Free Preview: The Hidden World of Nests and Eggs

(bird clucks)

(music)

(Robyn Bailey) Welcome to the course! I’m Robyn Bailey, and I’ll be your guide into the fascinating world of nests and eggs!

Nesting birds have captivated people for as long as we have lived alongside them. What is it about them that we find so fascinating? 

Other animals make nests, so it’s not a unique phenomenon…but still when you hear the word “nest,” you probably think of a bird nest. Maybe that’s because, for a short period of time, these flying wonders are bound to the earth.

Nests give us a chance to witness the lives of birds in ways we can’t during other times of the year. So, let’s dive in and explore what makes birds’ nests so interesting.

What’s the purpose of a nest? 

For birds, the nest is a place to provide warmth and safety for the eggs and young until they’re ready to explore the world on their own.

A nest can be as simple as a scrape on the ground or as elaborate as a one-ton Bald Eagle’s nest.

A nest is more of a “nursery” than a “home,” because it’s only needed for reproduction. The goal is usually to stay no longer than necessary. 

While you might think that the family would want to stay in their cozy nest for as long as possible, a nest is actually a vulnerable place to be for the young—and sometimes the adults as well. Eggs and most small chicks are “sitting ducks,” that is, defenseless and vulnerable to predators on the hunt for a nutritious meal. For pairs hoping to pass on their genes to the next generation, every day spent in the nest is a risk. They literally have all their eggs in one basket.

Let’s consider some of the natural pressures that influence life in the nest. The nest, along with the eggs and eventual hatchlings, need to be hidden from predators.

There’s a nest here but can you find it or see its opening? Predators like reptiles, mammals, and other birds would have a hard time seeing it too.

Weather extremes exist all over the globe. Having some shelter from the elements is very important. Imagine an early spring snowstorm…a nest like this one offers some protection for the eggs from the extreme cold and wind.

Local building materials play a role, too. Notice how these nests from different regions are built from what’s locally available. 

When we look at the variety of insects and blood-feeding parasites that are attracted to nests, some of which can have a big impact on the health of nestlings, birds have devised some ingenious behaviors to ward away such parasites.

My favorite example is that of Eastern Screech-Owls, which are known to bring a tiny, worm-like snake into their nest to eat parasites, in what scientists believe is a live-in, pest-removal service! Though, this doesn’t always end well for the tiny snake-housekeepers, as they may eventually become a quick meal.

Many other factors play a role in nest design, and sometimes individual bird preferences come into play as well!
So how do they handle the demands of nesting? Like most things—one step at a time!

In general, the nesting cycle involves some, or all, of the following steps depending on the species:
Choosing a mate
Selecting a nest site
Nest building
Copulation and egg formation
Egg laying
Incubation
Hatching
Feeding the young and
Leaving the nest
And all of this is carefully timed so that the eggs are hatching just as the primary food source is peaking.

That’s the general process, but nature is complicated and some of these steps can be happening at the same time or skipped entirely.

For example, for some species, nest-building can be part of the courtship process. Notice how this Chestnut-and-black Weaver demonstrates his nest-building skills while also quivering his wings seductively, in the hopes of attracting a female.

And as with anything in life, there are always exceptions to the rules. Some species don’t make a nest, while others manage to skip parental duties like caring for eggs and young altogether!

But more on that later.

Birds have evolved a staggering diversity of tactics to overcome the challenges that await them each breeding season, and there are as many approaches to nesting as there are species. And with more than 11,000 species on Earth, this variety is what makes them so interesting to study!