Time spent by males investigating flank-gland secretions of two different donor females in four conditions. The male was habituated to the odors of the first female and then tested in a dishabituation trial with the odors of a second female: (a) both female donors were in estrus; (b) both female donors were in diestrus-2; (c) the first female was in diestrus-2 and the second female in estrus; (d) the first female was in estrus and the second female in diestrus-2. E, estrus; Di, diestrus-2; *, P < 0.05; **, P < 0.01; ***, P < 0.001.