APPROACHING AND DEPARTING BEES LEARN DIFFERENT CUES TO THE DISTANCE OF A LANDMARK

Bees learn both the absolute distance and the apparent size of landmar ks in the vicinity of a foraging site. They learn about landmarks both when approaching and when leaving the site. Whereas learning on arriv al can take place on every visit to the food source, learning on depar ture is limited to the first few visits, when the bee Turns Back and L ooks (TBL) at the feeder in a stereotyped manoeuvre before flying off. We investigated whether one specific function of TBLs is to acquire i nformation about the absolute distance of landmarks from the feeding s ite. Bees were trained to forage from a feeder which lay at a fixed di stance from a cylinder. During training, bees were exposed to the cyli nder either only while they approached and landed on the feeder, or on ly on their departure from it, or at both of these times. Tests on tra ined bees immediately after the TBL phase revealed that those bees whi ch had viewed the cylinder only on arrival had learnt the apparent siz e of the cylinder, but not its distance from the feeder. In contrast, bees which saw the cylinder on departure had learnt its absolute dista nce. They also learnt the cylinder's apparent size, provided that the cylinder was close to the feeder. Bees which had viewed the cylinder o n arrival as well as on departure learnt both absolute distance and ap parent size. Distance dominated the bees' behaviour in the initial pha se of learning, apparent size was more important later on. We suggest that early during learning bees need information about the 3-D structu re of the environment so that they can identify those landmarks close to a foraging site which will specify accurately the site's position. This information is acquired during TBLs. Later, landmark guidance can be achieved by 2-D image matching.