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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 124. No. 2. June 2012 
Nelson's Sparrow. The former speeies is socially 
monogamous (Greenlaw and Post 1985, Hill and 
Post 2005). while the latter has a derived social 
system that hears some similarity to that of the 
Saltmarsh Sparrow, hut differs in the species’ 
practice of apparent male dominance access to 
females and mate guarding (Greenlaw and Rising 
1994, Shriver et al. 2007). The condition ancestral 
to the derived systems of the sharp-tailed 
sparrows almost certainly was social monogamy, 
in which male mate guarding and extrapair 
fertilizations were important adjunct mating 
tactics. Any plausible model for the evolution of 
social behavior must be able to account for a suite 
of related questions that address both species of 
sharp-tailed sparrows, and account for develop¬ 
ment ot promiscuity and sperm competition, loss 
of territoriality, disappearance of pair bonding, 
and absence ol paternal care. Considering the 
phylogenetic history of the group (Klicka and 
Spellman 2007), we suggest dial social evolution 
occurred in a two-step process in the sharp-tailed 
sparrows (Greenlaw 1993. model B). As yet, we 
do not have a single synthetic model that meets all 
these criteria and provides insights into the 
evolution ol the social system of Saltmarsh 
Sparrows. Much work remains to confirm and 
extend our findings, and to understand social 
evolution in these birds. 
ACKNOWLEDGMENTS 
A supplement that details well-observed examples o 
social interactions in Saltmarsh Sparrows taken from ou 
icld notes is available on request from the authors. W 
thank C. S. Elphiek for his helpful critique durin 
manuscript development. A draft of the manuscrip 
benefited from the comments and suggestions by (’ p 
Hraun and two anonymous referees, to whom wc an 
grateful. The work reported here was supported bv Nutiona 
Science Foundation Grant # HNS 77-07314 and b v fund 
rom the C. W. Post Research Committee of Long Islam 
University We thank the Long Island State Park Commis 
s.on and the Town of Babylon for allowing access to ou 
study areas. 
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