SHORT COMMUNICATIONS 
823 
The Wilson Journal of Ornithology 123(4):823—827, 2011 
Responses of Nesting Yellow-headed Blackbirds and Yellow Warblers 
to Wrens 
Diane L. H. Neudorf , 13 Katherine E. Sears , 1 and Spencer G. Sealy 2 
ABSTRACT.—We studied nest defense behavior of 
Yellow-headed Blackbirds ( Xanthocephalus xtmfhoce- 
pkjks) and Yellow Warblers (Dendroica petechia) in 
.nponse to two species of common nest destroyers. Wc 
rrtiented freeze-dried models of Marsh Wrens (ClJ* 
■■•nlioru! palustris) at Yellow-headed Blackbird nests 
aid House Wrens ( Troglodytes aedon ) al Yellow 
fabler nests during the incubation stage. We presented 
£ Clay-colored Sparrow [Spizella pallida) as a control 
tor both species. Male Yellow-headed Blackbirds 
responded more intensively to the Marsh Wren model 
than the control, and female blackbirds responded 
intensively to both models but were more aggressive 
toward the Marsh Wren. Most Yellow Warblers did not 
respond to the House Wren model with their typical 
predator responses (e.g., chip alarm calls). Some female 
warblers were aggressive toward the wren model, 
whereas others sat in their nest. Sitting in the nest as a 
defense to deter nest destruction by House Wrens needs 
turther investigation. Differences in response levels 
teln-een blackbirds and warblers may be related to 
differences in levels of nest destruction experienced by 
'he two species or differences in nest defense behaviors 
ured by ihe two species. Received 15 September 2010. 
^epte,l 2R March 2011. 
Several experiments have demonstrated that 
Marsh ( Cistothorus palustris ) and House (Trog- 
Mytes aedon) wrens peck and attempt to destroy 
^regardless of their size (Pieman 1977, While 
Kennedy 1997). Eggs and nesting material 
n,a y be removed from destroyed nests (Belles- 
^ftand Pieman 1986) and both species, at times. 
^ °r injure nestlings (Bellcs-Isles and Pieman 
■'^6. Pieman and Isabelle 1995). Eggs of 
Specifics and heterospecifics are often de- 
ll n>yed but typically are not eaten. Explanations 
,or nest destruction behavior include reduced 
Cu 'npetition for food (Pieman 1977), as well as 
Auction of reproductive success of competitors 
i^elJes-Isles and Pieman 1986). House Wrens are 
' Department of Biological Sciences. Sum Houston State 
University, Huntsville. TX 77341. USA. 
‘ Department of Biological Sciences. University of 
Manitoba, Winnipeg. MB R3T 2N2, Canada. 
'Corresponding author: e-mail: Neudorf@shsu.edu 
secondary-cavity nesters and may destroy nests to 
gain nest sites (Quinn and Holroyd 1989, Pribil 
and Pieman 1991). although they also destroy 
eggs and nestlings in open-cup nests (Belles-Isles 
and Pieman 1986). 
Species nesting in the vicinity of wrens, given 
the potential threat of nest destruction, should 
respond aggressively to them. Nest defense is a 
common behavior of birds to protect their nests 
and offspring from predators (Montgomerie and 
Weatherhead 1988) and avian brood parasites 
(Sealy et al. 1998). Yellow-headed Blackbirds 
(Xanthocephalus xanthocephalus) experience 
considerable nest destruction from Marsh Wrens. 
Pieman and Isabelle (1995) used cameras and egg 
damage to demonstrate that —11% of natural 
nests and 40% of artificial nests were destroyed 
by Marsh Wrens during their study in Manitoba. 
Yellow-headed Blackbirds respond aggressively 
toward playbacks of wrens near their nests (Bump 
1986, Pieman and Isabelle 1995). Nesting Yellow 
Warblers (Dendroica petechia) and House Wrens 
co-occur in upland forest areas in southern 
Manitoba. We have not observed Yellow War¬ 
blers behaving aggressively toward wrens and 
have not recorded egg damage caused by wrens in 
our study area (S. G. Sealy. pers. obs.). However, 
we were interested in examining if Yellow 
Warblers respond given that House Wrens are 
common in our study area and their potential for 
nest destruction (White and Kennedy 1997). 
Previous studies of Yellow-headed Blackbirds 
(Sealy et al. 1998) and Yellow Warblers (Hobson 
et al. 1988. Gill and Sealy 1996) demonstrated 
these species defend their nests against egg and 
nestling predators, and also against brood-parasit¬ 
ic Brown-headed Cowbirds (Molothrus arer). We 
tested recognition abilities of Yellow-headed 
Blackbirds by presenting freeze-dried models of 
Marsh Wrens at their nests to examine their 
response to a visual stimulus of this nest 
destroyer. We predicted Yellow-headed Black¬ 
birds should respond more intensely to the Marsh 
Wren mount than an innocuous control. We 
