Display of navigation in animals

Navigation can be defined as the process which enables a course or path from one place to another to be identified and maintained. This process is based on the capacity to plan and execute a goal-directed path (Gallistel, 1990). Behavioural and neurophysiologic mechanisms of navigation in animals belong to one of the most fascinating and seminal fields which is of great interest not only to biological sciences but also to engineering and robotics. In this and in the next section we content our consideration with a brief listing of displays and ways of navigation in animals just to create a draft of the whole picture and to find a room for intelligence in it.

Progress in technology enables students of navigation to observe animals’ migratory repertoire employing short-distance radar registrations as well as long-distance satellite radio telemetry. These methods of observation in particular give a possibility to look at migration’s trajectories from quite long distances and observe a sequence of straight vector courses. Our knowledge about animals’ navigating skills has essentially grown but many questions concerning basic mechanisms of their travelling still remain obscure.

The most mysterious display of mapping behaviour in animals is homing. Homing refers to the ability of animals to return to their local place from any distances, and very often this journey involves travelling across unfamiliar territory. The typical and at the same time impressive examples of homing concern so called central place foragers (Orians and Pearson, 1979). These animals undertake foraging trips which lead them away from their “central place” such as the nesting site and then return back. For example, at the Crozer Islands in the southern Indian Ocean, Wandering Albatrosses Diomedia exulans leave their nests for foraging flights which take them over distances of hundreds or even thousands kilometres. Finally, however, they return to their home island, a tiny speck within the vast expanse of water, with seemingly unerring precision (Jouventin and Weimerskirch, 1990).

Desert ants wander as far as 600 m from their nest which perhaps demands the same level of reliability of navigation systems from these small creatures. The most amazing thing is that when an ant finds an edible thing such as a dead insect, it carries this thing straight home in order to feed larvae there. In my experiments I used to give red wings of locusts to Cataglypis ants, whereupon it was easy to observe them carrying red “flags” for very long distances (Reznikova, 1982). Ant’s close relative, the honey bee flies up to 10 000 meters from its hive and then returns home (Visscher and Seeley, 1982).

With many other examples from natural history of different species described in thousands of scientific papers, these pieces of animals’ natural history enable us to consider a question to what limits intelligence is involved into the process of homing. We will return to this problem further in the chapter.

Migration does not require great feats of navigation because it is not oriented towards a specific goal. Migration is defined as “oriented, long-distance, seasonal movements of individuals “(Able, 1980). The role of learning could be rather modest in migration behaviour, at least in some species. In many cases of migration generations of the same species undertake almost the same journey. Gwinner (1972) suggested that the direction and duration of migration is largely under endogenous control and depends rather little on learning.

Migrating behaviour of the loggerhead sea turtles provides an instance of this type of migration (see Pearce, 2000). Loggerhead turtles hatch from eggs on the Atlantic beaches of Florida and then spend the next few years swimming in loops around the Sargasso Sea before returning to a beach in Florida. A series of experiments has revealed how newly hatched turtles are able to find their way to the Gulf Stream. Young turtles were placed into a large dish in which it was possible to measure their preferred direction of swimming (Lohman, 1992). When the experimental room was dark, except for the presence of a dim light source, the turtles were observed to swim towards the light. Apparently, newly hatched turtles emerge onto the beach at night and reflected light from the moon and stars makes the sea brighter than the land. By being attracted to light, the turtles are thus led towards the ocean. When the room was completely dark, the turtles had a tendency to swim head on into the waves, and also toward magnetic east. Once they have reached the ocean, the joint influence of these tendencies would then lead them to the Gulf Stream.

Long travelling insects have even less possibility to prove their free will. One of the most spectacular examples concerning large-scale insect migration is provided by the North American monarch butterfly Danaus plexippus (Brower, 1985; Wehner, 1997). From late August to early September, millions of monarchs leave their breeding sites in the eastern United States and Canada to migrate up to 3600 km to their overwintering sites in the high-altitude forests of central Mexico. Some individuals may travel 130 km per day. The return migration is completed by two or more short-living breeding generations. The role of different sensory cues have been discussed in migrating movements of butterflies such as the use of magnetic fields and sun-compass mechanism but it is most likely that these insects explore soaring using tailwinds. It seems reasonable that the overall migration pattern of monarch butterflies would not have evolved in the absence of large-scale weather patterns prevailing above North America. Rapid microevolutionary change has occurred in monarchs after they were introduced to Australia, together with their milkweed food plants. In contrast to their North American ancestors, the Australian butterflies have reversed the timing and direction of their migratory behaviour by 6 months and 180⁰, respectively (James, 1993; Wehner, 1997).

There is still a room for flexibility and decision making for these migrating insects. They must actively embark on air currents by launching themselves into the air at the right time, and must exploit lift by soaring in thermals, but should do so only when there is wind in the appropriate direction. They must also select the right flight vectors and control the track vectors by visual contacts with the ground. They also adjust their headings so as to compensate for wind drift.

In several bird species the way has been revealed in which learning interacts with endogenous processes in order to influence the direction of migration. At the same time results of many experiments with the birds being displaced a long distance from their home and then having reached places when they were born still remain a riddle (see Able, 1980; Pearce, 2000 for details). As it has been recently have been formulated (Ens et al., 1990; Piersma, 1994), upon departure and en route the birds must make a number of deliberate decisions. They must decide when to depart, at which altitude to fly, how to adjust their air speed and what heading to keep relative to the wind. We do not yet possess a relevant idea about how the birds switch from one decision to another and how do they integrate behavioural patterns into united process of migration. Finally, a “simple” question remains unclear, namely, are the birds innately informed about what directions to steer and what distance to cover.

The second part of this question can be answered, at least partly, by the example of European warblers travelling from their Palearctic breeding areas to various parts of Africa. The warblers exhibit a fairly sharp “migratory division”, with the western German and the eastern Austrian birds flying south-westwards and south-eastwards respectively. Studies of inexperienced, hand-raised birds tested in orientation cages at the time of day and year when they would normally migrate clearly show that the first-year migrants possess and use an innate vector programme. In cross-breeding experiments the first-generation offspring of mixed pairs of south-westwards and south-eastwards migrants choose migration directions that are in between of those of their parents (Helbig, 1994).

Although this is clear that the birds accomplish their endogenous vector programmes, these patterns seem to be rather flexible with respect to both migratory distance and direction. Within three to four decades, which have been characterized by progressively milder winter seasons, a fraction of the south-west migrating population has shifted its vector course and established new winter quarters in Britain (Berthold et al., 1990). As in the example with monarch butterflies cited above, the microevolutionary processes interact here with some displays of behavioural flexibility.