Detailed information is still lacking on structure and duration of calls of diurnal birds of prey as well on their vocal repertoire. The Lanner Falcon (Falco biarmicus) is considered a shy less-vociferous species but no quantitative data exist. Field evidence demonstrates that in the last decades this falcon did not improve its threatened status in Italy. We investigated call frequencies and their durations to ascertain the effectiveness of these signals, especially during the breeding season. In particular, if calls are honest signals about the genetic quality of males. We carried out this study during two breeding seasons in eastern Sicily where we monitored 25 nesting attempts at 19 breeding sites. During 114 observational sessions, we recorded (1) which sex uttered calls, (2) type of vocalisation (wailing and creaking calls) and (3) bird positions (flying or perched). In addition, we recorded duration of each vocal event because it seems to be significantly correlated with male quality. We checked nests annually to ascertain the number, age and gender of nestlings. Lanner mates employ calls mainly in crucial reproductive stages (courtship, incubation, the first week after hatching and when young are fledging) optimising their efforts. In addition, males performing shorter vocal events produce broods significantly smaller in size and with a sex ratio biased towards females. In addition, they seem to desert the breeding site in the subsequent year. We suppose that in Italian fragmented breeding populations of Lanners, call structure and rates can predict population viability.