Greenlaw and Post • SALTMARSH SPARROW SEXUAL BEHAVIOR 
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apparently was fairly easy on the ground but not on 
perches. All forced mountings that we observed by 
Saltmarsh Sparrows were on the ground, where the 
elongation of their cloacal protuberances may 
secondarily facilitate cloacal contact in passive 
females. 
If males do not achieve cloacal contact during 
forced mountings because females arc not coop¬ 
erating. their mounting behavior may still be a 
measure of their ability to successfully suppress 
female resistance. Their success may be affirmed 
vocally by post-mounting flight singing. The 
information gained by females about local males 
during meet-and-pounce interactions may be used 
when they are fertile to selectively choose mating 
partners. Male ability to suppress female resis¬ 
tance varied from non-involvement at multi-male- 
female meets (’watchers') and giving up during a 
mounting effort with female resistance, to suc¬ 
cessful mounting despite resistance. Such behav¬ 
iors may represent variation in male quality of 
importance to females in a promiscuous mating 
system in which forms of male dominance 
polygyny have not evolved. 
The primary support for the hypothesis of 
forced mating in Saltmarsh Sparrows is indirect 
evidence provided by very large cp (this paper) 
and testis sizes (Rising 1996) of males. The direct 
relationships between cp size versus sperm 
storage (Birkhead el al. 1993) and testis size 
versus copulation frequency (Moller and Briskie 
1995) in passerine birds are well established. 
Greatly enlarged cps and testes in males implies 
strong sperm competition (Birkhead and Mol let 
1992, Moller and Briskie 1995). Extreme testes 
sizes among passerines of similar body sizes are 
found in polygynandrous Smith's Longspur (C«/- 
cariuspictus), promiscuous sharp-tailed sparrows 
of both species, and obligatcly polygynous Lark 
Buntings (Calamospiza melanocorys) (Rising 
1996) . We suggest these morphological or 
anatomical adaptations (Briskie 1993) would not 
be as strikingly enlarged as they are in these 
species unless rates of solicited copulations were 
high (Birkhead et al. 1993). We believe we would 
have noticed the behavior more often than we did 
under our field protocols if solicited copulation 
rates were unusually high in Saltmarsh Sparrows. 
Apparently, solicited extrapair copulations from 
one or a few males are widespread in socially 
monogamous passerines, but none of these species 
exhibit extreme development of testis or cp sizes 
(Birkhead et al. 1993, Rising 1996, Stutchbury 
and Neudorf 1998). Thus, forced mating seems to 
be the only behavior in Saltmarsh Sparrows that 
might account for extreme testis and cp sizes in 
the species. 
We provide evidence for female control of 
forced mounting attempts by male Saltmarsh 
Sparrows. Nearly two-thirds of the pounce events 
reported in our study were thwarted by female 
resistance or aggressive calling. Under the 
hypothesis of female control, female resistance 
is viewed as a manipulative tactic rather than cost- 
reducing behavior (Westneat and Stewart 2003). 
Female resistance as cost-minimization implies 
little advantage to males that simply suppress 
female aggression and then fly off without 
prospect of future benefit. However, females that 
use information gained by their resistance to favor 
successful males later when females solicit 
copulations may be practicing a form of mate 
choice based on male vigor and persistence during 
forced mountings. Thus, although speculative, 
female control of unsolicited mountings in Salt¬ 
marsh Sparrows may involve some element of 
female choice later during her fertile period. 
Overall, the behavior described in our study under 
forced mating and female control hypotheses 
imply that extreme levels of mulli-parented 
broods in Saltmarsh Sparrows (Hill et al. 2010) 
may best be understood by the promiscuous 
behavior exhibited by both males and females. 
However, we cannot exclude the view that 
females selected to solicit matings from multiple 
males also can explain extreme levels of multi- 
parented broods in the absence of fertilizations 
during coerced mountings by males (Hill et al. 
2010 ). 
Evolution of Mating System .—Saltmarsh Spar¬ 
rows exhibit a highly derived social system. 
Several authors have offered views on the 
evolution of tidal marsh sparrows (Beecher 
1955. Greenlaw 1993. McDonald and Greenberg 
2006, Shriver et al. 2007), and others have 
identified specific social or ecological factors that 
may have been important during the evolution of 
sharp-tailed sparrows (Murray 1969, McDonald 
and Greenberg 2006. Shriver et al. 2007. Hill et al. 
2010). The marshland sparrows form a well- 
corroborated monophyletic group (Klicka and 
Spellman 2007). The conditions that favored the 
evolution of apparent scramble competition po- 
lygynv in Saltmarsh Sparrows may he elucidated 
by considering the behaviors of its closest 
relatives. Seaside Sparrow (A. maritimus) and 
