How an egg hatches

If the egg is incubated, the embryo inside develops. The parent(s) periodically rotates and rearranges eggs in a nest to ensure equal heating. This also prevents the shell membrane from adhering to the shell, which could interfere with hatching.

• First, circulatory, digestive and respiratory, and nervous systems start to differentiate.
• Then limbs may begin to move.
• An egg tooth is formed to help the bird break out of the shell when it hatches.
• The yolk sac gets smaller. In preparation for hatching, the embryo is in a tucked position. It uses its bill to puncture the innermost shell membrane at the blunt end of the egg (called internal pipping.)
• The embryo begins to breathe the pocket of air between the inner and outer shell membrane.
• After a few more hours, the egg tooth is used to break through the outer shell membrane and the shell (called external pipping - see cracks and holes in photo above.)
• When it penetrates the shell, the hatchling emerges from the egg.
• The parents generally do not help the young get out of the shell, although they may watch intently. They may remove or eat the egg shell after hatching.

More information:

• Egg production
• How Many Eggs Will a Female Lay?
• Why didn't the eggs hatch?
• Weird eggs (various species)
• Egg sizes (comparison table) for various small cavity nesters
• Nest and Egg Identification (photos and descriptions)
• Newborn bluebird photo
• Eggbound female
• Photo of blood smears on eggshell
• Supplementing Calcium - Feeding Chicken Eggshells, etc. to Birds

Previous Pictures of the Week: © Original photographs are copyrighted, and may not be used without the permission of the photographer. Please honor their copyright protection. If you would like to use a photo for educational purposes, you can contact me.

• Tips for photographing cavity nesters
• June 11, 2006 - Great Crested Flycatcher
• June 19, 2006 - Snake Lick
• June 26, 2006 - House Finch Nest
• July 3, 2006 - Tree Swallow in Flight
• July 17, 2006 - Bluebird Battle
• July 24, 2006 - Bear Attack
• August 1, 2006 - Neglected Nestboxes (House Sparrow nests)
• August 14, 2006 - Threesome (Bluebird Babes)
• August 28, 2006 - Peering (flicker)
• January 2007 - New Hill Trail (Sialis)
• February 12 2007 - Sharp-shinned? Hawk feeding on dead starling
• February 19, 2007 - Joe's Cafe (Suet/Mealworm Feeder)
• March 25, 2007 - Sunflower Eater
• February 2007 - Snags & Suet (Pileated Woodpeckers)
• May 2007 - Birdcam Shots and Birdcam Photo Album
• May 12, 2007 - Carolina Wren nest in a boot
• May 25, 2007 - Batman Bird (Tree Swallows)
• June 2007 - Bluebird nest of cattails, one with leaves, and a TRES nest with maple seeds
• June 20, 2007 - Nine Egger (Tree Swallow nest)
• June 27, 2007 - Black-capped Chickadees (funny and serious photos)
• July 7, 2007 - Anting and Sunbathing
• Red-shouldered Hawk perching on nestbox
• November 18, 2007 - Western Bluebirds at the Spa
• March 15, 2008 - Under Construction - Eastern Bluebirds Building a Nest
• April 9, 2008 - Bluebird Battle in PA
• April 10, 2008 - Mouse Surprise
• April 15, 2008 - Bluebird News (nest in paper box)
• April 23, 2008 - My personal nightmare
• April 25, 2008 - Brave White-breasted Nuthatch
• April, 2008 - How an egg hatches
• May 3, 2008 - Newborn Blue (baby hatching)
• May 3, 2008 - Brave Blue (female on nest)
• May 14, 2008 - House Wren Havoc (eggs pecked)
• May 25, 2008 - House Wren Takeover (of nest, more pecked eggs)
• May 29, 2008 - Take Your Pick (parents feeding fledgling)
• June 10, 2008 - That Look Belongs in a Holster (female MOBL)
• August 23, 2008 - Cat on Nestbox
• September 28, 2008 - HOSP on the House
• October 10, 2008 - Cuddling nestlings (taken in summer time)
• October 27, 2008 - HOSP in flight
• October, 2008 - Possible double and dwarf egg in one nest
• December 16, 2008 - The Next Generation (children building boxes)
• January 22, 2009 - Blue with Cold
• January 28, 2009 - Prothonotary Warbler on a camper | Nest building PROW | PROW nesting in tree cavity
• May, 2009 - To Kill a Mockingbird (Snake eating mockingbird - may be disturbing)
• May 21, 2009 - Should I Stay or Should I Go Now? (Titmouse nestling in box)
• May 25, 2009 - Which of these is not like the others? (Cowbird egg)
• May 23, 2009 - The Honeypot at the end of the rainbow (bumblebee nest)
• June 20, 2009 - House Wren nest decorated with Western Bluebird feathers
• June 20, 2009 - Wonderful WEBLS of WA
• June 20, 2009 - Bluebirds of Bickleton
• July 12, 2009 - Hairy Shrimp (newborn bluebirds)
• July 2009 - Diet (bluebird with earthworm in beak)
• July 2009 - Bluebirds nesting outside of cavity
• July 19, 2009 - HOSP on Holiday
• July 20, 2009 - Pink bluebird eggs
• August 2, 2009 - Pinkies (baby mice)
• August 2, 2009 - En garde (male bluebird in box)
• September 29, 2009 - 1917 instructions for bird house construction
• I forget when - Rainbox