Wednesday, October 26, 2011

Following Birds Following Ants

What is mental time travel? Sounds a little like something from Star Trek or Dr. Who. Actually its pretty simple, its really just a type of memory. It can be broken down in to 2 elements: the ability to remember past events (episodic memory) and the ability to anticipate and plan for future ones (future thinking). One of the reasons it sounds so simple is that, as humans, it is something that we can do. There is some evidence that a number of animals such as corvids, chickadees, rats, and great apes can remember past events in terms of what happened when and where, and there is some evidence that corvids and primates engage in future planning. However, the issue is whether animals engage in mental time travel.

A new ideas paper in Behavioral Ecology reviews mental time travel by looking at bivouac-checking, a specialized behavior of birds that interact with army ants. Army ants (Eciton burchellii) have regular alternating periods of high (nomadic) and low (statary) raiding activity. The statary period often lasts for several days, but when the ants enter the nomadic phase they raid the forest many days in a row. Several species of birds will follow the ants back to their temporary nest (called a bivouac) to inspect its location and assess this activity. This checking occurs in the evening and then the birds return the next morning to check the bivouac before feeding at the ants' raid. Now this raid is the important part. The army ants swarm across the forest floor and flush out leaf-litter dwelling arthropods. This flushing allows the birds to forage the fleeing arthropods. So you can see why it would be beneficial that the birds know when these raids will happen by checking up on the ants, and it is even more benefical to keep track of multiple bivouacs. And this is where the mental time travel comes in to play.

Bivouac-checking behavior may require episodic-like memory. The birds must remember the location of the bivouac so that they can return to it the next morning while also remembering which nests are in the nomadic phase. They must also get there before the ants start their raid. Element 2 of mental time travel is future thinking. That's a tough one. I mean, how do you test whether a bird is making plans for the future? The birds do exhibit some behavior that may indicate future thinking. They check bivouac when they are sated. A bird with a full tummy doesn't immediately benefit by checking a bivouac. There is, however, a delayed benefit when the bird returns the next morning to find the ants raiding again. This dissociation of current state and future need suggests anticipation of future events.

Being an ideas paper this isn't an actual study. The authors are really just suggesting a good model system for the study of mental time travel by describing the merits of the system and providing some interesting questions for a future study.

Read the paper here:
Logan, Corina J., Sean O'Donnell, and Nicola S. Clayton (2011) A case of mental time travel in ant-following birds? Behavioral Ecology: 22(6), 1156-1165. (DOI: 10.1093/beheco/arr104)

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