{"id":31239,"date":"2017-06-12T21:02:20","date_gmt":"2017-06-13T01:02:20","guid":{"rendered":"https:\/\/www.allaboutbirds.org\/news\/?p=31239"},"modified":"2026-04-06T11:52:04","modified_gmt":"2026-04-06T15:52:04","slug":"the-beauty-and-biology-of-egg-color","status":"publish","type":"post","link":"https:\/\/www.allaboutbirds.org\/news\/the-beauty-and-biology-of-egg-color\/","title":{"rendered":"The Beauty and Biology of Egg Color"},"content":{"rendered":"<div class=\"wp-block-group sidebar-alignright sidebar-space order-bottom\"><div class=\"article-list list-style alignright\"><h2 class=\"article-list-header\">More From Living Bird<\/h2><ul><li class=\"article-item\"><div class=\"article-item-container\"><div class=\"article-item-media  content-living-bird-toc\"><figure class=\"article-item-media-ratio\"><img decoding=\"async\" src=\"https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/LB-TOC-FI.jpg\" srcset=\"https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/LB-TOC-FI.jpg 658w, https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/LB-TOC-FI-240x135.jpg 240w, https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/LB-TOC-FI-480x270.jpg 480w\" sizes=\"\" alt=\"Kirtland's Warbler by Amanda Guercio\/Macaulay LIbrary\" loading=\"lazy\" \/><\/figure><\/div><div class=\"article-item-body\"><span class=\"article-item-header\">Living Bird Summer 2017\u2014Table Of Contents<\/span><\/div><\/div><\/li><li class=\"article-item\"><div class=\"article-item-container\"><div class=\"article-item-media  content-living-bird-toc\"><figure class=\"article-item-media-ratio\"><img decoding=\"async\" src=\"https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2023\/07\/living-bird-latest.png\" srcset=\"https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2023\/07\/living-bird-latest.png 720w, https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2023\/07\/living-bird-latest-240x180.png 240w, https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2023\/07\/living-bird-latest-480x360.png 480w\" sizes=\"\" alt=\"Living Bird-latest issue\" loading=\"lazy\" \/><\/figure><\/div><div class=\"article-item-body\"><span class=\"article-item-header\">Living Bird Magazine\u2014Latest Issue<\/span><\/div><\/div><\/li><li class=\"article-item\"><div class=\"article-item-container\"><div class=\"article-item-media  content-article\"><figure class=\"article-item-media-ratio\"><img decoding=\"async\" src=\"https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2023\/07\/living-bird-acrhive.png\" srcset=\"https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2023\/07\/living-bird-acrhive.png 720w, https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2023\/07\/living-bird-acrhive-240x180.png 240w, https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2023\/07\/living-bird-acrhive-480x360.png 480w\" sizes=\"\" alt=\"Living Bird archives\" loading=\"lazy\" \/><\/figure><\/div><div class=\"article-item-body\"><span class=\"article-item-header\">Living Bird Magazine Archives<\/span><\/div><\/div><\/li><\/ul><\/div><\/div>\n<p><small><em>From the <a href=\"https:\/\/www.allaboutbirds.org\/news\/living-bird-summer-2017-table-of-contents\/\">Summer 2017<\/a> issue of <\/em>Living Bird<em> magazine. <a href=\"https:\/\/join.birds.cornell.edu\/ea-action\/action?ea.client.id=1806&amp;ea.campaign.id=24577&amp;ea.tracking.id=CTA\">Subscribe now<\/a>.<\/em><\/small><\/p>\n<p>Fish do it. Frogs do it. Even insects lay eggs with color. But birds do it best.<\/p>\n<p>Only birds produce eggs in such a wide range of eye-pleasing shades and intricate patterns on the hard surface of their eggs.<\/p>\n<p>Like gems in a jeweler\u2019s window, they vary in base color, how shiny they are, and whether they are covered in Sanskrit-like scrawls or patterns of spots.<\/p>\n<p>But, how does the color get there? What is it made of? Does it benefit the embryo? And, why are some eggs plain white?<\/p>\n<p>Egg pigmentation is surprisingly complex.<\/p>\n<h3>Building the Egg<\/h3>\n<div class=\"wp-block-image\"><figure class=\"alignright size-large\"><img decoding=\"async\" src=\"https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/EggProcess-720x1118.jpg\" srcset=\"https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/EggProcess-720x1118.jpg 720w, https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/EggProcess-768x1192.jpg 768w, https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/EggProcess-480x745.jpg 480w, https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/EggProcess.jpg 800w\" sizes=\"(max-width: 720px) 100vw, 720px\" alt=\"The production process of eggs resembles a miniature assembly line inside a female bird. Eggs receive their signature color and patterning during the last few hours before they are laid. Graphic from Handbook of Bird Biology, 2nd edition.\" loading=\"lazy\" \/><figcaption>The production process of eggs resembles a miniature assembly line inside a female bird. Eggs receive their signature color and patterning during the last few hours before they are laid. <em>From Handbook of Bird Biology, Second Edition.<\/em><\/figcaption>\n              <\/figure><\/div>\n<p>An egg\u2019s story begins in a female bird\u2019s single ovary. When an ovum is released into the oviduct and fertilized, it is just a protein-packed yolk. The albumen\u2014the gelatinous egg white\u2014is added next. The blobby mass then gets plumped up with water and encased in soft, stretchy membrane layers. The first globs of the calcium carbonate shell are then deposited on the exterior, with the mineral squirting from special cells lining the shell gland (uterus). Pigmentation, if any, comes next, with an overall protein coating added before the egg is laid. It takes about 24 hours to build a single egg.<\/p>\n<p>In his book <a href=\"https:\/\/www.theguardian.com\/books\/2016\/apr\/17\/most-perfect-thing-inside-birds-egg-tim-birkhead-review-alex-preston\">The Most Perfect Thing: Inside (and Outside) a Bird\u2019s Egg<\/a>,\u00a0University of Sheffield zoologist Tim Birkhead compares the pigmentation process to an array of \u201cpaint guns.\u201d Each gun is genetically programmed to fire at a certain time so that the signature background color and spotting of a species\u2019 eggs is produced.<\/p>\n<p>\u201cExamination of birds\u2019 oviducts at the time the color is placed on the egg suggests that the color is produced and released over a very short time frame,\u201d Birkhead says, \u201cusually in the last few hours before the egg is laid, and that makes it very hard to study.\u201d<\/p>\n<div class=\"wp-block-image\">\n              <figure class=\"size-large alignnone\"><img decoding=\"async\" src=\"https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/BowerbirdEgg-Weinstein-1280x677.jpg\" srcset=\"https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/BowerbirdEgg-Weinstein-720x381.jpg 720w, https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/BowerbirdEgg-Weinstein-768x406.jpg 768w, https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/BowerbirdEgg-Weinstein.jpg 1280w, https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/BowerbirdEgg-Weinstein-480x254.jpg 480w\" sizes=\"(max-width: 1280px) 100vw, 1280px\" alt=\"The intricate squiggles of the Great Bowerbird egg make it stunningly beautiful. Photo by John Weinstein, \u00a9 2014 The Field Museum. Egg from the collection of the Western Foundation of Vertebrate Zoology.\" loading=\"lazy\" \/><figcaption>The intricate squiggles of the Great Bowerbird egg make it stunningly beautiful. <em>Photo by John Weinstein, \u00a9 2014 The Field Museum. Egg from the collection of the Western Foundation of Vertebrate Zoology.<\/em><\/figcaption>\n              <\/figure>\n            <\/div>\n<h3>Coatings of Many Colors<\/h3>\n<p>Despite the variety of egg colors and patterns, the palette is surprisingly small. Egg pigments are versatile substances made of complex molecules synthesized in a bird\u2019s shell gland. Only two pigments are at work. Protoporphyrin produces reddish-brown colors. Biliverdin produces shades of blue and green. More of one pigment, less of the other, and the egg gets a different background color, spots of a different color, or a combination of both.<\/p>\n<div class=\"wp-block-image\">\n              <figure class=\"size-small alignnone\"><img decoding=\"async\" src=\"https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/CettiWarbler200-Weinstein.jpg\" srcset=\"\" sizes=\"\" alt=\"Cetti\u2019s Warbler egg. Photo by John Weinstein, \u00a9 2014 The Field Museum.\" loading=\"lazy\" \/><figcaption>Cetti\u2019s Warbler eggs are an intense brick-red. <em>Photo by John Weinstein, \u00a9 2014 The Field Museum.<\/em><\/figcaption>\n              <\/figure>\n            <\/div>\n<p>For example, the intense brick-red of Cetti\u2019s Warbler eggs comes from protoporphyrin alone. All birds are likely to have the basic genetic\u00a0machinery to produce the two pigments, even if they use only one of them, or use none at all and produce plain white eggs.<\/p>\n<p>A female bird needs to take in extra calcium in order to produce the egg\u00adshell, and her diet can also be a factor in the production of the type and quantity of pigments. Paler-than-normal colors may be the by-product of a bird\u2019s poor diet or an immune system challenged by disease. Even in the same clutch, each egg will be pigmented somewhat differently.<\/p>\n<div class=\"wp-block-image\">\n              <figure class=\"size-small alignnone\"><img decoding=\"async\" src=\"https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/MurreEggs.jpg\" srcset=\"\" sizes=\"\" alt=\"All of these eggs were laid by Common Murres. Each has a distinctive color or pattern so parents can identify their own egg among all the others in a breeding colony. Photo by Pat Leonard from the Cornell University Museum of Vertebrates collection.\" loading=\"lazy\" \/><figcaption>All of these eggs were laid by Common Murres. Each has a distinctive color or pattern, possibly to help parents identify their own egg among all the others in a breeding colony. <em>Photo by Pat Leonard; eggs from the Cornell University Museum of Vertebrates.<\/em><\/figcaption>\n              <\/figure>\n            <\/div>\n<p>\u201cBirds that lay multiple eggs, such as thrushes and flycatchers, seem to change the color of their eggs through\u00adout the laying cycle as if they were running out of the pigments,\u201d says Cornell PhD Mark Hauber, who wrote <em>The Book of Eggs <\/em>and studies them at Hunter College of the City University of New York.<\/p>\n<p>And over time, eggshell colors and patterns within a species can also change. Mark Hauber feels bird-egg pigmentation may have evolved and disappeared multiple times and says it seems to be a rather \u201cpliable\u201d trait.<\/p>\n<p>\u201cWith just two mutations, a Japa\u00adnese Quail, which lays beige eggs with brown speckles, can start laying plain blue eggs,\u201d Hauber says. \u201cSo, it\u2019s really easy to genetically regulate metabolic pathways to start laying different col\u00adored eggs.\u201d<\/p>\n<p>The deep history of egg color re\u00admains unknown. Some scientists think the dinosaur ancestors of birds pro\u00adduced only white eggs, as reptiles still do today, and that pigmentation came later. Others suggest dinosaur eggs could have been blue.<\/p>\n<div class=\"wp-block-image\">\n              <figure class=\"size-large alignnone\"><img decoding=\"async\" src=\"https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/FinishingTouches-egg-1280x854.jpg\" srcset=\"https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/FinishingTouches-egg-720x480.jpg 720w, https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/FinishingTouches-egg-768x512.jpg 768w, https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/FinishingTouches-egg.jpg 1280w, https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/FinishingTouches-egg-480x320.jpg 480w\" sizes=\"(max-width: 1280px) 100vw, 1280px\" alt=\"Left: The eggs of the Black Tinamou (top) and the Red-winged Tinamou (bottom) get their high-gloss shine from a protein-based coating. Right: Guira Cuckoo egg background colors range from gray to the lovely turquoise shade shown here. Note along the broken edge, the turquoise color is not just deposited on the surface but permeates the entire shell. Photos of tinamou eggs by John Weinstein \u00a9 2014 The Field Museum. Cuckoo egg by Paula and Michael Webster\" loading=\"lazy\" \/><figcaption>Left: The eggs of the Black Tinamou (top) and the Red-winged Tinamou (bottom) get their high-gloss shine from a protein-based coating. Right: The background color of a Guira Cuckoo egg can range from gray to the lovely turquoise shade shown here. Note along the broken edge, the turquoise color is not just deposited on the surface but permeates the entire shell. <em>Photos of tinamou eggs by John Weinstein \u00a9 2014 The Field Museum. Cuckoo egg by <a href=\"http:\/\/living-wild.net\/\">Paula and Michael Webster<\/a>.<\/em><\/figcaption>\n              <\/figure>\n            <\/div>\n<h3>Finishing Touches<\/h3>\n<p>Though all bird eggs are made of calcium carbonate, the underlying shell structure differs among species. The outer coating of the shell\u2014the cuticle\u2014can also make a difference in the finish of the egg. For example, the glossy eggs of the tinamou family\u2014from the reddish-purple egg of the Red-winged Tinamou to the emer\u00adald green of the Elegant Crested-Tina\u00admou\u2014give off a high-wattage shine.<\/p>\n<div class=\"wp-block-image\"><figure class=\"alignright size-large\"><img decoding=\"async\" src=\"https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/CuckooEgg-Weinstein-e1496779979869.jpg\" srcset=\"\" sizes=\"\" alt=\"The white deposits on the exterior of this Guira Cuckoo egg resemble the surface of the moon. Photo by John Weinstein, \u00a9 2014 The Field Museum.\" loading=\"lazy\" \/><figcaption>The white deposits on the exterior of this Guira Cuckoo egg resemble the surface of the moon. <em>Photo by John Weinstein \u00a9 2014\nThe Field Museum.<\/em><\/figcaption>\n              <\/figure><\/div>\n<p>The Guira Cuckoo\u2019s egg is a wonder. Before the egg is laid, the base color is covered with a chalky layer of flaky cal\u00adcium carbonate called vaterite that is structurally different from the eggshell itself. During incubation, the outer layer flakes off in patches, revealing a smoky gray or turquoise underneath in intricate patterns, rather like an artist\u2019s scratch\u00adboard. It\u2019s one of Hauber\u2019s favorite eggs.<\/p>\n<p>\u201cIt\u2019s like having a little jewel in your hand,\u201d he says. \u201cThe eggs of some spe\u00adcies of anis are like this, too. Among communal nesters that chalky lay\u00ader might act as a bumper to prevent damage when the eggs knock against each other. We\u2019re trying to figure out if that flaky white material has any pigments in it.\u201d<\/p>\n<div class=\"wp-block-image\">\n              <figure class=\"size-large alignnone\"><img decoding=\"async\" src=\"https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/Killdeer-Biermbaum-1280x697.jpg\" srcset=\"https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/Killdeer-Biermbaum-720x392.jpg 720w, https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/Killdeer-Biermbaum-768x418.jpg 768w, https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/Killdeer-Biermbaum-1280x697.jpg 1280w, https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/Killdeer-Biermbaum-480x261.jpg 480w, https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/Killdeer-Biermbaum.jpg 1290w\" sizes=\"(max-width: 1280px) 100vw, 1280px\" alt=\"Killdeer on nest by Wayne Bierbaum via Birdshare\" loading=\"lazy\" \/><figcaption>A Killdeer on its nest with well-camouflaged eggs. <em>Photo by <a href=\"https:\/\/flic.kr\/p\/83F92Z\">Wayne Bierbaum<\/a> via <a href=\"https:\/\/www.flickr.com\/groups\/birdshare\">Birdshare<\/a>.<\/em><\/figcaption>\n              <\/figure>\n            <\/div>\n<h3>Pigmentation as a Parental Cue<\/h3>\n<div class=\"wp-block-image\"><figure class=\"alignright size-large\"><img decoding=\"async\" src=\"https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/SPPlover-Sonerholm.jpg\" srcset=\"https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/SPPlover-Sonerholm.jpg 600w, https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/SPPlover-Sonerholm-480x330.jpg 480w\" sizes=\"\" alt=\"Semipalmated Plover eggs are laid in the open, and both eggs and chicks are extremely well camouflaged for protection from predators. Photo by Doug Sonerholm via Birdshare.\" loading=\"lazy\" \/><figcaption>Semipalmated Plover eggs are laid in the open, and both eggs and chicks are extremely well camouflaged for protection from predators. <em>Photo by <a href=\"https:\/\/flic.kr\/p\/73u2a4\">Doug Sonerholm<\/a> via <a href=\"https:\/\/www.flickr.com\/groups\/birdshare\">Birdshare<\/a>.<\/em><\/figcaption>\n              <\/figure><\/div>\n<p>Some egg pigment functions are well established by science. Camouflage is one. Many species that nest on the ground produce speckled or streaked eggs that blend in well with their surroundings and befuddle predators. Look at the eggs of any shorebird and you\u2019ll find nearly all of them are speckled to blend in among rocks, pebbles, and sand to foil egg-stealing snakes, lizards, squirrels, and raptors.<\/p>\n<p>As a general rule, birds that lay all-white eggs tend to be cavity-nesting species, such as owls and woodpeckers. Their eggs are already hidden from view so there\u2019s no reason to produce pigmented eggs. There\u2019s also a theory that white eggs show up better in a dark cavity.<\/p>\n<p>But, there are exceptions. Even though camouflage makes sense for most species that lay their eggs in nests on the ground, some ground-nesting species\u2014such as tinamous and nightjars\u2014produce bright-colored, conspicuous eggs, which means other forces are at work. It helps to understand a species\u2019 life history.<\/p>\n<div class=\"wp-block-image\"><figure class=\"alignright size-large\"><img decoding=\"async\" src=\"https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/GGOwl-Quinton.jpg\" srcset=\"https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/GGOwl-Quinton.jpg 500w, https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/GGOwl-Quinton-480x718.jpg 480w\" sizes=\"\" alt=\"Great Gray Owls lay dull white, unmarked eggs in old nests built by other birds. Photo by Michael Quinton\/Minden Pictures.\" loading=\"lazy\" \/><figcaption>Great Gray Owls lay dull white, unmarked eggs in old nests built by other birds. <em>Photo by Michael Quinton\/Minden Pictures.<\/em><\/figcaption>\n              <\/figure><\/div>\n<p>Several Great Tinamou females may lay their shiny, unspeckled turquoise eggs on contrasting brown leaf litter in the same depression or scrape on the ground without building an actual nest of sticks or mud. Cornell PhD Patricia Brennan, now at the University of Massachusetts, Amherst, studied these birds in Costa Rica, noting that the eggs are not camouflaged or well concealed despite the threat of predation. Brennan suggests that egg color is a signal to other females, drawing their attention to the nest and promoting synchronous laying. The benefit to the birds is that, even if a predator does strike, it cannot eat all the eggs and those of any one individual stand a better chance of surviving.<\/p>\n<p>Scientists say some species get away with laying conspicuous eggs because\u00a0the parents sit tightly on the nest, with both male and female sharing round-the-clock incubation duty so the eggs\u00a0are almost never exposed to view. In fact, another novel, though disputed, explanation for brightly colored, conspicuous eggs is called the \u201cblackmail theory.\u201d Bucknell University\u2019s Daniel Hanley has theorized that, because conspicuous eggs are at greater risk of predation, females may lay them to blackmail their mate into more active participation at the nest. If the male wants the showy eggs to stay covered up and protected, he must take turns incubating on the nest himself or bring food to the female so she can stay on the nest.<\/p>\n<div class=\"wp-block-image\">\n              <figure class=\"size-large alignnone\"><img decoding=\"async\" src=\"https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/Prinia-CuckooFinch-Spottiswoode-1280x779.jpg\" srcset=\"https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/Prinia-CuckooFinch-Spottiswoode-720x438.jpg 720w, https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/Prinia-CuckooFinch-Spottiswoode-768x467.jpg 768w, https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/Prinia-CuckooFinch-Spottiswoode.jpg 1280w, https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/Prinia-CuckooFinch-Spottiswoode-480x292.jpg 480w\" sizes=\"(max-width: 1280px) 100vw, 1280px\" alt=\"The Parasitic Weaver lays its eggs (right) in the nest of the Tawny-flanked Prinia (left). But the weaver cannot replicate the prinia\u2019s fine squiggles. Photo by Claire Spottiswoode.\" loading=\"lazy\" \/><figcaption>Tawny-flanked Prinia eggs (left) often sit side by side in their nest with eggs laid by the Parasitic Weaver (right). The colors are similar, but the weaver cannot replicate the prinia\u2019s fine squiggles. <em>Photo by Claire Spottiswoode.<\/em><\/figcaption>\n              <\/figure>\n            <\/div>\n<h3>Pigmentation as Identifier<\/h3>\n<p>Some eggs are pigmented and patterned in defense against brood parasitism, which is when one species lays its eggs in the nest of another species as a ploy to get host parents to raise its young. Brown-headed Cowbirds are among the most famous nest parasites in North America, inducing Red-winged Blackbirds and other species into caring for cowbird nestlings.<\/p>\n<div class=\"wp-block-image\"><figure class=\"alignright size-large\"><img decoding=\"async\" src=\"https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/CowbirdEgg-Stylurus.jpg\" srcset=\"https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/CowbirdEgg-Stylurus-720x561.jpg 720w, https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/CowbirdEgg-Stylurus-768x598.jpg 768w, https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/CowbirdEgg-Stylurus-480x374.jpg 480w, https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/CowbirdEgg-Stylurus.jpg 1182w\" sizes=\"\" alt=\"A cowbird egg stands out in a Yellow Warbler nest. Photo by Stylurus via Birdshare\" loading=\"lazy\" \/><figcaption>A single, reddish-brown-spotted cowbird egg sits next to three smaller, whiter Yellow Warbler eggs. <em>Photo by <a href=\"https:\/\/flic.kr\/p\/4ZnhLZ\">Stylurus<\/a> via <a href=\"https:\/\/www.flickr.com\/groups\/birdshare\">Birdshare<\/a>.<\/em><\/figcaption>\n              <\/figure><\/div>\n<p>Evolutionary biologist Claire Spottiswoode from the University of Cambridge says egg speckling can be a strategy to help parents differentiate their own eggs from those laid by an intruder. But it doesn\u2019t always work.<\/p>\n<p>\u201cIt seems likely that natural selection seized on egg speckling and elaborated upon it to generate the complex egg signatures of identity that we see in host birds,\u201d explains Spottiswoode. \u201cBut those patterns can also be mimicked to some degree by their parasites.\u201d<\/p>\n<p>Spottiswoode\u2019s studies of a species called the Parasitic Weaver in Zambia attempt to measure the competing pressures on both host and parasite in what she terms a \u201ccoevolutionary arms race.\u201d\u00a0The battle between host and parasite often plays out in alternating egg pigmentation changes. Over time, the host species alters the look of its eggs, which the parasite then tries to mimic closely enough so that its eggs are not rejected. These changes happen surprisingly quickly\u2014even within a few decades.<\/p>\n<div class=\"wp-block-image\"><figure class=\"alignright size-large\"><img decoding=\"async\" src=\"https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/SpeciesEggs.jpg\" srcset=\"https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/SpeciesEggs-720x631.jpg 720w, https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/SpeciesEggs-768x673.jpg 768w, https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/SpeciesEggs-1280x1121.jpg 1280w, https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/SpeciesEggs-480x420.jpg 480w, https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/SpeciesEggs.jpg 1440w\" sizes=\"\" alt=\"Bird eggs from various species can be pigmented in a variety of patterns, including spots, blotches, scrawls, and streaks. Illustration by Katherine A. Smith.\" loading=\"lazy\" \/><figcaption>Bird eggs from various species can be pigmented in a variety of patterns,\nincluding spots, blotches, scrawls, and streaks. <em>Illustration by Katherine A. Smith.<\/em><\/figcaption>\n              <\/figure><\/div>\n<p>\u201cWhat we\u2019ve seen in Zambia is primarily a shift in the frequency of existing colors, given that the range of egg pigments is actually quite limited,\u201d Spottiswoode says. \u201cWe know from other systems that natural selection can sometimes be startlingly effective in generating evolutionary change and that eons aren\u2019t always needed!\u201d<\/p>\n<p>But again, nature throws in a few wrinkles that are hard to explain. For example, the Tawny-flanked Prinia produces fine squiggles on its eggs that are impossible for Parasitic Weavers to replicate, yet the weaver often successfully parasitizes prinia nests.<\/p>\n<p>\u201cThis is a real mystery to me because having apparently evolved a perfect signature, the prinias seem not to use it,\u201d Spottiswoode says. \u201cUnsquiggled eggs are clearly accepted at least sometimes, otherwise this strain of parasites would be defeated and have died out.\u201d<\/p>\n<div class=\"wp-block-image\">\n              <figure class=\"size-large alignnone\"><img decoding=\"async\" src=\"https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/RobinNest-Fisher-1280x768.jpg\" srcset=\"https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/RobinNest-Fisher-720x432.jpg 720w, https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/RobinNest-Fisher-768x461.jpg 768w, https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/RobinNest-Fisher.jpg 1280w, https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/RobinNest-Fisher-480x288.jpg 480w\" sizes=\"(max-width: 1280px) 100vw, 1280px\" alt=\"Robin nest by Steve Fisher via Birdshare\" loading=\"lazy\" \/><figcaption>&#8220;Robin&#8217;s-egg blue&#8221; isn&#8217;t just a fanciful term: American Robins and many other thrushes lay eggs that are a lovely sky-blue to blue-green color. <em>Photo by\u00a0<a href=\"https:\/\/flic.kr\/p\/c8NowL\">Steve Fisher<\/a> via <a href=\"https:\/\/www.flickr.com\/groups\/birdshare\">Birdshare<\/a>.<\/em><\/figcaption>\n              <\/figure>\n            <\/div>\n<h3>Pigmentation as Sun Block<\/h3>\n<p>Pigment may also have a specific func\u00adtion related to sunlight. David Lahti, at Queens College of the City Universi\u00adty of New York, and Cornell PhD Dan Ardia at Franklin and Marshall College, studied specimens of Village Weaver eggs from Africa, which naturally vary from white to blue-green. Their theory is that egg color can represent a balanc\u00ading act between two impacts of light\u2014one good, one bad.<\/p>\n<p>\u201cThere must be a trade-off between embryo protection from damaging UV rays, what we call the parasol effect, and the cost of additional pigmenta\u00adtion causing overheating, the dark-car effect,\u201d Ardia explains. \u201cWe found good evidence that DNA-damaging UV light transmits more easily through the egg\u00adshell when there isn\u2019t much pigmen\u00adtation. But heavily pigmented eggs do heat up faster, which is also very dan\u00adgerous for the embryo.\u201d<\/p>\n<p>Lahti plans further studies to explore whether light levels have an influence on egg colors in other species.<\/p>\n<p>Multiple studies have examined egg color in relation to the embryo\u2019s growth. Some theories suggest that variable amounts of pigment at each end of an egg allow differing levels of light to filter through, which may help the embryo develop a sense of direction and also cue the development of specific structures in its body. Another idea is that darker or lighter colors among eggs in the same clutch might play a role in whether the eggs hatch all at once or in sequence.<\/p>\n<p>Some researchers think the intensity of an egg\u2019s color may say something about the health of the female bird, important information for males who may be decid\u00ading how much time to invest in incubat\u00ading eggs and bringing food to the nest.<\/p>\n<p>\u201cThere are many competing hy\u00adpotheses to explain egg coloration and they\u2019re not all mutually exclusive,\u201d Ardia points out. \u201cPigment function is almost surely a complicated combination of factors depending on the idiosyncrasies of each species.\u201d<\/p>\n<h3>More Questions<\/h3>\n<p>Despite the research already done on the colors and patterns of bird eggs, plenty of questions remain.<\/p>\n<p>For example, what do the <em>birds <\/em>see when they look at the eggs? Mark Hau\u00adber\u2019s lab is investigating how some birds see more of the light spectrum than hu\u00admans do.<\/p>\n<div class=\"wp-block-group legacy-sidebar sidebar-alignright has-lightgray-background-color has-background\">\n<h3>Explore More with a Bird Academy Course<\/h3>\n<div class=\"wp-block-image\">\n              <figure class=\"size-small alignnone\"><img decoding=\"async\" src=\"https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/ClaudiaBrasiliero1.jpg\" srcset=\"\" sizes=\"\" alt=\"\" loading=\"lazy\" \/><figcaption><em>White-tailed Goldenthroat by Claudia Brasileiro \/ Macaulay Library.<\/em><\/figcaption>\n              <\/figure>\n            <\/div>\n<p><!--img class=\"wp-image-31306\" src=\"https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/NestsEggsGuide.jpg\" alt=\"Nests and Egg Guide\" width=\"120\" height=\"244\" \/--><\/p>\n<p>Continue to explore the exciting science of eggs, nests and baby birds in our self-paced online course, <a href=\"https:\/\/academy.allaboutbirds.org\/product\/the-hidden-world-of-nests-and-eggs\/\">The Hidden World of Nests and Eggs<\/a>.<\/p>\n<\/div>\n<p>\u201cSome birds, such as most galliforms or ducks, don\u2019t see ultraviolet light,\u201d Hauber explains. \u201cBut some gulls, hum\u00admingbirds, most songbirds, and even ostriches do see UV light and might be picking up more information from egg colors and patterns than we can see.\u201d<\/p>\n<p>Lahti is fascinated by instances in which some birds lay only blue eggs, but other individuals of the same species lay only white eggs, as is the case with East\u00adern Bluebirds.<\/p>\n<p>\u201cI don\u2019t know what\u2019s going on there,\u201d he says. \u201cBluebirds are in the Turdidae family in which nearly all species have blue eggs. But bluebirds may be mak\u00ading an evolutionary transition to white eggs, which would be expected since they nest in cavities or nest boxes.\u201d<\/p>\n<p>\u201cOne persistent mystery is why many open-nesters like the American Robin lay blue eggs. Is this camouflage? Does it sig\u00adnal, as one study strongly suggests, female quality? We don\u2019t know,\u201d muses Birkhead. \u201cAmong other species, we also don\u2019t know how those exquisite pencil-like scribbles are produced on some eggs.\u201d<\/p>\n<p>Whether scientists are trying to un\u00adlock their secrets, or simply enjoy their beauty, bird eggs are one of nature\u2019s lit\u00adtle miracles\u2014a fragile, self-contained, breathable package evolved to protect the tender bud of life unfolding within.<\/p>\n<div class=\"wp-block-group well-gray has-lightgray-background-color has-background\">\n<h4>Ten Cool Facts About Eggs<\/h4>\n<div class=\"wp-block-image\"><figure class=\"alignright size-large\"><img decoding=\"async\" src=\"https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/OstrickEgg-Jabruson.jpg\" srcset=\"https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/OstrickEgg-Jabruson.jpg 500w, https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/OstrickEgg-Jabruson-480x355.jpg 480w\" sizes=\"\" alt=\"Ostrich egg photo by Jabruson\/Minden Pictures\" loading=\"lazy\" \/><figcaption>Ostrich egg. <em>Photo by Jabruson\/Minden Pictures<\/em>.<\/figcaption>\n              <\/figure><\/div>\n<ol>\n<li>In passerines, eggshell formation takes place mainly at night.<\/li>\n<li>Depending on species, eggshells can have anywhere from a few hundred pores to tens of thousands.<\/li>\n<li>An egg loses 18 percent of its mass, on average, between laying and hatching, mostly from water loss through shell pores.<\/li>\n<li>The size of the air cell is smaller in newly laid eggs, so they sink in water. Older eggs have more air space and will float.<\/li>\n<li>More than 100 types of antimicrobial enzymes are found\u00a0in albumen, the egg white.<\/li>\n<li>Regardless of an egg\u2019s position, the yolk rotates so that in the early stages of development the embryo always floats to the top.<\/li>\n<li>Up to 10 percent of the calcium used for shell formation can come from the female\u2019s bones.<\/li>\n<li>A bird\u2019s ovum must be\u00a0penetrated by multiple\u00a0sperm in order for the\u00a0embryo to develop.<\/li>\n<li>Precocial chicks, which\u00a0hatch covered in downy\u00a0feathers, come from larger yolks. Altricial chicks,\u00a0which hatch naked,\u00a0come from smaller yolks.\u00a0With less food available\u00a0inside the egg, the latter\u00a0hatch at an earlier stage of development.<\/li>\n<li>The egg of an Ostrich is the largest living cell on Earth.<\/li>\n<\/ol>\n<p><em><small>Source:\u00a0The Most Perfect Thing, by Tim Birkhead; Handbook of Bird Biology, 2nd edition.\u00a0Cornell Lab of Ornithology.<\/small><\/em><br \/>\n<\/div>\n<p><!--[sidebar]\n\n\n<h4>A New Guide for Bird Egg ID<\/h4>\n\n\n<img loading=\"lazy\" decoding=\"async\" width=\"172\" height=\"350\" class=\"wp-image-31306 size-full\" src=\"https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/NestsEggsGuide.jpg\" alt=\"Nests and Egg Guide\" \/>The Cornell Lab of Ornithology and Waterford Press have teamed up to offer a series of handy, folding pocket field guides about birds, including a Nests and Eggs guide for North American backyard birds. The guide includes illustrations and descriptions of eggs and nests for 24 common bird species. <a href=\"https:\/\/cornelllabpgstore.com\/product\/all-about-birds-pocket-guide-series\/\">Find out more<\/a>.\n[\/sidebar]--><\/p>\n","protected":false},"excerpt":{"rendered":"<p>From the Summer 2017 issue of Living Bird magazine. Subscribe now. Fish do it. Frogs do it. Even insects lay eggs with color. But birds do it best. Only birds<a class=\"excerpt-read-more\" href=\"https:\/\/www.allaboutbirds.org\/news\/the-beauty-and-biology-of-egg-color\/\" title=\"ReadThe Beauty and Biology of Egg Color\">&#8230; Read more &raquo;<\/a><\/p>\n","protected":false},"author":4,"featured_media":31251,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_tec_requires_first_save":true,"_birdpress_living_bird_toc":0,"_birdpress_living_bird_toc_title":"","_birdpress_featured_image":false,"_birdpress_hero_toggle":false,"_birdpress_hero_type":"image","_birdpress_hero_image_type":"image","_birdpress_hero_style":"default","_birdpress_hero_ratio":"","_birdpress_hero_h1":"","_birdpress_hero_media_id":0,"_birdpress_hero_media_array_id":[],"_birdpress_hero_media_array":[],"_birdpress_hero_media":0,"_birdpress_hero_video_id":0,"_birdpress_hero_video":0,"_birdpress_hero_youtube":"","_birdpress_hero_content":true,"_birdpress_hero_byline":"","_birdpress_hero_byline_bottom":"","_birdpress_hero_button_link":"","_birdpress_hero_button_text":"","_birdpress_hero_button_color":"","_birdpress_hero_date":false,"original_guid":"","_birdpress_hide_search":false,"_birdpress_page_width":"","_birdpress_global_cta":false,"_birdpress_widget_sidebar":"","_birdpress_next_article":0,"_birdpress_next_article_title":"","_birdpress_prev_article":0,"_birdpress_prev_article_title":"","_birdpress_sub_navigation_id":0,"_birdpress_sub_navigation":"","_birdpress_sub_navigation_title":false,"_birdpress_anchor_navigation_id":0,"_birdpress_anchor_navigation":"","_birdpress_postType":"both","_birdpress_categoryID":0,"_birdpress_tagID":0,"_birdpress_parentPostID":0,"_birdpress_parentPostTitle":"","_birdpress_menuID":0,"_birdpress_menuName":"","_birdpress_listHeader":"","_birdpress_listLayout":"card-display","_birdpress_listColumns":"","_birdpress_maxItems":12,"_birdpress_listPaginate":true,"_birdpress_displaySort":true,"_birdpress_sortOrder":"DESC","_birdpress_sortBy":"date","_birdpress_listID":"","_birdpress_listClass":"","_birdpress_displayImages":true,"_birdpress_displayCaptions":false,"_birdpress_displayExcerpts":false,"_birdpress_attTop":"","_birdpress_attBottom":"","_birdpress_showLogos":false,"_birdpress_post_logo":0,"_EventAllDay":false,"_EventTimezone":"","_EventStartDate":"","_EventEndDate":"","_EventStartDateUTC":"","_EventEndDateUTC":"","_EventShowMap":false,"_EventShowMapLink":false,"_EventURL":"","_EventCost":"","_EventCostDescription":"","_EventCurrencySymbol":"","_EventCurrencyCode":"","_EventCurrencyPosition":"","_EventDateTimeSeparator":"","_EventTimeRangeSeparator":"","_EventOrganizerID":[],"_EventVenueID":[],"_OrganizerEmail":"","_OrganizerPhone":"","_OrganizerWebsite":"","_VenueAddress":"","_VenueCity":"","_VenueCountry":"","_VenueProvince":"","_VenueState":"","_VenueZip":"","_VenuePhone":"","_VenueURL":"","_VenueStateProvince":"","_VenueLat":"","_VenueLng":"","_VenueShowMap":false,"_VenueShowMapLink":false,"_tribe_blocks_recurrence_rules":"","_tribe_blocks_recurrence_description":"","_tribe_blocks_recurrence_exclusions":"","wds_primary_category":0,"wds_primary_topic":0,"wds_primary_content-format":0,"wds_primary_cornell-lab-project":0,"wds_primary_host-project":0,"wds_primary_read-more-tag":0,"footnotes":""},"categories":[1],"tags":[],"topic":[1145,997],"content-format":[1055],"cornell-lab-project":[1069],"host-project":[],"read-more-tag":[],"class_list":["post-31239","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-uncategorized","topic-anatomy","topic-biology","content-format-article","cornell-lab-project-living-bird-magazine"],"metadata":{"associated-posts":[""],"wpa_off":[""],"_edit_lock":["1775490724:2"],"_edit_last":["2"],"wdsi_message_id":[""],"wdsi_do_not_show":[""],"custom-byline":["<h5>By Pat Leonard<\/h5>\r\n<small>One of the key functions of egg pigmentation is camouflage. These Little Ringed Plover eggs blend in with their stony surroundings. <em>Photo by Michel Poinsignon\/Minden Pictures.<\/em><\/small>"],"banner-video":[""],"banner-image":["https:\/\/www.allaboutbirds.org\/news\/wp-content\/uploads\/2017\/06\/banner-KilldeerEggs.jpg"],"fallback-videobanner-image":[""],"original_guid":[""],"banner-text-style":["light"],"banner-style":["default"],"featured-image-display":["no"],"hide-from-search":["no"],"_birdpress_next_article":[""],"_birdpress_prev_article":[""],"_webdados_fb_open_graph_specific_image":[""],"_thumbnail_id":["31251"],"_webdados_fb_open_graph_specific_description":[""],"_wds_focus-keywords":[""],"_webdados_fb_open_graph_specific_title":[""],"_wds_trimmed_excerpt":["From the Summer 2017 issue of Living Bird magazine. Subscribe now. Fish do it. Frogs do it. Even insects lay eggs with color. But birds do it best. Only bir ..."],"_birdpress_hero_transcript":[""]},"_links":{"self":[{"href":"https:\/\/www.allaboutbirds.org\/news\/wp-json\/wp\/v2\/posts\/31239","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.allaboutbirds.org\/news\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.allaboutbirds.org\/news\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.allaboutbirds.org\/news\/wp-json\/wp\/v2\/users\/4"}],"replies":[{"embeddable":true,"href":"https:\/\/www.allaboutbirds.org\/news\/wp-json\/wp\/v2\/comments?post=31239"}],"version-history":[{"count":0,"href":"https:\/\/www.allaboutbirds.org\/news\/wp-json\/wp\/v2\/posts\/31239\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.allaboutbirds.org\/news\/wp-json\/wp\/v2\/media\/31251"}],"wp:attachment":[{"href":"https:\/\/www.allaboutbirds.org\/news\/wp-json\/wp\/v2\/media?parent=31239"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.allaboutbirds.org\/news\/wp-json\/wp\/v2\/categories?post=31239"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.allaboutbirds.org\/news\/wp-json\/wp\/v2\/tags?post=31239"},{"taxonomy":"topic","embeddable":true,"href":"https:\/\/www.allaboutbirds.org\/news\/wp-json\/wp\/v2\/topic?post=31239"},{"taxonomy":"content-format","embeddable":true,"href":"https:\/\/www.allaboutbirds.org\/news\/wp-json\/wp\/v2\/content-format?post=31239"},{"taxonomy":"cornell-lab-project","embeddable":true,"href":"https:\/\/www.allaboutbirds.org\/news\/wp-json\/wp\/v2\/cornell-lab-project?post=31239"},{"taxonomy":"host-project","embeddable":true,"href":"https:\/\/www.allaboutbirds.org\/news\/wp-json\/wp\/v2\/host-project?post=31239"},{"taxonomy":"read-more-tag","embeddable":true,"href":"https:\/\/www.allaboutbirds.org\/news\/wp-json\/wp\/v2\/read-more-tag?post=31239"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}