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201321Dec12:15

Hun­gry agoutis risk their lives to be eaten by ocelots

Infor­ma­tion
pub­lished 21 Decem­ber 2013 | mod­i­fied 03 Novem­ber 2014
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Hun­gry rodents that wake up early are much more likely to be eaten than rodents get­ting plenty of food and shut-​eye, accord­ing to new results from a study at the Smith­son­ian Trop­i­cal Research Insti­tute (STRI) in Panama. The study was pub­lished this month in the jour­nal Ani­mal Behav­iour’s early online edition.

Ocelot with radiocollarSci­en­tists equipped agoutis, com­mon rain­for­est rodents, and ocelots, their feline preda­tors, with radio col­lars and tracked them 247 via an auto­mated teleme­try sys­tem on Barro Col­orado Island. Agoutis were most active in the day­time. Ocelots were most active at night.

We knew that hun­gry ani­mals tend to take more risks. But this is the first study to so thor­oughly doc­u­ment the behav­iour of both preda­tor and prey.
« Patrick Jansen, research asso­ciate — STRI, assis­tant pro­fes­sor — Wagenin­gen Uni­ver­sity, the Netherlands

“Agoutis eat tree seeds; ocelots eat agoutis,” said Jansen. “Where food is hard to find, agoutis spend more time for­ag­ing and are more likely to be eaten by an ocelot.”

To deter­mine when it was dan­ger­ous for agoutis to be active, sci­en­tists first recorded daily activ­ity pat­terns of agoutis as well as ocelots. Cam­era traps placed across the island pho­tographed all ani­mals that passed in front of the lens and recorded the time. Dur­ing the day, thou­sands of agoutis were active, but few ocelots prowled the island. Around sun­set, as agoutis sought the shel­ter of their bur­rows, the ratio of ocelots to agoutis jumped, and then dropped again around sunrise.

Radio sig­nals pro­duced by an animal’s trans­mit­ter col­lar were simul­ta­ne­ously picked up by radio tow­ers around the island. Researchers could “watch” the ani­mals’ activ­ity online. When an ani­mal stopped mov­ing, sci­en­tists saw a flat line, much like the elec­tro­car­dio­gram of a heart-​attack vic­tim, on their screens. When agoutis died, researchers quickly arrived on the scene to deter­mine the cause of death. Plac­ing a video cam­era at the scene allowed them to know if a preda­tor returned to eat the remains.

Ocelot vs Agouti
Ocelot return­ing to the scene of the crime to eat an agouti it killed the pre­vi­ous day. The agouti was radio-​tracked as part of a study on their ecol­ogy and mor­tal­ity by Enzo Aliaga-​Rosel on Barro Col­orado Island, Panama:

(footage by NRCBio­di­ver­sity on YouTube)

Sev­en­teen of 19 dead agoutis found in the study were killed by ocelots. Most kills hap­pened just before sun­rise and just after sun­set, when rel­a­tively few agoutis are active.

Sci­en­tists com­pared daily activ­ity pat­terns of agoutis between parts of for­est with con­trast­ing abun­dance of palm seeds. First, they deter­mined at what times agoutis entered and exited their bur­rows based on changes in radio sig­nals. Sec­ond, they placed cam­era traps at the entrances and recorded the time an agouti entered and exited.

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.

Next, the researchers will exam­ine what the dif­fer­ences in pre­da­tion risk mean for seed dis­per­sal by agoutis, which bury seeds as food reserves in numer­ous scat­tered caches. “Once an ocelot kills an agouti, the agouti can no longer eat its food reserves,” Jansen said. “These seeds may ger­mi­nate and estab­lish a new tree. Hun­gry agoutis plant trees but may never see the fruit of their labour — a fas­ci­nat­ing feed­back loop.”

(Source: Smith­son­ian News­desk news release, 17.12.2013)


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