% Egg Htch: Percent of bluebird eggs that hatched
* Year started pairing boxes
AY/N Htch: Average young per nest hatching at least one
A Fl/N Htch: Average young fledged per nest hatching at least one
A Fl/N Fl: Average young fledged per nest fledging at least one
% Y H = Fl: Percent young hatching resulting in young fledging
% Egg = YF: Percent eggs laid resulting in young fledging
IOWA - Johnson County Songbird Project - Jim
Walters
Jim wrote that he has not worked with paired boxes on a bluebird
trail, but he sent along a copy of an article relating to two-box sites.
The following is from the study "Eastern Bluebirds Are Attracted to
Two-Box Sites" by Jonathan H. Plissner & Patricia Adair Gowaty,
published in the Wilson Bulletin, Vol. 107, No. 2, June 1995:
"ABSTRACT - In early March, just prior to the onset of the
breeding season, responses by Eastern Bluebirds to playbacks of the
territorial song of conspecific are more likely on site with two nest
boxes rather than one. One or two boxes were placed randomly at
potential territorial sites during early winter; so responsiveness is
not explained by territoriality of the previous season. Explanations for
our observations include that bluebirds prefer potential territorial
sites with two boxes because of increased habitat quality or that
bluebirds locate two-box sites more readily than one-box sites. We infer
from our result that potential territorial sites with two nesting boxes
are more attractive to bluebirds than sites with only one nesting
box."
[The Plissner/Gowaty study considered several hypotheses and was
designed to examine the "attractiveness" of two-box sites to
bluebirds as opposed to the fledgling numbers resulting from their use
of two-box sites.] The study concluded with the following:
"These hypotheses to explain our observations predict that
territories on two-box sites will suffer higher intrusion rates by
conspecifics than territories on one-box sites. Harris . . . reported
higher rates of territorial aggression by breeding resident Tree
Swallows when nesting boxes were 1 m apart than when they were separated
by 30 m. Also, Meek and Robertson . . . observed more intrusions of
Eastern Bluebird territories by Tree Swallows at territories containing
two nesting boxes than at those with single boxes. In a study of nest
guarding, Gowaty. . . found that both males and females remained closer
to boxes during nest-building and egg-laying periods, when territories
are most susceptible to usurpation and conspecific nest parasitism, but
not during incubation or while nestlings were present.
Extrapolation from our observations also suggests that bluebirds may
initially appear in greater numbers in areas with many rather than fewer
nesting boxes. A test of this idea would vary the density of nesting
boxes randomly over areas that currently have few or not bluebirds. They
hypothesis would be supported if significant differences in the numbers
of bluebirds initially nesting were found in areas with higher densities
of nesting boxes. Finally, if bluebirds are more attracted to two-box
sites than one-box sites, managers interested in attracting bluebirds
might have greater success associated with potential territories
containing two nesting boxes.
MINNESOTA - Minnesota Bluebird Recovery Program (BBRP) -
Dorene Scriven
I hope you get good feed back on the pairing discussion. I think
distance between boxes is important (as well as terrain, distance to
water, etc.). For instance, I do not consider 50' to 100' as pairing.
MBRP also recommends placing nest boxes 20 to 25 feet apart, 22 feet
appears to work best. They also recommend to start pairing when tree
swallows inhabit 50% of the boxes on your trail.
From Bluebird News, Vol. 9, No. 1: Pairing
Revisited
Despite some very strong arguments based on statistics which Joe
O'Halloran of Bluebird Restoration Association of Wisconsin (BRAW) has
put forth in the Wisconsin newsletter, BBRP is still convinced that pairing
of nest boxes can have real advantages where tree swallow populations
tend to exceed bluebird populations. To further our position, we
cite some of our own statistics from the 1996 reports; the research done
by BBRP Research grantee Jason Smith sent in late October; and a
communiqué from Professor Raleigh Robertson, Biology Department,
Queen's University of Ontario, Canada.
The study of Jason Smith, on the spacing preferences at Nest-Sites
between Bluebirds and Tree Swallows in Bemidji, was influenced by the
very late spring in which tree swallows arrived before bluebirds. he had
nest boxes spaced 7 yards, 15 yards, and 30 yards apart. Initially, tree
swallows selected boxes spaced at 15 yard, then 30 yards, and then a
couple chose 7 yard spacing, though in this spacing actually chose
15-yard between pairs. The later-arriving bluebirds nested in the 7-yard
spacing area. From his study, Jason concluded that tree swallows
probably prefer 15-yard spacing and that a 7-yard spacing would be
successful between bluebirds and tree swallows, and keep tree swallows
from taking over a trail or area.
Professor Raleigh Robertson and his graduate students focused mainly
on tree swallow spacing, but by nature also included eastern bluebirds.
The nest boxes, arranged in grids, have been studied by Professor
Robertson and his students for many years, and he was kind enough to
send us many of his published papers. "There are many factors. .
.in analyzing the effects of "pairing," such as habitat,
distance between boxes in a pair, overall nest box density in an area,
etc. It is a fairly complex issue, which must be examined with a careful
experimental approach, including appropriate controls. "For
expressing nesting success, it seems, as some of the BBRP information
points out, that you need to consider a measure other than simply number
fledged per box. For a solitary species like eastern bluebirds, once
you reach habitat saturation, increasing the number of boxes will not
increase your number of pairs of bluebirds. So, if you add boxes beyond
the habitat saturation point, you will effectively lower your success,
as measured by fledgling per box. A better measure would be fledglings
per unit area, or perhaps [by length] of trail."
"For tree swallows, which are quite colonial, at a certain
spatial scale, the habitat saturation point is much higher. So by adding
boxes, you will keep attracting tree swallows, to a much higher level.
While this may be detrimental to bluebirds, I doubt it."
Dr. Robertson's former students, Linda Whittingham and Peter Dunn,
are establishing a tree swallow research program in Wisconsin. We hope
they will share their findings and enlighten us further on pairing.
--------
418 of the 478 reports BBRP received last fail, indicated whether
nest boxes were paired. Results are interesting, if not necessarily
significant:
As Professor Robertson states, there are many parameters, including
maximum saturation levels for each species, which make pairing a complex
issue.
MISSOURI - Project Bluebird - Harold & June Cox
We do not have Tree Swallows in our area but we will read with
interest your results. We hope, over the coming years, to work in areas
beyond Missouri. Our [bluebird] work is moving along very well and we
are doing it virtually full-time. Thanks for your writings and support.
Wish we could make your conference. Maybe 1998.
MONTANA -Art Aylesworth, "Bluebird Man of Ronan"
I received your letter today regarding paired bluebird boxes. For the
last 12 years I've had 7 miles of nest boxes involving 70 boxes. These
are all along a large river bottom that has a big population of
swallows. They are along a railroad track on railroad telephone poles
with very low wires which create excellent perching habitat for both
bluebirds and swallows as far as the nest box is concerned. Swallows
eliminated the bluebirds almost entirely through this area until I
paired the boxes. Now we have swallows and bluebirds both in probably
50% of the paired boxes. Six of the paired boxes are 10 feet apart and
at that distance there have been two times that the swallows have
claimed both nest boxes. The balance of the boxes are back to back on
the telephone poles under that telephone line. I have never had two
pairs of bluebirds and I've never had two nests of tree swallows in any
of those boxes that are back to back. One year I had a Mountain Bluebird
use one nest box and a Western Bluebird build a nest and laid one egg in
the opposite box but then abandoned it, so I question whether even that
difference in species will overcome the territorial experience.
In addition to this, I have probably 30 people with smaller nest box
trails using paired boxes and it works beautifully. There is no question
in my mind but what nest box placement of 20 to 50 feet apart on a nest
box trail will eventually be solid tree swallow nesting. This is so
because as the number of swallows increase, they simply gang up on the
male bluebird until they drive him away and then the female is gone
also. I encourage my people to place their nest boxes in open country
not more than 5 to the mile. With this box placement, the bluebirds will
pretty well occupy all the boxes. In some cases we have 250 boxes
without a swallow but this is on open range land where there are no
trees for at least a half a mile. As soon as we get into some open pine
forest area, the boxes can be placed closer together but again, probably
not closer than 250 yards. The nest box trail on which I have the most
nest boxes is 13 miles long with 95 boxes. However, some of these are on
little spurs back away from the main trail.
NEW HAMPSHIRE - "New Hampshire Bluebird Conspiracy"
- Bruce Burdett
If you mount your Bluebird houses in pairs about 10 to 15 feet from
each other, you will find that Tree Swallow competition will be much
reduced, even eliminated. Neither species will nest that close to its
own kind, and each seems capable of living side by side with the other
without fighting. Houses mounted singly will almost always be taken by
the swallows, which are more numerous and aggressive. Remember, too,
that Bluebirds are territorial, and will not normally nest closer than
about 400 feet from other Bluebirds. . . .
With paired houses, Bluebirds and Tree Swallows work hand in hand to
fight off intruders in the vicinity of their nests. . . .
Let me say briefly that without pairing Tree Swallows would take 95%
of my houses. This was my experience before I started pairing 4 years
ago. Furthermore, of the 5% that Bluebirds managed to occupy, most were
harassed by the swallows until they abandoned their nest and eggs. It
was a no-win situation. Perhaps my experience is typical of New
Hampshire but not of Wisconsin, Iowa, or Nebraska. In most areas of New
Hampshire, Vermont, and Maine that I have heard about, the swallows out
number the Bluebirds by a wide margin. Many letters to me confirm this.
With paired houses the two species live side by side without strife. Our
Bluebird population density in N.E. is still quite thin (sparse) though
it is improving steadily.
OHIO - Robert E. Orthwein
I do not consider anything over 7 yards to be a properly paired box
site. Actually, when I change a location or add a box, I am now using a
5-yard spacing. On rare occasions, I have had Tree Swallows nest side by
side 7 yards apart. This has occurred when a late-nesting Swallow pair
moved in next to an early-nesting Swallow pair with young.
Over the years, on a few rare occasions, I have had Bluebirds build
nests in both paired boxes but lay eggs in only one. I also had Titmice
do this on one occasion. One Bluebird did lay 3 white eggs in one box
and two white eggs in the other box 7 yards away. The three hatched and
fledged. In all cases the boxes were identical. I have painted some of
my boxes an earth-tone tan and left the others green. No double nesting
has occurred at these sites but it is so rare, it doesn't matter much. I
suspect that these confused double nesters were first year, first time
birds.
Paired and triple-box sites do reduce Bluebird production per box and
this should be expected. In 1996, one of my best trails of 10 boxes on a
140-acre farm produced 39 Bluebirds and 6 Tree Swallows. This trail was
in ideal, low-grass, almost wren-free habitat. Locations were 200 to 250
yards apart and not saturated. There were no ponds or streams to attract
swallows. All locations were 40 to 45 yards in the open. Three locations
had 5-foot to 8-foot perching posts near the boxes. There were no
Bluebird or Swallow casualties due to House Sparrows and no Wren damage.
A perfect Bluebird trail.
The 10 boxes were at 4 locations - a 2-Gilbertson box location, a
3-Gilbertson box location, a 3-raised roof box location, and a
2-conventional box location. Bluebird production per box was 3.9, but
9.75 per location. Production per location and House Sparrow
protection is all that I am interested in.
My paired and tripled boxes have not produced hoards of Tree
Swallows. In the past 17 years I fledged 2,212 Bluebirds and 690 Tree
Swallows. Properly monitored paired boxes provide some protection from
House Sparrow attacks and triple boxes provide a lot of protection.
WISCONSIN - Bluebird Restoration Association of Wisconsin,
Inc. (BRAW) - Tom Whalley
I'm enclosing our last newsletter which has some of our data analysis
for the last year. Up until this point, I have paired most of our boxes
but the data right now is bringing out some questions. We have a virgin
trail where we are still doing a pairing study with Olsen & Peterson
boxes. This data is not consistent with the generalizations that Joe
O'Halloran had. I'm sure Joe O'Halloran would be glad to share our data.
From Wisconsin Bluebird, Winter 1996, Vol. 11, No. 4
Pairing - Good or Bad for Bluebird Production? Bad!
by Joe O'Halloran, Chair, BRAW Data Analysis Committee
Congratulations to all BRAW monitors, whether you monitored a
paired-box trail, or singles-box trail. Over 90% of you took part in the
1996 study by simply specifying whether the boxes you reported were
singles or paired. The massive study is a huge success.
We are still getting more late-filed monitor reports at the time of
this writing. However, Carol McDaniel and I wanted to shared the preview
of the 1996 results with you, for three reasons. First, because the
results are of vital importance to bluebirders. Secondly, because the
pattern seen now with the database at over 4,600 boxes (about 82% of the
/size of last year) is the same pattern found at 75%, 60%, and at 40%.
Thirdly, by getting this news out now, it may help you in "Helping
Bluebirds Through Wise Management," as the BRAW motto says, while
you are getting ready for the spring 1997 bluebird season opening.
If a box was within 100 feet of another box, this study counted it as
"paired." Hence, the monitors reported all their paired boxes,
be they paired within 10, 20, 30, 40, 50 feet, etc. and up to 100 feet
from another box, as in the "paired-box" category. The
conclusions are not statistics-based speculations or extrapolations, and
they don't required esoteric hypotheses. This study reports actual bird
production results, for singles-boxes and for paired-boxes.
With box pairing, the bluebird fledged per box numbers dropped to
about half, and the tree swallow fledged per box increased by about a
fourth, when compared to the singles results. Hence, in paired
situations, tree swallow production, per box site, more than doubled,
generally speaking.
The drop in bluebird production with pairing should be emphasized?
Another impact of paring for bluebirders, shown by this BRAW study, is
that box pairing shifted the bluebird/tree production balance downward,
in favor of tree swallow production. Moreover, the 1996 BRAW data
clearly suggests that in your area of Wisconsin, if you did not produce
an excess of tree swallows using singles, you probably would produce an
excess of tree swallows using paired boxes. The BRAW data also clearly
suggests that in your area of Wisconsin, if you started out by producing
an excess of tree swallows using singles, your situation would have
gotten even worse by pairing, and much worse is you use Hill Lake boxes.
The production numbers appear to me to be saying that, as far as the
bluebirds are concerned, the second box in the box pair causes the box
site to be supersaturated with boxes. But, as far as the tree swallows
are concerned, the second box does not cause the box site to be
supersaturated with boxes.
BRAW members and monitors should be proud that in the BRAW paired-box
study, monitors reported the actual numbers of bluebirds and tree
swallows fledged, and hence the actual production of bluebirds and tree
swallows was determined. To our knowledge, no other state or provincial
bluebird organization does that, not even the fine large organization in
Minnesota.
DISCUSSION - Some pairing partisans, with no data that we know of to
support it, have expressed "common sense" positions that if
they don't pair, they don't keep a box "open" for bluebirds,
etc. There seems to be no end of the hypotheses in favor of pairing in
the popular literature, but none of it has any data to support it, to
the best of our knowledge.
Quite to the contrary, thanks to the 1996 BRAW monitors, we now have
the actual bluebird and tree swallow production numbers for both singles
and paired boxes from the entire State of Wisconsin. And these actual
bird production numbers clearly showed (a) that pairing did not enhance
bluebird production, and in fact dropped it, and (b) that pairing caused
tree swallow production to overrun bluebird production.
And, the production results say to me that if more bluebird
production is wanted, single box trail management is the choice that
will do it, and that box pairing is the choice that will work against
it.
Here in NEBRASKA, I personally have had great success with
paired boxes. I submitted the following article to NABS which appeared
in Sialia (Spring 1997, Vol. 19, No. 2.)
To Pair or Not to Pair
To pair, or not to pair, that is the question. Whether 'tis wiser
on the trail to suffer the slings and arrows of swallow overpopulation,
or to take arms against a sea of swallows and by pairing, end them.
Do I have a computer full of figures, statistics, and data analysis?
No. Am I an expert statistician? No. Did I pass my basic high school
math courses? Barely. What I want to share with you is four years of
trail experiences and observations of tree swallows with paired boxes on
Wachiska Audubon's Bluebird trails in southeast Nebraska. Please keep in
mind that this is not, by any means, any type of research project nor do
I consider myself to be an "expert" bluebirder.
These trails were originally put up in 1986-1987 by Nebraska Game
& Parks Commission on wildlife areas in the Salt Valley recreational
areas around Lincoln, Nebraska. Because of a lack of staff by Game &
Parks, Wachiska Audubon (the local Audubon chapter) took over the
monitoring of these trails.
I became chairperson of Wachiska's Bluebird Recovery Committee in
1993 and was in charge of their trails through the 1995 season. Sanford
Downs took over my position in 1996, but I have remained actively
involved with the trails.
The original boxes on these trails were all NABS boxes mounted on
fence posts 3 to 4 feet from the ground. After taking over the trails,
reviewing their past records, and seeing the decline in the bluebird
numbers in recent years, it became obvious that a major trail renovation
was in order.
In early March of 1993, the renovation began. Most of the old NABS
boxes were in poor condition and had to be replaced. The majority of the
boxes removed were replaced with Peterson boxes with some being replaced
with Gilbertson PVC boxes. The Peterson boxes were mounted on 1-inch
pipe and the PVC boxes were mounted on a 1/2-inch conduit placed over
1/2" rebar. Many of the original boxes on the trails were already
paired; but after the renovation, all boxes on the trails were
paired, approximately 15 to 20 feet apart. Some of the box locations
were relocated because of an overgrowth of cedars and/or sumacs.
Before the 1993 trail renovation began, there were 278 boxes on 10
trails. After three years of work and expansion, there are now 355 boxes
on 14 trails. Wachiska Audubon is very lucky to have a good number of
volunteer trail monitors. There is a standard form filled out and mailed
to the chairperson after each weekly trail walk. I set up a record
system where each box has a separate sheet with that box's data recorded
on a weekly basis. This became a tremendous educational experience for
me, as it allowed me to follow the progression of each box on a weekly
basis without having to actually walk each trail myself. (The weekly
report form also provides a space for the trail monitor to indicate any
problems or "unusual activity" happening in or around a
specific box.) I do walk some of the trails on a regular basis and
occasionally substitute on some of the rest, so I do manage to stay very
familiar with these trails. The 52 boxes on my own trail are also paired
(with a high occupancy by tree swallows).
As the chart below shows, there was a dramatic increase in both
bluebirds and tree swallows from 1993 through 1996. Unfortunately, there
is no reliable information on tree swallows fledged prior to 1993.
The Tree Swallows had a 109% increase, compared to the 68% increase
in Bluebirds in that same four-year period. The largest yearly jump for
both birds was 1993-1994, with a 42% increase in bluebirds, compared to
a 54% increase in Tree Swallows.
I believe that if your trail consists of single boxes and your tree
swallow numbers increase to where they are in direct competition with
bluebirds for a box, the only solution is to pair the boxes on your
trail. Referring back to Sialia (Vol. 13, No. 1), Richard Tuttle's
article on tree swallows and paired boxes talks about how the bluebirds
actually benefit from having tree swallows in the neighboring paired
box. His theory is that tree swallows will defend the territory around both
of the boxes, protecting them from usurpation from House Wrens and House
Sparrows. When I am walking a bluebird trail and find a pair of boxes
occupied by tree swallows and bluebirds, I feel good knowing that there
are two pair of birds defending the nesting territory.
In the past four years, I know of only three times that tree swallows
nested in both boxes, and in one instance, one of the tree swallow nests
had been abandoned. In order to discourage tree swallows from nesting in
both boxes, I believe that 25 feet should be the maximum distance
between paired boxes. On the other hand, I would keep a minimum distance
of 15 feet between paired boxes because of the natural competition
between the two species.
I believe there are numerous benefits to pairing boxes. But there are
certain circumstances when box pairing won't eliminate conflicts and
competition between these two birds. When the bluebirds' first nesting
attempt is delayed due to weather conditions, the bluebirds' and tree
swallows' first nesting attempts coincide. If the the bluebird hasn't
laid claim to a nesting box before the tree swallows arrive, there may
be direct competition for a particular box. Nest failure by one or both
birds can also affect the compatibility of these two birds, as well as
nest usurpation by both species.
As pointed out earlier, what I have shared here are simply four years
of observations from established bluebird trails in Nebraska. For more
detailed information on the compatibility of the bluebird and the tree
swallow, I would refer you to two excellent reports written by Richard
Tuttle which are found in Volume 9, No. 1 and Volume 13, No. 1 of
Sialia.
Remember, also, that we should be helping other cavity-nesting birds
such as the tree swallow. They are always a pleasure and add an extra
dimension to walking a bluebird trail.
