When I first saw the nest on June 4th, one adult was present and was keeping quite close to the nest, although she was not yet incubating. When I returned on June 12th, she was sitting on an undetermined number of eggs. Eastern Kingbirds lay two to five eggs; the incubation period lasts 14-17 days and the nestling period lasts 16-17 days. When I returned on June 19th, the eggs had not yet hatched and one adult was sitting patiently in the nest despite the sweltering heat.
The kingbird was sitting with its mouth open; songbirds, including chickadees, crows and jays, often do this on hot, windless days. Because birds lack sweat glands, they cannot cool their bodies by perspiring as humans do. Instead, they open their mouths and pant like dogs. This increases the airflow and causes more moisture to evaporate, thus cooling the bird’s body.
When I returned a week later, the eggs had hatched. Both parents were present this time; one was standing on the edge of the nest while the other hunted over an open, grassy area nearby. The nestlings were too small to be seen, and as the nest is above my head I couldn’t look inside to see how many there were. I couldn’t hear any begging sounds, either.
The adult returned to the nest a couple of times while I was there, and had to submerge his head inside to deliver the food to its young.
One of the adults stands by patiently in between food deliveries:
I returned to the nest during the first week of July and was pleasantly surprised to see that the nestlings were not only visible, but too large to fit inside the nest together! There were four of them, all chirping away and practicing their vocalizations. They still had little white tufts of down sticking out of their heads but otherwise resembled the adults. These wispy feathers are not essential and usually break off or fall out within a week or so after a bird leaves its nest. As such, the presence of these feathers can often determine a young bird’s age fairly accurately.
I could also see the yellowish fleshy gape at the corners of their mouths. In young birds the brightly coloured gape appears very soft and swollen, but once the birds are old enough to have fledged, the gape begins to harden, become less prominent, and darken with age.
The insides of their mouths are also brightly coloured. When the parents bring food to the nest, the nestlings all open their mouths as wide as possible, presenting a bright red or orange or yellow target that tells the adults where to stuff each juicy tidbit. In this image, an adult had just landed on a branch above the nest, causing four hungry mouths to open!
The adult then swooped down and fed one of the babies, leaving the others to cry out for their share. The adult then flew off to find more food.
As this was a once-in-a-lifetime chance to see baby kingbirds in the nest, I decided to shoot some video. Given the vigorous wing-flapping I witnessed, I don’t think it will be long before they fledge; they will likely be gone from the nest the next time I visit. The sound isn’t the best as there is a busy road nearby, but you can hear them chirping away as well as a Warbling Vireo in the background. This video is available in HD.
Watching the kingbird family has been a fascinating experience; it is thrilling to see new life come into the world and watch as they become self-sufficient. Hopefully they will survive the dangerous fledging period and be successful as they learn to fly and to catch food for themselves in the weeks to come!