The early bird becomes the cat food

We all know the feeling – sometimes there just aren’t enough hours in the day to get all our work done.  Such is the life of agoutis living in low-quality territories, who have to scrounge around the rainforest floor not only for today’s meal, but also to find seeds they can cache underground for the late rainy season when there will be even less food.  To push ourselves as deadlines approach we set the alarm extra early, and have an extra cup of coffee to keep working later.  Our latest discovery shows that hungry agoutis also stretch the hours of their day, but face much more dire consequences than a short-night’s sleep.

Our new paper published today in Animal Behavior, led by Lennart Suselbeek from Wageningen University, shows that hungry agoutis that wake up early or stay up late are much more likely to be eaten by ocelots, while those who have plenty of food sleep in and avoid the dangerous dusk and dawn periods.

Ocelot (dashed line) and agouti (solid line) activity patterns over a typical day (time on x axis).

We used radio-collars and camera traps to measure animal activity.  The camera data showed the expected overall patterns of the population in general, with agoutis out in the day (95% of photos) and ocelots working the night-shift (78% of photos).

However, there was some overlap, especially at dusk and dawn.  Comparing the ratio of ocelot:agouti pictures at different times of day puts a number on this risk.  During the day we’d get 500 agouti photos for every one ocelot picture – this is a safe time for agoutis to roam around with a low chance of running into a predator.  At night this flips to 30 ocelots for every 1 agouti – this is the dangerous time when ocelots are on the prowl and agoutis are hiding in their dens (as we showed in another recent paper).

We also radio-tracked agoutis and used our Automated Radio Telemetry System to monitor them 24/7.  The live data stream alerted us when animals died, giving a flat-line on the activity graph, and giving us a chance to run out and try to determine the cause of death. Most of these (17/19) were confirmed as ocelot kills.  What more, we were able to pinpoint the time of day that the kill occurred, confirming that the dark hours of the night, especially dusk and dawn, are deadly for agoutis.

Radio signal of predated agouti

If the in-between periods are so important, why would an agouti get up before the sun was up, or stay up into the evening, when they must know ocelots are still active? This required us to focus in on individual agoutis, not general population-wide surveys.  First, we looked at our radio-collared animals to see when they started and ended activity based on the radio signal. Then, to get more specific, we also put a camera trap on their burrows, to see exactly when they went in and out of their bedroom. They key part of this comparison was that we knew how much food each animal had available in their home range from our tree surveys.  The results were simple but striking.

Both methods showed that agoutis in areas with less food left their burrows earlier and entered their burrows later than agoutis in food-rich areas. Hungry agoutis were much more active at twilight, and were more likely to get killed by an ocelot.

Start and end of activity by agoutis related to the food they had available to them, showing that hungry agoutis are more likely to be active when its dark.

In the end it’s the predator that delivers the final blow, but this shows that hunger is driving them to take risks, and highlights the importance of having a good quality territory with lots of food.

So agoutis are kind of like us, busy mammals with too much to do, and not enough time in the day.  The next time your alarm seems too early, and the sky is still dark outside, consider the chances there is an ocelot outside your bedroom – maybe its ok to hit snooze one more time.

 

Agouti Horror Show

It’s the classic horror scene – a defenseless young victim sleeps as a bloodthirsty predator stalks just outside the bedroom.  This plays out nightly in the rainforest as ocelots stalk past agoutis sleeping in hollow logs or tree holes.  Our camera traps on BCI occasionally record the end result of this drama, for example, this ocelot toying with a baby agouti in the middle of the night.

From previous work we knew that ocelots eat a lot of agoutis, often catching them at night near their burrows.  However, we didn’t know if this was just random encounters, or if the ocelots were seeking out the sleeping rodents.  This question is more than simple curiosity given the importance that refuges are thought to play in how animals move around when they aren’t sleeping too.

The ‘Central Place Forager’ hypothesis suggests that prey should stick close to their refuges so they can quickly run to safety if they detect a predator sneaking up on them.  However, if predators cue in on sleeping sites, prey should avoid these areas when they aren’t actually sleeping.  Two opposite predictions  – so which is it?

To answer this question Willem-Jan Emsens led an effort to radio-track agoutis to find where they slept, then ran camera traps to monitor the agoutis as they come and go.  These cameras also recorded ocelots.  Not only did the ocelots walk by, but our videos show them actively trying to get into the agouti hide-outs.

Our camera traps recorded ocelots at agouti refuges more than 2x as often as at non-refuge sites, and showed that they hung out at agouti holes  5x longer than other sites.   Ocelots apparently could tell if the refuge was occupied or not, as they spent about a minute trying to get at agoutis in holes, but took just a few seconds to figure out that no one was home, and move on.  No agoutis were harmed by ocelots while our cameras were running, but they must have been well terrified as the cats tried to claw their way in.

So the answer is YES – ocelots do target agouti refuges, but agoutis seem safe as long as they stay tucked away out of reach.  Their bed is safe, but their bedroom (the area around the refuge) is risky.  I just hope they don’t have to get up in the middle of the night to go to the bathroom!

Based on our new paper “Prey refuges as predator hotspots: ocelot (Leopardus pardalis) attraction to agouti (Dasyprocta punctata) dens” in Acta Theriologica 2013.

 

Cache monitoring by agoutis

An agouti can bury hundreds or thousands of seeds in the forest. This scatter-hoarding behavior is interesting to many scientists because it raises the question of how these animals can remember the locations of so many seeds. Agoutis may not be the Einstein’s of the animal world, but the ability to remember the locations of all these seeds is really impressive. The problem is, nobody really knows if these agoutis actually remember the location of their seed caches! Our new paper published in the journal Animal Behaviour sheds some light on this interesting question.

As previously discussed in this blog, we placed camera traps next Astrocaryum seeds that had been buried by agoutis to determine if they were eventually dug up by cache owners (i,e, the animal who stored it there in the first place), or cache thieves. However, these cameras also recorded a lot of other animal action in the area. When looking through the photos, I noticed that cache owners often visited their hidden seeds. It looked like the agouti cache owners were purposely re-visiting their buried seeds every few days. But why would they do that?

Could the agoutis be monitoring their seeds to determine if/when they have been stolen, or is there another reason why the agoutis would want to visit their seeds?

To investigate this question I talked to Tim Roth (now a professor at Franklin and Marshall) who is an expert on cognition and seed caching birds. Tim recently wrote a paper on long-term memory and seed caching in black-capped chickadees which gave me some great ideas. Previous studies of chickadees indicated that these small birds were able remember the locations of buried seeds for about a month, but not much longer. In those experiments, birds were allowed to cache a seed in an enclosure, and then were allowed to return after a given amount of time. After a month, the chickadees were not able to recover seeds at better than random levels. Just like in humans, the spatial memory of the chickadees degraded over time. But in the wild, these birds (as well as agoutis) often need to recover seeds that have been stored longer than a month. So, if memory degrades over time, how can scatter-hoarders remember where their seeds are over long time periods? Well, it turns out that Tim discovered a difference between those experiments and wild animals – free living birds may be able to revisit their cache locations to reinforce their spatial memory. This is important because it provides a potential mechanism for a species with limited brain power to still be able to remember the location of their seeds for longer time spans. When Tim tested this hypothesis, he found that chickadees allowed to revisit cache sites could indeed remember the location of seeds after 6 months!

Agoutis need to save their seeds until the season of lowest food availability, and so they should want to store their Astrocaryum seeds in the ground for at least 3-4 months. It would make sense if agoutis also acted like the chickadees in Tim’s experiment. If agoutis repeatedly revisit their caches to remind themselves of the locations of their caches this should lead to increased long-term memory.

To test this idea using our videos, we counted how many times agoutis visited their caches and then compared this to control cameras that were placed nearby (where no caches were known to be buried). We found that cache owners were almost four times more likely to pass in front of cache cameras than control cameras, and that cache owners visited their caches about once every five days. We also noticed that cache owners acted differently when they passed the cache location, often walking directly above the seed location and sniffing the ground where the seed is. In these cases, we believe that these agoutis are reaffirming that their cached seed is indeed still buried at that location. Sometimes non-cache owners would also investigate the cache locations before stealing the seed. In contrast, cache owners purposely left their caches in the ground to save for later consumption. The behaviors we’ve seen are consistent with the idea that agouti cache owners are revisiting their seeds to reinforce their memory (and acting as a census of caches for stolen seeds). If this is indeed the case, these agoutis may be using this behavioral strategy to lengthen their memory. This is a really cool result, because if true, scatter-hoarding animals that want to increase their long-term memory abilities don’t have to evolve bigger hippocampuses (the part of the brain responsible for memory), they can simply behave differently. We expect that similar behavioral patterns may be commonly used by other scatter-hoarding animals, but nobody has tested it in the wild yet!

By: Ben Hirsch

 

Agouti directed seed dispersal

One of the big discoveries of our project is that agoutis disperse Astrocaryum palm nuts in a complex step-wise manner: agoutis bury a seed, then dig it up and move it to another site over and over again. While collecting data in the field, and following seeds from one place to another over many weeks, we noticed that the movements didn’t seem to be completely random with respect to the surrounding trees. Astrocaryum palm trees are very conspicuous because they are covered in big spines, you have to keep an eye out for them when your walking off trail to avoid getting pricked.  When tracking down radio-tagged seeds, it almost seemed as though the seeds ended up in areas far away from other Astrocaryum trees. If this was true, this could be a really important phenomenon, because of something known as “Janzen-Connell effects”.

Vero tracking seeds

Janzen-Connell effects, first identified by Drs Janzen and Connell (of course), result in seeds falling below their parent tree being attacked by enemies while those that escape their mother’s shadow are more likely to also escape their enemies  (parasites and predators). For this reason, our previous result that step-wise dispersal led to long-distance dispersal was so important. By carrying these seeds away from their parent trees, agoutis are helping these seeds survive, and helping trees to reproduce.

Graph showing Janzen-Connel effects: the further away from a mother tree the seed moves, the greater its chance of survival.

BUT, this phenomenon comes with a big caveat. It is possible that when agoutis take a seed away from its mother tree, the seed might be buried right underneath another Astrocaryum tree, and therefore at high risk for predation or parasitism. This pattern is called contagious dispersal because if agoutis dispersed seeds in this manner, they would simply carry them from one Atrocaryum tree site to another Astrocayum tree site. If certain pests (such as insects and fungus) are more common when plants are found at high densities, seeds should survive best when not surrounded by many trees or seeds of the same species. For this reason, contagious dispersal has been hypothesized to be a major limiting factor in seed survival in some systems. (For those interested in more on the subject of distance and density dependent mortality, John Terborgh recently published a great paper in American Naturalist where he discusses this subject.)

So, if our impression that agoutis carried seeds away from adult trees is confirmed, agoutis could be dispersing seeds in a manner which would be really helpful to these trees. The question then was: how do we test this question?  Luckily, we had the data at our fingertips.  During our study we recorded the exact location of each seed cache, and we also recorded the coordinates of all Astrocaryum trees in the area. We were thus able to calculate the number of adult trees near (within 25m) our seed locations using a GIS and see if the seeds went from high to low density areas.

Path of one seed (brown oval) in relation to adult Astrocaryum trees (orange dots).

We found that the seeds indeed went from high to low density areas. But, could this have happened randomly? If a seed starts out in a high density area, no matter which way it moves, it would end up in a lower density area. To really test this question properly we created a computer model of random dispersal: we had pretend seeds moving in random directions and random distances (based on the observed dispersal kernel), and then compared the random movements to the observed movements actually made by agouti-carried seeds. What we found was that the observed seeds indeed moved to areas with fewer adult Astrocaryum trees than the random movements.

Ultimately, agoutis carried seeds to areas with 36% lower density than their original locations. This should greatly benefit the survival of Astrocaryum seeds.  But the agoutis aren’t going the extra mile just for the seeds sake, as our earlier research discusses, seeds buried in areas with fewer Astrocaryum trees are less likely to be stolen by other agoutis. So whats good for the cacher is also good for the cachee.

We think this new paper just published in Ecology Letters, and our recent PNAS paper show pretty conclusively how important scatter-hoarding rodents are to the survival of Astrocaryum trees.

By Ben Hirsch

 

Not exactly what we were looking for, but it involves Gomphotheres, so it must be cool.

Sometimes in science, the answer you end up with is not exactly the question you started with.  The path to discovery is not always predictable.  Researchers have to constantly evaluate what they are finding, and be ready to adjust their course when the data leads down a different path.  This is especially true in tropical ecology, where there is so much basic information yet to be learned.

Such is the case with our new paper published this week in the Proceedings of the National Academy of Sciences (PNAS).

We started tracking the fate of tropical seeds with small radio-transmitters because we thought that the predation of agoutis (the main mover of palm seeds) by ocelots (the main predator of agoutis) would leave a bunch of “orphan seeds” buried in the forest where no other agoutis would discover them.  These orphaned seeds would thus be free to germinate and grow into new palm trees.  It was a cool idea, and would show how predators affect prey, ultimately trickling down through the tropic levels to affect seed survival, forest regeneration, etc…  We had all the hypotheses, sub-hypotheses, and sub-sub-hypotheses worked out.  Now we just had to go into the jungle and prove ourselves right.

A Illustration of a buried seed with our radio tag by Patricia Kernan, NYSM.

We set out to map all the palm trees, radio-collar a bunch of agoutis, have them disperse our special radio-tagged seeds, and then wait for the ocelots to pick them off one-by-one.  Earlier research suggested that only about 1/3 of these rodents survive one year, with most falling to the island’s ocelots. If we did our part we knew we could count on the ocelots to do theirs.

This was actually a huge amount of work, we needed “our agouti” to move “our seed”, and bury it in a little hole for safe-keeping.  Camera traps told us whether one of “our agoutis” moved a particular seed, and more often than not it was an un-marked agouti, or a rat or squirrel. Initially animals just ate most of the seeds, but once they recovered from the recently-ended hungry season, they started storing seeds in scattered underground caches for later, when little fresh fruit will be available.

An agouti trying to decide which seed to take next.

Finally our radio-tagged seeds were moving.  Only, and here’s where the change in the-path-to-discovery comes in, the seeds didn’t stop moving.  Once a seed was buried we figured we’d just sit and wait till it was dug up and eaten, sometime in the next few months or year.  Instead, the seeds were quickly dug-up, moved, and buried again, and again, and again.  During our first season of field-work this high rate of movement caught us off guard and the additional work of tracking down these crazy seed movements completely wore down everyone on the project.  Given the super-high rates of seed movement, we realized we needed to look for (actually, listen for radio-signals) moving seeds every single day.  Even daily checks didn’t catch all the movements because we observed some seeds actually move twice in one day.

What the heck was going on?  Why were agoutis moving seeds so often?  Some seeds were going 100’s of meters. Were agoutis shifting home-ranges and taking their seeds with them?  Or, were there thieves amongst us?

For our second field season we decided to switch tactics a bit, and investigate this new research path illuminated by the crazy seed movements. We mounted a major trapping effort to try and capture and mark as many agoutis as we could. By being able to recognize lots of animals in one area, we hoped to determine who was taking the seeds. We hid motion-sensitive cameras next to the buried seeds to see which animal’s dug the seeds up.  Our videos (example above) showed that most (84%) of seeds were being stolen by robber-agoutis.  These unscrupulous rodents weren’t just eating the buried treasure, but often moved it over to the center of their territory, where they could more easily find it during the upcoming hungry-season.  This repeated thievery resulted in seeds moving much further than you would expect from a single agouti.  Slightly more than 1/3 of seeds moved more than 100m, which is typically considered far enough to escape the competition of sibling-seeds that just drop underneath the mom-tree. One seed was cached 36 different times, traveling over 749 m back-and-forth between territories until it was 280 m from its starting point.  We made a movie illustrating this amazing amount of movement (shown below with a fun soundtrack).

Although our test of the predator-mediated seed dispersal hypothesis didn’t go off exactly as planned, our results incidentally disproved it. Even if seeds do become “orphaned” by predated agoutis, we now know that the rates of seed theft are so high that these orphaned seeds still have a good probability of being discovered. While this particular route of influence between predators-prey-trees is probably not important to forest dynamics, our other work  shows how other behavior of these agoutis is heavily influenced by the threat of predation (recent biotropica paper, and another one in the works).

This discovery of robber-rodents helping trees by moving their seeds long distances was made even more interesting by the fact that the dispersal of this particular type of tree has been a tropical enigma since Janzen and Martin published “Neotropical anachronisms: The fruits the gomphotheres ate.” In 1982.  This paper, and dozens since it, suggested that the very largest fruits and seeds found in the Neotropics must have co-evolved to be dispersed by the now-extinct Pleistocene Megafauna.  How these trees have survived the >10,000 years since megafaunal extinction has puzzled tropical ecologists for decades. These results are also important when applied to current mammalian extinctions. If tree species are able to survive due to “disperser substitution” maybe this holds a glimmer of hope for trees that are dispersed by mammals that are currently being hunting to extinction or local extirpation. Alternately, our results also show how important of a role these little agoutis can play in their ecosystems. When poaching gets so bad that they also deplete these smaller-sized mammals, the trees seeds may have no chance to survive.

Our accidental discovery of robbing rodents offers a new potential answer to this mystery, and highlights the potential rewards of following thieves down the dark and mysterious scientific path to discovery.

 

By Roland Kays

 

All the fancy agouti neighborhoods are lined with palm trees (our new publication in Biotropica)

To some, the continuous green canopy of BCI’s rainforests looks the same across the island,

Rainforest Canopy

even though the forest is made up of 100’s of different tree species.  To an animal trying to make a living off seeds dropped out of these trees, however, there are the good and the bad areas.  The good neighborhoods have lots of food and the bad neighborhoods have little food.  From an agouti’s perspective, this comes down to how many palm trees are around, since palm nuts are their favorite food.

Our tree mapping already showed that there is huge variation in the number of palms in different agouti ‘neighborhoods’ across the island. In this new paper just published in the journal Biotropica, we added radio-tracking data collected both by following animals around in the forest, and by using our Automated Radio Tracking System.  We show that “rich” agoutis living in areas with palm (Astrocaryum) density had much smaller home ranges than their poorer island-mates. The reason behind this pattern is straightforward: if you have a high-quality all-you-can-eat restaurant just around the corner, why would you bother to waste your time and energy and face the risk of getting run over by a truck while going to the exact same restaurant eight blocks farther away? Although there are not too many trucks driving around on the BCI-trails, there are ocelots hunting agoutis, and the more an agouti has to run around looking for food the higher risk it has of running into an ocelot-truck.

But, agoutis live in holes in the ground or in hollow logs, not expensive houses.  These do provide refuge from ocelots, as dramatically shown in the below video.  So, if you are an agouti stuck in a bad neighborhood, why not just dig a few extra holes around your territory to give yourself more places to hide from the ocelot-trucks?  This seems like such a good idea the theory even has an official name ‘multiple-central place foraging’.  Do agoutis ‘multiple-central place forage’ to reduce ocelot predation risk in crappy neighborhoods?

Surprisingly, no, agoutis do not increase their ‘multiple-central place foraging’ in bad neighborhoods.  We tracked them down at night to see where they were sleeping, using our radio-tracking antenna to push through the thick vegetation and find their hide-outs.  Although most animals had more than one hidey-hole, there was no relationship with range size – big territories did not have more refuges.

And so we end with the classic scientific conundrum, answer one question, get a bunch of new ones.  WHY don’t agoutis make more holes in large territories?  Are refuges a limiting resource?  Do they need to import more armadillo construction workers to dig more holes?  Or maybe running away from ocelots isn’t that big of a concern for agoutis? We just don’t know, yet….

by Willem-Jan Emsens and Roland Kays

Agouti RefugeTypes

 

Observations on Predation Point – Mammals vs. Reptiles

Predation has strong influences on most animal populations but is almost impossible to observe because it happens unpredictably, and only once in the life of a given potential prey species. This spring with the aid of camera traps, I was lucky enough to record a wide array of predatory behavior on Barro Colorado Island (BCI) in Panama. I was on BCI conducting noninvasive genetics research with ocelots (Leopardus pardalis) ,a mid-sized spotted cat. As part of my research I placed camera traps on ocelot latrines hoping to catch them ‘in the act’ in order to match photo records to genetic fingerprints from scat DNA. One latrine site in particular, in an open area on the end of a peninsula named Harvard, turned out to have a lot more than ocelot toilet behavior going on.

In late February spiny tailed iguanas (Ctenosaura similis) began to nest along the shoreline of Lake Gatun, and I got many photo records of these large reptiles basking in the sun out on Harvard point. I also began to get video records of stalking ocelots crouched low to the ground.  Soon enough, I got amazing footage of a male ocelot dragging off very large iguanas twice during the course of one week. While checking my cameras the day after his second kill I was lucky enough to see the ocelot in person, likely still guarding his meal in the underbrush. Many people mistakenly believe that ocelots are nocturnal, however although they frequently hunt at night, they are opportunists and hunt iguanas during the middle of the day when the cold-blooded reptiles are out basking in the sun. Around this same time another male ocelot killed several iguanas along the shore in front of the BCI labs, to the delight of the on looking scientific residents.

Not long after this other reptiles began visiting the point. My cameras frequently captured a very large crocodile (Crocodylus acutus) coming well up from the water, causing me to keep looking over my shoulder each time I scooped ocelot poop from the latrine. Did she have a nest nearby?

Next, turtles (Trachemys scripta) from the lake began to come ashore to lay their eggs in the dirt near the latrine.  Like clockwork, white-nosed coatis (Nasua narica) appeared to dig up the eggs and eat them. During the preceding weeks coatis visited every day, resulting in thousands of photo records, and leaving the point strewn with shallow holes surrounded by chewed up turtle egg shells. Then one day in late March I found a starling sequence of photos. In one photo a coati is standing directly in front of the camera, and in the next photo taken less than 2 seconds later, a crocodile is flying across the frame mouth wide open to snap! During the next few weeks I also recorded several videos of the crocodile going after coatis.

In the instances I recorded, the coatis pursued by crocodiles narrowly escaped, however not all coatis are so lucky. According to Dr. Matthew Gompper from the University of Missouri who conducted his PhD. Research on coati behavior on BCI in the early 90’s, one radio collared coati from his study was killed by a crocodile. It was witnessed by one of the forest guards, and for a month or so afterwards he could hear the collar beeping forlornly from the lake, presumably still transmitting from the stomach of the croc. Eventually he recovered part of the skull but never found the collar. According to Ben Hirsch, a postdoc on the agouti project who conducted his PhD. work on coatis in Argentina, coatis tend to like riverine ecosystems, and on BCI they may spend a large portion of time on the lake edge. Thus crocodiles might be an important source of mortality on BCI. In addition, the population of large crocodiles has been steadily increasing in the Canal Zone as a result of a prohibition on crocodile hunting put in place when Panama took control of the canal in 1999. Everyone agrees, there are more BIG crocodiles circling BCI now than any time in the last 100 years. This may be increasing the effective isolation of mammal populations on BCI, due to a greatly increased risk of mortality during swims to and from the mainland.
Interestingly however, it may be predation of crocodiles by coatis that has a strong influence on crocodile demography, not the other way around. In late April on a trip to the point to check my cameras I found a number of large, bloody, mostly eaten crocodile eggs surrounding a shallow hole. I had been walking directly over the crocodile’s nest several times per week for the last three months without even knowing it was there! Over the next few days the coatis dug up and ate every last one of the crocodile’s eggs, ruining her chances for reproduction during this nesting season. This time it was the coatis that had the last meal.

Written by Torrey Rodgers

 

New adaptive GPS provides freeze-frame quality picture of animal movement.

If you have ever tried to take a ‘freeze-frame’ photograph your pet leaping in a trick move, a bird flicking past your feeder, or your kid at a sporting event, you have probably looked at more than a few blurry photographs.  Getting a crisp photograph of a body in motion requires a faster shutter speed to provide a sharp image of what is happening at the instant the photo is snapped.

A blurry photograph of a mother tamandua carrying its baby.

Using GPS tags to study animal movement can be compared to taking snapshots of behaviors we can’t observe with our own eys – scientists connect a series of locations taken by an animal’s GPS collar to create a picture of how the animal uses its environment.  The schedule of the GPS unit sets the resolution of the picture we get about the animal movement.  More frequent fixes (e.g. every few minutes) give a high resolution image of where the animal goes while less frequent fixes (e.g. every few hours) are analogous to a blurry photograph. But as anyone who has ever used a handheld GPS unit knows, they chew through batteries like nobody’s business if they collect fixes constantly.  Unfortunately, wild animals won’t change their collar’s batteries when they run out, so scientists have to make the most out of one battery, and therefore face a dilemma in how to program the collars they will use on animals: infrequent GPS sampling will make the collar last longer, but give a fuzzy picture of movement paths; more frequent GPS sampling gives sharp paths but dramatically shortens battery life.  This is an especially difficult problem when animals spend long stretches of down time in tree cavities, burrows, or thick vegetation where a GPS collar has little hope of successfully connecting with satellites and wastes even more battery power in futile attempts to record locations on schedule.

What is needed is a flexible GPS schedule tied to the behavior of the animal wearing the collar.  A more active animal would trigger the GPS unit to record locations more often, while a resting animal would signal the GPS unit to record locations less often.  What kind of sensor monitors the moment-by-moment behavior of wild free-living animals in any type of habitat?  An accelerometer—a matchbook-sized wireless device that measures the change in speed of an animal’s body over time as it moves through its environment.  Accelerometers are in everything from vehicle airbags to Nintendo Wii handsets and over the past few years they have exploded onto the scene in the world of animal movement research.  They are an ideal sensor for linking animal behavior to the location recording schedule of a GPS collar because they are low-cost, can easily be incorporated into a standard GPS collar and they sample movement behavior every few seconds without using much battery power.  So in theory a researcher can have the best of both worlds: a long-lasting GPS collar that gives sharply focused pictures of the paths animals take as they move around their habitats.

Testing the performance of just such a collar is the subject of a paper we recently published in Wildlife Society Bulletin (Brown et al 2012).  We worked both with fisher in upstate New York and Tamandua anteaters on Barro Colorado Island in Panama, testing two types of GPS: one that recorded locations on a fixed schedule every 15 minutes and the other with a flexible schedule that recorded locations every 2, 15 or 60 minutes based on accelerometer-measured movement behavior.  The accelerometer-informed collars performed considerably better than the traditional GPS collars: they attempted 74% more locations per day and had 62% higher location success rates, which means that on days animals were more active, GPS collars recorded more locations thus providing more detailed movement paths.  At the same time they spent 28% less time searching for satellites and recorded 67% fewer locations when animals were at rest, reducing the overall amount of battery power used for each unique location and lengthening the lifespan of the collar.  Ultimately the accelerometer-informed GPS collars produced more information about animal movement for a given battery size and study period when compared to traditional fixed-schedule collars.  This technological development is a boon for researchers and potential study animals alike: ecologists get higher quality data with little additional cost per collar and can instrument fewer study animals for shorter periods of time than they would using traditional collars because the snapshots of daily movements are so much clearer.  Currently only two companies (e-obs (used by our study) and Telemetry Solutions) produce accelerometer-informed GPS collars, but as word gets around, those scientists studying animal movement ecology are sure to appreciate the value of this novel tool.

Map showing high resolution 'picture' of the life of Phineas the Fisher as recorded by an adaptive GPS collar. Click the map to zoom in on the map at Movebank.org

Reference:  Brown, D.D., LaPoint, S., Kays, R., Heidrich, W., Kuemmeth, F. and M. Wikelski.  2012.  “Accelerometer-Informed GPS Telemetry: Reducing the Trade-Off Between Resolution and Longevity” Wildlife Society Bulletin 36(1):139-146.

 

Written by Danielle Brown

 

Big Island, Mini Deer

Biologist love islands. It’s true, we really do. Animals isolated on oceanic islands inspired both Charles Darwin and Alfred Wallace to independently come up with the theory of evolution by natural selection, and continue to be a focus of research today. Thus, it is surprising that so little is known about the fauna of Central America’s largest island, Coiba Island. The lack of research is even more surprising when you consider that the island has a unique form of what may be North America’s most studied wild mammal, the White-tailed Deer, living on it.

view from Coiba

Approximately 27 miles off of Panama’s Pacific coast, Coiba was formed over 20,000 years ago, providing enough time for substantial genetic isolation to occur on any species able to colonize it. To date, 17 terrestrial mammal species, excluding 25 bat species, have been identified on the island. Nine of these were likely to have been introduced within the last century, leaving only nine native terrestrial mammals, five of which are endemic. The only proper survey of the mammals of Coiba Island was conducted by J.H. Batty in 1902, and for good reason (Olson 2008). Research on Coiba has certainly been limited by the penal colony established on the island from 1919-2004, where Panama sent some of its most notorious criminals and gang members such as those of “Los Hijos de Dios” (The Children of God), and “Los Chuckys” (named after the possessed doll of the 80’s horror flick “Child’s Play”). Vivid tales of violence, torture, and political murder during the dictatorship of Torrijos and Noriega filtered back to the mainland instilling a general fear of the island. While rough on the people living on Coiba, this penal period provided protection to the island’s forest and approximately 80% of Coiba’s forest still remains today (ANAM 2009). With the prison now closed, Coiba is gaining a reputation as a popular tourist destination and is protected as a World Heritage Site and National Park.

But what animals patrol underneath the forest canopy? Are the rumors of big cats existing on the island true? Is it possible that, somewhere within the 50,000 hectare island, mammals remain that have yet to be documented? These mysteries were the motivation behind our new camera trap pilot survey of the island’s mammals

In May of 2011, I deployed ten cameras along a trail on the Northeast corner of Coiba Island to capture a snapshot of the diversity, abundance, and activity patterns of its terrestrial mammals. In total, only four mammal species were documented: the Coiban Agouti, Panamanian White-throated Capuchin, Coiba Island White-tailed Deer, and Black-eared Opossum. Compared with our similar surveys on mainland Panama, the agoutis and capuchins of Coiba Island were very common; the agoutis were photographed 2-7 times more often than typical mainland sites and the monkeys 10-100 times more. This information alone is extremely interesting and may suggest two things: 1. There is a general lack of native predators on the island, causing an expected spike in smaller mammal populations. 2. Coiba’s capuchins may come to the ground more frequently than those of the mainland.

One of the shiest animals I photographed was the Coiba Island White-tail Deer (Odocoileus virginianus rothschildi). Our camera trap photos show that they walked in front of our cameras twenty-eight times, or about once every 10 days, and that they are active throughout the day with an apparent peak around dusk (17:00 – 19:00). These photos generated the most attention from Coiba’s park rangers back at the ANAM dining hall, the only place at the station with both a table and electricity during the day. Their interest came as a bit of a surprise since I saw deer so frequently in the mornings while hiking on Coiba, but reminds me why they are the most popular mammal on the continent. And these are special deer – they look like no other white-tailed deer in the world.

This male, being kind enough to model, provides us with a nice look at the various characteristics of the head:
A. Notice the white markings on his muzzle and around the eyes. B. A perfect example of his dark facial markings. Notice the reddish “crest” on the forehead. C. Here the coloration of the chin and throat are easily viewable.

Oldfield Thomas first described the Coiba Island White-tail Deer in 1902 while documenting the private collection of Walter Rothschild, the very same specimens that J.H. Batty collected during his trip to Coiba earlier that year (Olson 2008, Thomas 1902, Allen 1904). The most distinguishing characteristic, aside from their isolated range, is their size; much smaller than Panama’s mainland white-tail species O.v. costaricensis. Additionally, adult O. rothschildi have much darker coats and the white spots of fawns tend to be more inconspicuous. Are their coats more cryptic in response to hunting, was there once a significant non-human predator on the island that influenced this potential adaptation, or is this simply the result of a founder effect?

Average dimensions of the animal are unknown although both Allen and Thomas included measurements in their descriptions. I say this because Thomas’ measurement of the head and body (1120mm) differ from Allen’s (avg. 2287mm) by over 1000mm. In addition, the measurements described by Allen were supplied by Batty, whose information often prompted complaints from Allen, and at times was unreliable or completely fictitious (Olson 2008). Both Allen and Thomas collected measurements from the skulls of six individuals (avg. length 205mm; avg. breadth 86mm). Even then both Thomas and Allen agree that this is the smallest in its genus, humorously describing it as a, “tiny little deer…”

There is obviously much to learn about this little guy as well as the rest of the mammals of Coiba. Plans to continue and expand the camera trap operation are underway. Proper measurements, as well as blood, tissue, and fecal samples also need to be collected. These can help, as they say, set the record straight, and provide valuable behavioral, genetic, and physiological data for future research.

Despite its horrific past, Coiba’s future is has huge potential. The number of scientific research projects on and around Coiba is steadily increasing, such as the recent submarine expedition of Hannibal Bank. Tourism is also increasing with visitors attracted to the unparalleled experience of scuba diving in one of the world’s richest marine biodiversity hotspots. Be sure to visit Coiba if you have the chance. Spend some time diving. Get a tour of the historical prison. Maybe even catch a glimpse of the tiny Coiba Island White-tail Deer. I know you’ll have a great time. After all, biologists are not the only ones who love islands…

By Zach Welty

 

Allen, J.A. 1904. “Mammals from Southern Mexico and Central and South America.” Published by order of the Trustees, American Museum of Natural History. v20.

ANAM. 2009. “Plan de Manejo del Parque Nacional Coiba.” Compiladores JL Maté, D Tovar, E Arcia,Y Hidalgo, STRI.

Olson, Storrs L. 2008. “Falsified Data Associated with Specimens of Birds, Mammals, and Insects from the Veragua Archipelago, Panama, Collected by J. H. Batty.” American Museum Novitates 3620(1):1. Retrieved (http://www.bioone.org/perlserv/?request=get-abstract&doi=10.1206%2F592.1).

Thomas, O. 1902. “On Some Mammals of Coiba Island, Off The West Coast of Panama.” Novitates Zoologicae 9:135-137.

 

New paper testing a method to obtain full seed dispersal distributions from truncated data

We have a new paper out in the journal Methods in Ecology and Evolution:

http://onlinelibrary.wiley.com/doi/10.1111/j.2041-210X.2011.00183.x/abstract#.Tvt1QWJ0ql0

One of the biggest problems studying seed dispersal is that seeds are hard to follow! With traditional seed tagging methods, many seeds simply cannot be found, especially when they travel long distances. One method researchers have used is to limit their search to a reasonable distance and track all the seeds within that radius. The problem with this method is that it tells one little/nothing about long distance dispersal. Given that long distance dispersal is believed to be particularly important, this lack of information is problematic. Patrick Jansen and colleagues developed a statistical method to reconstruct the shape of the tail of the seed dispersal distribution using the shape of the distribution inside the search radius. We thought this was a cool method and had the potential to be used more widely. Unfortunately, this method had never been tested with empirical data. Fortunately, we had a perfect dataset to test the method because we used radio-transmitters to track seeds in our project. We also decided to give it a name: the Censored Tail Reconstruction method (CTR). In general, we found that the CTR method worked exceptionally well at recreating the long-tail of the seed dispersal distribution. On the other hand, this method was highly sensitive to which mathematical function was used in the method, and what percentage of seeds were ‘overlooked’ by researchers searching for seeds. The upshot of our paper is that it is possible to calculate fairly accurate dispersal kernels using censored data collected with traditional low priced tagging methods. The caveat to this is that researchers need to be certain that they are able to find the vast majority of seeds within their search radius, and they must choose the most appropriate mathematical function for use in the CTR method (using AIC selection). We think this method should be widely adopted, especially by researchers who cannot afford tons of radio-transmitters.