The Case of the Disappearing Eggs

Text and photos © 2015 Adele Wilson, author of Bonding with the Barn Swallows

Unhatched Bluebird Eggs

Bluebird pair, May 12, 2015

If you are following this blog, you know that a pair of Eastern Bluebirds began nesting in Box #1 on May 10^th.  The photo to the right shows the male and female Bluebirds on May 12th.  The female is holding straw to carry into the box.

The female Bluebird laid five eggs, one per day, beginning on May 19^th.  However, as of June 6^th, I had not seen the female around for a couple of days.  I did not observe her presence on the following days, either.

The five eggs never hatched.  It had become obvious that the female Bluebird had abandoned her nest without having incubated her eggs.

[Note:  At the end of this post is a timetable giving significant dates and observations.]

Tree Swallow Eggs

In the meantime, a pair of Tree Swallows had begun nesting in Box #2 on May 19^th and the female had begun laying eggs on May 28th.  By June 3^rd when I checked the box, I saw at least five Tree Swallow eggs.  There could even have been additional eggs that were being obscured by a feather.

Male on fence, female peeking out of box

Unlike the Bluebirds, the Tree Swallows were diligently incubating their eggs and protecting their nest.  Each day from my porch I would observe the male Tree Swallow guarding the box while perching on the fence several feet away from it.  The female would be inside the box, often peeking out of the entrance hole.  When the female went out to catch food, the male would take over incubation duty.

On June 9^th, I checked the Tree Swallow box again.  The female was inside the box, but flew from it when I was about 5 feet (1.5 meters) away.  I opened the door and held a mirror above the nest, but all I saw was a heap of feathers.

Tree Swallows typically use feathers to cushion and protect their eggs; so I was not surprised.  However, I decided not to tamper with the feathers for fear of alarming the birds.  After all, from my observation on June 3^rd, I already knew that the nest contained at least five eggs.

The New Bluebird Nest  

New female Bluebird, June 12, 2015

The male Bluebird continued hanging around the Bluebird box, even after his mate had left the premises and abandoned the eggs.  Fortunately, as described in my previous post, a new female Bluebird arrived at the box on June 12^th.  What an exciting day that was!

The new female began carrying straw into the box, a sign that she was building her own nest on top of the old nest, that is, the nest that had been built by the previous female.

On June 15^th, I decided to check the Bluebird box.  I opened the door, held up a mirror, and was shocked by what I saw.  All five unhatched eggs laid by the previous female were missing!

I was dumbfounded.  Had the eggs been removed by a predator – perhaps a bird, a snake, or even a human?

It had been a clean removal.  There was no evidence of crushed eggs.  There were no eggshells in the nest or on the ground below the box.  Eggshells or crushed eggs would have been evidence of a raccoon, sparrow, wren, or possibly a cat, having preyed upon the eggs.

  

I frantically began researching Bluebird nesting behavior.  I discovered that, when a new female Bluebird arrives at a previously built nest that contains unhatched eggs, she will either build a nest directly on top of the old eggs or remove the eggs and continue adding to the previously built nest.

The fact that the old, unhatched eggs had disappeared from the nest in such a clean, sanitary way therefore led me to consider the possibility that the new female had removed them.  At any rate, it was just as well that the old eggs had been removed because it freed me from the decision of whether to remove them or not.

Barring the possibility that a human had been responsible for the removal of the eggs, the only other type of predator that could have removed the eggs so cleanly would have been a rat snake.  Both of our bird boxes are mounted on 3/8-inch (0.95 cm) diameter poles, 4 to 5 feet (1.2 to 1.5 meters) above the ground.  Both boxes’ entrance holes are 1 9/16 inches (4 cm) in diameter.  The poles do not have predator guards; so predation by a rat snack could have been a possibility.

However, despite the fact that three different species of birds have nested on my porch each summer since 2011, I have never seen a rat snake on or near the premises.  I will “never say never”, though.

I concluded that when the new female Bluebird arrived on June 12^th and began adding straw to the old nest, she decided to do some thorough house cleaning.  She must have removed the old female Bluebird’s unhatched eggs in preparation to lay her own.

That seemed like reasonable explanation for the old Bluebird eggs disappearing.

Checking the Tree Swallow Nest – the Surprise

On June 15^th, just a moment after I had checked the Bluebird box (Box #1) and discovered that the unhatched Bluebird eggs were missing, I walked over to Box #2 to check the Tree Swallow nest.  As usual, the male Tree Swallow was perched near the box and the female was inside the box peeking through the hole.

But there was something very different occurring this time.  The female Tree Swallow inside the box was acting unusually jittery and skittish.  She was extremely alarmed that I was approaching her nest.  The photo to the left shows the way the female would usually look when she was peeking out of the box.  But on this day, I could see her twitching her head and scurrying about on the inside of the box.

I decided not to try to open the door on the Tree Swallow box.  The female Tree Swallow would have certainly flown from the box, but I didn’t want to upset her any further.

A day later, on June 16^th, I decided it was again time to try to check the Tree Swallow box.  Based on my calculations of egg-laying dates and incubation times, the Tree Swallow eggs should have started hatching by that date.

To my dismay, the Tree Swallows were nowhere near their box.  Strangely, neither the male nor the female Tree Swallow had been around all day.  Each day for the past three weeks both the male and female Tree Swallows had been fiercely guarding their box.  But that was not the case today. 

I walked to the box, opened the door, held up a mirror, and saw what to me was a ghastly sight.  The nest was completely bare – no feathers, no eggs!!!

There was no evidence of the eggs having been pierced or crushed, and there were no eggs or fragments of eggs on the ground below the box.  The bottom of the nest was clean.  It had been a sanitary removal, identical to the removal of the eggs in the Bluebird box.

My conclusion was that whatever entity removed the eggs from the Bluebird box also removed the eggs from the Tree Swallow box.

Again, I thought about the possibility of a rat snake preying upon both sets of eggs – those in the Bluebird box and those in the Tree Swallow box.  The thought made me cringe.

The Aftermath – Thoughts and Theories

I became extremely depressed.  Now that the Tree Swallows had left the premises, there would be no birds around to swoop at would-be predators.  There are a number of feral cats roaming around, and the Tree Swallows had been doing a good job of keeping them at bay.

The photo above, from May 20th, shows the Tree Swallow box in the background with the Bluebird box in the foreground.  Although the photo does not show it well, the Tree Swallow box is about 75 feet (23 meters) from the Bluebird box.  We had tried to mount the Tree Swallow box at a closer distance, as is often recommended by Bluebird and Tree Swallow organizations, but we were unable to do so.  A distance of 6 feet (1.8 meters) from the Bluebird box had been thwarted because of a rock bed directly under the ground surface, and other locations were restricted by our landlord due to grass-mowing concerns.

Besides, the Tree Swallows had been able to happily nest in their box during the time period when the original female Bluebird had laid her eggs.  It was only a few days after the new female Bluebird arrived that the Tree Swallow eggs went missing.

New female Bluebird, June 14, 2015

Perhaps the new female Bluebird is more vigilant and cautious than was the previous female.  My theory so far is that the previous female was relatively inexperienced at nesting, while the new female is perhaps a little older in age and more aware of the hazards than can exist when nesting close to other birds.  Perhaps, therefore, the new female Bluebird had not only removed the old eggs from her box, but had also, in her desire to have no other birds nesting near her own nest, removed the eggs from the Tree Swallow box.

I have observed some different behavior by the new female that leads me to believe that she is indeed more experienced, and I will cover this behavior in a future post.

On June 18^th, I removed the Tree Swallow nest from Box #2 and thoroughly cleaned the box with a 10% bleach solution from a spray bottle.  The box ended up being soaked, and on top of that we had a fair amount of rain afterwards.  I then decided to have my neighbor take the Tree Swallow box down for a couple of days so that I could bring it inside to dry out.  On the morning of June 21^st, I remounted the box.

Time will tell if there is an egg predation problem occurring in this neighborhood.  If the new female Bluebird lays eggs and the eggs remain undisturbed, it will lessen the possibility that a rat snake or human preyed upon the eggs in both nests.  You can follow this blog to find out what becomes of the new Bluebird nest and whether other birds decide to nest in the now-empty Tree Swallow box.  All you have to do is enter your email address at the top right of this page.

Timetable:

May 10^th – Bluebirds arrive at Box #1

May 19^th – Female Bluebird lays the first of 5 eggs

May 19^th – Tree Swallows arrive at Box #2

May 23^rd – Female Bluebird lays last egg, incubation supposedly begins

May 28^th – Female Tree Swallow lays the first of at least 5 eggs

June 6^th – Female Bluebird has not been around for a couple of days, 5 unhatched eggs still in nest

June 12^th – New female Bluebird arrives

June 15^th – Discovery that unhatched Bluebird eggs had been removed from Bluebird nest

June 16^th – Discovery that Tree Swallow eggs had been removed from Tree Swallow nest

 

If you have found this story interesting, you might want to check out my book, Bonding with the Barn Swallows.  Its 117 photos include closeups of the baby Barn Swallows that were hatched on my porch during 2011 and 2012.  There are also photos of the parent swallows guarding the nest and feeding their young.  As an extra bonus, the book includes photos of five different juvenile Barn Swallows, just ten days after fledging.  You will be amazed at their varied markings.  The book describes how one special male Barn Swallow communicated to me by his body language on the utility wire and how, only two days later, I discovered what he was trying to tell me.  To find out more about the book and read a preview, just click on the image to the right.

 

Two Nest Boxes, Two Bird Families: Bluebirds and Tree Swallows!

Text and photos © 2015 Adele Wilson, author of Bonding with the Barn Swallows

Yes!  Tree Swallows have claimed the second nest box!  After the original Tree Swallow nest in Box #1 was hijacked by Bluebirds on May 10th, we finally mounted a second box (Box #2) on May 19th. 

A pair of Tree Swallows claimed Box #2 on May 23rd and have now started building a nest inside of it.  The photo to the right shows the female Tree Swallow peeking out of Box #2 and holding straw in her bill, straw that she would be adding to the nest inside the box  The male is to the left, flying away from the box.

Sadly, however, this pair of Tree Swallows does not appear to be the same pair of Tree Swallows who were chased out of Box #1 by the Bluebirds on May 10th.

I felt so sorry for the female Tree Swallow who had been building a nest in Box #1 for 9 full days when she and her mate were chased away by the Bluebirds.  The female Tree Swallow and her mate kept hanging around my yard for several days thereafter, mating on the fence during the mornings.  I knew that the female was ready to lay eggs and hoped and prayed that she would find a place to lay them.

Back to Box #1:  The Bluebirds seem to be doing fine, and the female has laid five eggs!  The female is often inside the box incubating the eggs, but she sometimes takes breaks and leaves the box, especially during warm afternoons.

While the female is inside the box, the male brings her food and feeds her through the box's hole, just as if he is feeding a baby. This is an excellent way for him to practice what he will have to do once the eggs hatch!

A couple of mornings ago, I observed the female Bluebird peeking out of the hole of the nest box.  Soon the male came to the box and fed her through the hole.  To my surprise, when the male flew from the box, the female left the box and flew after him!  I wonder if she was chastising him for not feeding her often enough.

The size of the hole on a Bluebird nest box easily accommodates Tree Swallows as well as Bluebirds.  In geographical regions where both species breed, the two species commonly compete for nest sites. 

It is often recommended to mount nest boxes in pairs, one for Bluebirds and one for Tree Swallows.  The reason for this is that Bluebirds and Tree Swallows can coexist in the same breeding territory as long as they both have boxes in which to nest.  Also, the Tree Swallows can help defend both boxes from predators by swooping at any bird, animal, or even a human, that comes close to the boxes.

A pair of Bluebirds requires a radius of 300 feet for its territory and will chase away any other Bluebirds within that radius.  However, Bluebirds that are already established in a nest will not chase nearby nesting Tree Swallows away.

Tree Swallows defend a territory from other Tree Swallows, but only within a 100-foot radius.  They will tolerate Bluebirds in their territory because the diets of Tree Swallows and Bluebirds differ immensely.

While Bluebirds feed on insects and larvae on the ground, Tree Swallows feed on flying insects.  Thus, there is no competition for food within the same territory.

The photo on the right shows the male Bluebird, who has just captured some food.

The recommendation is to mount the two boxes, one for Bluebirds and the other for Tree Swallows, no more than five to ten feet apart.   We tried to do that, but were unsuccessful.

We were restrained by the parameters specified by Bluebird organizations and also by restrictions from our landlord.  Bluebird specifications dictate that, in order to help guard against predators (and we have plenty of roaming cats around here), a Bluebird box must be mounted on a pole and in an open area, preferably at least 20 feet from a building, fence, or tree.  Our landlord restricted us from being able to mount the boxes in the middle of the lawn.  The reason for the restriction was that this type of location would add complications to the chore of lawn mowing.

We received permission from our landlord to mount a box near the septic tank opening, which is about 25 feet from our building.  So that is where we mounted Box #1 on April 24th.

It took only a week for birds to claim Box #1, but the birds ended up being Tree Swallows rather than Bluebirds.  After Bluebirds hijacked the box from the Tree Swallows only nine days later, we decided that we needed to mount a second nest box, one for the Tree Swallows.  The photo to the left shows the two Bluebirds on Box #1 the day they hijacked the box.  The female Bluebird is peering through the hole to check the inside of the box.  The male on the roof looks like he is jumping for joy at having procured a suitable nest box!

We tried to mount Box #2 about 5 feet from Box #1 where it would have not interfered with lawn mowing.  However, a layer of rock about 6 inches below the surface of the ground prevented the driving of the pole far enough into the soil.

The only option at that point was to mount Box #2 along the horse pasture fence where our landlord had also given us permission.  To mount a nest box along a fence is not an optimal choice because predators can sometimes use a fence to gain access to a nest.  However, this is the only choice our landlord gave us based on avoidance of lawn-mowing complications.

We ended up locating Box #2 between two metal fence poles that are about 4.3 feet high and 8 feet apart.  The box is located 28 feet from a 11-foot high wooden fence post that serves as a lookout tower for several different species of birds.  We are hoping that the fence post is far enough away from Box #2 that a large bird cannot use the post to prey upon the birds using the box.

The photo below, from the morning of May 28th, shows Box #2 on the left, separated from the high fence post by three metal fence poles.

The photo below, from May 20th, the day after we mounted Box #2, shows Box #1 in the foreground on the right, with Box #2 in the background.  The two boxes are about 75 feet apart although in the photo they look closer.  This photo was taken three days before the Tree Swallows arrived and claimed Box #2.  I cannot identify the bird perching on top of Box #2 in the photo, but the Bluebirds from Box #1 are perching on the fence.  The male Bluebird is on the wire at the center of the photo, and the female is on top of the fence pole on the right.

While Box #1 is about 4.3 feet high, we mounted Box #2 a little higher.  The distance from the ground to the lower edge of Box #2 is about 5.3 feet.

The higher a nest box is from the ground, the lesser the chance that House Sparrows will use the box.  This is a matter of great concern because we do have House Sparrows in close proximity, and House Sparrows have been known to enter a nest box and destroy the young of the host species.

The day after we mounted Box #2, I noticed a House Sparrow hovering near the entrance hole of that box and perching on the fence next to the box.  To my delight, the male Bluebird from Box #1 immediately flew to Box #2 and chased the House Sparrow away!

Also to my delight, when the Tree Swallows arrived and began investigating Box #2 on May 23rd, the Bluebirds did not chase them away!  What I had read about Bluebirds and Tree Swallows peacefully nesting near one another had proven true.  To this day, the Tree Swallows are still guarding Box #2, and the Bluebirds have not bothered the Tree Swallows.

The photo below shows Box #2 on the morning of May 24th, just one day after the new pair of Tree Swallows claimed the box.  The male Tree Swallow is perching on the fence pole, while the female is inside the box, peeking out.

Optimally, we should have already had Box #1 mounted by early March when our local Bluebirds start choosing their mates and searching for nest sites.  But we did not get it mounted until April 24th. For one thing, my neighbor was mounting these boxes for me as favor.  For another, it took a great deal of time for us to decide upon a nest box design, plan its location, and gather the parts needed for mounting.  Besides, in early March it was likely that the ground would have been too frozen for driving a pole into the ground.

In early March, no Tree Swallows would have been on the scene.  That is because, while Bluebirds remain in this area all winter long, Tree Swallows are migratory and do not arrive here until early April.  Although Bluebirds tend to be feisty and defensive of their chosen nesting sites, they would not have had any competition from Tree Swallows during March.

If you don't want to miss the news about the hatching of the Bluebird eggs or whether the female Tree Swallow lays eggs in Box #2, you can follow this blog by entering your email address at the top right of this page.

If you have enjoyed these photos, you might want to check out the 117 photos in my book, Bonding with the Barn Swallows.  Many of them show closeups of the baby Barn Swallows that were hatched on my porch during 2011 and 2012.  There are also photos of the parent swallows guarding the nest and feeding their young.  As an extra bonus, the book includes photos of five different juvenile Barn Swallows, just ten days after fledging.  You will be amazed at their varied markings.  The book describes how one special male Barn Swallow communicated to me by his body language on the utility wire and how, only two days later, I discovered what he was trying to tell me.  The book is available at Amazon at:   http://www.amazon.com/gp/product/1494481464/ref=as_li_tl?ie=UTF8&camp=1789&creative=390957&creativeASIN=1494481464&linkCode=as2&tag=barnswalfrie-20&linkId=5WME3VAHNSX3EXHH

Yes, it was a hijack! Bad news, good news ...

Text and photos © 2015 Adele Wilson, author of Bonding with the Barn Swallows

Bluebird, May 10, 2015

Yes, it was a hijack! The Eastern Bluebird, so charming and friendly to humans, can be quite nasty toward other birds. Eastern Bluebirds can fight ferociously to defend a nest – or even to seize a nest from another bird, as they did in my yard on May 10th. (See my previous post, “The Hijacking of the Nest Box – Who will win?”, at http://barnswallowfriends.blogspot.com/2015/05/the-seizing-of-nest-box-who-will-win.html.)

During this past March (2015), I did not observe as many Bluebirds around here as I had during March 2014.  Why?  There could be several reasons.

Bluebird, Nov. 9, 2014

For one, we had unseasonably wintry weather here during November 2014.  It was extraordinarily cold, and we had two snowfalls that month – quite unusual for this area.

During the winter of 2013 to 2014, each month I would observe at least one Bluebird around my yard.  But this past winter was different.  The Bluebird shown on the left that I saw on November 9, 2014, would be the last Bluebird I would see until March 9, 2015.  On March 9th I sighted a pair of Bluebirds, one at a time, on the wire across the road from where I live.  I did not see any Bluebirds near my yard until March 23rd.

Although our local Bluebirds stay around during the winter, they are unaccustomed to extremely cold weather during the month of November.  As winter approaches, Bluebirds look for warm places to roost during frigid nights.  They often roost either inside the nest boxes they used during the past summer or inside building structures where there are entrance ways into attics or crevices that lead to the undersides of roof beams.  These birds can also roost in pre-existing cavities within large tree trunks, places where they have nested during warmer weather.

However, when it came to finding warm winter roosting spots, I don’t think our Bluebirds had much warning last fall with our sudden frigid temperatures and snow storms.  It is said that one of the worst enemies of the Bluebird is “Jack” – Jack Frost, that is.  With “Jack” descending on us so quickly during late 2014, I think it caught the Bluebirds off guard, and some of them may have perished that month.

Our past winter of 2014 to 2015 was extremely cold, but we did not have the record-breaking amount of snowfall that the Northeastern US received.  Nevertheless, Jack Frost may have played a role in diminishing our Bluebirds’ winter survival rate.

An unusual event began taking place around here in mid January 2015 – one that may well have had a negative impact on our local Bluebirds’ survival.

In mid-January, a contractor hired by our local power company began chopping down trees and branches that were threatening to fall on power lines during high winds and heavy snowfall.  The process was noisy and lasted for several weeks.

If any of those trees contained old woodpecker holes in which Bluebirds were roosting at night, the tree-cutting process could have caused some of our Bluebirds to lose their warm, nocturnal sleeping stations, resulting in the demise of those birds.

I did notice that, when the contractor first began cutting trees, a Pileated Woodpecker began appearing at my suet feeders and continued to do so for many weeks thereafter.  I have wondered if the tree-cutting resulted in the removal of dead tree trunks inside which the Pileated Woodpecker had been finding beetle larvae.  Pileated Woodpeckers are able to feed on that type of larvae during the cold months.  The answer is unclear, but it seemed that SOMETHING had brought that Woodpecker out in the open at exactly that time. 

Female Pileated Woodpecker, morning of Jan. 12, 2015

Since we had so few Bluebirds around this past March, I took that as an imperative to put up a Bluebird nest box.  I began talking to my very mechanical next-door neighbor about it.  Perhaps, if we put up a nest box, a pair of Bluebirds would find it and raise some babies in it, resulting in an increased Bluebird population in our neighborhood during the spring of 2016.

By mid-April I had purchased a Bluebird nest box.  I had already purchased one last October at a craft show, but that one was too heavy to be mounted on a thin pole.  The reason for mounting the box on a pole would be to help guard against predators.

My neighbor was studying the specs for mounting the nest box. We began planning the location of the box in accordance with permission from our landlord and the guidelines for mounting Bluebird boxes.

Tree Swallow on wire

On April 17th, my neighbor and I were standing on our porch, discussing plans for the nest box. I pointed to a Tree Swallow that was perching on the nearby wire and told my neighbor, “That’s what we’ll probably get: Tree Swallows.” I said this because it was well past the beginning of the first brooding season for Bluebirds. Bluebirds can build two or three nests per season, but the first nesting season generally begins in March. By April 17th, our local Bluebirds were probably well underway with their first nests of the season.

I then told my neighbor not to be disappointed because “we might not get a Bluebird.” Just as I said the word “Bluebird”, an uncanny event occurred. A Bluebird landed on the wire right above our driveway! See “Did the Bluebird hear me call its name?” at https://www.facebook.com/notes/adele-barger-wilson/did-the-bluebird-hear-me-call-its-name/10153174426857040. The photo below shows the Bluebird that landed on the wire that moment.

The Bluebird that landed on the wire when I said "Bluebird"

We finally got the nest box mounted on April 24^th.  According to my research, we were far too late to have Bluebirds claim the box for their first nest of the season.  

Tree Swallows claim nest box, May 1, 2015

Just as I had suspected on April 17th, when I had pointed to the Tree Swallow on the wire, we did not get Bluebirds claiming the box. On May 1st a pair of Tree Swallows showed up and began building a nest inside the box that very day.

We were so fortunate to get birds claiming the nest box only one week after we had mounted it!  Although they were not Bluebirds, I was overjoyed!  Tree Swallows eat flying insects, acting as a natural form of pest control.  And we would be helping to increase our local population of this species, a species that I had not begun to observe in this neighborhood until April 2013.

But on May 10^th, the nest was hijacked!  The poor Tree Swallows!  The female was still in the process of building a nest inside the box that morning, when, not just one, but TWO male Bluebirds appeared and fought over the box.  One Bluebird won, and then started fighting the male Tree Swallow for possession of the box.

Sadly for the Tree Swallows, the Bluebird and his mate won.  They began adding to the nest, building its edges up higher.

The magical part of the story is that yes, the Bluebird DID hear me call its name on April 17^th while I was talking to my neighbor on the porch!  Yes, we did get Bluebirds!

Feeling sorry for the Tree Swallows who lost their nest, I convinced my neighbor to put up a second nest box, which he mounted on May 19th. The new nest box was mounted about 75 feet from the first one. It was the best location given the parameters for the mounting of Bluebird boxes and restrictions by my landlord regarding the location of the box.

Immediately, the two Bluebirds who had claimed the first nest box began perching on the second box and investigating it.  Oh no, I thought, will the Bluebirds prevent other birds from using the second box?  The Bluebirds had seized their current box from the Tree Swallows; would they also keep the second box under guard?

Below is a photo, taken May 20th, of the second nest box in the background, with the first nest box in the foreground.  The Bluebirds who were nesting in the first nest box are perching on the fence near the second (more distant) box!  The male Blue bird is on the top fence wire, and the female is on the second fence pole to the right of the second box.  I do not know what type of bird is perching on top of the second box!

So, did any birds end up claiming the second nest box?  And how about the Bluebirds?  Did they continue to use the first box, or did they shift to the second box?  And did any eggs get laid in the first box?  You can follow this blog at the upper right to find out!

I first began having intimate encounters with wild birds when Barn Swallows nested on my porch during 2011 and 2012.  During those encounters, I became convinced that humans and birds can develop meaningful rapports, communicate with each other, and enjoy mutually beneficial relationships.  You can read about how one special Barn Swallow communicated to me in my book Bonding with the Barn Swallows, available at Amazon at:   http://www.amazon.com/gp/product/1494481464/ref=as_li_tl?ie=UTF8&camp=1789&creative=390957&creativeASIN=1494481464&linkCode=as2&tag=barnswalfrie-20&linkId=5WME3VAHNSX3EXHH

The Hijacking of the Nest Box – Who will win?

Text and photos © 2015 Adele Wilson, author of Bonding with the Barn Swallows

The morning of May 10^th began in typical fashion.  The female Tree Swallow was perched on the top of the nest box holding straw in her bill – straw to carry into the box to finish building her nest.

While the female Tree Swallow flew into the nest hole with straw, the male Tree Swallow would guard her from either the top of the box or from the nearby fence post.

I wondered when the female would finish building the nest. She and her mate had claimed the nest box on May 1st, just one week after we had put it up, and she had started building the nest that very day.

The last time I had looked inside the box – on the evening of May 8th – there had been a beautifully woven, circular nest inside. Two dark feathers had been placed at the right front of the nest.

All seemed calm and peaceful that sunny morning of May 10^th.  But then, a surprising event occurred.  A pair of Eastern Bluebirds showed up – male and female – and landed on the box!  The Tree Swallows were nowhere in sight.  Perhaps they were flying over the nearby hayfield, catching a late breakfast of flying insects.

Both the male and female Bluebirds immediately began investigating the box.  While one bird perched on the top of the box, the other would peek through its entrance hole.  The photo to the right shows the male on top of the box, with the female on the front.  The hole does not show in the photo, but the female is pointing her bill toward it.  From the photo you can see the brightness of the colors of the male in comparison to the duller colors of the female.

Eventually, the female Bluebird flew from the box, while the male stayed.  All at once, another male Bluebird appeared, and a fight ensued between the two males – right on top of the nest box!

I am not sure which Bluebird won the fight, but soon afterward, the male Tree Swallow returned to the top of the box and started another fight.  This time, two different species were fighting for ownership of the nest box – the Tree Swallow and the newly arriving Bluebird!

As I watched the two males lunge at each other, one bird dropped to the ground, and the other bird followed.  For a few seconds, it looked like the Tree Swallow was on top of the Bluebird, pecking away at him.

The Bluebird then escaped and flew to a nearby tree.  I was hoping that he was not injured and that he had survived the attack.

Later that day, I began second-guessing myself about having seen two male Bluebirds fighting over the box earlier that morning.  Perhaps one of the birds in the skirmish had actually been the male Tree Swallow.  In the right type of sunlight, it might be easy to mistake a male Tree Swallow for a male Bluebird because of the brilliant blue on their backs.

After all, our local Bluebirds are said to begin their first nests of the season around mid March at the earliest. It was now only May 10th and I had not yet seen any baby Bluebirds around here. Would our local male Bluebirds actually be searching for nest sites in early May?

In this region of the US, it is recommended to have Bluebird nest boxes up by mid March in order for the Bluebirds to use them for their first brood of the season. However, we were late mounting our nest box and did not get it up until April 24th. No chance of Bluebirds very soon, I thought! We were consoled with the thought that Bluebirds might use the box for their second brood, perhaps during late June after the Tree Swallows were finished with it.

 

I doubted whether our local Bluebirds, if they had begun their early broods in March or April, would be finished with the stages of egg-laying, egg-incubation, feeding and fledging the nestlings, and continuing to feed the fledglings outside the nest for a couple of weeks thereafter.  The period from the laying of the first egg to the fledging of the young lasts at least 33, but sometimes up to 45, days. Another 12 days would have to be added to that because that is the length of time that baby Bluebirds still need to be fed once they leave the nest.  And it is the male parent Bluebird who often endures the sole burden of feeding the fledglings because the female is sometimes off to build another nest during that time.  Therefore, the length of time that a male is occupied with breeding activities can be from 45 to 57 days, at least a month and a half.  And that does not include the time period of mating that precedes egg-laying.

Well, I suppose it would be possible for the male Bluebirds to have completed their first brood of the season by May 10th.  Or perhaps the males had experienced unsuccessful nesting attempts or found their mates later in the season then usual.  Another possibility is that cold weather had delayed early nesting attempts.

To attempt to solve the mystery, I reviewed my photos from May 10^th and found proof that I had indeed seen two male Bluebirds!  Here is a photo I took of a tree in my yard that morning.  It shows two male Eastern Bluebirds on the branches, identified by their bright blue plumage.  (The females display a much duller blue and have brownish heads.)  In the photo, the bird barely visible at the lower right next to the feeder is actually a Blue Jay.

By the time the skirmishes were finished, it was late morning.  A pair of male and female Bluebirds kept returning to the top of the box.  I don’t know whether the male was the one who had been in the fight with the Tree Swallow.  But I do know that, by the time the pair of Bluebirds seemed to have claimed the nest box, I didn’t see either of the pair of Tree Swallows on or around it.

Meanwhile, the male and female Bluebirds continued to investigate the box.  Just as the Tree Swallows had done nine days previously, the Bluebirds, one by one, would test the hole for size and enter the box to examine its contents.  Neither stayed in the box for long.  They were too busy checking out the remainder of the box. The photo on the right shows the female peering inside the hole.

In the Eastern Bluebird species (and in other bird species as well), the female is the one who must approve of the nest site.  The male will first find the nest site and “present” it to her, but she is the one who must give the go-ahead to use the site for nesting.

The female Bluebird therefore seemed to be more thorough in her investigation of the box.  After all, she was the one who would have to approve of it.  Consequently, she diligently inspected the outside of the box as well as the inside.  The photo to the left shows the female examining the back of the box.

But wait! What about the Tree Swallows? They were the ones who had originally found the nest box on May 1st, only a week after we had mounted it. The female had started a nest that very day. She had begun gathering straw and grass in her bill and flying into the nest hole with it.

So which species would be using the nest – the Bluebirds or the Tree Swallows?  I began reading stories of joint nests between the two species, nests in which both Bluebirds and Tree Swallows would lay their eggs and help rear the young.

Time would tell whether Tree Swallows, Bluebirds, or both would be using the nest.  You can find out what eventually occurred by following this blog at the top right of this page. 

I first began having intimate encounters with wild birds when Barn Swallows nested on my porch during 2011 and 2012.  During those encounters, I became convinced that humans and birds can develop meaningful rapports, communicate with each other, and enjoy mutually beneficial relationships.  You can read about how one special Barn Swallow communicated to me in my book Bonding with the Barn Swallows, available at Amazon at:   http://www.amazon.com/gp/product/1494481464/ref=as_li_tl?ie=UTF8&camp=1789&creative=390957&creativeASIN=1494481464&linkCode=as2&tag=barnswalfrie-20&linkId=5WME3VAHNSX3EXHH