Movement patterns of an invasive crayfish, Procambarus clarkii, in a temporary stream of southern Portugal F. GHERARDI 1,3 , E. TRICARICO 1 and M. ILHÉU 2 1 Dipartimento di Biologia Animale e Genetica, Università di Firenze, Via Romana 17, 50125 Firenze, Italy 2 Departamento de Ecologia, Universidade de Évora, Rua Romão Ramalho 59, 7000- 671 Évora, Portugal Received 15 October 2001, accepted 15 May 2002 Radio-telemetry was used to determine the spatial behaviour of the inva- sive crayfish, Procambarus clarkii (Girard), in a temporary stream in southern Portugal during the dry period. One aim was to understand the behavioural mechanisms that allows crayfish to withstand extreme environmental conditions. This study can also provide data relevant to developing programmes for the pre- vention of this species’ expansion. During a drought, the red swamp crayfish does not aestivate. Except for one female, radio-tagged specimens dispersed within the habitat with a speed ranging 1-11 m·d -1 . A wide inter-individual varia- tion was shown in the extent of locomotion. Locomotory speed was significantly correlated with crayfish size. Movement was not related to sex, the hour of the day, or several abiotic parameters of the habitat, with the exception of the water depth. Movement patterns appeared complex: one or more short peaks of intense locomotion often alternated with periods of slow speed or no movement. Pro- cambarus clarkii maintained its temperature below environmental extremes, largely by occupying burrows or refuges. Although shelters were limiting in the habitat under study, following a move, radio-tracked individuals did not re-occupy the same burrow, but rather entered the first one found vacant. Refined orient- ing capabilities have been described in decapods including crayfish, but in this context homing behaviour seems not to occur. KEY WORDS: movement, invasive crayfish, Procambarus clarkii, temporary streams, radio-telemetry. Introduction . . . . . . . . . . . . . . . . . 184 Methods . . . . . . . . . . . . . . . . . . 184 Results . . . . . . . . . . . . . . . . . . 186 Discussion . . . . . . . . . . . . . . . . . 192 Conclusions . . . . . . . . . . . . . . . . . 194 Acknowledgements . . . . . . . . . . . . . . . 195 References . . . . . . . . . . . . . . . . . 195 Ethology Ecology & Evolution 14: 183-197, 2002 3 Correspondence author (E-mail: gherardi@dbag.unifi.it).