I may not have a nuclear-powered DeLorean parked in my driveway, but I can travel in my own personal time machine anytime I want, and so can you.
Through what’s known as mental time travel, or MTT, you can move backwards and forwards through time – visiting the past when you remember a specific event you’ve already experienced, and then zipping forward to the future as you use this memory to predict, plan for and shape events that are yet to come.
Mental time travel is no mean feat: it implicates sophisticated cognitive processes and is thought to form the foundation for advanced forms of consciousness such as self-awareness and the ability to attribute independent thought, desires and intentions to others (an ability sometimes referred to as “theory of mind”).
So, can other animals engage in mental time travel? Perhaps not surprisingly, this has been a controversial topic, and many have argued that we humans are the only ones able to mentally flit about the fourth dimension, leaving all other animals stuck in the here and now. Although this may be partly attributable to our anthropocentric world view1, the language barrier between humans and other animals also poses a real problem, as it’s difficult to design MTT experiments that don’t involve interviews, since the best time travel evidence may consist of the voyager’s personal and subjective reports of the experience. Accordingly, solid evidence for MTT in other animals has been limited, and much of the evidence that does exist consists of anecdotal accounts and a small number of experiments involving great apes and western scrub-jays.
In a paper2 published in the October 14, 2011, issue of Behavioral Ecology, though, a research team led by Corina Logan of the Department of Experimental Psychology at the University of Cambridge proposed an intriguing new avenue for further research, one that might significantly expand the number of species that may be tested for MTT abilities. More specifically, Logan and her colleagues identified a specialized strategy among birds – army ant bivouac checking – that may provide conditions in the wild that could favor the development of mental time travel in a variety of species.
While many tropical rain forest birds earn an opportunistic living by gobbling up insects and other small invertebrates flushed out of hiding by army ants on food raids, a subset go a step further – after raids by a specific army ant species (Eciton burchellii), these birds follow the ants back to their temporary nests (known as a bivouacs) in the evening, and then return to check on the bivouacs the next morning before the ants raid again. To date, twenty one different “bivouac-checking” bird species have been identified.
Tracking army ant bivouacs is more complicated than one might think. As the ants raise their young, they cycle through two distinct phases: one (approximately 20-day) phase during which they remain in a set location, conducting most of their raids at the beginning and end of the phase and relatively few during the middle two weeks; and a second (approximately 14-day) nomadic phase, during which they move their bivouac on a daily basis and conduct raids almost every day.
From the perspective of a bivouac-checking bird seeking a reliable food source, these varying phases are significant. When the ant colony is stationary, it may be relatively easy to find, but its raids will be sporadic; when the colony is nomadic, it may be more difficult to find, but its raids will be quite regular. Clearly, a bird will do better if it can keep track of multiple stationary colonies that conduct raids only sporadically, if it can quickly find nomadic colonies based on their prior locations and previous movements, and if it can remember whether particular colonies are in phases in which they’re likely to conduct raids.
The researchers identified these conditions as providing a potential testing ground for MTT. While the birds obviously can’t be interviewed, their environment may elicit behavior that shows that they have an “episodic-like memory” (that is, they can recall the what-where-when aspects of past events) and that they can take action in anticipation of future motivational states independent of their current needs (that is, they can plan flexibly for the future).
After noting that the birds appear to form specific memories about locations (since they return in the morning after evening bivouac checks), the researchers hypothesize that the birds may remember which colonies are in which locations and what phase the colony is in, “and that they may be using episodic-like memory if they prefer to check those bivouacs from army ant colonies in the nomadic phase.” Moreover, they continue:
We suspect that future planning could be involved in bivouac-checking bird behavior because birds check bivouacs when sated (conferring no immediate benefit), a behavior that does not make sense until the next morning on return to the bivouac when the bird finds the ants raiding again and encounters its next meal (a delayed benefit). Because bivouac checking occurs after foraging at a raid, there is no immediate benefit to conducting this behavior in terms of acquiring a meal in the next few minutes. Instead, the benefit occurs the next morning when the ants begin raiding again; bivouac-checking birds return and are the first to begin foraging at the raid. This could indicate a dissociation between their current state (sated) and a future need (will need to eat tomorrow), which suggests anticipation of future events. (Citations omitted.)
Logan and her colleagues call for additional field research and, if their hypotheses are supported, laboratory experiments that will enable experimenters to vary bivouac locations and colony phases under controlled circumstances, and to determine whether the birds use specific memories and flexible future planning or whether they engage in automatic behavior using vision, smell, circadian rhythm or other cues in checking on bivouacs.
At this point, the researchers’ hypotheses need additional experimental support, but it’s already clear that they’ve made some keen observations about specialized behavior in the wild and have opened the door to substantially expanded testing for mental time travel in animals. As more researchers come up with similarly elegant ways of investigating abilities previously thought to be unique to humans, I think we will see additional barriers fall.
1As regular readers know, this is a recurrent AnimalWise theme. Time and again we humans have claimed that we are the only ones to have a particular skill, only to discover later on that, in fact, many animals may share the same or comparable abilities with us. Prior posts have discussed this phenomenon in areas including tool use (many different fish, crested rats, ants, dolphins, chimpanzees, crows), language (bees and prairie dogs), analogic reasoning (capuchins and baboons), grief and mourning in various animals, and self-recognition (dogs, magpies).
2Logan, C., O’Donnell, S., & Clayton, N. (2011). A case of mental time travel in ant-following birds? Behavioral Ecology DOI: 10.1093/beheco/arr104.