Fig. 1.

Songs in sympatry are more different from songs in allopatry. (A) P. bilineatus is typically larger than (B) P. subsulphureus. (C–F) Spectrograms are examples of the species' mean song frequencies for allopatric P. bilineatus at Wakwa (C), sympatric P. bilineatus at Mabira Forest (D), sympatric P. subsulphureus song at Obala (E), and allopatric P. subsulphureus song at Budongo (F). The Africa map illustrates the species' distributions. P. bilineatus completely encompasses the range of P. subsulphureus, but in lowland rainforests P. bilineatus is rare. Site locations are illustrated for P. bilineatus in allopatry (white circles); P. subsulphureus in allopatry (black circles); P. subsulphureus common, P. bilineatus rare, and thus effective allopatry for P. subsulphureus but sympatry for P. bilineatus (black circles with white dots); P. bilineatus common, P. subsulphureus rare, and thus effective allopatry for P. bilineatus (white circles with black dots); and both species common in sympatry (half-filled circles). [Tinkerbird illustrations are by Nik Borrow, from Birds of Western Africa (38), by Nik Borrow and Ron Demey, with permission from the publishers, Christopher Helm, London.]