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Abstract

Seasonal and lifetime spatial movements were studied in the field in a large number of marked individuals. Most snails were resident, each within a small part of the suitable habitat. Three different types of spatial movement patterns could be recognized. Characteristic of most snails were radiating movements between permanent core areas in the wood and principal feeding areas in glades, and sometimes explorations. The duration of the excursions was usually between a week and a month. Two different return strategies seem to exist in Helix, one adapted to the utilization of known habitats within the home range, and one adapted to secure site fidelity. Explorations were usually shorter than the critical homing distance and thereby the risk of disorientation was reduced. Juveniles spent much time in feeding areas maximizing growth, whereas adults in midsummer spent much time in the wood thereby probably increasing the chance of survival for next year's reproduction and of exploring new feeding areas. It seems that a rather permanent home range develops from birth on through unlearned orientation responses, exploration, topographic learning and return movements. Some individuals in the study area were extremely stationary, others used an exploratory strategy and increased their home ranges with new feeding areas. The exploratory strategy of resident snails may be an investment which pays off if the suitability of the habitat decreases. There is some evidence that different feeding places are assessed and that a home range can be partially changed according to this. Snails in one habitat of decreasing quality showed a relatively high emigration frequency. They used one of two different strategies: Exploration and gradual home range displacement, or exploration and sudden emigration over a relatively long distance. Emigrants always settled in a good snail habitat, and habitat assessment is probably part of both strategies. Non-strategic, “accidental” emigration also occurred. No evidence of age-dependent dispersal was found. Relevant parts of the animal migration model presented by Baker (1978) are confirmed.