Reproductive characteristics of the black-tailed brush lizard, Urosaurus nigricaudus (Phrynosomatidae)

The reproductive characteristics of Urosaurus nigricaudus at El Comitan, Ba ja California Sur, Mexico, were determined through the necropsy of 33 males and 60 females during 1992. The average size of clutch per female was 4.06 +/- 1.86 eggs; 3.58 eggs for the first clutch and 4.75 eggs for the second clutch. Testicular size exhibits two peaks, one each in May and August. Fe male and male reproductive cycles are synchronized. In comparison with othe r Urosaurus species, U. Nigricaudus is atypical because males have two peak s of testicular mass.