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The Wilson Journal of Ornithology 123(1): 183-185, 2011 
Mobbing of Common Nighthawks as Cases of Mistaken Identity 
Jeffrey S. Marks , 15 C. Scott Crabtree , * 2 Dedrick A. Benz , 3 and Matthew C. Kenne 4 
ABSTRACT.—We report five instances of small 
birds mobbing Common Nighthawks (Chordeiles mi¬ 
nor). In each case, the nighthawk was roosting in a tree 
during daytime and was mobbed by a group of birds in a 
manner typical of that directed toward an avian 
predator. We found only four previously published 
accounts of perched caprimulgiforms being mobbed. 
Mobbing birds probably mistake caprimulgiforms for 
owls because of convergence in plumage coloration and 
pattern between these two groups of crepuscular- 
nocturnal birds. Received 29 September 2010. Accepted 
9 December 2010. 
Most species of “typical” owls (Strigidae) and 
nightjars (Caprimulgidae) have variegated brown, 
black, gray, and white plumage that helps provide 
camouflage for individuals at nests and roosts 
(Cleere 1998, Marks et al. 1999). Many owls prey 
on small birds and are frequently mobbed by them 
(Altmann 1956, Gehlbach and Leverett 1995). In 
contrast, nightjars feed almost exclusively on 
aerial insects and are not normally targeted by 
mobbing birds, presumably because they pose no 
threat to them. We describe five instances in 
which a Common Nighthawk ( Chordeiles minor ) 
'4241 SE Liebe Street, Portland, OR 97206, USA. 
2 2847 Cox Neck Road, Chester, MD 21619, USA. 
3 422 West 11th Street, Winona, MN 55987, USA. 
4 709 North Phillips Street, Algona, IA 50511, USA. 
s Corresponding author; e-mail: jeffl7_marks@msn.com 
was mobbed by a group of small birds. We also 
review the scant literature on mobbing of perched 
caprimulgiforms, none of which appears in the 
most recent reviews of caprimulgiform biology 
(e.g., Poulin et al. 1996; Cleere 1998, 1999, 2010). 
The behavior probably results from similarities in 
plumage between caprimulgiforms and owls. 
OBSERVATIONS 
On 23 August 1998, at 1330 hrs MST, JSM 
encountered a group of warblers mobbing a 
Common Nighthawk perched on a horizontal 
limb about 7 m high in an ash tree ( Fraxinus 
sp.) in the town park at Scobey, Montana. During 
the next few minutes, the warblers gave chip 
notes, flicked their wings, and hopped from 
branch to branch <1.0 m from the nighthawk, 
always facing it while they mobbed. The group 
consisted of at least 10 Yellow Warblers (Den- 
droica petechia ), two Blackpoll Warblers ( D . 
striata ), and two American Redstarts ( Setophaga 
ruticilla). The warblers did not strike the night- 
hawk, which was oriented parallel to the branch 
and made no obvious movements in response to 
the mobbing birds. The warblers departed from 
the tree in <10 min, while the nighthawk 
remained on its perch. JSM later found several 
other perched nighthawks in the park that were 
not mobbed while he was present. 
On 4 August 2001, CSC heard mobbing calls 
