Ethology 77, 3OC-316 (1988) zyxwvut 0 zyxwvut 1988 Paul Parey Scientific Publishers, Berlin and Hamburg ISSN 0179-1613 zyxwvutsr Dipartimento di Biologiu Animale e Genetica dell’ Universita, Florence zy Locomotor Activity in the Freshwater Crab Potamon zy fluviatile: The Analysis of Temporal Patterns by Radio-telemetry FRANCESCA GHERARDI, FEDERICA TARDUCCI & MARCO VANNINI With 12 figures Received: September 23, 1986 Accepted: May 13, 1987 (W. Pflumm) Abstract Locomotor activity in a field population of the freshwater crab, Potamon fluviatile, was studied during the breeding season by means of radio-telemetry and by direct counts of active animals along a transect of the stream. The basic pattern of crabs’ locomotor activity can be described as a sequence of short distance movements around the shelters (foraging movements), followed by rarer long distance displacements (wandering movements). Whilst direct counting showed that the crabs exhibit a broadly nocturnal rhythm in foraging movements, no daily periodicity in wandering activity was revealed by telemetry. There is sexual difference in these latter excursions: females move farther along the stream and into the surrounding terrestrial habitat than do males. This behaviour is in contrast to observa- tions made during the non-breeding season and is probably related to the stage of female reproduc- tion. Introduction Locomotor rhythms have been extensively investigated in decapods (DE COURSEY 1983; WEBB 1983). Most of these studies were performed in the laborat- ory and centered around the basic question of biological clocks (DE COURSEY 1976; NAYLOR & HARTNOLL 1979), whilst description of movement in the field and information as to its adaptive value have very often been neglected. Furthermore, as ATKINSON & NAYLOR (1973) observed, studies have often been conducted with the animals kept in atypical surroundings, and consequently z U.S. Copyright CIearancc Center Code Sraremenr: 01 79-1613/88/7704-0300$02.50/0