Whether simply dipped in food coloring or painstakingly hand painted with intricate designs, decorated eggs are a centuries-old tradition at Easter.
Nature has been there for eons.
A look inside the Field Museum’s egg collection, which numbers in the tens of thousands, reveals a startling range: from some the size of jellybeans to others as big as soccer balls, some are shiny, some are speckled, and some are even shaped. looks more like pears than eggs.
John Bates, curator of birds at The Field, shared a dozen of his favorites. Let’s crack.
1. Common Murre
Common murres are found on both the Atlantic and Pacific coasts of North America, and their eggs are notable for multiple reasons. Each female produces her own pattern, which is believed to help parents spot which ones are theirs in crowded breeding grounds. The unusual shape — heavier at the bottom and less, well, egg-like — also serves a purpose: if an egg is nudged, it tends to spin rather than roll off the cliffs where the guillemots nest.
2. Japanese bush warbler
These terracotta-colored eggs are particularly shiny. And no one really knows why, Bates said. “It’s a big debate,” he said. “Where does it come from and why would you want it?” Eggs have been largely overlooked in terms of scientific studies and are an untapped source of information, Bates said.
3. Cuckoo Guira
There can be up to 20 eggs in a guira cuckoo nest, not because a female is so prolific, but because they share common nests. These cracked eggs owe their appearance to a chalky white layer deposited on a blue-green base. During incubation, the powdery layer begins to fade in patches, revealing the color underneath.
Ground-nesting birds tend to lay eggs in shades of brown, Bates said. “In some cases, we know very clearly that it’s designed for camouflage,” he said. Oystercatchers live on shores and nest in beach vegetation, where these eggs blend inconspicuously.
Blue is most associated with robin eggs, so much so that Crayola has a crayon shade named “robin egg blue.” But many other birds, including the catbird, lay eggs in shade variations.
It takes about 24 hours for a bird to build a single egg, and females need to consume more calcium to produce the shell. Colors, squiggles and patterns are placed on the egg towards the very end, in a process that is not yet fully understood.
7. Cactus Wren
Where are the magenta and chartreuse eggs? Well, nature’s palette is actually quite limited, depending on the Cornell Bird Lab. Birds only use two pigments: one that produces reddish-brown colors — as seen in these pinkish cactus wren eggs — and one that produces blues and greens. All the variety on display comes from different combinations – more of one, less or none of the other – of the two.
8. Cedar waxwing
Here’s a fun fact from Cornell Lab: eggshells have pores. Depending on the species, the number can vary from hundreds to tens of thousands. Eggs will lose about 18% of their mass through these pores, mostly as water, between the time of laying and hatching.
9. Northern Jacaranda
There are a number of mysteries surrounding eggs that scientists have not yet solved. There are competing hypotheses, for example, surrounding the darker pigmented eggs, and whether it protects the embryo from harmful UV rays or heats the egg more than the lighter coloring. Another theory is that paler than normal colors could indicate a nutritional deficiency in the female.
10. Peregrine Falcon
Egg collecting was a popular pastime in the late 19th and early 20th centuries, and most of Field’s specimens date from this period. But the museum’s peregrine falcon eggs are a recent addition, as part of the Chicago Peregrine Program, supervised by Mary Hennen. Hennen collects the non-viable eggs for further study.
The emu is second only to the ostrich in terms of size, so, unsurprisingly, its eggs are huge. These shells are rock solid and can withstand a strong blow from a person’s knuckles, with a cast iron-like look and feel.
12. Elephant Bird
The flightless elephant bird is often described as the “largest bird that ever lived”. It took up residence in Madagascar and has been extinct for at least 800 years. The Field Museum has a replica of an elephant bird’s egg in its collection (l) – like the basketball or the softball of an emu – as well as pieces of a real eggshell. Shards are still occasionally found on beaches in Madagascar, Bates said.
Contact Patty Wetli: @pattywetli | (773) 509-5623 | [email protected]