TY  - BOOK
AU  - Johnson, Ned K.
TI  - Character variation and evolution sibling species in the Empidonax difficilis-flavescens complex (Aves : tyrannidae)
T2  - University of California publications in zoology ; vol 112
SN  - 0520095995
PY  - 1980///
CY  - Berkerly
PB  - University of California Press
KW  - Birds
N1  - Acc. No. 07967
ER  -