 The female corn crake may give a call that is similar to that of the male ; it also has a distinctive <unk> sound , similar in rhythm to the main call but without the grating quality . The female also has a high @-@ pitched <unk> call , and a oo @-@ oo @-@ oo sound to call the chick . The chicks make a quiet <unk> @-@ <unk> contact call , and a <unk> used to beg for food . Because of the difficulty in seeing this species , it is usually <unk> by counting males calling between 11 pm and 3 am ; the birds do not move much at night , whereas they may wander up to 600 m ( 660 yd ) during the day , which could lead to double @-@ counting if monitored then . <unk> individual males suggests that just counting calling birds <unk> the true count by nearly 30 % , and the discrepancy is likely to be greater , since only 80 % of males may call at all on a given night . The corn crake is silent in Africa . 
