Why bird nests aren't covered in poop

So I want to show you something that is bringing me joy right now. Because it is spring, this little bird nest has a little egg in it. That was me a few months ago. That's crazy! Right after I discovered this bird's nest with a single bright blue egg sitting on this porch swing. A few days later, it had four eggs. Guess what happened next? They hatched. And you better believe I named them. This is Goose, Pepperjack, Dot, and Rocco. For a few weeks when I was really bored during lockdown, I watched these little baby birds grow and grow and grow. And I started to film them. And they let me get really close. I even filmed them in slow motion. You'll find out later why. As I watched them grow, a million questions popped in my head. Why is this egg blue? How long do the eggs take to hatch? What type of bird is this? When do baby birds eat bees? Why is bird day white? When do they grow feathers? Are they safe in the nest? But my biggest question? How is this tiny little nest not full of poop? To answer all my questions, I tracked down this guy. My name is Michael Murphy. I'm a professor of biology at Portland State University in Portland, Oregon. He's an ornithologist, which means he studies birds. My personal interest is in behavior of birds and the population biology of birds. And when he says birds, he means a lot of birds. Tree swallows. Barn swallows. Cliff swallows. Eastern phoebes. Spotted toeys. I've worked on a species known as the eastern kingbird since 1979. As you can see, I have a tattoo of a creek there. He studies all of their behaviors, like where they sleep, what they eat, and how they travel. And he also knows a lot about bird poop, which brings us back to the eggs I found on my porch. So what type of birds are in these eggs? Well, that was an American robin. When it grows up, it's got this fiery orange belly. It's impressive. This animal breeds across an enormous swath of North America. It travels as far north as Alaska to breed in the springtime and as far south as Mexico during the cold winter months. That's over 5,000 miles. It seems as long as you've got a structure it can put a nest on, and as long as it can get some good mud to build a nest, you're going to find it. So it's just extremely adaptable. So let's walk through the life of my porch robins. First, they're just four little eggs. Why are they blue? Well, that's a big question. The coloration of bird eggs is extremely variable. What we do know is that bird eggs come in all sizes and colors. White eggs, like this giant ostrich egg, have been around for millions of years. Over time, the eggs, just like the birds themselves, have adapted to survive. Some are speckled because they want to blend into their environment. So do you see the three eggs in this photo? Look closer. And for blue eggs? Well, the blue color is caused by a pigment in the mother. It's the same pigment that makes bruises turn blue. And some butterflies, like this one, have bright blue in their wings. Pigments also strengthen eggshells. So it's actually an active area of research still trying to figure out why birds' eggs are blue. So the mother lays the bright blue eggs. And the parents incubate those eggs. It takes about 14 days for them to complete their development in the egg. And then they hatch out. And then they're going to spend roughly 12 days more in the nest. And over that 12-day period, they, as you saw in your films, change enormously. They go from a non-flying individual that is completely helpless. They're completely blind. They have no feathers except for a little down. They really look like aliens. Within 14 days, they are out of the nest. Instead of little bald aliens, they look like grumpy old men. And within just a few more days, they're actually able to fly. Not like an adult, but they can fly. So what exactly happens in those two weeks in the nest? I don't know if you've ever tried to raise a baby bird. But it's just so time-consuming. They just eat and process food all day. Watch this. Dot, Goose, Rocco, and Pepperjack are deep in sleep. But when they hear their parents come, they shoot right up, super fast. They eat worms, bees, caterpillars, and flies. And they have to eat so much because they have to grow so quickly. The selection to grow fast to get out of the nest is probably mostly related to the fact that lots of things eat baby birds. Therefore, it's a dangerous point in their life. Getting through that quickly is important. Now, if I know one thing about babies, it's this. They eat, they sleep, and they poop. And it can get very messy. But somehow, this nest is spotless. So where on earth does all the poop go? I recorded hours upon hours of footage to figure out exactly where this poop was going because it seemed to just disappear into thin air. And then, I spotted it. Turns out, the hatchlings definitely poop. A whole lot. But they were pooping directly into their parents' mouth. And the parents were eating it. Your observation that the nest is extremely clean is very accurate. And it's because they have those structures referred to as fecal sacs. They're basically like baby bird diapers. So instead of bird poop making a huge mess, the fecal sacs keep it nice and contained. I mean, it really looks like a disposable diaper. But the adults, as you filmed, they'll wait at the rim of the nest for that baby to pick up that fecal sac the moment it emerges from the body. Now, once the parent has the fecal sac, they do one of two things. If you've got young that are sedentary and they're going to be in one spot for days, maybe weeks, you don't want that getting too dirty. So sometimes, the parents fly away with it to drop it off somewhere else far away from the nest. But in many cases, the parents ate the fecal sac. As I was watching your film, I started to get a little sick to my stomach after a while. Oh yeah. I know birds do this, but after a while, you watch them do it, that many times you go, oh man, isn't that bad? You know, why don't you just throw them all away? One of the hypotheses as to why they eat them is that there is useful material in the fecal sacs. And so it might behoove the parents, since they're already working really hard to keep those babies fed, to just eat them and capture the energy and water that is still remaining in the fecal sacs. Tasty. Not all birds do this. So this is an osprey nest. What they do instead is the babies, well, when they're really young, they probably do poop in the nest a little bit. But as they get older, the youngsters position themselves, when they have to go, over at the edge of the nest. They point their butts out over the edge, and then they'll just poop right off the edge of the nest. The world is their toilet. After 12 to 14 days growing in the nest, hatchlings start to get really crowded. Here's a moment where Goose literally fell out the nest because he barely fit. Don't worry, Goose made it back in. Getting to that point is rough because probably 60% of nests fail. But this nest, it made it. The very last piece of footage I captured was this. Rocco just flew right off the porch. Of those that do get out of the nest, they're going to have to make it through to their first year. And maybe only about 30% of them actually survive. Now they've got to begin the important process of reproduction. Basically, in just one year, the hatchlings become parents. And the process starts all over again. What can birds teach us? Hard work. Birds are hard-working individuals, that's for sure. They can teach us about ourselves, but they can also teach us about the world we live in. What they are showing us is how connected the world is. Birds migrate huge distances, and then there are some species which literally call the world their home. Increasingly, as time goes on, we study them to preserve them and to conserve them. So I think they really are showing us that we have to take a large picture view of the world.