Greenlaw and Fust • SALTMARSII SPARROW SEXUAL BEHAVIOR 
259 
192 male-male encounters among the 512 inter¬ 
actions of this type that we w itnessed (Table I ). 
Wc observed 143 (74.5%) non-agonistic meetings 
between males, in which one or several males 
approached another male and then separated. 4b 
(23.9%) cases of attempted perch takeovers by 
supplants, and three short chases (possible sex 
mis-identification) and two brief fights (1.6%). 
Seventy-nine percent of the perch-takeovers were 
successful and. in most cases, no further interac¬ 
tion occurred. The only agonistic displays that we 
saw during male-male aggressive interactions 
were gaping by a male when it was approached 
too closely by another, or ‘head-forward threats' 
(crouch and bill pointing) that usually forestalled 
a perch takeover. 
Male Sexual Activity in Relation to Female 
Reproductive State.—Wc observed meet-and- 
pounce interactions in all stages of the nest cycle. 
We were able to ascertain the incidence of forced 
mountings in relation to females’ reproductive 
status in 69 cases. We normalized the number of 
observed mountings by the length of the nest 
stages (nest-building lasted 6 days; deposition and 
incubation of eggs. 15 days; care of dependent 
young, 25 days). The highest rate of forced 
mountings, 4.0 mountings/day (»/ 24). occurred 
during nest-building, when females are assumed 
to be fertile. This rate declined to 1.5/day (» : 23) 
during the egg stage, and 0.9/day (n 22) when 
the female was provisioning young. The occur¬ 
rence of forced mountings differed between nest 
stages (x 2 = 23.6. df = 2. P < 0.001). 
Male Dispersion in Relation to Females. —Use 
of space by males was related to locations of 
fertile females (Fig. 2). Male social activity was 
significantly contagious in areas where at least 
one female was nest-building or egg-laying (C'hi- 
square tests, P < 0.01; mean coefficient of 
dispersion D t = 3.2 ± 1.62, n - 29) (Fig. 2). 
Maximum observed I), values were associated 
with female presence near nests under construc¬ 
tion (mean D, = 4.5 ± 1.38. n = II). Males 
usually left Two-calling females alone at such 
times after they met them and were not concen¬ 
trated near their nests in the same area (Fig. 2B). 
The mean D, was 1.9 - 0.92 tn = 18) (e.g.. 
Fig. 2A) on days when no active nests were in the 
focal areas. 
Cloaca! Protuberance. —Breeding male Salt- 
marsh Sparrows have large cloacal protuberances 
(cps). Size of cps increased from a quiescent 
condition at the time residents arrived in late April 
until peak size was reached in mid-May. Volume 
of cps averaged 562.8 ± 12.39 mm’ (n = 156) 
after mid-May. Most (70%) cps were >500 mm 3 . 
Mean protuberance height was notable as well, 
averaging 7.4 ± 0.08 mm. 
The range of cp sizes in young males (11- 
12 months of age, or I yr) included the range of 
older (>l yr) males. The variance was signifi¬ 
cantly greater in young males than in older males 
(one-tailed) (F = 2.943, df = 18, 16; P = 0.041). 
Fifty-six percent of young males in our sample 
had cp volumes at least as small as the minimum 
cp size (445 mm’) of older males. 
DISCUSSION 
Characteristics of Mating System .—This study 
focused on the sexual and agonistic behaviors that 
characterize the mating system of Saltmarsh 
Sparrows. Our work provides an important but 
only partial perspective of the mating system in 
the species. Genetic information on parentage is 
equally valuable, and findings from the two 
perspectives should be in agreement (Johnson 
and Burley 1997). Hill et al. (2010) reported an 
extreme level of multiple mating in Saltmarsh 
Sparrows. All broods that were fully sampled in 
their study exhibited evidence of multiple pater¬ 
nity. 
Our work is the first to describe the behavioral 
dynamics of mating in detail in Saltmarsh 
Sparrows. The earliest reports by Montagna 
(1940, 1942) and Woolfenden (1956) were 
suggestive of an unusual mating system in the 
species, but their accounts were anecdotal, 
incomplete, and partly contradictory. Montagna’s 
(1940. 1942) important contribution was his 
description of multi-male meetings with a female 
that involved apparent attempts to mate with the 
female against her resistance. He also reported 
male-only meetings. Woolfenden (1956) docu¬ 
mented non-territorial behavior, and absence of 
paternal care and pair bonds. He witnessed 
lighting in male-female and in all-male groups, 
but his views were qualified and uncertain. 
Our evidence confirms that some aspects of 
sexual behavior in this promiscuous species are 
unusual and, perhaps, unique among passerine 
birds. Fertile females also solicit copulations 
silently from males in an otherwise conventional 
fashion among emberizid sparrows (Andrew 
1961). The most visible characteristic of male 
sexual behavior is the meet-und-pounce interac¬ 
tion initiated by the male. Males spend morning 
