Every year, one of the first signs that Spring is on its way is the hurry and flurry of robins.
From before dawn to after dusk, we see them busy hunting for worms and flying to and fro. If you’re lucky, you may catch sight of a pair of robins building a nest. This year, I’m fortunate enough to have a breeding pair building a nest on my bedroom windowsill. That means I’ve got a front row seat to watch the fascinating process of new life emerging.
As I’ve followed the process of the robins building the nest, mama robin laying her eggs, and (hopefully) soon, the hatchlings emerging, I’ve been very curious about robin behavior and birds in general. I’ve learned many interesting things, and wanted to share them all with you.
First, let’s briefly examine what sets birds apart from all other animals.
Fast Facts About Birds
- In terms of taxonomy, it comes as no surprise that birds belong to the animal kingdom. Specifically, they belong to Phylum Chordata and Class Aves. Because birds contain a backbone, they are considered vertebrates.
- Birds are warm-blooded, which means they have the ability to regulate their own body temperature. This is one thing that sets them apart from other animals (like reptiles and amphibians) that are cold-blooded.
- The bodies of birds are covered with feathers. You may be surprised to learn that not all feathers are created equally.
- Down feathers provide insulation.
- Flight feathers (found on the wings and the tail) provide lift. (Yes, this is the same “lift” that is at work in an airplane.)
- Contour feathers found on the head and wings provide coloration.
- Many adaptations allow birds to keep up with the demands of flight.
With a basic understanding of what sets birds apart from other members of the animal kingdom, let’s turn our attention to robins, in particular.
All About Robins
The American Robin is a common sight in yards across the country.
Robins are large songbirds with round, gray-brown bodies, striking orange underbellies, and white patches on the underside of their tail feathers. Unlike some species (such as the Northern Cardinal), it is hard to tell the difference between a male and female American Robin. Males have darker heads than the females. This makes the heads of male robins stand out from their bodies a bit more than in the females.
American Robins can be found across North America. Unlike other birds, robins often spend the whole year in one location (and are even a common sight in the winter snow).
Robins are omnivores and eat both plants and animals (including insects and worms). In the winter when insects are few, robins eat fruit that remains on trees. If the fruit has started to rot and ferment, robins may become intoxicated. Because robins frequently obtain their food by foraging in lawns, they are susceptible to poisoning from pesticides.
So how do robins find a mate?
In the spring, male robins attract a mate by singing. They also advertise by “ raising and spreading their tails, shaking their wings and inflating their white-striped throats” (https://www.allaboutbirds.org/guide/American_Robin/lifehistory). When a male and female robin decide to mate, they may approach each other on the ground holding their bills open (and they may even touch their bills…kind of like a robin “public display of affection”).
Nesting Behavior, Breeding, and Eggs
An American Robin is capable of producing three broods in a single year. Unfortunately, only 40% of robin nests result in live young. This fact became all too clear to me when I witnessed a Common Grackle steal 2 eggs from the nest on my windowsill. Despite my initial outrage at this thievery, I quickly realized that this was just a fact of nature.
It is the female of a robin breeding pair that chooses the site of their nest. This may be in a tree, on a windowsill, or even in a gutter. It is also the female who builds the nest, using materials such as dead grass and twigs. From allaboutbirds.org:
Females build the nest from the inside out, pressing dead grass and twigs into a cup shape using the wrist of one wing. Other materials include paper, feathers, rootlets, or moss in addition to grass and twigs. Once the cup is formed, she reinforces the nest using soft mud gathered from worm castings to make a heavy, sturdy nest. She then lines the nest with fine dry grass. The finished nest is 6-8 inches across and 3-6 inches high.https://www.allaboutbirds.org/guide/American_Robin/lifehistory
This was an amazing sight to witness, and one I hope you’re able to see for yourself someday. The way the mama bird sat in her nest and twisted to round out the inside was simultaneously brilliant and adorable.
Once the nest is built, the male robin will often provide “courtship feeding” to the female. This courtship feeding can supply up to a third of the female’s food during this time. This is important, since building a nest and laying eggs requires a significant amount of energy from the female.
After mating has occurred, the female will lay her clutch of eggs. Surprisingly (to me, at least), she doesn’t lay all the eggs at once. Instead, she lays a new egg each morning and an average clutch may range in size from 3-5 eggs.
As expected, the mating pair is very sensitive to disturbances during the period of nesting. The nest may be abandoned if the robins feel they are in danger from predation. That’s why I set up a fancy privacy screen for the robins’ nest on my windowsill.
After the eggs have been laid, the mother will sit on the eggs until they hatch. This can last anywhere from 12-14 days. She will spend the majority of her time on the nest, other than brief forays for food. (I suspect it was during one of her food runs that the grackle stole her two eggs). The male robin may also spend time on the nest.
While I haven’t witnessed this myself, female robins are said to maintain a relatively constant temperature in the eggs by rolling the eggs with her bill.
The male robin stays close to the nest, and keeps an eye out for predators. The males can be feisty. Last year when we had a robins’ nest under our deck, the male would “bark” at our dog every time she ventured near the nest. The male robin even went as far as to peck at my dog and pull her hair, which left my pup more than a little traumatized to venture into the backyard.
When the time is right, each hatchling will emerge from its egg using a specialized egg tooth. The baby birds will often hatch a day apart and in the order in which they were laid. Both parents will protect the hatchlings, taking turns hunting for food and feeding the babies. After up to 16 days in the nest, the baby robins will learn to fly and leave the nest.
Answers to Common Questions About Robins (and Birds in General)
Why are robins’ eggs blue?
The blue color of robins’ eggs is due to the deposit of the pigment biliverdin on the eggshell as the female lays her eggs. What is the biological purpose of blue eggs? The current theory is that the brightness of the eggs determines how well the male robin will care for the resulting hatchlings. It is thought that the “blueness” of the eggs is an indicator of the health of the mother and her babies. Studies have shown that male robins are more attentive to offspring that come from eggs that are brighter blue.
Why do I often find robins’ egg shells on the sidewalk or other places where there’s no nest to be seen?
This is a cool phenomenon I’ve also witnessed!! It turns out that after the eggs have hatched, the parents will take the egg shells and carry them far away from the nest. This discourages predators by throwing them off the trail and keeping them from finding the nest and the helpless hatchlings.
How are a bird’s eggs fertilized?
Fertilization of the eggs takes place internally inside the female. Following mating, the male’s sperm is stored in specialized areas within the female’s reproductive tract. This sperm can stay viable for many days. As the egg passes through the female’s reproductive tract, it comes in contact with the stored sperm and is fertilized. Female birds of all species are capable of laying eggs, regardless of whether or not mating has occurred and sperm has been deposited. This is why we are able to harvest unfertilized eggs from domestic hens.
How does a baby bird breathe inside its egg?
How do birds learn how to sing?
I’m sure you recognize that we’ve just scratched the surface of all that we could explore about birds.
I hope I’ve kindled your interest to take this study further. If so, here are some fun resources and ideas for learning more about birds.
Take It Further
Hands-on Activities for Studying Birds
It’s no secret that bird-watching is a favorite hobby of mine. Not only is it easy to do, scientific studies have demonstrated that bird-watching is good for you!!!
If you’d like to learn more, including some of my favorite apps and tools for bird watching, you’re in luck. I’ve got a whole blog post about it: Why You Should Add Bird-Watching to Your Day.
Build a Nest
A great activity that will get your whole family considering how and why birds build their nests the way they do is to try to build a nest yourself. You can do this using the same types of materials that the birds in your yard have available.
Two of my friends have done this activity as a family and blogged about their experiences. You can find them here:
Learning About Bird Nests from The Barefoot Mom
Make Your Own Nest from Susan Evans
Study How Bird Beaks are Related to Diet
If you’ve spent much time bird-watching, you’ve likely observed that not all birds are the same. This is especially true when it comes to bird beaks. In a classic example of “form follows function”, you can tell a lot about the diet of a bird based on what type of beak it has.
The Barefoot Mom has created a great hands-on way to study the relationship between a bird’s beak and what type of food it eats in this blog post: Learning About Birds: Beaks and Diets.
Participate in the Great Backyard Bird Count
I look forward to participating in this citizen science project each year. During this annual event, people around the world can help biologists get a better understanding of current bird populations.
Participating in the GBBC couldn’t be easier. Participants are asked to count birds for as little as 15 minutes at a time on one or more of the days of the event. Then they report their observations on the GBBC website. Despite the name, you don’t have to limit your observations to your backyard. You can even list birds you see while you’re travelling by car.
You can learn more about how to participate on their website.
Websites and Other Resources for Studying Birds
All About Birds: An amazing resource with just about everything you’d ever want to know about birds all in one place.
The Merlin Bird ID App: My favorite FREE bird identification tool. I have it on my phone, so I’m always ready to identify birds I see while I’m out and about.
50 Bird Species and the Sounds They Make: Another great FREE resource for identifying popular birds. What I love about this is that it helps you identify birds that you hear but can’t see.
Here are some websites I used to write this post.