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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 123, No. 1, March 2011 
from a stand of trees near Owings Mills, Maryland, 
and found a perched Common Nighthawk being 
mobbed by a group of birds that included several 
juvenile Eastern Bluebirds ( Sialia sialis) and a Pine 
Warbler ( Dendroica pinus ), Prairie Warbler (D. 
discolor ), Black-and-white Warbler ( Mniotilta 
varia), Canada Warbler ( Wilsonia canadensis ), 
and Baltimore Oriole ( Icterus galbula). After about 
2 min, CSC accidentally flushed the nighthawk; the 
mobbing birds flew but did not pursue the 
nighthawk. About 15 min later, CSC encountered 
another group of birds vigorously mobbing a 
second perched nighthawk in the same manner as 
the earlier observation, although he did not record 
the species composition of the group. The mobbers 
exhibited typical behaviors of hopping from branch 
to branch within 1 m of the nighthawks, giving 
scolding calls, and flicking their wings, but they did 
not strike either nighthawk. 
On 19 September 2007, at 1600 hrs CST, DAB 
heard scolding calls as he walked along a road 
near Winona, Minnesota. He looked up and found 
a Common Nighthawk perched on a horizontal 
branch above the road, surrounded by a group of 
mobbing birds that consisted of a Downy 
Woodpecker ( Picoides pubescens), an Eastern 
Phoebe (Sayornis phoebe), two Eastern Bluebirds, 
and a Magnolia Warbler ( Dendroica magnolia) . A 
passing car flushed the nighthawk, which flew 
from view. The mobbing birds immediately 
dispersed as well. 
On the morning of 25 August 2009, MCK 
spotted a Common Nighthawk perched on a dead 
branch in a maple tree (Acer sp.) near Algona, 
Iowa. Shortly thereafter a Black-capped Chicka¬ 
dee (Poecile atricapillus ) landed nearby and 
mobbed the nighthawk. It was soon joined by 
six more chickadees and a Black-and-white 
Warbler. The birds mobbed for several minutes 
and then flew away. The nighthawk remained on 
its perch the entire time. 
DISCUSSION 
We found only three previous accounts of a 
perched nightjar being mobbed. Pickwell and 
Smith (1938:212) reported that “8 or 10 English 
Sparrows and 6 robins were noted mobbing an 
Eastern Nighthawk ( Chordeiles minor) as it sat 
lengthwise on an elm tree...on May 12, 1927 ” 
Ficken et al. (1967) watched five Carolina 
Chickadees (Poecile caro linens is), five Tufted 
Titmice (Baeolophus bicolor), two Blue-gray 
Gnatcatchers (Polioptila caerulea), and 10 war¬ 
blers of four species mobbing a Chuck-will’s- 
widow ( Caprimulgus carolinensis) that was 
perched in a tree. The mobbing lasted ~10 min, 
during which the nightjar did not change its 
posture. More recently, Kent (1999) observed a 
group of about 40 small birds mobbing a Common 
Nighthawk in Iowa on 30 August 1999. Mobbing 
species included Northern Flicker ( Colaptes 
auratus). Downy Woodpecker, Blue Jay (Cyano- 
citta cristata). Black-capped Chickadee, Tufted 
Titmouse, White-breasted Nuthatch (Sitta caroli¬ 
nensis), American Robin ( Turdus migratorius ), 
Gray Catbird ( Dumetella carolinensis), eight 
species of warblers, Northern Cardinal (Cardina- 
lis cardinalis), and Rose-breasted Grosbeak 
(Pheucticus ludovicianus ); the mobbing behavior 
lasted —10 min. In each case, the authors 
suggested the mobbers mistook the nightjar for 
an owl. 
Castro-Siqueira (2010) watched a Common 
Potoo (Nyctibius g rise us) in central Brazil being 
mobbed by three Rufous Horneros ( Fumarius 
rufus), two Great Kiskadees ( Pitangus sulphur- 
citus), and seven Chalk-browed Mockingbirds 
(Minins satuminus) for 15 min before the mobbers 
left the tree in which the potoo was perched. The 
same group of mockingbirds returned in 5 min 
and resumed mobbing the potoo; less than 5 min 
later they were joined by three horneros, two 
kiskadees, a Tropical Kingbird (Tyrannus mel¬ 
ancholic us), and a Rufous-collared Sparrow 
(Zonotrichia capensis), each of which mobbed 
the potoo for another 10 min. None of the 
mobbers struck the potoo, which remained 
motionless on its perch during both mobbing 
bouts. Castro-Siqueira (2010) considered the 
mobbers to mistake the potoo for an owl but cast 
doubt on that notion because a Burrowing Owl 
(Athene cunicularia) that was perched in plain 
view 20 m from the potoo was not mobbed. 
Owls and caprimulgiforms have converged in 
evolving cryptic plumage and thus resemble one 
another, at least superficially. We agree with 
Pickwell and Smith (1938), Ficken et al. (1967), 
and Kent (1999) that this resemblance at times 
causes small birds to mistake perched caprimulgi- 
forms for owls and mob them accordingly. An 
alternative hypothesis is that nighthawks and 
potoos are mobbed because they resemble 
Chuck-will’s-widows, which occasionally prey 
on birds (Thayer 1899, Owre 1967). We cannot 
reject this hypothesis but consider it unlikely 
because birds that mobbed the potoo in Brazil and 
