We analyzed the capability of a blindfolded California sea lion to discriminate objects differing in size and/or shape by active touch with its mystacial vibrissae. In a two-alternative forced-choice procedure, equilateral triangles and disks with surface areas ranging from 60 to 0.5 cm 2 served as stimuli. The determination of size difference thresholds (&5') for the discrimination of triangles revealed that the animal was capable of discriminating size differences as low as 2QOI6. Presented with triangles and disks having identical surface areas, the sea lions' discriminations relied on the apparent size difference of~34% between the longest measurable lines of both shapes (side length> diameter). When this size difference was reduced to :55%, the sea lion needed visual information about the shapes before it was able to discriminate them tactually. When the size of these shapes was gradually reduced, the animal was able to make the discrimination down to a longest measurable line of both shapes of 1.70 em. This tactual performance comes close to that achieved by mammals with prehensile tactile organs.

No abstract

No abstract

The present study analyzed haptic abilities of four squirrel monkeys. Using a two-alternative forced-choice procedure, stimuli were presented in a visually opaque box, allowing unrestrained test subjects to grab through a small opening and touch the discriminanda. Difference thresholds were determined by a modified method of limits. In the first experiment we determined size difference thresholds for the discrimination of circular cylinders using standard stimuli differing in diameter from 10 mm to 35 mm. In the second experiment a texture difference threshold was obtained for the discrimination of grooved surfaces (groove width 2-7 mm). The squirrel monkeys achieved a mean size difference threshold of 8% stimulus difference. The linear increase of absolute thresholds as a function of the starting stimulus size showed that haptic size discriminations in squirrel monkeys correspond to Weber's law. Three of the animals achieved a texture difference of 10% stimulus difference, while one monkey showed a distinctively lower haptic acuity. An analysis of the exploratory behavior points to a subject-related difference in the significance of cutaneous and kinesthetic information during size discriminations. Whereas differences in the animals' exploratory behavior did not correlate with the size difference threshold a subject achieved, different thresholds for texture discrimination can be explained by the different exploratory procedures the monkeys used to touch grooved surfaces. The low difference thresholds determined for the squirrel monkeys in the present study point to the significance of unrestrained test conditions for the assessment of the haptic capacity of a species.

-In this study the efficiency of bee traps used to evaluate mortality in a bee colony and their influence on undertaking behaviour was tested in twelve colonies of Apis mellifera L. Four types of bee traps (Original-Gary-Trap, a Modified-Gary-Trap, the IPSAB-Trap and the Muenster-Trap), commonly used in practical research, were compared to each other and to control colonies without a trap. The use of different bee traps led to incomparable results. In the Original-Gary-Trap, many stray bees were trapped and eventually died within the glass collecting jars, leading to artificially high estimates of mortality. Bees removed the dead bees from the Modified-Gary-Trap, especially during good flight conditions. Dead bees disappeared from the IPSAB-Trap because of predators and wind. Both Gary-Traps had a negative effect on undertaking behaviour; the number of behavioural components involved in removing a dead bee from the colony was large and thus, undertaking took a long time. In IPSAB-Trap, the undertaker bees showed the same number of behavioural components and took similar times to remove dead bees as the control colonies without traps. The newly developed Muenster-Trap, equipped with an easily accessible hive entrance, a collecting box for dead bees and an outlet for stray bees, gave a significantly improved performance.Apis mellifera / undertaking behaviour / bee traps / mortality evaluation 315 Apidologie 33 (2002) 315-326