Study species and sample collection
Tinkerbirds are African barbets (Lybiidae) that while omnivorous, feed
primarily on fruit, and have a particular preference for mistletoe
(Godschalk, 1985; Dowsett-Lemaire, 1988). Species in the genus differ
subtly in plumage characters in spite of millions of years of divergence
in mitochondrial DNA (mtDNA) between currently recognised sister species
(Kirschel et al., 2009; Kirschel et al., 2018; Nwankwo et al., 2018;
Nwankwo et al., 2019). P. pusillus pusillus (hereafterpusillus ) and P. chrysoconus extoni (Layard, 1871)
(hereafter extoni ) are the subspecies of red-fronted and
yellow-fronted tinkerbird, respectively, that meet at a contact zone in
southern Africa (Monadjem et al., 1994). They differ in plumage
characters beyond the forecrown colour in the yellower supercilium and
dorsal streaking in pusillus – whiter in extoni , the
deeper amber and greater percentage of carotenoid pigment over melanin
pigment on the wing coverts in pusillus – paler yellow and more
black in extoni (Fig. 1). The two species might also differ more
subtly in underpart coloration, such as in throat and breast colour
(Hockey et al., 2005).
Fieldwork was performed at 16 sites across the contact zone where
subspecies extoni and pusillus meet in southern Africa.
Fieldwork took place in Tanzania June – September 2013, and in South
Africa and Eswatini in March and December 2015, and January – February
2017. Methods used to obtain DNA and feather samples have been
previously described (Nwankwo et al., 2019). Briefly, 79 birds were
caught in mist nets and ringed, of which 37 were from within the contact
zone. Blood samples were obtained via venepuncture of the brachial vein,
and crown feathers were plucked and placed in envelopes for spectral
reflectance analysis in the lab. Photographs of 78 birds were taken from
several angles using either a DSLR Camera or smartphone for subsequent
plumage scoring. Fieldwork was performed with ringing permits obtained
from SAFRING, Eswatini’s Big Game Parks, Mpumalanga Tourism and Parks
Agency, the Game and Fauna Service of Cyprus, and with research and
collecting permits from the respective authorities (see
Acknowledgements).