All over Oakland Township – along the Paint Creek Trail and in Draper Twin Lake, Charles Ilsley and Bear Creek Parks – citizen scientist volunteers are busily monitoring nest boxes twice a week for Cornell Ornithology Lab’s Nestwatch program . I posted last year about the training we receive through our township stewardship manager, Dr. Ben VanderWeide’s annual workshop and Cornell’s online resources.
As a volunteer monitor for the boxes at Bear Creek Nature Park this year, I’ve kept my eye on two species of bright blue native birds : Tree Swallows (Tachycineta bicolor) and Eastern Bluebirds (Sialia sialis) . It’s been such a joy, and it’s also taught me that citizen science can sometimes challenge the heart.
Eastern Bluebirds From Egg to Flight
The Bluebirds have had a good year in the brand new boxes at Bear Creek. Fourteen baby birds from three different boxes have taken the big plunge and ultimately flown out into the summer sunshine. It always strikes me that the moment that little birds fly is really a second birth for them after emerging out of their eggs. What a moment that first flight must be – much like exiting from the womb for human babies – moving from a cozy darkness to a big, bright, demanding world outside.
It all begins, of course, with a nest and an egg. The male Bluebird attracts a mate to a tree cavity or nest box by dropping in a little nesting material and either popping in and out of the hole or sitting on the box fluttering his bright blue wings. But once a pair has mated, the female builds the nest – a cup of nicely woven grasses and occasionally some pine needles. She lays one small egg each day, usually in the morning. Bluebird females don’t stay on the nest all day. They come and go to feed. Incubation takes 11 to 19 days. (Click on photos to enlarge; hover cursor for captions.)
Bluebird babies hatch out naked, blind and completely helpless. The ornithology term is “altricial” as opposed to “precocial,” which refers to baby birds like the Killdeer that emerge from the egg ready to run and feed. At first, black feathers appear under the nestlings’ skin looking like blue-black splotches. Gradually feathers emerge here and there on their tiny bodies. I’ll bet the beaks of nestlings are lined in white because they help the parent stick the caterpillars in the right place inside that dark cavity.
From hatchling to fledgling takes another 17-19 days for bluebirds. The feathers develop first in spiky looking “sheaths.” I think that’s what we’re seeing in this photo about a week after the nestlings hatched.
Gradually the sheaths drop away, leaving a white dust. The feathers begin to unfurl. As you can see below, nests get pretty crowded as the nestlings grow. Perhaps feeling a bit cramped is nature’s way of encouraging these little birds to take flight. Also, according to Stokes’ Guide to Bird Behavior (Vol.3), the parents feed them less often just before fledging, so that they are more motivated to get out where the food is. Tough love in the bird world evidently!
This summer, I haven’t been lucky enough to arrive at the Bear Creek nest boxes when fledglings are emerging from a nest box. But last year, I was fortunate to be home, camera at the ready, when the first bluebird took off from a nest box in our field. First it hesitated with its tiny feet at the hole and looked around.
After a bit of nervous looking around, it gathered its courage and dropped from the hole, wings up ready for the downward stroke, body and legs hanging below!
And then those blue wings, still partially in spotted brown, spread out for the first time. So exciting!
Normally, the fledgling will fly onto a low branch of a nearby tree or shrub and then flutter their way to higher branches. According to Stokes, the parents will bring the fledgling food for the next three to four weeks. But if the adults mate again during that time, the job of feeding the young falls to the male while the female starts another clutch of eggs.
A variety of predators, of course, can interrupt this miraculous cycle. In the park this year, three bluebird eggs in one nest box simply disappeared a few days after they were laid. I could only guess at the culprit. House Wrens are known to dispose of other birds’ eggs by removal or pecking and they would fit in a nest box hole. It seems doubtful that a snake or raccoon managed to get past the predator guard. Whoever was the nest thief, the bluebird adults were resilient. About a week later, three more eggs appeared in the nest box. This time, they hatched and are now almost fully feathered. I expect them to take wing some time next week.
Tree Swallows Literally Feather Their Own Nest!
The beautiful blue and white Tree Swallows had a tougher time than the Bluebirds this year but nine little Tree Swallows added their blue to the sky anyway. They arrived in late April and began mating displays.
I was pleased to find the beginnings of nest building in the boxes. But shortly thereafter, we had a severe cold snap and the Tree Swallows disappeared for a week or so at least. My fellow monitors and I guessed that the insects that they feed on in flight were wiped out by the cold so the Tree Swallows temporarily flew farther south. According to The Stokes Guide, this behavior isn’t uncommon for Tree Swallows in inclement weather.
By mid-May, the swallows returned and began adding material to their nests. Tree Swallows use grasses as a base for their nests, but they line the nest with feathers, white ones being a particular favorite. Eventually I began to see little white eggs not much bigger than a large jelly bean in three of the boxes. I was so glad to have the swallows nesting again that I decided to forego taking a photo. So here’s a photo of a single Tree Swallow egg shared by a generous iNaturalist.org photographer who uses the name caw33iii.
Eventually, one of my three Tree Swallow boxes had six eggs. Tree Swallows incubate their eggs for 11-19 days also. When I arrived on the 21st day, I was greeted by this lovely sight – one or two day old hatchings! I couldn’t resist a quick cellphone photo. You can see the blue pigment of feathers beneath the skin and of course, white beaks again and completely blind eyes. Such a pretty variety of feathers in this soft, cozy nest!
These babies did just fine, because they seemed to have very experienced parents. Unlike Bluebird parents who will usually flush from the nest as I approach or simply scold from a nearby tree while I monitor, Tree Swallow parents take, let’s say, a more active role! Once when I approached to monitor, a female Tree Swallow just stuck her head out the hole and refused to leave. I went my merry way without data.
Every time I arrived to peek in this nest box, an adult swooped over me repeatedly, issuing liquid warning calls. I’m glad that these parents so fiercely protect their young, so it made me laugh each time. I trust these skillful fliers; they’re just sending a warning to an interloper they have no reason to trust. I always finish my peek in any nest box in less than a minute anyway, as the Nestwatch training advises. The last thing I wanted to do was discourage this conscientious couple!
I believe I arrived late on this clutch’s fledge day, because I heard lots of twittering deep in the nearby bushes. Generally all the fledglings leave on the same day, though occasionally one of them needs an extra day. And indeed, when I took a quick, careful peek into the box, only one little fledgling was left there, probably still screwing its courage to the sticking point. Again, the parents sailed over my head, encouraging me to leave. I took their advice. When I visited again three days later, I was pleased to see that the last little fledgling had taken off into the blue as well.
Tree Swallow fledglings are much more precocious than fledgling bluebirds. They can fly and scoop insects out of the air on their own in just 2 or 3 days! Since I have no Bear Creek fledging photos, here’s one I took two years ago of a fledgling Tree Swallow at Draper Twin Lake Park. It had flown high up onto a guy wire but was having a little trouble sticking the landing!
Another Tree Swallow nest box at Bear Creek did not fare so well this year. Three eggs never hatched and the other three fledglings simply died shortly before their fledge date. I gently removed them from the nest, limp in my palm, and carried them a distance away in the deep grass under a shrub, so predators would not be attracted to the other boxes. A sad afternoon. Perhaps I missed signs of violence but I looked and didn’t see any. Perhaps the parents were less adept at finding food after the cold spring delayed the hatching of insects. But I’m just guessing. It may have just been a challenging year for these Tree Swallows.
Despite a few casualties, the Bear Creek nest boxes have already fledged nine Tree Swallows and fourteen Eastern Bluebirds. And we still have 3 Bluebird eggs and 4 Bluebird hatchlings in two boxes. And that’s just the six boxes in one park! Imagining these small blue birds out in the greenery all over the township, growing, practicing their foraging and flying skills and preparing to make the fall migration makes me very happy.
Both of these species have suffered steep declines over the years. Bluebirds are recovering largely because humans began to provide nest boxes for them back in the 1960’s and 70’s. Tree Swallow numbers have declined by 49% in the last 40 years, but perhaps the nest boxes and the information gathered from them will eventually boost their numbers as well. We have to hope so, because summer would not be as glorious without these little scraps of blue sky winging their way above our flowered fields.