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Home , Bird egg, Egg tooth

BirdWalk Newsletter Walk Conducted by Perry Nugent and Ray Swagerty

Newsletter Written by Jayne J. Matney

Cover Photo by Robyn and Dana Hogan Snowy Egret on nest with pale blue

Two of the articles I read and obtained information from this week were appropriately titled: “The Art of Hatching an ”, excerpted from “The Most Perfect Thing: Inside (And Outside) A Bird’s Egg” by Tim Birkhead, 2016, on Audubon.org and “The Incredible Egg”, by Linda Pesek DVM from Winged Wisdom Pet Bird Magazine. High praise for a small, round to oval shaped object that only lasts for a limited number of days. So, what is all of the excitement over? Nature has a way of putting us in a state of awe- sometimes with something so simple, and sometimes with something very intricate. Most people are so used to taking egg laying and hatching for granted and usually think nothing of it except when eating a nice omelet for breakfast, baking a cake, or seeing chicks running around their momma. Not so fast! Getting a comprehensive view of egg formation, laying, and hatching may open your eyes to a whole new perspective. When looking at these topics, a multitude of other topics impose on our curiosity levels. Birkhead states, “from the making and coloring of eggs to the self-sanitizing power of a parent’s touch” and questions such as “which end of the egg comes first” or how do the chicks know their siblings and mothers from the start? How do chicks in the egg “breathe”? Are incubation times different according to species? On the quest to answer these questions, many details come to light. Looking at the egg formation itself, it is noteworthy that, unlike humans, most only have a functioning left and . The right is present but undergoes shrinking or “regression” when adults.

Prothonotary Warbler incubating eggs in nest Photo by Perry Nugent

Timing of fertilization to formation of egg varies from one type of bid to another. The first stage is when the ovary receives the portion, comprised of proteins and lipids (fats), from the liver. The yolk is actually suspended in the center of the egg by fibers. It then takes about 24 hours for the unfertilized egg to pass along the oviduct while also being fertilized. Fertilization usually occurs in about the 5th hour of its travels. The egg then develops within the . Once there, “plumping” occurs first, where the egg gains fluids and the egg doubles in weight because of this procedure. Then the shell starts to form by calcium carbonate secretions. The hen’s bones begin to add this calcium into the bloodstream where it begins to collect at the egg. The hen’s diet is critical to the amount of calcium the parent can provide to the production of that egg’s shell. Thin shells translate into a poor diet of calcium and fragile bone structure for the embryo. The size of the egg and the thickness of the shell is dependent upon the bird type. For example, the extreme cases of the hummingbird and the ostrich. The egg must be able to stand up to the weight of the parent during incubation. So obviously, the hummingbird shell does not have to be as thick as the ostrich shell. Egg color is determined by genetics. Believe it or not, egg shells are porous. These pores allow the egg to absorb oxygen and water, and expel excess water or carbon dioxide when needed. Have you ever dyed eggs and seen the coloring reach the surface of the egg beneath the shell once you crack the egg open? There is cuticle on the surface which acts mostly as a barrier to germs on the outside and to decease water loss. But it too has its own cracks in its surface. The development of the embryo within the egg is the next stage. Now that the inside of the egg is taking on necessary water, White-eyed Vireo incubating eggs Photo by Ray Swagerty minerals, and gases, the embryo begins to take on a chick’s shape and body parts- this is also governed by genetic activity. During the development of the chick, the laying of the egg comes into play before it can be incubated. Through the 1700’s and 1800’s, it was thought that the egg came down the vaginal pathway in the same position, and the blunt end always came out first. Heinrich Meckel von Hemsbach, D’Arcy Wentworth Thompson, and J. Arthur Thomson were all well- known scientists that supported this theory. However, in the 1980’s, Jan Purkinje and Karl Ernst von Baer reported the support for the blunt end coming first, but also theorized that the egg travels through the oviduct pointed end first. Finally Heinrich Wickmann put an end to the controversy by conducting experiments with his (Thankfully, tame chickens that were comfortable enough to lay eggs on his desk!) to actually illustrate the flipping of the egg before it is laid. Once he could see an egg in the oviduct, he used a pencil to mark the closest end of the egg. Once the egg was laid, the pencil mark was located in the opposite position. The surface of the egg coming out to be laid had no pencil mark- but the following end did! Later research with x-ray technology by John Bradfield revealed this turn around before laying the egg was done in a horizontal fashion. In other words, not end-to-end but a swivel along the length of the eggs in a 180 degrees rotation. The shape of the egg, the correct end first, and the overturned boat shape to the bird’s pelvis (along with a little help from gravity) all contribute to a successful deposit of eggs. Critical to the development is obviously temperature. The maintaining of the needed temperature levels is different with different species mostly dependent upon the environment where this egg is forming. Adaptations are set in place for the incubation of the developing chick inside the egg. One universal behavior that is usually vital to the proper development within the egg is the successful turning over Great Egret with eggs in nest Photo by Angie Bridges of the egg periodically by the parent. This allows the fetus to remain suspended and not set to one portion in the egg. Cliff nesting birds take full advantage of a more exaggerated egg shape that causes the egg to move in a circular motion when nudged instead of rolling off the cliff! Different species have varying incubation periods and frequencies. Penguins and are known for their long term dedication for continual incubation by the parents. According to “Incubation Period of Other Species”, Penn State Extension, 2017, below is a chart to give you a feel for the differences in incubation periods according to days required to incubate before hatching:

Bobwhite Quail: 23-24 Coturnix Quail: 16-18 Guinea Hens: 27-28 Ostrich: 42 Canary: 13 : 28 Muscovy Ducks: 35 : 35 : 21 Geese: 28-33 Pheasant: 24-26 Turkey: 28 Chukar Partridge: 23-24 Pigeon: 16-19

Eventually, the embryo becomes large and well developed. Again, the amount of development at hatching depends upon the type of bird. For example, wading birds and species may have a more developed chick once it hatches because it needs to be able to stand sooner and get around sooner as not to drown. In contrast, song birds are basically helpless, featherless and have Photo by Perry Nugent more trouble regulating temperature. Again, cliff nesting chicks do not need to be running around on the cliff edge. Therefore, they are less developed as well.

Many people don’t realize that while developing within the egg casing, the incubating chick can communicate with the siblings and the parents. In many cases, this is important for the recognition and survival of the clutch. Communication between the chicks before hatching sometimes helps them hatch at the same time! A study by Margaret Vince showed that they communicate by tactile and auditory signals. Clutches where the eggs are close together can communicate better with each other through a clicking noise and through vibrations inside the egg passing from one egg to the other. When artificial vibrations are put to the eggs, the chicks do synchronize hatching according to these signals. To get to the point of hatching, the egg loses water and yolk and an air pocket, called the , will form for the use of the chick when getting ready to hatch. This will be a transition factor for the chick to become independent of the egg and begin using lungs for oxygen intake and life in the outside world. The chick also begins shutting off the blood supply lining the inside of the shell. The little remaining yolk is suctioned in at the abdomen of the chick for energy supply during hatching and early life on the outside. Pre- hatching posture is described by Birkhead as “a fully developed embryo lies scrunched up inside the egg with its ankles at the pointed end and the head towards the blunt end; its neck is bent so that the head lies adjacent to the breast with the poking out from under the wing up against the egg membrane.” The chick then begins to press its shoulders and legs against the confining egg shell. “Pipping” will soon commence. This is when the bird begins to tap on the egg shell from the inside, and the is used to make the first cracks into the shell. By the way, reptiles and the few egg laying mammals also have an egg tooth. This egg tooth will either fall off or be absorbed into the beak of the bird after the bird hatches. The hatching becomes obvious as the egg shell breaks away, usually at the top of the egg. Wading birds are an exception in that they break through on the side of the egg, which makes for a more awkward hatching. ______Information gathered for this article were: Pesek, Linda DVM, “The Incredible Egg” Winged Wisdom Pet Bird Magazine, 1999; Ehrlich, Paul, Dobkin, David, and Wheye, Darryl, “Incubation Time”, web.stanford.edu 1988; “Incubation Period of Other Species”, Penn State Extension, 2017; ”, Birkhead, Tim, “The Art of Hatching an Egg” excerpt from “The Most Perfect Thing: Inside(And Outside) A Bird’s Egg, Audubon.org 2016.

“In seed time learn, in harvest teach, in winter enjoy.” William Blake ______

It’s the first Sunday of March. Ray Swagerty set out with 4 participants on this cool and breezy day. In the parking lot, a White–eyed Vireo, a Hermit Thrush, and an Eastern Towhee started the count. During the walk, Ringed-billed flew over 2 to 3 at a time. Another fly-over was an immature Bald Eagle. Ravenswood Pond and the Audubon Swamp are always busy in the mornings. Wood Duck, Gadwall, American Wigeon, Blue-winged Teal, and Common Moorhen were located in the ponds there. In addition, Anhinga, Great Blue Heron, Great Egret, Little Blue Heron, White Ibis were gathered on the islands and edges. A Red- shouldered Hawk was also heard calling in this vicinity. Six Rusty Blackbirds were seen in the Audubon Swamp. Scattered throughout the grounds were: Red-bellied Woodpecker, An Anhinga captures its meal by spearing it underwater and Downy coming up to the water’s surface with the catch! Woodpecker, Photo by Eric Barlow Eastern Phoebe, American Crow, Fish Crow, Carolina Chickadee, Tufted Titmouse, Carolina Wren, Ruby-crowned Kinglet, Blue-gray Gnatcatcher, Eastern Bluebird, Northern Parula, Yellow- rumped Warbler, Yellow-throated Warbler, Pine Warbler, , Red-winged Blackbird, and Common Grackle. The Northern Parula are increasing in numbers and are being very vocal. Black and Turkey Vultures were seen above. A Pileated Woodpecker and a Swamp Sparrow were seen near the cabins, while Yellow-bellied Sapsucker, White-eyed Vireo, and Chipping Sparrow were seen on Oak Grove Trail. A White-throated Sparrow was located at the pavilion field near the oaks. As the group approached the house on the entrance road along Oak Alley, two Palm Warbler were observed fluttering around in the azalea bushes there. Two American Robin were seen enjoying the sunshine large lawn in front of the house. A few Northern Mockingbirds were noted in the office gardens.

Blue-gray Gnatcatcher Photo by Guenter Weber