Relationship between compass systems of orientation in equatorial sandhoppers

I investigated the relationship between the sun compass and the magnetic co mpass in zonal orientation of the equatorial sandhopper Talorchestia marten sii. I carried out experiments in Kenya, in a confined environment, during the equinoctial phase, in which it is theoretically difficult to use the su n as an orienting cue because of the marked variation in the hourly azimuth al speed and zenithal distance. My results show that the sun compass and th e magnetic compass coexisted but were not always used contemporaneously or, at least, did not have the same importance. At the equinox this depended i n large part on the height of the sun: when the zenithal distance was < 10 degrees the magnetic compass prevailed. The relationship between the two co mpass mechanisms revealed in the present study overcomes the problem of the need to postulate a differential compensation for the apparent motion of t he sun by equatorial sandhoppers. (C) 2001 The Association for the Study of Animal Behaviour.