Saw this AUK article posted on-line and thought someone might be
interested in it:

Rangewide Population Genetic Structure of Xantus's Murrelet
(Synthliboramphus hypoleucus)
Tim P. Birt, Harry R. Carter, Darrell L. Whitworth, Anne McDonald, Scott
H. Newman, Franklin Gress, Eduardo Palacios, Josh S. Koepke, and Vicki L.
pg(s) 44-55

Population genetic structure was characterized in Xantus's Murrelet
(Synthliboramphus hypoleucus) by analyzing variation in the mitochondrial
control region (505 samples) and 12 microsatellite loci (428 samples) in
birds captured at all 13 current breeding areas in southern California and
northwestern Baja California, Mexico. The two types of molecular markers
were consistent in revealing strong genetic differentiation between the
two currently recognized subspecies (S. h. hypoleucus and S. h. scrippsi)
and little or no differentiation among breeding areas within subspecies.
Estimates of gene flow were essentially zero, and no evidence for
admixture was found. Gene flow among breeding locations within subspecies,
on the other hand, was seemingly high. Given these genetic results, as
well as clear morphological differences between the subspecies and the
apparent lack of interbreeding at breeding areas where the two forms are
sympatric, we suggest that two species be recognized. Both forms are
genetically distinct from Craveri's Murrelet (S. craveri), a closely
related species whose breeding range partially overlaps that of Xantus's
Murrelet. Taxonomic subdivision of Xantus's Murrelet introduces new
conservation concerns, especially for S. h. hypoleucus, which urgently
requires greater study and protective efforts.

I understand the AOU Checklist committee will be reviewing this proposed split.

Ian Paulsen