Erratum to: Behav Ecol Sociobiol

DOI 10.1007/s00265-011-1306-z

The original version of this article unfortunately contained a mistake. The factor in the denominator of the third equation is missing.

Please see the correct equation below.

$$ {{\widehat{k}}_p} = \frac{{{{{\widehat{\lambda }}}_f}}}{{{{{\widehat{\lambda }}}_p}}} = \sqrt {{\frac{{\left( {{{\Sigma }_i}{{k}_i}} \right)\left( {{{\Sigma }_i}{{l}_i}} \right)\left( {{{\Sigma }_i}\pi x_i^2} \right)}}{{{{n}^2}\left( {\frac{1}{2}{{\Sigma }_i}\pi y_i^2} \right)}}}} $$