All About Birds Blog

First-Ever Bluebird Twins Found Via Project NestWatch—Plus More Opportunities to Discover

By on Tuesday, March 25th, 2014 - 14 Comments


By Pat Leonard

There’s something immensely uplifting and hopeful about seeing feathered families coming together in spring to build nests, raise their young, and then send them off into the big world. And there’s also a lot of useful data there. The Cornell Lab has an entire citizen-science project built around our fascination with bird lives—it’s called NestWatch. NestWatchers have been tracking trends in the nesting success of hundreds of species of birds across the country for nearly 50 years—and discovery can happen at any time.


Four eggs (including an unusually large one, lower right) hatched into five chicks—a first report for Eastern Bluebirds. Photo by Gerald Clark.

Case in point: During the 2013 NestWatch season, participant Gerald Clark monitored a bluebird nest and noticed one egg was much larger than the others. Wonder of wonders, at hatching time twin bluebirds emerged!

“It’s the first ever report of twinning in Eastern Bluebirds,” says NestWatch project leader Robyn Bailey. “The finding was so remarkable that it was written up and published in a scientific journal. We learn new things all the time, even about a species as well studied as the Eastern Bluebird.”

You heard that right, the first ever report of bluebird twins. Twinning is extremely rare in wild birds, despite the odd double-yolked chicken egg that may turn up on occasion.

You Can Help With a New Nestwatch Study on Barn Swallows and Light Levels

Barn Swallows are iridescent, fork-tailed acrobats that have adapted to live near humans and plaster their mud nests in eaves, under bridges, or on a barn beam. In partnership with colleagues at Syracuse University, and the Globe at Night project, Cornell Lab researcher Caren Cooper is hoping to learn what impact artificial light has on the circadian rhythms of Barn Swallows and is calling on NestWatchers to help gather data.


Barn Swallow chicks by Lynne Marsho/GBBC.

“Specifically, we’re hoping to learn if the artificial light has an effect—good or bad—on what we call the ‘pace of life,’” says Cooper. “It’s been established that creatures that live in areas where daytime is shorter during breeding, such as the tropics, have a lower metabolism and a longer life span. On the flip side, animals that breed where there is more daylight tend to have a faster metabolism and shorter life. We want to find out if the pace of life for Barn Swallows is increasing if they live in areas where the days seem even longer because of all the artificial lighting. And how does that play out when it comes to the long-term health and survival of Barn Swallow chicks?”

NestWatch participants will be asked to measure and report light levels near Barn Swallow nests after sundown. If you’re interested, please sign up and we’ll email you more information about what the study entails.

Whether you watch one nest or 20, monitor Barn Swallows, bluebirds, or bobolinks, you’ll map any open-cup nest or birdhouse location on the NestWatch website. The project is free and open to anyone; participants complete a short online course about how to responsibly monitor nests without causing disturbance. Report the species of nesting bird and the timing for how many eggs are laid, how many eggs hatch, and how many young leave the nest. Surprises may be in store as the lives of these feathered families unfold.

(Top image: Eastern Bluebird feeding young by Lindell Dillon via Birdshare)

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  5. jody wilson says:

    That is the coolest thing. If I had one of those larger eggs in my nest box, I would have wondered what the heck was going on. This is why nest box cameras are so vital in monitoring EBB’s.

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  7. Carol says:

    Amazed with now knowing our Bluebird species is increasing especially with a double in an egg.

  8. Melanie Grieco says:

    Awesome story, I’m in W. Central FL and we just don’t see BBs here. :-(

    I did see one about an hour north, when visiting family. They are so beautiful!

  9. Suzy Solvesky says:

    I’m wondering if the ‘twins’ are smaller than siblings, so it’s clear which two they are? What fun it would be to watch them hatch together! :)

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  11. michael says:

    I love your bluebird picture! I have a second brood about to start, they have been working on building their nest,, take a look at my recent post, Bluebirds Building Nest.


  12. michael says:

    Oh wow, how cool is that to have 5 chicks from 4 eggs! Never seen or heard of that before but that is cool!! :)

    I love your pictures, great shots. Check out my recent post if you get a chance on my bluebirds building their second nest.

  13. Niki says:

    Regarding statements: “It’s been established that creatures that live in areas where daytime is shorter during breeding, such as the tropics, have a lower metabolism and a longer life span. On the flip side, animals that breed where there is more daylight tend to have a faster metabolism and shorter life.” This seems counter-intuitive. Do you have a source to back these statements up?

    • Hugh says:

      Hi Niki, Good question. This is a pretty well-known pattern and the general trend is apparent just comparing the known lifespans of similar types of birds in the tropics vs. in the temperate zone. In general, tropical birds live longer. There is also scientific evidence for this and for the differences in metabolic rates—for instance this paper in Proceedings of National Academy of Sciences: Thanks for asking and hope this answers your question. – Hugh

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