Vol. 5, No. 2; Spring 1983 - North American Bluebird Society

Invertebrate Fauna of
Eastern Bluebird Nests
William Chow, Edward H . Burtt, Jr. and Donald E. Johnston
Young Eastern Bluebirds (Sia/ia sia/is) share their nests with a remarkable variety
of arthropods, a group of animals that in cludes insects, spiders, and mites.
Some arthropod s (e.g. mites, flies) parasitize young bluebirds and may reduce
reproductive su ccess (Mo ss and Carnin 1970, Pin kowski 1977). Other arthropods depend
on bluebirds onl y indirectly, either sc avenging among debris in the nest (e.g.
mites, bo ok lic e) or preying on the small arthropods attracted to the nest (e.g.
spiders, wasps). The quantitative description of the ecological community within
bluebird nests, particularly the co mmunity of mites, was the fo cus of our study.
METHODS
Duri ng th e su mmer of 1980, 13
bluebird nests were collected just after
the young left. The nests were placed
in funnels within 48 hr. The funnels
were lined with a thin layer of ch eesec
loth to prevent debris from falling into
the collect in g jars at the bottom of the
funnels. A 60-watt bulb mounted 10 cm
above the nest caused the in ­
vertebrates to mo ve to th e bottom of
th e funnel away from the heat and
li ght. Once at the bottom of th e funnel
they fell into 5 % formaldehyde solution
in the collecting jar. Once a day
the cheesec loth-wrapped nest was
lifted from the funnel; animals clinging
to the c hee sec lot h were gently
brushed into the funnel whence they
slid into th e col lecting jar. At the end of
three days, nests were removed from
the funnels. The volume of the nest
was calculated by measuring the
height, length , and width of th e nest .
Each nest and it s c or res pond ing jar of
invertebrates received an identification
number.
Using ta xonomic keys found in
Borror et al. (1976) and Krantz (1978), invert
ebrates were identified to family
and c ounted under a binocular dissecting
microscope. Because of their
small size and numerical import ance,
mites were photographed through a
scanning electron microscope at the
U.S. Department of Agriculture
laboratory in Delaware, Ohi o. Represent
at ives of each type were then sent
to the Acarology Laboratory, ThE) Ohio
State Uni versity, for spe cies identification.
Volume 5, Number 2
Populations of mo st invertebrates
were too small to permit statistical
ana lysis. Pears on 's product-moment
c arrelation coeffici ent (Rosc oe 1975)
was used to evaluate the correlation
between populations of mites and
potential influential fa ctors. Spearman's
rank c orrelation c oeffic ient
(Roscoe 1975) was used with the s maller
populations of other species .
RESULTS
Bluebird nests were occupied by
two families of mites and one family of
spiders, all from the class Arach nida,
and eleven fami lies fr om t he class lnsecta
(Table 1). However, comparisons
are most c lear wh en families are
grouped by diet instead of ta xonomy.
Para sites
Among parasitic families (Table
1), only Dermanyssidae (Mo ss and
Camin 1970, Krantz 1978) and
Calliphoridae (Maso n 1944, Pinkow ski
1977) parasitize nestling bluebirds and
onl y Dermanyssidae, represented by a
s ing le s pec ies, Dermanyssus birundinus
(Fig. 1), occurred in sufficient
numbers to pose a potential health
hazard to nestlings. D. hirundinus lives
in the nest, climbs onto young
bluebirds to suck blood, and returns to
the nest between blood meals. Furthermore,
larger bro ods of bluebirds supported
s ignific ant ly larg er populations
of D. hirundinus (Fig. 2), whereas
populations of lar val blowflies (Call i­
phoridae), the ot her bluebird parasite,
were not correlated with brood siz e.
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