Easter is one of my favorite holidays because each year it arrives alongside the return of spring and the natural world begins to transform around us. The trees begin to bud, and the flowers start to bloom as if the plants are stretching out after taking a nice long nap. The plants transform into a relaxing shade of green, and the bird’s songs seem somehow more chipper.

With the arrival of Easter and spring comes an invitation to go outside and explore, perhaps even hunt, for the promising signs of a new beginning.

Take the classic egg hunt, for example. This Easter tradition began long ago with the egg as a symbol of rebirth. Today colorful eggs, some hard-boiled and dyed, others plastic, are hidden around for kids of all ages to discover. The eggs come in all colors of the rainbow and can be found covered in glitter or with a metallic sheen. While natural eggs aren’t quite to the level of store-bought fabricated eggs regarding hues, they do come in a wide array of shapes, colors and sizes, depending upon the species that has laid them.

For oviparous species (animals which lay their eggs to develop outside of the mother) an egg is a container for an embryo to develop in after fertilization. The embryo will continue to develop until the animal within is ready to hatch. Birds, reptiles, amphibians, fish, invertebrates and even some mammals all lay eggs. On most days, including Easter, the eggs we enjoy have not been fertilized and come from domesticated chickens.

Chicken eggs themselves are available in a large variety of sizes and colors, which are dependent upon the species of hen that laid them. These eggs all feature a hard shell made of calcium carbonate, and the interior, which contains the familiar yolk and albumen (the egg white).

Most eggs laid by vertebrates are white due to the calcium carbonate of which they are made, however, some eggs can vary in color depending upon various pigments that are deposited into the shell while it develops inside the mother before being laid. Robins, for example, lay bright blue eggs thanks to a pigment called biliverdin. Studies have shown that the shade of blue is dependent upon where the robin lays her eggs. If she lays the eggs in a more open area, the egg will be a darker shade of blue to protect the embryo from the sun, whereas brighter shades of blue are laid in areas with more coverage.

Color is only one type of variation that occurs in eggs. Eggs that are laid out of the water, such as bird and reptile eggs, have an outer shell to protect the embryo. However, reptile egg shells, such as those from a snake or a turtle, feel rubbery rather than hard, are very flexible and are often buried for protection. Some amphibians, fish and invertebrates will lay their eggs in water to develop on their own, without any parental care afterward. Only five species of mammal lay eggs, the duck-billed platypus and four different species of echidnas, all of whom reside in Australia or New Guinea.

This season, I hope you have several opportunities to spend time outdoors as the warming temperatures invite wildlife to begin again. In your time outside, if you come across nests that have fallen, it is safe to gently place them back in the nearest tree. You may also find yourself examining an egg that has dropped or even a baby bird. The best thing to do is to leave them where they lay, as mom and dad are waiting for a safe opportunity to approach. If you hunt for eggs this weekend, I hope your basket is as full and plentiful as the natural world around us and that you have a happy Easter!

Emily Sexson is an education specialist at Lee Richardson Zoo.