SHORT COMMUNICATIONS 
189 
TABLE 1. Number of experimental Red-winged 
Blackbird nests that survived (no predation) or failed 
(depredation) when an experimental Sora nest was present 
or absent 
Locution 
Sora nesi 
Falc of Red-winged Blackbird ned 
Survived 
Failed 
Northwest 
Present 
8 
1 
marsh” 
Absent 
9 
9 
Northeast 
Present 
4 
3 
marsh* 1 
Absent 
3 
11 
Southeast 
Present 
4 
1 
marsh' 
Absent 
9 
4 
‘ Fisher exact lest P = 0.0912. 
. Fisher exact lest P = 0.1564. 
1 Fisher exact test P = 1.000. 
44 in SE). The experimental nests were placed in 
ihe marshes at the center of randomly chosen 
quadrats between 7 and 30 June 2010, spanning 
the period of peak nesting activity and extending 
io the end of the nesting period for most 
blackbirds in the study population (Forbes 
2010). Three eggs were placed in each nest and 
were removed 48 hrs later. Nests were checked 
daily for the occurrence of predation. Red-winged 
Blackbirds and Sora nested in all three marshes. 
Marsh Wrens (Cistothonis palustris) and their 
nests were observed in the NW and NE marshes 
bui not in the SE marsh. Evidence of egg 
predation consistent with Marsh Wrens was found 
in NW and NE marshes but not in the SE marsh. 
OBSERVATIONS 
Between 28 and 67% of experimental Red- 
winged Blackbird nests were depredated, consis- 
,enl with estimates of nest predation in active 
blackbird nests (reviewed by Beletsky Id96). 
Avian predators were responsible for most preda¬ 
tion of experimental nests in all three study sites. 
Twenty-nine (44%) of the 66 experimental black¬ 
bird nests placed into the marshes were depredated: 
-8 ot 29 depredated nests were due to avian 
predators, and at least 16 of the 28 nests (57%) 
were depredated by Marsh Wrens based on the 
Presence of punctured eggs in the nest (Pieman 
i^77). There was no obvious relationship between 
n est fate of experimental blackbird and Sora nests 
'Tisher exact test, two-tailed: P = 1.00). 
We used two-tailed Fisher exact tests to 
examine the effects of interspecific neighbors 
(Sora) on nest predation of blackbirds. The results 
for individual marshes were not statistically 
significant (Table 1). However, when data for 
the two marshes (Northeast and Northwest) where 
nesting Marsh Wrens were present were com¬ 
bined. a significant effect was observed (Table 1; 
Fisher exact test. P = 0.031). Conversely, in the 
one marsh where nesting Marsh Wrens were 
absent, no effect of a Sora nest on the likelihood 
of predation on a blackbird nest was observed 
(Table 1; Fisher exact test, P = 1.00). 
We found no obvious effect of the presence of 
an active Red-winged Blackbird nest in the same 
quadrat as a dummy nest on predation. There were 
active blackbird nests in most quadrats at the 
beginning of the season, but the attrition of active 
nests both due to predators and Hedging meant 
that few of our dummy nests overlapped with 
active blackbird nests. Further, some dummy 
nests were placed in quadrats with active Marsh 
Wren nests with no obvious effect. We suspect 
this was not because the proximity to Marsh 
Wrens was unimportant, but rather because the 
spatial scale of quadrats and territories was 
dissimilar. We observed Marsh Wrens ranging 
widely in the NW and NE marshes, but they were 
not present in the SE marsh. 
We examined the likelihood of predation on 
active Red-winged Blackbird nests in relation to 
distance from a Marsh Wren nest in the NE marsh 
where the location of all Marsh Wren nests was 
known. We found a positive but non-significant 
effect: 10 of 11 nests within 20 m of a Marsh 
Wren nest were depredated, compared to 23 of 34 
nests >20 m from a Marsh Wren nest (Fisher 
exact test, P = 0.24). 
DISCUSSION 
Red-winged Blackbird nests in marshes with 
Marsh Wrens, placed near Sora nests, were less 
likely to be depredated than solitary blackbird nests. 
This result was unexpected. Rather than attracting 
additional predation as we initially expected, the 
presence of a Sora nest appeared to confer some 
level of protection to a blackbird nest. The effect 
was not due to group defense by blackbirds as only 
artificial nests were used and there were no adults 
associated with the experimental nests. 
The behavior of Marsh Wrens seems most 
likely to account for the observed results. Marsh 
Wrens were the main predator in the NW and NE 
marshes but were absent from the SE marsh. We 
suggest that quail eggs in the experimental Sora 
nests acted as a supernormal stimulus, distracting 
the Marsh Wrens from the neighboring blackbird 
