Thursday, May 21, 2015

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 10th 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 10th.  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 10th 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:

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