Skip to main content

LATEST UPDATES: Tracking COVID-19 | Vaccines | Racial Justice

NATURE: The Egg: Life’s Perfect Invention

Airs Wednesday, April 10, 2019 at 8 p.m. & Sunday, April 14 at 3 p.m. on KPBS TV + April 14 at 8 p.m. on KPBS 2

Sir David Attenborough holding a swan egg at Abbotsbury Swan colony in Dorset...

Credit: Courtesy of Mike Birkhead Associates

Above: Sir David Attenborough holding a swan egg at Abbotsbury Swan colony in Dorset. The swan egg is one of the largest bird eggs in the UK.

Join Sir David Attenborough to reveal the incredible egg, piece by piece, from creation to hatching.

The egg is perhaps nature’s most perfect life support system. These remarkable structures nurture new life; protecting it from the outside world while still allowing it to breathe.

Eggs are strong enough to withstand the full weight of an incubating parent and weak enough for a hatchling to break free.

But how is an egg made? Why are they the shape they are? And perhaps most importantly, why lay an egg at all?

Step by step as the egg hatches, host David Attenborough reveals the wonder behind these incredible miracles of nature in "The Egg: Life's Perfect Invention."

The Egg: Life’s Perfect Invention: Preview

The egg is perhaps nature’s most perfect life support system. Step by step as the egg hatches, host David Attenborough reveals the wonder behind these incredible miracles of nature.

Photo credit: Courtesy of Mike Birkhead Associates

Male swans often do some of the incubation, but not as much as the females because female swans have a centrally heated brood patch on their bellies.

Featured birds include the domestic chicken, emperor penguin, great tit, blue tit, ostrich, mute swan, albatross; kiwi, goldcrest, cuckoo, reed warbler and common guillemot.

Photo credit: Courtesy of Mike Birkhead Associates

Sir David Attenborough and Professor Tim Birkhead examine a huge collection of Guillemot eggs - Professor Birkhead’s speciality. The eggs come from a collection that belonged to the infamous Victorian collector George Lupton.

Noteworthy Facts:

  • There are nearly 10,000 species of birds on Earth and each one lays eggs. From the smallest Bee hummingbird egg to the biggest ostrich egg, birds create eggs in an infinite array of sizes, shapes, colors and patterns.
  • Birds are hotter than mammals, with an internal temperature of 104 degrees Fahrenheit. No embryo can develop at such high heat, but since they lay eggs, birds can incubate their embryos outside their bodies. Birds also wait to incubate their hatch of eggs until they are all laid, manipulating hatching dates until the ideal time, typically when there is enough food available to feed the babies upon birth.
  • Bird fertilization is much different than with mammals. After mating, females can store sperm for a few days up to a few months - until the female has collected enough food to enable her ova to amass a yolk big enough to transform into a chick. Only then will the egg be fertilized and begin the 24-hour journey to becoming a full-shelled egg.
  • In order for the embryo to breathe, miniscule pores lead from the surface of the egg to the embryo’s blood supply. However, this porousness comes with risks, such as bacterial infection from water. To combat this threat, the egg develops a microscopic protective layer as well as an albumen, a colorless second layer between the yolk and the shell – the “egg white.”

The clever way the tiniest bird warms her nest

This little goldcrest may not be big enough to cover all her eggs, but thanks to a unique technique she can still keep them warm. The secret to her success can only be revealed through thermal cameras and has been caught on film for the very first time.

Buzzworthy Moments:

  • The goldcrest is smallest bird in Europe. A female goldcrest’s eggs weigh 18 percent of her body weight, and her tiny body can only cover a few eggs at time while maintaining an incubation temperature of 98.6 degrees. Thermal cameras reveal the secret to her success – the goldcrest has “hot” legs that pump extra blood to radiate heat. No other bird on Earth is known to do this.
  • The cuckoo never builds a nest or cares for its young. Instead, it tries to trick other species, such as reed warblers, into accepting its egg and raising its baby. Birds see a much more richly colored world than humans so this makes egg mimicry tough to accomplish. Scientists test how closely a cuckoo’s egg must match another bird’s eggs by placing a wrong-colored egg into a reed warbler’s nest. The warbler immediately notices something is amiss and starts to destroy the egg. New research has shown that the cuckoo’s forgery skills are increasingly being put to the test by the warblers, which are producing more elaborate patterns on their own shells – like watermarks on paper money.
  • Close-up footage of a chick breaking out of its egg shows how the shell has been getting thinner while the chick has been absorbing calcium into its bones, making it stronger and the egg weaker. It also uses the shell‘s calcium to create a jagged tip on the beak to make breaking free even easier. Despite this, it can still take a chick hours or days to hammer its way out of a shell.

How an Egg Hatches

How is it possible that an egg can be strong enough to provide protection, yet soft enough that a baby bird can break through? See the remarkable way hatchlings are able to break out of their eggs.


Episodes will be available for streaming on demand for a limited time after broadcast. Extend your viewing window with KPBS Passport, video streaming for members ($60 yearly) using your computer, smartphone, tablet, Roku, AppleTV, Amazon Fire or Chromecast. Learn how to activate your benefit now.

Photo credit: Courtesy of Mike Birkhead Associates

A beautiful selection of clutches of eggs from Tring Natural History Museum that has one of the largest collections of bird eggs in the world – mostly from Victorian bird collectors, as egg collecting was banned in the UK some time ago.


NATURE is on Facebook, Tumblr and you can follow @PBSNature on Twitter. #NaturePBS


NATURE is a production of THIRTEEN PRODUCTIONS LLC for WNET and PBS. For NATURE, Fred Kaufman is Executive Producer. Bill Murphy is series producer and Janet Hess is series editor. "The Egg: Life’s Perfect Invention" is a Mike Birkhead Associates production for THIRTEEN PRODUCTIONS LLC and BBC Studios in association with WNET. The documentary is directed, produced and written by Beth Jones and Mike Birkhead. Roger Webb is series editor for BBC. Presented by David Attenborough.


San Diego News Now podcast branding

San Diego news; when you want it, where you want it. Get local stories on politics, education, health, environment, the border and more. New episodes are ready weekday mornings. Hosted by Anica Colbert and produced by KPBS, San Diego and the Imperial County's NPR and PBS station.

  • Every weekday afternoon, we’ll send you our top TV picks so you can hear about upcoming programs and never miss your favorite shows.

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.

Want more KPBS news?
Find us on Twitter and Facebook, or sign up for our newsletters.

To view PDF documents, Download Acrobat Reader.