We define fecundity as the number of offspring per adult bird in the population. \citet{Garcia_Heras_2016} observed that 31% of 223 monitored Black Harrier nests failed to produce any offspring and that the average number of chicks produced by a nest was 1.65 (n = 222). The maximum number of offspring observed was four. In addition, \citet{Garcia_Heras_2019} observed that only 2 out of 11 tracked birds bred successfully. This suggests that the number of breeding pairs (as opposed to nests) with no offspring may be higher than the 31% estimated during nest monitoring.