Originally published by Wild River Audubon:
Last spring thousands of bluebirds were lost when they encountered wet, freezing weather while migrating north through the central states. As the monitor of the bluebird trail in Wild River State Park, I wondered how many of “my” bluebirds would return to the park’s nesting boxes.
This is my fifteenth year as the monitor of bluebird boxes in Wild River State Park. I do it for the park and the Bluebird Recovery Program of Minnesota. I check nineteen pairs of boxes on a weekly basis, looking for nests and counting eggs and nestlings. I clean out the boxes after the nestlings have fledged. Frequently the birds nest a second time.
The boxes are in pairs spaced about ten feet apart so Tree Swallows can use one box and Eastern Bluebirds can use the other. I had fifteen Tree Swallow nests this year. I don’t count their eggs and hatchlings for two reasons: they use found feathers in their nests, making it hard to count without reaching in and moving feathers; and I report to the Bluebird Program, not the Tree Swallow Program.
In the spring I was concerned because I didn’t see any eggs during the month of April. In the previous five years all the first eggs of the season were laid in April. The earliest, in 2020, was laid on April 15th. This year I first had eggs on May 4th.
At that point I feared the worst. This was a late start. But then eggs started showing up in other nests, and although I didn’t expect to end up with the 102 fledglings of the previous year, I knew this year wouldn’t be a bust.
Bluebirds lay one egg a day and don’t start incubating them until the last one is laid. Then they all hatch the same day. Eggs hatch about fifteen days after the last one is laid. The hatchlings grow quickly and are ready to fledge at about eighteen days old.
The end of the season was interesting. Usually all of the babies have fledged by the end of July or during the first week in August. This year I found a new clutch of eggs on July 18th and two new clutches on July 25th. One was a third nesting. Very unusual! The other two were first nests in those locations. Maybe they were second year birds that needed time to find mates and boxes before starting.
Another fear this summer was the hot weather. Would nestlings become overheated and die in the nest? No. A couple of times I found a nest or two with babies that looked slightly lethargic, but they were fine the next time I checked. In my experience the heat does not kill baby birds. I’ve had more trouble in years when eggs hatch in the early spring, and then we have cold rain. Sometimes newly hatched babies don’t survive that.
When I checked the boxes on August 9th, all three of the late nests had hatchlings in them. I was struck by the fact that in all three nests, the babies were lying with their tails in the center of the nest and their heads going outward. I’ve seen this many times before, but I never thought about about it beyond the beautiful radial symmetry they produce (Art Teacher here). But then I thought about the heat. Their radial design is good for dealing with the heat. It keeps their vital organs away from each other’s body heat. Cool! (In more ways than one)
Oh, I suppose you want to know the final fledgling count:
- 2021 – 74
- 2020 – 102
- 2019 – 73
- 2018 – 65
- 2017 – 67
- 2016 – 89
This year’s count bettered three of the previous five years’ counts!