What can we learn from 1500 junco bills?

Every scientist has a few favorite science stories: those papers or sets of papers that we read early in our careers and then reread often, that we think of when we imagine our own ideal research program. One of mine—not exactly a hidden gem, as it’s in all the textbooks now, and is the subject of a very good general-audience book, The Beak of the Finch—is the Grants’ work on Galápagos finches. Peter and Rosemary Grant have spent decades documenting how bill size and shape in these finches fluctuates as rainy years and droughts change the food available on their small island. It’s as complete a picture of evolution in real time as anyone has ever drawn, and a powerful argument for predictable rules (like “bills must be the right size to open the seeds that are available”) leading to unpredictable outcomes in the complexity of a natural system. It’s beautiful.

I wanted to see if I could see similar patterns in the juncos. Like the finches, juncos are primarily seed-eaters. Unlike the finches, the juncos are not neatly contained on a small island; and unlike the Grants, I did not have 30 years to study them. Fortunately, I work in a museum, which is basically a biological time machine. Want to know what junco bills looked like in 1915? No problem!


Thus my time communing with the long-dead feathered denizens of the specimen drawers. Where the Grants had had to live through the decades of data they acquired, I took a shortcut.

Like all shortcuts, however, there were some downsides. I did not get to live in the Galápagos. Also, I was very limited in which juncos I could measure: I might be interested in juncos from a certain mountain range, but if a junco from that range hadn’t been stuffed and placed in a drawer 70 years ago, I was out of luck.

Unsurprisingly, the popularity of junco-stuffing has waxed and waned over the years. My data ended up being “clumpy”: I might have 20 juncos from 1923 from Fresno, but none from Fresno in 1924. This meant that I needed to get creative in analyzing my data. Fortunately, in addition to my time machine, I had two other valuable resources: data on weather going back to the 1800s thanks to the PRISM Historical Climate Dataset, and some very sharp former field asssistants who could help me figure out how to work with those data.

I ended up measuring over 1500 junco specimens.


Sadly, in order to perform a fair statistical test, I had to reduce that sample size to just over 800. (That faint sound you hear is Katie-from-three-years-ago screaming “You what?!”)

I had my data, and I had some predictions: the Grants had shown that bills are shaped by food availability. This makes a lot of sense: the bill is a bird’s primary tool for handling, opening, and consuming food. Work by Greenberg and colleagues had demonstrated that bills can be shaped by temperature: it turns out that birds lose a lot of heat through their bills. So the juncos’ bills should be influenced by temperature and the available food. (I couldn’t directly measure available food, but I did know rainfall—which affects vegetation—and habitat type.)

Three guesses as to whether my predictions were correct.


This is juncos, remember—the birds that nest in cow hoofprints and come back from the dead. Of course they didn’t do what I expected.

I didn’t find any of the relationships I had expected to see based on the Grants’ work. I did find some evidence of an effect of temperature on the bill, but it was small. Strangest, I found that habitat type did have an effect on the bill—but only on its surface area.

Here’s something that is endless fascinating and endlessly frustrating about biology: you can never assume that two things are the same. The Galápagos finches do one thing, and juncos do another. Even as we discover and clarify general rules, we find exceptions and complications. Most frogs lay eggs in the water—but here are some who carry their eggs on their back! And here’s one who broods its eggs in its mouth!

The allure is that, if you learn enough, you’ll be able to put even the exceptions into a logical framework. No, the juncos don’t do what the Galápagos finches do; but doesn’t that make sense, when you think about their respective contexts? The juncos aren’t trapped on an island. When a drought comes, they can move. And yet, temperature does have some impact on the bills, so the juncos aren’t perfectly able to follow ideal weather where ever it goes—there are limits too, not as strict as on an island, but present nevertheless. The juncos aren’t the same as the Galápagos finches, but maybe they are following the same rules.

Just give me a few more decades—I’ll figure it out.

(Although next time I need to measure over a thousand specimens, I’m picking a prettier bird.)



LaBarbera K, Hayes KR, Marsh KJ, Lacey EA. 2017. Complex relationships among environmental conditions and bill morphology in a generalist songbird. Evolutionary Ecology doi:10.1007/s10682-017-9906-3

14 thoughts on “What can we learn from 1500 junco bills?

  1. Hello! Help! I have three baby Junos in s next on my porch and it suddenly 107 degrees out and they are lifeless!!!! Is there anything I can do that would save them but not make their momma abandon them? We live in Portland Oregon where it rarely over 85. Maybe 90. We have another two days of heat coming and I don’t want to lose them!! I’ve watche her build her nest, lay eggs and then hatch. They are one week old.

    • Oof, that’s quite the heat wave. Can you shade them? Set up a small fan to get air moving? If they were older you could spritz them gently with water to cool them off, but I hesitate to recommend that for chicks in the nest. I suppose it would be possible to put a cold pack in the nest with them (covered with cloth so as not cause frostbite), although there’s a danger that they might leave the nest if you did that.

      This is a hard situation for me to give concrete advice because it all depends how much danger they are in from the heat, and I’m not present to evaluate their state. Tonight should give them relief, at least. If tomorrow is as bad, and the chicks are open-mouthed and seem in danger, and shade and a breeze isn’t helping, perhaps consider a cold pack wrapped in a thick sock and placed beside them in the nest, just for the hottest part of the day.

      • Well the good news is they have a smart mama. She built her nest on an old 3′ wooden cross and that has a large grapevine wreath on it and it’s tucked away very nicely and it’s very safe. It’s on our front porch wall but, that being said there’s absolutely no breeze or airflow. The good news is we have very cool evenings- should get down to about 66°. But tomorrow it is supposed to be up to 109°-which is very abnormal for the Northwest. They were not moving at all when I got home at 4 o’clock. I was in panic mode. I know we aren’t supposed to touch nests and babies, but I have watch this whole process (Nest being built. Eggs. Eggs hatching) and I just couldn’t stand seeing them in distress. Mom wasn’t around so I carefully took the cross off the wall without touching the nest or babies, and carried the cross inside for about 10 minutes until they were more active. It definitely helped it. They were so lethargic and barely breathing. Their mouth’s were open and their necks were all the way bent backwards so I just sat and watched them, I am a prayer, so I prayed for them and said “God, that mother made a nest for her sweet babies on this old wooden cross. That was not by chance…” 😊 So after about 10-15 minutes they were looking stronger, so I carefully picked up the cross & put it back on the wall. As soon as I did mama came right back with a mouthful of food and she began feeding them and has been sitting on the edge of nest watching over them ever since. I’ve been out several times watering etc, and she is still there. Just like any other day we go out. So I believe I didn’t do any harm. 🤞🏼

        Good idea on the cold pack I will try to get it close as possible as to not to touch the babies with my hands or the ice pack. I was trying to attach pictures, but I didn’t see a way to do it.

        Thx again!

        • Good luck! I didn’t realize that there was a way for you to move the nest without damaging it; that’s a good option for the hottest moments, as long as you don’t keep the nest away for too long. (You don’t want it to be absent long enough for the parents to decide it’s permanently gone.)

          Don’t worry too much about touching the chicks. It’s not true that birds won’t feed their babies after they have been touched by humans. Try to disturb them as little as possible, of course, but if you end up touching a few fingers to the chicks or the nest, you don’t need to worry about it.

          Let me know how they do!

          • Well I have not even thought about being able to move the cross itself and is not damaging the vast. I’m so thankful you came to my mind. As of this morning they were doing pretty well. I will definitely keep you posted. Today is supposed to be 105°. I am going home from work in a little bit to go figure out the ice pack situation. It’s now 91°

          • I JUST re read my last comment. 😂 I meant “I’m so glad IT came to my mind” I didnt even know about YOU! Lol

            Today was worse. 105 again but when I check on them at 1230 they weren’t even moving!!!! I brought them in again. Fanned them eventually they started moving. It took them about 10 min to even move. I thought they were dead!!! I couldn’t really put an ice pack anywhere close to nest. I went and bought a tall fan at 5pm. I put it a out 6′ away with a cold wet towel on the back of the fan. It slowly cooled the area around them. Momma is still around. I’m glad she hasn’t abandoned them. It’s going to hover around 100 for the next week. But the low is always around 55-60. I’ll keep the fan going all day. Poor little things.

          • This morning I went out to hear momma screeching. She was sitting on the hanging lights across the porch from nest. I checked nest and just below was one of the babies!!!! He was just hanging out looking at me, sitting on the wreath that is around the cross! I scooped him up and put him right back. Immediately went into the house and momma came right to the nest. Whew

  2. This morning everyone was in the nest. I got home after three hours and the nest’s side was pulled down and empty. I could here momma chirping near by and found one. Any in the porch. I scooped him up and fixed the nest and placed him in. At what age do they leave the nest? They’re about 2 weeks old.

    • They leave between 12-15 days old, so it’s right about that time. He probably won’t stay in the nest at this point. It should be okay – it will be easier for them to stay cool outside of the nest, where they can find shade and don’t have to be snuggled up against their hot siblings.

      Congratulations! They might not have survived to fledge if it weren’t for you. You should be proud.

      One thing you might consider doing is leaving out a shallow dish of water on the porch. That will help the parents cool off, and possibly the fledglings will use it too; and in this kind of heat, there may not be much water available.

      • You made my day! Today is day 15.

        But….now we see mom and dad searching the grass. So maybe they lost them????

        • The parents are probably foraging for bugs to feed the chicks – fledglings are hungry little beasts! Keep an eye out and in the next week you should start to see the fledglings following the parents around, begging insistently. (You won’t see them right now because they’ll be hiding while they grow their flight feathers in.)

          Also, if you notice the parents making a low “chip – chip – chip” sound, that’s them warning the fledglings to keep their heads down because something scary (like a squirrel or a human) is nearby. So that would be another indication that the fledglings are still around.

          • Thank YOU for your willgness to help me out!!! I love all creature and great and small. 😊 Sorry I hijacked your message board. I couldn’t see where to send a new message. Sorry everyone!

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