Response of Eastern Bluebirds (Sialia sialis) to Artificial Nesting Boxes in

Montgomery Bell State Park, Tennessee

A Research Paper Submitted to the Faculty of the University of Tennessee at Martin Fulfilling the Requirements for the Degree of

Master of Science in Agriculture and Natural Resources

Submitted by John Bass December 2011

Photo by: John Bass

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Acknowledgements

I would like to thank my supervisor, Pat Wright (Park Manager), at

Montgomery Bell State Park for allowing me to put up and monitor the

nest boxes in the park. I would like to thank Dr. Barbara Darroch for

all of her patience throughout my entire research project and graduate

degree. The statistical help and final paper edits that Dr. Darroch

provided me with were invaluable. I would like to thank Dr. Joseph

Mehlhorn for his inputs, edits and cheerful demeanor. I would also like

to thank Dr. Philip Smartt for his encouragement, support and

friendship throughout earning both my bachelor’s and graduate

degree. I would also like to thank my parents for instilling a work ethic

that gave me the strength and determination to achieve something I

never thought possible. Most of all I would like to thank my loving

wife, Lisa, for all of the long nights that I was in my office working on

my graduate degree and research project. Without her support and the

support of the special people listed above, none of this would have

been possible.

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Abstract

Eastern bluebirds (Sialia sialis) are a common sight throughout

Tennessee all year long and can be recognized by the male’s brilliant

blue plumage. From 2008 until 2011, research was conducted on the

response of eastern bluebirds to artificial nest boxes in Montgomery

Bell State Park. The objective of this study was to determine nest box

use, as well as egg, fledgling, predation, and abandonment rates. In

2008, 28 “Peterson Style” nest boxes were erected near the roads

throughout the park. Each year, from the end of March until the first of

August, the bluebird boxes were monitored every 7-10 days. The

absence or presence of a nest, eggs, and young were noted as well as

any other data such as signs of predation and abandonment or the

presence of non-target species. The number of fledglings varied

significantly (p=0.0006) from year to year with 195 fledglings in 2008,

the most productive year, to 100 fledglings in 2011, the least

productive. Month had a significant effect on the number of fledglings

with largest percentage of young fledged in May of all four years.

There was significant (p < 0.0001) relationship between year and

month for the number of birds fledged. In 2009 and 2011, some

bluebirds fledged as early as April while no fledglings were observed in

April of 2008 or 2010. Data on predation and abandonment rates

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indicated that predation became more of a problem with successive

years. Nest boxes that were located in more open habitat performed

better than boxes in more wooded locations. This study has yielded

new information concerning the response and success of bluebird

nesting boxes within Montgomery Bell State Park and can be used as a

baseline for future studies.

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Table of Contents

Introduction ............................................................................. 1

Literature Review .................................................................. 4

Description and Physical Characteristics ................................... 4

Range .................................................................................. 4

Diet .. ....................................................................................7

Nest Boxes ........................................................................... 8

Raising Offspring ................................................................. 10

Feeding Rates ..................................................................... 10

Population Status ................................................................ 12

Objectives .............................................................................. 14

Materials and Methods ........................................................... 15

Results ................................................................................... 19

Effect of Year on Fledgling Success ....................................... 19

Effect of Month on Fledgling Success .................................... 20

Effect of Habitat on Nest Box Use and Success ....................... 22

Effect of Predation and Abandonment on Nest Success ........... 24

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Non Target Species ............................................................ 28

Conclusion .............................................................................. 29

Reference List ........................................................................ 30

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List of Figures

Figure Page

Figure 1. The range of the eastern bluebird within the United States is represented by the dark grey shaded area while the location of Montgomery Bell State Park is represented by the red star .................................................................. .1

Figure 2. Female eastern bluebird entering nest box ........................ 2

Figure 3. Male and female bluebirds perched on nest box, showing color differences ............................................................ 5

Figure 4. The modern day range of the eastern bluebird in the United States ................................................................ 6

Figure 5. Population data for eastern bluebirds in the United States from the Audubon Society's Christmas Bird Count from 1941-2003 .................................................... 7

Figure 6. An example of a “Peterson Style” nesting box .................... 9

Figure 7. The percentage of food contributed by the males and the variations in feeding frequency between the male and female ................................................................. 11

Figure 8. The change in eastern bluebird populations from 1978-1987 .......................................................... 13

Figure 9. The location of Montgomery Bell State Park within the state of Tennessee, as indicated by the red star ......... 15

Figure 10. Newly finished nest boxes ready to be put up in the park ................................................................ 16

Figure 11. Aerial photo of Montgomery Bell State Park with the nest box locations represented by the blue dots ...................... 17

Figure 12. Nest boxes were placed 5 to 6 feet above ground level on posts, trees and poles throughout the park ........ 18

Figure 13. Total number of bluebird fledglings produced each year ... 19

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Figure 14. Effect of year on success rate of bluebird nests ............... 20

Figure 15. Effect of month on number of fledglings produced ........... 21

Figure 16. Sixty-three percent of the successful nests were in the boxes located in the more open habitat. ....................... 22

Figure 17. Sixty-two percent of the total number of fledglings were produced in the boxes located in the more open habitat. . 23

Figure 18. From 2008-2011, the number of unsuccessful nests increased while the number of successful nests decreased. ................................................................ 24

Figure 19. The relationship between successful nests, predation and abandonment ............................................................ 25

Figure 20. Black rat snake after consuming a brood of juvenile eastern bluebirds ....................................................... 26

Figure 21. The number of successful nests decreased while the number of predations and abandonments increased from 2008-2011 ........................................................ 26

Figure 22. Effect of predation on nesting success ........................... 27

Figure 23. Effect of abandonment on nesting success ..................... 27

Figure 24. Utilization of nest boxes by non-target species as compared to utilization by eastern bluebirds .................. 28

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Introduction

Eastern bluebirds (Sialia sialis) are found throughout

Montgomery Bell State Park. Their calls can be heard year round and

the fleeting glimpse of a bright blue flash of their plumage is not an

uncommon sight. Eastern bluebirds are found over much of the United

States (Figure 1).

Figure 1: The range of the eastern bluebird within the United States is represented by the dark grey shaded area while the location of Montgomery Bell State Park is represented by the red star. (Copyright © 2003 Shaw Creek Bird Supply)

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In 2001, an access fee program was implemented to help relieve

the budget shortfalls of the Tennessee State Park System. Although

the access fee program was planned for all 54 State Parks, it was

implemented in only 23 state parks including Montgomery Bell State

Park. Many aluminum pay tubes on 4x4 posts were erected within the

park to collect the $3.00/day access fee.

When Governor Bredesen was elected in 2003, he promised to

abolish the access fee program during his term and, in 2006, access

fees were eliminated in all Tennessee State Parks. The 4x4 posts that

had been used as access fee signposts made excellent places to mount

eastern bluebird nest boxes. “Peterson Style” bluebird boxes (Figure

2) were chosen because the angled front and the oversized roof would

deter predators. The oval hole also makes it more difficult for

undesirable species such as House Sparrows and European Starlings to

occupy them.

Figure 2. Female eastern bluebird entering nest box.

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By spring of 2007, thirteen boxes were attached to the old access

fee sign posts scattered throughout the park. The months that

followed proved to be some of the most extreme weather that

Tennessee had experienced in years, with temperatures dropping to

the high teens in late April and record drought conditions the following

summer. Despite these conditions, the bluebirds adapted fairly well

and utilized ten of the thirteen boxes and had 34 fledglings for 2007.

By the end of the 2011 nesting season, the park was home to 60 nest

boxes devoted to the propagation of the eastern bluebirds. For the

purposes of this research the data from only 28 of the nest boxes was

used. These 28 boxes were in continuous use from 2008 to 2001 and

their location has not changed during that time period.

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Literature Review

Much of eastern North America is home to the eastern bluebird. Its

beautiful song can be heard throughout the year. Although this species

historically had a thriving population, human activities of the 18th and

19th century reduced eastern bluebird populations throughout most of

its range. Within the last 30 years, however, populations of eastern

bluebirds have recovered to much of its historic ranges (Zimmerman

2009).

Description and Physical Characteristics

The eastern bluebird is 7 inches tall with an average wingspan of

13 inches (Sibley 2000). It has a reddish orange breast that fades to

white on its belly. The female is drabber in comparison to the male

which displays a brilliant blue color on its back (Figure 3). These

physical characteristics make it easy to distinguish the two sexes.

Range

The eastern bluebird ranges from the Rocky Mountains to the

Atlantic Ocean; its range extends north to Canada and south past

southern Mexico (Figure 4). There are small populations in Cuba,

although it is not a native species there.

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Figure 3. Male and female bluebirds perched on nest box, showing color differences. The male is perched to the left of the female showing his brilliant blue coloration that is visible on his head and shoulder. The female, dressed in her muted plumage, prepares to add some finishing touches to her nest. Photo: John Bass

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Many leading researchers believe that eastern bluebird

populations peaked around 1900. There was a marked population

decline that started in 1938 and continued until the late 1970s (Dione

1981). One of the most efficient ways that researchers maintain

records on bird populations is through the Audubon Society’s

Christmas bird counts. These counts are conducted every year on

Christmas day by birdwatchers all over the country to document the

number and species of the birds that they observe. These counts show

the decline in eastern bluebird populations until the late 1970s, with

Figure 4. The modern day range of the eastern bluebird in the United States (Sauer et al. 2008).

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an increase in numbers since then (Figure 5). Prior to 1941, very little

population research on bluebirds is available (Zimmerman 2009).

Diet

Eastern bluebirds are omnivores but 68% of a bluebird’s diet is

made up of insects (Beal 1915). Research has indicated that while

eastern bluebirds are foraging, they prefer to be perched and descend

on their food source. Hunting bluebirds normally search the ground

while perched upright (Pinkowski 1977b). As bluebirds prefer to hunt

from an elevated position this makes their habitat selection more

critical as well. Habitats having few or no perches are rarely used by

Figure 5. Population data for eastern bluebirds in the United States from the Audubon Society's Christmas Bird Count from 1941-2003. (http://www.sialis.org/history.htm)

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eastern bluebirds; these areas elevate the energy demands imposed

on foraging birds by necessitating more prolonged flights as the birds

move from one foraging situation to another (Pinkowski 1977b).

Optimum conditions for bluebirds occur in areas containing an

abundance of dead trees and limbs that are used as nest cavities and

as foraging perches. In addition, poor soil and a sparse ground cover

help create ideal feeding conditions (Pinkowski 1977b).

Nest Boxes

Whereas foraging habits of bluebirds dictate their habitat

preferences to some extent, the availability of nesting sites can be

more critical. The eastern bluebird, a cavity nester, relies on

woodpeckers and natural forces to create nest cavities (Zeleny 1976).

To encourage bluebird nesting, nest boxes have been constructed and

placed in open and semi-open areas (Delvin et al. 1983). Many

different styles of nest boxes are available for cavity nesters such as

eastern bluebirds. There are a few general rules about nest box

design. For instance, a large roof that can provide shade as well as

shed water is preferred (Figure 6). The absence of a perch is best

when trying to eliminate the box’s use by undesirables such as house

sparrows. Drainage holes and rough lumber are also preferred. The

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ability to access the nest for periodic cleaning does seem to improve

nesting success. Use of nest boxes by the eastern bluebird can be

enhanced by placing them in the correct habitat configuration, near

adequate perches and abundant food sources (Delvin et al. 1983).

The height that the nest box is placed is not crucial because bluebirds

will nest in boxes or cavities located 2 feet above the ground to 30 feet

above ground (Pitts 2011). To monitor nesting boxes it is best to place

them at a height that can be checked easily.

Figure 6. An example of a “Peterson Style” nesting box. The slanted oversized roof helps with water runoff and deters predators. Photo: John Bass

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Raising Offspring

Eastern bluebirds generally breed and raise their broods from

March to July and are generally thought to be monogamous. In some

instances, other behavior has been observed. On three separate

occasions, male bluebirds began new nests with different females

before young of the previous nest were independent, a behavior not

seen among female bluebirds. Many adult males began working on

new nests before the previous offspring were independent (Pinkowski

1978). Although feeding duties during rearing are shared there are

tendencies exhibited by both the male and female during different

stages of the offspring’s growth (Figure 7).

Feeding Rates

Pinkowski (1978) found that the size of the brood did not affect the

feeding rates of male or female bluebirds. For most brood sizes, the

number of feedings per hour by females remained consistent while the

feeding rates varied for males. As a result, the larger broods did not

receive as many feedings per day as the smaller broods (Pinkowski

1978). That feeding rate did not increase with brood size may, in part,

reflect a decrease in heat loss because of more insulation as well as

less surface exposure in bigger broods (Mertens 1969). Less heat loss

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means less food required. Feeding rate of males and females together

was quite steady throughout the day, although females fed young

more often earlier in the day and males seemed to prefer to feed the

offspring later in the day (Pinkowski 1978). Although the feeding rates

of both male and female were comparable, Pinkowski (1978) found an

interesting trend in the type of prey males would catch and feed

compared to the type that the females preferred to feed. The larvae of

Figure 7: The percentage of food contributed by the males and the variations in feeding frequency between the male and female. This graph is based on 168 hrs. of observation and the line shows the significant linear regression.(From Pinkowski 1978)

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Lepidoptera were the most regular food of both the nestlings and

fledglings. It comprised 32.4% of the nestling diet. Orthoptera were

also common (25.6%) primarily during the summer months. Spiders

(11.3%) proved to be particularly important early in the season and

for newly-hatched young. Fruit, on the other hand, was uncommon in

the diet of nestlings but was fed to fledglings in summer and made up

11.0% of all fledgling foods recorded. Males and females tended to

feed different foods to the offspring, thus partitioning the feeding role.

Males fed considerably larger percentages of crickets (Gryllidae) and

earthworms while females fed bigger percentages of prey from

Arachnida and Acrididae (Pinkowski 1978). These findings were

interesting and lead to the question of whether or not it is the size of

the prey items that influence the choice of prey or is it nature’s way of

promoting nutritional diversity among fledgling bluebirds?

Population Status

In the past, the population status of the eastern bluebird has been

the subject of considerable public concern (Sauer and Droege 1990).

Today the eastern bluebird still faces many of the problems that

plagued its population during much of the 20th century. Invasive

species such as the European starling (Sturnus vulgaris) or the English

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house sparrow (Passer domesticus) compete with native species such

as the eastern bluebird for food and nesting sites. Habitat availability

is a key factor. In addition, our planet’s ever changing climate may

affect bluebird populations in the future. Bird community structure and

species population dynamics are affected by periods of severe climate

which keep populations below levels at which competition between

species could play a major role in structuring communities (Wiens

1977). Figure 8 demonstrates the population increases for the eastern

bluebird from 1978-1987. According to the Audubon Christmas bird

counts the population’s trends are still increasing (Figure 5).

Figure 8: The change in eastern bluebird populations from 1978-1987 (from Sauer and Droege 1990)

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Populations of the eastern bluebird have steadily increased in the last

few decades. This increase can be attributed to many circumstances

such as increased environmental awareness among the general public

as well as countless years of research that have given a better

understanding of the life of the Eastern Bluebird.

Objectives

The objectives of this study were to:

1. Determine if eastern bluebirds (Sialia sialis) within

Montgomery Bell State Park will use artificial nest boxes.

2. Determine in which month most fledglings are produced.

3. Measure the predation and abandonment rates from year to

year.

4. Determine the number of eggs laid versus the number of

successful fledglings.

5. Determine the non-target species that utilized the artificial

nest boxes.

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Materials and Methods:

This project was conducted within the borders of Montgomery

Bell State Park which covers almost 4,000 acres just east of Dickson,

Tennessee (Figure 9). All nest boxes were built on site (Figure 10) and

placed along roadways or along the edges of the golf course in the

park. Nest box placement began in 2007 with 13 boxes. The number

of boxes increased to 30 in 2008, to 57 in 2009, and to 60 for the

2010 and 2011 nesting seasons. Out of the 60 boxes placed in the

park, 28 nest boxes have not been moved in the last 4 years (Figure

11). From 2008 until 2011, these locations (Figure 11) have had a

nest box. The data for this research paper were collected from those

28 boxes to maintain consistency from year to year. The nest boxes

were placed five to six feet above ground level and were located on

trees, power line poles or 4x4 posts (Figure 12).

Figure 9: The location of Montgomery Bell State Park within the state of Tennessee, as indicated by the red star.

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Figure 10: Newly finished nest boxes ready to be put up in the park Photo by: John Bass

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Figure 11: Aerial photo of Montgomery Bell State Park with the nest box locations represented by the blue dots.

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From 2008 until 2011, the nest boxes were checked every 7 to 10

days from the end of March until first of August. Recorded

observations included whether a nest was present, number of eggs,

number of young, number of predation occurrences, number of

abandoned nests and number of successful nests per box location. At

the end of each nesting season, data were compiled to determine

yearly totals for each category. These statistics and totals were

entered into Excel to summarize the data and create graphs. Chi-

squared tests were used to determine significant relationships within

the data.

Photo by: Kristin Lyons Photo by: Kaitlin Hargrove

Figure 12: Nest boxes were placed 5 to 6 feet above ground level on posts, trees and poles throughout the park.

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Results

Effect of Year on Fledgling Success

Throughout this study, bluebirds used the artificial nesting boxes

and successfully fledged young every year. The most bluebird

fledglings were produced in 2008 (195 Fledglings), followed by 2010

(166 fledglings; Figure 13). The fewest fledglings were produced in

2011. Overall success rates of bluebird nests within the nest boxes

varied significantly (p=0.0006) from year to year; 2008 had the

highest percentage of successful nests, while 2011 had the lowest

(Figure 14).

Figure 13: Total number of bluebird fledglings produced each year.

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Effect of Month on Fledgling Success

In every year of this study, most fledglings were produced in May.

The relationship between month and year was significant

(p < 0.0001). The relationship probably resulted from the young that

were fledged in April of 2009 and 2011, while no fledglings were

observed in April of 2008 or 2010. The high percentage of July

fledglings in 2011 may also have contributed to this significant effect.

Figure 14: Effect of year on success rate of bluebird nests. The relationship between year and success rate was significant (Chi-squared p=0.0006)

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Figure 15: Effect of month on number of fledglings produced. The relationship between month and number of feldglings produced was significant (Chi-squared p=1.8 x 10-10) 

Although May had the highest numbers of fledglings, most of the

eggs are laid in April. The young that hatch from those eggs actually

fledge in May. As the summer progresses, the fledgling numbers

gradually fell until bluebirds stop building nests in mid to late August.

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Effect of Habitat on Nest Box Use and Success

There were 14 nest boxes located in primarily open habitat and 14

placed in primarily wooded habitats. There were 147 successful nests

from 2008-2011. The preference for the boxes located in more open

habitat was apparent with 63% of successful nests found in open areas

(Figure 16). The relationship between the two was significant

(p=0.0023).

Figure 16: Sixty-three percent of the successful nests were in the boxes located in the more open habitat. The relationship between habitat and number of successful nests was significant (Chi-squared p= 0.0023) 

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With the greater number of successful nests located in the open

habitat, the number of fledglings that they produced was also greater

(Figure 17). The relationship between the two was significant

(p < 0.0001). While the number of fledglings produced is much

greater than the number of successful nests, the percentages

respective to their totals were almost the same.

Figure 17: Sixty-two percent of the total number of fledglings were produced in the boxes located in the more open habitat. The relationship between habitat and number of fledglings was significant (Chi-squared p= 1.4 x 10-9) 

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Effect of Predation and Abandonment on Nest Success

In 2008, the number of successful nests exceeded the number of

nests that were lost due to predation and abandonment. Over the next

three years, the number of successful nests dropped while the number

of unsuccessful nests increased (Figure 18) and the relationship

between nesting success and year was significant (p=0.00057).

Figure 18: From 2008-2011, the number of unsuccessful nests increased while the number of successful nests decreased. The relationship between nest success and year was significant (p=0.00057).

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As the percentage of successful nests decreased from 2008-2010,

the percentage of predations and abandonments increased (Figure

19). The common predators were feral cats, raccoons and black rat

snakes (Figure 20). The relationship between year and

predation/abandonment/success was significant (p=0.0006). As

research continues in the park, efforts must be made to decrease the

amount of predation by experimenting with different types of predator

guards. While the percentages of successful nests decreased over

time. The total number of nests fluctuated very little, with the

exception of 2009 (Figure 21).

Figure 19: The relationship between successful nests, predation and abandonment. Nests lost to predation and nests lost to abandonment and year was significant (p=0.0006).

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Figure 21: The number of successful nests decreased while the number of predations and abandonments increased from 2008-2011.

Figure 20: Black rat snake after consuming a brood of juvenile eastern bluebirds. Photo by John Bass

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From 2008 -2011 predation acoounted for the loss of 26% of the

total nests built (Figure 22) while abandonment accounted for the loss

of 22% of the total nests built (Figure 23).

Figure 22: Effect of predation on nesting success. Out of 288 nests that were built between 2008 and 2011, 76 were lost to predation.

Figure 23: Effect of abandonment on nesting success. Out of 288 nests that were built between 2008 and 2011, 62 were lost to abandonment.

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Non-Target Species

Inevitably when nest box structures are erected, species other than

the one that is being targeted will take advantage of the nesting site.

Throughout the four year study, non-target species did occupy some of

the boxes. These species included Carolina Wrens (three nests),

Carolina Chickadees (two nests) and Southern Flying Squirrels, which,

in 2011, took over four of the research nest boxes that were located

on trees (Figure 24). If the trend with Southern Flying Squirrel use

continues, measures must be taken to deter them from the boxes such

as providing them with their own artificial habitat located higher on the

tree or relocating the boxes to a pole or post.

Figure 24: Utilization of nest boxes by non-target species as compared to utilization by eastern bluebirds.

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Conclusion

Eastern bluebirds will readily use artificial nest boxes within

Montgomery Bell State Park. From 2008 to 2011, 288 bluebird nests

were built in the 28 artificial nesting boxes monitored in this study. A

total of 147 successful nests were observed during this time period,

with 605 fledglings produced. The most fledglings were produced

during May of each year, but there was a significant (p < 0.0001)

relationship between month and year for the number of fledglings

produced. Nest boxes located in open habitat had higher success rates

than those in wooded locations. The greatest number of fledglings

were observed in 2008, with the fewest observed in 2011. Decreasing

nesting success during this study was due, in part, to increased

predation rates. Efforts must be made to deter predation to increase

the effectiveness of the nesting boxes. As the research continues, it is

planned to experiment with different styles of predator guards to

determine their effectiveness.

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Reference List

Beal, F. E. L. 1915. Food habits of the thrushes of the United States. USDA Biol. Surv. Bull. 288.

Delvin, W. J., Gates, W and Willner, G. R.1983.Nest box use by

cavity-nesting birds American Midland Naturalist.109(1): 194-201.

Dione, Andre P.1981 Return of the bluebird. http://audubon-omaha.org/bbbox/history2.htm

Mertens, J. A. L. 1969. The influence of brood size on the energy metabolism and water loss of nestling Great Tits, Parus major major. Ibis lll:ll-16.

Pinkowski, B.C. 1977b. Foraging behavior of the eastern bluebird.

The Wilson Bulletin. 89(3): 404-414

Pinkowski, B.C. 1978. Feeding and nestling of fledgling eastern bluebirds. The Wilson Bulletin. 90(1): 84-98.

Pitts,T. David. 2011. Studying eastern bluebirds. Redleaves Publishing. 261p

Sauer, John R. & Droege, Sam. 1990. Recent population trends of the eastern bluebird. Wilson Bull. 102(2): 239-252.

Sibley, David A. 2000.The Sibley guide to birds. Alfred A. Knopf Inc. 401p.

shawcreekbirdsupply.com/eastern_bluebird_map.htm Wiens, J. A. 1977. On competition and variable environments.

Amer. Sci. 65:590-597. Zimmerman, Elizabeth A. 2009. A draft history of bluebirds and

bluebirding. Sialis.org, Woodstock CT. Retrieved from Sialis online: http://www.sialis.org

Zeleny, L. 1976. The bluebird: How you can help its fight for survival. Indiana Univ. Press, Bloomington. 170p.