ILLINOIS AUDUBON BULLETIN rf 
Observations on Bird-Squirrel Interactions 
by STEPHEN P. HAVERA 
There are a number of observations on interspecific aggression between 
birds competing for nest cavities, especially involving species of wood- 
peckers, Great Crested Flycatchers (Myiarchus crinitus), House Wrens 
(Troglodytes aedon), Eastern Bluebirds (Sialia sialis), White-breasted Nut- 
hatches (Sitta carolinensis), House Sparrows (Passer domesticus), and Euro- 
pean Starlings (Sturnus vulgaris) (Ridgway, Bird-lore 17:91-103, 1915; 
Williams, Bird-lore 20:217-218, 1918; Musselman, Bird-banding 6:117- 
125, 1935; Bent, U.S. Natl. Mus. Bull. 174:21, 1939; Smith and Dumont, 
Audubon Mag. 47:6-7, 1945; Zeleny, Atl. Nat. 24:158-161, 1969; and 
others). However, | have found relatively little on mammal-bird interactions 
although the ecological significance of such relationships may be as impor- 
tant as that between species of birds. It, therefore, seems worthwhile to place 
on record three brief observations on squirrel-bird encounters. 
Lyon (Audubon Bull. 20:31-32, 1930) observed a Yellow-shafted 
(Common) Flicker (Co/aptes auratus) removing a squirrel’s winter nest from 
a cavity in the presence of the squirrel. 
Lawrence (Am. Ornithol. Union Monogr. 5, 1967) observed a pair of 
Yellow-bellied Sapsuckers (Sphyrapicus varius) and a male Yellow-shafted 
(Common) Flicker successfully defend, during incubation, their nest tree and 
his nesting cavity, respectively, against Red Squirrels (Tamiasciurus hud- 
sonicus.) | observed an encounter in which a much smaller species of bird, a 
White-breasted Nuthatch, appeared dominant to a Gray Squirrel (Sc/urus 
carolinensis). On 8 April 1975 on Forest Glen County Preserve in Vermilion 
County, Illinois, | examined and released an adult male Gray Squirrel that 
had been livetrapped. The adult male is the dominant animal in the Gray 
Squirrel hierarchy (Pack et a/., J. Wildl. Manage. 31:720-728, 1967). The 
Gray Squirrel ran approximately 25m to a Pignut Hickory tree (Carya 
glabra). He ascended the tree toward a cavity in the trunk, approximately 
7 cm in diameter and 12 m above the ground. A White-breasted Nuthatch 
was on the trunk of the tree a few cm above the hole. The Gray Squirrel tried 
to enter the opening. The nuthatch, however, assumed a threatening posture 
with its feathers fluffed and wings spread and the squirrel retreated. After a 
short hesitation the squirrel again attempted to enter the hole but was again 
repelled by the nuthatch. The squirrel then descended the tree and hastily 
left the area. The next day a male and a female nuthatch were observed 
emitting chirping sounds adjacent to the opening in the hickory tree. The 
nuthatch pair were probably using this cavity as a nest site. Unfortunately, 
the cavity was inaccessible for closer inspection. 
Another instance of interspecific interaction at a nesting cavity was 
observed on 5 May 1976 in Trelease Woods in Champaign County, Illinois. 
An adult female Fox Squirrel (S. niger) was involved in a radiotelemetry 
study for the previous 3 months. Her home den was in a cavity located 
