI.

    Robert Horan, University of Georgia

    13:20-13:45 How do small groups survive? Intergroup competition and imbalances of power in white-faced capuchins.

    Meg Crofoot, STRI & MPI-O

    13:45-14:10 Better to be breakfast lunch or dinner: effect of feeding time on seed dispersal by toucans determined from GPS tags and accelerometers.

    Roland Kays, New York State Museum

    14:10-14:35 Intrapopulation niche differences: do they exist for northern tamandua anteaters?

    Danielle Brown, University of California, Davis

    14:35-15:00 Surveying forest mammals using camera traps: From BCI to SIGEO

    Patrick Jansen, Smithsonian Tropical Research Institute & Wageningen University

    15:00-15:25 Sleeping on the limb- atypical sleep patterns in wild sloths.

    Bryson Voirin, Max Planck Institute for Ornithology

    15:25-16:00 Break

    16:00-17:00 From ARTS to ICARUS: perspectives on global animal tracking

    Martin Wikelski, Roland Kays, Meg Crofoot