What scatter-hoarding animals have taught us about small-scale navigation

Abstract

Many animals use cues for small-scale navigation, including beacons, landmarks, compasses and geometric properties. Scatter-hoarding animals are a unique system to study small-scale navigation. They have to remember and relocate many individual spatial locations, be fairly accurate in their searching and have to remember these locations for long stretches of time. In this article, we review what is known about cue use in both scatter-hoarding birds and rodents. We discuss the importance of local versus global cues, the encoding of bearings and geometric rules, the use of external compasses such as the Sun and the influence of the shape of experimental enclosures in relocating caches or hidden food. Scatter-hoarding animals are highly flexible in how and what they encode. There also appear to be differences in what scatter-hoarding birds and rodents encode, as well as what scatter-hoarding animals in general encode compared with other animals. Areas for future research with scatter-hoarding animals are discussed in light of what is currently known.

Figure 1.

(a) The caching arena in Vander Wall (1982) during control (solid lines) and during landmark-shift (dashed lines) conditions. (b) The distance between a probe and the nearest cache on the y-axis as a function of the original position of the cache in the x-axis. Line A represents cache recovery and line B represents the expected ΔX if birds use the shifted objects as cues. Therefore, if the birds followed a shift, a ΔX score of 20 cm would be expected. Adapted from Vander Wall (1982).

Figure 2.

(a) Diagrammatic representation of the logic of one trial associative tasks. (i,ii) Figures showing training trials. One of the stimuli is randomly designated correct on each trial (with new, ‘trial-unique’ stimuli used for each trial). The bird is then rewarded when it chooses the correct stimulus (in this case the dot-filled star). The display then disappears for a retention interval, and the same display is presented for choice, and the bird is rewarded for choosing the same stimulus. (b) (i,ii) Once training is complete, the bird receives occasional dissociation test trials. These trials differ from training trials in that the spatial locations of two of the stimuli are switched. If the bird chooses the same visual stimulus (the dot-filled star, in this case), this indicates control by the stimulus. But if the bird chooses the old location (the hexagon), it suggests spatial control. Spatial location and visual stimulus have been dissociated.

Figure 3.

Typical set-up (not to scale) for experiments on landmark displacement with an edge and a single landmark present. The birds are initially trained with the cylinder in the location indicated by the solid circle (top right in the inset with perspective of looking down from above). They are then tested with occasional non-rewarded trials at each of the three test positions (dashed circles), representing displacements perpendicular, parallel and diagonal to the long axis of the nearest edge.

Figure 4.

The star (G) is the goal location and A, B, and C are three landmarks. The direction from the goal to a landmark (e.g. GA) is an absolute bearing. The length of GA is the goal–landmark distance. The arcs between the landmarks (e.g. AB) represent relative bearings.