 The red @-@ billed chough 's loud , ringing chee @-@ ow call is clearer and louder than the similar vocalisation of the jackdaw , and always very different from that of its yellow @-@ billed congener , which has rippling preep and whistled sweeeooo calls . Small subspecies of the red @-@ billed chough have higher frequency calls than larger races , as predicted by the inverse relationship between body size and frequency . 
