Population Biology of Meroles anchietae and an Elusive Sex Ratio

We conducted seven multiple-day capture-recapture surveys of a population of shovel-snouted Lizards, Meroles anchietae, near Gobabeb, Namibia, from 1997–2009. During most sampling days and over the course of an entire survey year, we captured significantly more males than females. However, for marked individuals with accumulation of more sampling days, the sex ratio reached 1:1 in all but two survey years. Field observations showed that males were active on the surface more frequently and for longer periods of time than females. However, females had higher field metabolic rates when scaled to mass. Subsequent modeling of survivorship, probability of detection, and population estimates using Program MARK and behavioral observations support the hypothesis that sex ratio was 1:1 and that the apparent discrepancy was the result of different foraging modes between sexes. Our results indicate that short-term, single surveys may not be reliable for estimation of population variables and sex ratio.