When Baby Bluebirds Leave the Nest
When it is time for a baby bird to fledge and leave the nest, how does it know how and when to fly away? If you have ever wondered how this fundamental avian life event comes about, this story about Western Bluebird nestlings is for you.
Imagine, for a moment, what it is like to fly. If you have ever watched a hang glider jump off a cliff into the wild blue yonder on a wing and a prayer, you might understand what a bird experiences performing the very same act when it decides to quit its nest.
Bluebird nestling looking outside the nest box
Up until that very moment, the only world a Western Bluebird (Sialia mexicana) hatchling knows exists solely within the bounds of a nest where it has been fed and sheltered by its parents since it pipped its way out of a shell, blind and naked. As the chick rapidly grows and becomes feathered, it can begin to peer over the edge of its confines, out over a brave new world without bounds. What does it think about what it sees?
Should I stay, or should I go? Humankind has wrestled with this existential question since before time, when our evolutionary ancestors went out of Africa. Many thousands of years later, the same question continues to perplex our lives.
What about birds?
The answer, of course, is already predetermined by their biological evolution. There is no doubt the nestling will leave. Instinctively, it knows how to fly. But just exactly when will it go? Today or tomorrow? I was determined to find out.
A few years ago, in anticipation that Western Bluebirds would look for a tree cavity in which to place their bet on a new generation during the coming spring, I installed a nest box on the side of an oak tree in my yard. I placed it at a height of about eight feet above tall grass that would, my hopeful thinking went, cushion a chick in the event of an untimely fall. My reasoning was not based upon any scientific recommendation, but it seemed like a good idea. After all, what did I know about birds falling out of trees? On the other hand, I purposefully pointed it in an easterly direction where it would be illuminated by early morning light, good for the photography project I intended to undertake.
Once bluebirds began nesting in that box, my plan was to position a blind on a knoll 20 feet away, which would put me slightly above eye level with the activity. There, with my presence and movements hidden, I would be able to observe the activity of adult bluebirds occupied with nest building and hatchling care. Most important for me, the ultimate in observational experience would be to witness the exact moment those nestlings became fledglings by taking flight.
Things did not go exactly as I had planned.
It takes about a week for the female to construct a woven, grass cup nest; she then lays one egg per day until the clutch is complete (2-6 eggs) before beginning incubation, which might last twelve to eighteen days. Hatchlings will fledge once having gained enough weight, and grown strong enough to go out on their own (14-21 days).
I was able to document each of these stages because I had been fortunate enough to observe a two adults performing courtship routines around my tree. I wrote about this event in my narrative, Bluebird Tango here.
Since I knew when, within a few days, the nestlings would most likely fledge, I began carefully watching the nest box everyday in anticipation of the big day. When rain started to fall one morning, I chose not go outside with my camera equipment. Of course, that would be the day those little birds left the nest. To compound my feeling of disappointment, two days later, I found their tiny bodies on the ground, perhaps victims of starvation due to parental neglect (bluebird fledglings need parental attention for three to five days, sometimes more).
Aaah!
In spite of that setback, I remained hopeful that the pair would lay another clutch of eggs, and that I’d have another opportunity to see bluebird chicks take flight. Instead, Ash-throated Flycatchers set up shop in that same nest box, so something different was now in play.
Would I have a new, unexpected opportunity to watch and learn about flycatchers reproductive cycle? Not a chance: they abandoned the nest site after only a few days. The sole consolation to be had was the discovery that these insectivores often line their nest with fur, and in this case, I discovered a piece of ground squirrel tail tucked in with the other nesting materials.
That nest box remained empty, much to my chagrin, the following year. During that time, bluebirds seemed to have settled elsewhere, as I seldom saw or heard them around the property, including December when my pyracantha tree becomes loaded with fruit, and many fruit-loving birds gather there. I had to set my sights on spring of 2024 for another opportunity to materialize. It was a long wait.
Having detailed all of the aforementioned information, and not wanting to leave you in suspense, I’ll tell you here and now that it all worked out to my satisfaction. Not as I had anticipated, mind you, as you will soon discover. When nature is involved, I’ve learned to expect the unexpected.
It was on April 18, 2024 when, by pure chance, I observed adult bluebirds going in and out of the nest box. I just happened to be passing by with a wheelbarrow full of planting materials for the expanded native plant garden my wife and I had been diligently preparing during the preceding weeks. Because of that preoccupation, I had completely missed noticing their arrival, courtship displays, and nest building activities.
It was evident that the adults were now feeding chicks, and I was ecstatic at the prospects for close observation. I just knew this would be the year I would get answers to my questions about how and when the chicks would spread their wings, and fly off into the wild bluebird yonder. Would they practice beforehand? If so, how would they do it while confined as they were? The answer would become manifest soon enough.
Both adults entered the box with food in their beaks. When they exited, they carried out fecal sacks the nestlings excreted after each feeding. Between the two adults, they averaged 30 trips per hour, and often arrived within seconds of each other. No need for air traffic controllers, these birds landed without ever having a collision. They’ve earned their wings.
I did the math: even assuming they kept this pace for only six hours of, say, a ten hour day, the two adults delivered an astonishing number of food servings for their offspring, not to mention for themselves, during the time the chicks remained in the nest.
Did they have helpers? It is not unusual for an un-mated, male Western Bluebird adult offspring from a previous generation to help out, but I did not observe any evidence of that behavior this year.
Bluebird removing fecal sac from nest
The first days of my observations, I could see no movement in the shadows of the box. Because of that fact, I surmised that the embryos had probably hatched only three or four days before. Knowing their approximate age, I had a reasonable idea of when to begin paying closer attention to the nest box activity.
While adult Western Bluebirds do consume fruits, nestlings require a strict protein diet in order to grow quickly. Invertebrates provide that nutrition, some coming from the air, some from leaves or branches, some from the ground, and some from around water.
Without having closely observed my bluebirds, I would never have imagined that around my property (and perhaps yours, too) there existed such an extraordinary smorgasbord of invertebrates: caterpillars, grubs, beetles, butterflies, moths, and other flying insect that the adult bluebirds seemed to find with ease. The list even included a 6” long worm that became the object of an epic tug-of-war between adults and chicks. It is no wonder, then, that before pesticides, farmers often installed nest boxes in their fields to reduce insect damage to their crops.
Bluebird pulling huge worm from baby bird
The following chronology details how the final eleven days of the nestling drama unfolded:
April 24 - Through the opening, I now watch three little heads jostling around inside the box.
April 30 - From time to time, a single chick manages to poke its face up into the opening.
May 3 - A single chick juts its head out, filling the entire opening, such that I cannot see any other heads at the same time. That head then retracts, and a few moments later another head appears. Are the chicks taking turns, climbing on top of each other to be able to look outside?
Their cavernous mouths are wondrously agape, and eager to engulf, whole, whatever morsel is placed inside. How can those little orifices stretch so far? The chicks are clearly larger now, fully feathered, and more aggressive in their movement; repeatedly, they thrust their bodies into the box opening.
Bluebird gaping mouth
May 4 - This will be the day, I’m sure, for which I had been waiting so many months. I can just tell by the extent the chicks push their shoulders outside the nest box, enabling them to turn their heads up, down, and around in every direction, surveying the surroundings.
Bluebird chick leaning outside of nest box
From all appearances, they are now thinking outside the box. For these three nestlings, the pivotal life question, “should I stay or should I go,” has been decided.
I covertly wait inside the blind for the decisive moment to happen. All the while, a little voice whispers: “don't take your eyes off the box; don't fiddle with camera settings; don't check your notes; don't blink. You will miss the show. Just don’t.” Fortunately, having learned from past experiences, I heed that sage advice.
Honestly, I wasn’t sure exactly how things would transpire, having never witnessed a bird fledge. Had the nestlings been in an open, unconfined nest, I could imagine that the future flyers would stand erect and flap their wings, testing their strength before an attempt to defy gravity. Alternatively, perhaps they might hop out onto an adjacent twig to perform the same exercise. Inside the box, however, those options were not available.
The lift off happened so much faster than I ever could have had imagined. With determination, the first chick wiggled its shoulders completely outside the hole, leaned far forward, and with both feet hanging out over the edge, it gave a non-retractable shove.
Bluebird fledgling leaving nest
Swoosh! It was gone.
My first time experience of watching a bird fledge was truly a thrill. A second chick followed two minutes later. It is possible that I might actually have blinked and missed something, but thank my lucky star, I filmed it all to be sure.
It would be normal for all the nestlings to fledge in succession. So, to tell the truth, I was now hoping for a threesome.
Above, in the adjacent sycamore tree, an adult bluebird made repeated encouraging calls, which I loosely translated as meaning: “come on, fly baby fly.” Achingly, the coaxing was to no avail.
The third chick stayed put. Alternatively, it appeared in the box opening, without leaning too far out, and then retreated back into the darkness of the box.
Bluebird nestling face
Storm clouds began rolling in, true to the morning forecast. The temperature quickly dropped ten degrees. Would this chick fledge under these worsening conditions? It demonstrated no inclination to leave. The adults ceased their entreating calls. Instead of continuing to feed their recalcitrant chick, they departed. Now lacking both food and encouragement, that third chick looked, if only in my mind’s eye, so forlorn whenever it gaped its hungry mouth outside the box.
All things considered, and pleased with having witnessed two chicks successfully leave the nest, I decided to pack up my gear, like I had done two years before when it began to rain. I would return early the next morning to verify if anybody was still home.
May 5 - Nature, once again, had a surprise in store when I went outside before the sun rose over nearby Revis Mountain in the foothills of the Sierra, south of Yosemite National Park, where I make my home. Can you guess what it was?
I went outside shortly after 5:00 a.m. to see if anything was happening at the nest box. With the aid of binoculars, which helped me peer through the faint morning light, I could see being fed, not just one chick, but two. So, all along, there had been a fourth chick that I had not previously counted.
Photographing these two remaining chicks would be a well deserved bonus for my bluebird photography efforts. With experience now behind my belt, I knew what to do. What a serendipitous turn of events.
Since it was still dark, and anticipating that these remaining chicks would not wing away until after sunrise (just like their siblings the previous day), I retreated to my kitchen to make breakfast.
At 7:15 a.m., and with great expectations, I returned to the blind. That would allow just enough time to set my tripod and camera in place before 7:30 a.m., when the rising sun would illuminate the nest box and provide another hour of soft, early morning illumination.
I waited.
And then, well … I waited some more. Something was off. The distinctive sounds, those of adult bluebirds chattering and nestlings begging, that accentuated the avian dawn chorus soundscape on previous days, had gone silent. Now, all my bluebird fledglings were gone with the wind. The nest box, empty and still, remained as reminder of past failure and success, and hope for a future generation of bluebirds.
Nest box for bluebirds
The following video is a chronological compilation of several clips that illustrate the various behaviors that occurred during the final week of my bluebird nest box miniseries, including the exact moment, and surprising denouement, when two nestlings become fledglings. With it, I hope that you will experience the same excitement that that motivated me to create it for you. View in full screen for closeup view. Please turn on your speakers.
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