Summary: Using the concept of sample coverage, we derive an approximation of the bias in the Jolly-Seber population size estimators [\textit{G. M. Jolly}, Biometrika 52, 225-247 (1965; Zbl 0141.366); \textit{G. A. F. Seber}, ibid., 249-259 (1965; Zbl 0141.366)] due to heterogeneity of capture probabilities. The resulting bias is expressed as a function of sample coverage, average capture probability, and the coefficient of variation of individual capture probabilities. The effect of unequal catchabilities on the Jolly-Seber survival rate estimators is also briefly discussed. We propose new population size estimators which incorporate the heterogeneity of capture probabilities. A simulation study investigates the performance of the approximation formulas of biases and the proposed estimation procedure. A real data set of male black-kneed capsids illustrates the method.