Springer et al • CHANGES IN WHITE-THROATED SPARROW MUSCLE 
119 
sition associated with migratory condition. How¬ 
ever, the lack of adults in the captive study may 
have precluded observation of the seasonal pattern 
demonstrated by wild birds. It is also possible the 
photoperiod manipulation caused the birds to 
display classic migratory behavior (Zugunruhe 
and hyperphagia), yet was not sufficient alone to 
induce changes in the PC/PE ratio. Seasonal 
changes to the PC/PE ratio may only be induced 
by the higher intensity training of migratory flight 
itself, rather than pre-migratory conditioning, as 
suggested previously for membrane fatty acid 
composition (Price et al. 2010). A training effect 
is plausible, given that Gorski et al. (1999) found 
that PE increased relative to PC in the red 
gastrocnemius muscles of rats after exercise 
training. 
Klaiman et al. (2009) concluded that diet was a 
greater factor than exercise or migratory condition 
in producing the patterns they observed in their 
study of seasonal changes in membrane fatty acid 
composition in White-throated Sparrows. Diet can 
atfect phospholipid class composition as well 
(Innis and Clandinin 1981), and could explain the 
current results from wild birds, but only if adults 
and juveniles forage in different ways during 
winter. This is also supported by the high PC/PE 
ratios observed in the captive sparrows (relative to 
wild sparrows), as they were fed the same 
commercial diet that may differ from natural 
lorage. Our study indicates that composition of 
phospholipid classes in muscle membranes can 
var y seasonally, but data linking phospholipid 
class compositional changes directly to migratory 
exercise or migratory condition, rather than diet 
variation, remain equivocal. 
ACKNOWLEDGMENTS 
fhis work would not be possible without the organization 
Stance of collaborators D. J. Cerasale and D. M. 
^jac. We thank J. T. McFarlan for help with field work. 
ar > Gartshore and Peter Carson generously provided 
p CC ^ ss t0 ^eir land and other assistance. Paul Hammil and 
Moore aided our fieldwork and provided a collection 
Permit for wintering birds. C. L. Milligan provided valuable 
^'* ce an( l criticism. Funding was provided to CGG by an 
• kC Canada Discovery Grant, the Canada Foundation 
| 0r Innov ation, and the Ontario Ministry of Research and 
^novation. 
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