Hawkins • THE 'FIRST BASIC PROBLEM' REVISITED 
411 
TABLE 1. Proposed interpretations of the H-P system. 
Issue 
H-P System 
Proposed interpretations 
Numbering of prebasic molts and 
basic plumages ('first basic 
problem') 
Definition of the 'first molt cycle' 
Consecutive, starting with the Consecutive, starting with the conventional first 
conventional first prebasic molt prebasic molt and tirst basic plumage, 
and first basic plumage, if present whether or not present 
(e.g., Howell el al. 2003) 
None' The period starting with commencement of the 
initial acquisition of contour feathers and ending 
with commencement of (1) a unilormly- 
complete first prebasic molt that has equivalent 
timing as subsequent prebasic molts, if 
applicable, or (2) the second prebasic molt 
molt strategies identified by Howell et al. (2003), 
which 1 maintain can be identified with conven¬ 
tional molt terminology. 
RE-EVALUATION OF 
HOWELL ET AL. (2003) 
The goal of the H-P system was to provide a 
system of naming molts and plumages that could 
be applied broadly across taxa to reflect both 
interspecific homologies (i.e., molts and plumages 
that are similar because of shared ancestry) and 
intraspecific homologies (molts and plumages that 
occur within an individual at different stages in its 
life cycle but result from a similar genetic 
program or physiological process) (Humphrey 
and Parkes 1959, 1963; Rohwer et al. 1992). The 
truth regarding these homologies is unknown 
because we cannot precisely reconstruct evolu¬ 
tionary history and do not have a full understand¬ 
ing of the genetic and physiological processes that 
control molts and plumages (Thompson 2004. 
Dawson 2006). However, we can make strong 
inferences about interspecific and intraspecific 
homologies, particularly in the case of closely- 
related species, by comparing the relative timing 
and extent of molts, and the color and pattern of 
the resulting plumages (Rohwer et al. 1992. 
Thompson 2004). 
Howell et al. (2003) shared Humphrey and 
Parkes’ goal of naming molts and plumages based 
on presumed homologies, but their modifications 
to the H-P system are primarily concerned with 
placing all birds on the same numbered molt 
cycles and ensuring the first molt cycle has a 
duration that is similar to subsequent molt cycles. 
Definition of 'Molt' 
Humphrey and Parkes (1959:6) defined ‘molt' 
as "the normal shedding of feathers and the 
replacement of most or all of these by a new 
generation of feathers". Under this and similar 
definitions (e.g.. Campbell and Lack 1985, 
Ehrlich et al. 1988), avian molt is a physiological 
process that involves feather loss and feather 
growth. 
Humphrey and Parkes (1959) started their 
analysis of plumage succession at the time of loss 
of juvenal plumage and did not address prior 
acquisitions of feathers in a subsequent article as 
they intended. Humphrey and Parkes (1959) thus 
did not discuss an interpretive issue with their 
definition of ‘molt* in the case of the initial 
acquisition of feathers (natal down or juvenal 
plumage, as applicable). Under the definition ol 
‘molt’ in Humphrey and Parkes (1959). taxa with 
a natal down undergo a prejuvena! molt because 
(he growth of juvenal plumage replaces shed 
feathers (i.e., natal down). However, many taxa do 
not have a natal down, including all Piciformes, 
many Psittaciformes, most Coraciiformes, and 
some Corvidae (Jcnni and Winkler 2004), and do 
not undergo a projuvcnul molt because the growth 
of juvenal plumage does not replace shed feathers. 
This discrepancy may he addressed by defining 
‘molt’ as "the normal and regular growth of 
feathers by which plumages are attained", which 
is the definition of this term adopted by Howell et 
al. (2003: 636) without explanation, Howell et al. 
(2003) likely eliminated the requirement of 
feather loss in the definition of ‘molt* to maintain 
that taxa that lack a natal down have a prejuvenal 
molt that is equivalent with definitive prebasic 
molts. Another result of their approach is ihe 
initial acquisition ot natal down occurs hy molt 
even though it does not replace shed leathers. 
Humphrey and Parkes (1959. 1963) emphasized 
the growth aspect of the molt process and believed 
that loss of the previous generation of feathers is a 
