Nesting Abundance and Clutch Size of the Eastern
Bluebird
Research By: Chris Carson
Wildlife &Fisheries Science/Undergraduate, Department of Biology
Tennessee Technological University
38505
Keywords
Eastern blue bird, Sialia sialis, nesting abundance, clutch size, Scott County, Tennessee,
Chris Carson, Tennessee Technological University, Fecundity
Abstract
Eastern Bluebirds (Sialia sialis) have been studied in many locations but studies have
not been conducted in the central portion of Scott County, Tennessee. The objective of
this project is to study and make available the nesting abundance and clutch size of the
eastern bluebird in the central portion of Scott County, Tennessee.
By constructing bluebird nest boxes and monitoring them at 7 to 10 day intervals an
average nest abundance and clutch size can be determined. My expectation is that the
eastern bluebird will have a nesting success of approximately 80%. The average nesting
abundance and clutch size can be used to determine the fecundity of the species.
Introduction
Eastern Bluebirds have been studied extensively; however, their nesting abundance
and clutch size have not been studied in the central portion of Scott County. Eastern
Bluebirds (Sialia sialis) are secondary cavity nesters that experienced a population
decline in the later part of the 19th century due to habitat loss and competition from
exotic species (Radunzel, L.A. et al. 1997). “Placement of nest boxes in suitable habitat
can increase populations of cavity nesting birds, especially if natural cavities are
limiting” (Parren, S.G., 1991).
Secondary cavity nesters may be limited more by the availability of nesting cavities
than by food (Von Haartman 1957:339). Nest-box management has compensated for the
reduction availability of natural nest sites for eastern bluebirds (Zeleny 1978). The
objective of this project is to make available the nesting abundance and clutch size of the
eastern bluebird in the central part of Scott County, Tennessee. My hypothesis is that the
average clutch size of the eastern bluebird varies widely in artificial nest boxes.
Methods and Materials
Artificial nest boxes were constructed from 2.54cm x 15.24 x 304.8cm boards. Nest
boxes were constructed using plans provided in the Tennessee Wildlife Resources
publication Wildlife Management for Tennessee Landowners.
All nest boxes will be placed at a height of 1.50 meters and a minimum distance of
100 meters from other boxes. The boxes will be spread out over a 404.68 hectare family
farm in Scott County, Tennessee. All boxes were placed with the entrance hole facing
nearby woody debris or trees.
The boxes were monitored for activity at 7 to 10 day intervals (Radunzel, L.A. et al.
1997), using a data form (figure 2.1). An average of nest box activity and clutch size was
conducted to determine the clutch size and nesting success for bluebirds in the central
part of Scott County, TN.
Results & Discussion
I found that eastern bluebirds nest readily in artificial nest boxes. Boxes were placed
in open habitat preferred by eastern bluebirds (Prescott, 1982). Exactly 9 of 10 boxes
paced on a 404.68 hectare study area were found to be occupied. The average nesting
abundance and clutch size can be used to determine the fecundity of the species in the
central part of Scott County, Tennessee. Clutch size is defined by Radunzel, L.A. et al.
1997 as the number of eggs observed in each nest.
Other studies have shown that the average clutch size of eastern bluebirds varies
based on location (Dhondt, 2000). These variations are shown in figure 3. The average
number of eggs present in nest boxes was found to be 3.3 (figure 1, table 1). These
numbers were slightly lower than normal numbers for early season nests but may be a
result of normal annual variation in bluebirds (Lumsden, 1986).
Conclusion
Based on the data I collected during my study in the central portion of Scott County,
Tennessee I have concluded that the eastern bluebird has a mean clutch size of 3.3 and a
average hatch rate of 3 young. Based upon this data I conclude that the species is
considered stable at this time. However, further long term monitoring is needed to make
a definite conclusion about the fecundity of the species.
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Literature Cited
Dhondt, A. A. , Kast, T. L. and Allen, P. E. 2000. Clutch-size Variation in
Bluebirds. Birdscope, Volume 14, Number 2: 3-5.
Eastern
Lumsden, H.G. 1986. Choice of nest boxes by eastern bluebirds. Can. Field-Nat.
100:343 -349.
Parren, S.G., Wildlife Society Bulletin. 1991. Evaluation of Nest-Box Sites Selected by
Eastern Bluebirds, Tree Swallows, and House Wrens. 19 : 270-277.
Prescott, H.W. 1982. Using paired nesting boxes to reduce swallow-bluebird
competition. Sialia 4:3-7.
Pitts, D.T.,1988. Journal of Field Ornithology. Effects of Nest Box Size on Eastern
Bluebird Nests. 59-4: 309-313.
Radunzel, L. A. and Muschitz, D.M. 1997. Journal of Field Ornithology. A Long-Term
Study of the Breeding Success of Eastern Bluebirds by Year and Cavity Type.
68:7-18.
Von Hartman, L. 1957. Adaptations in hole-nesting birds. Evolution 11:339-347.
Zeleny, L. 1978. Nesting box programs for bluebirds and other passerines. Pages 5560.
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Appendix A
Location:
Time:
Temperature:
Box Number
Date:
Observer:
box
occupied?
eggs
present?
number of
Eggs
habitat
# of eggs
hatched
Figure 2.1
-4-
Appendix B
6
5
4
Number 3
Clutch Size
2
Hatched
1
0
1 2 3
4 5 6
7 8 9 10
Box Number
Figure 2
Figure 1
Box #
Clutch Size
Hatched
1
2
2
2
4
4
3
3
3
4
0
0
5
4
3
6
2
2
7
6
4
8
3
3
9
5
5
10
4
4
Table 1
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Average
3.3
3