November 2009

Animals facing changes in food abundance over the year can either defend an area large enough to always have enough food, or fight to expand their territory when times get tough.

By the start of the dry season in Panama there is little new food for agoutis, and they are largely living off the seeds they have hidden in caches earlier in the year.  Then Dipteryx starts fruiting, offering a fresh fruity exterior with a nutritious nutty inside.

This is the time of year where you can see hoards of agoutis hanging out under Dipteryx trees, and some have speculated that they give up on their territoriality in this time of year and all fatten up on Dipteryx like grizzly bears at an Alaskan salmon stream.

Annemarie found this wasn’t exactly the case.  Agoutis were 5 times more common underneath Dipteryx trees than other locations, but radio-collared agoutis didn’t abandon their territories to camp out under these trees.  Some animals would boogie out of their normal range for a quick breakfast at a nearby tree, but returned to spend most of their day back home.  The degree to which they changed home range depended on how many Dipteryx there were nearby, and also the local density of Astrocaryum trees, their primary cache fruit.  One agouti seemed to do just fine without any Dipteryx in his home range at all , presumably living off the numerous seeds he cached earlier in the year.

Congratulations to Annemarie on a very successful thesis!

Camera traps are hard to run in the trees.

First of all, you have to get them up there.  Most tropical trees have a long trunk with no branches for the first 10m, so you need to get a rope up on a sturdy branch and climb that (we prefer the giant-slingshot method).

Next problem, trees sway and blow in the wind.  This can trigger the camera trap, filling your memory card up with moving vegetation but no animals.

But there is at least as much action up in the rainforest canopy as down on the ground, so we need to start aming our cameras upwards to get the full picture.  Vivian Maas took on this challenge, focusing on fruiting palm trees.  She scoured the forest to find fruiting trees with another tree nearby that could host the camera, then got some climbing help, and crossed her fingers.

The inital returns were dissapointing – no animal action.  It seems we were a bit early and the fruit wasn’t ripe yet.  Once it did ripen, Vivian captured a variety of frugivores incluing monkeys, opossums, parrots, and my favorite – the kinkajou.

Here is a troop of howler monkeys in a spiny-palm that is just loaded down with fruit.

Finally, a few trouble-making capuchins that bump the camera a few times.