Of all vertebrates, only birds and dinosaurs lay colored eggs. Therefore, unless you’re a keen paleontologist, peering into a nest of colored eggs means trying to identify types of bird eggs. There are guides and textbooks that can help, though the best bet is usually spotting the parent bird in attendance, unless the nest has been parasitized by a cuckoo or similar.
Factors such as nest shape, egg color and size typically help to categorize wild bird eggs in a purely descriptive way. Taking egg categorization a step further eluded researchers for many years until August 2021, when researchers finally created a universal mathematical formula to describe types of bird eggs of all shapes.
Identifying Types of Bird Eggs
Bird eggs are generally the same kind of construction in that they are rounded and not angular, and have a solid shell that protects the contents. They range in shape from almost spherical to elongated, ovoid, pyriform, conical and pear-shaped. Wild bird eggs vary based on the size and shape of the bird species that lays them and are also influenced by factors such as nest site. Keen birders know not to disturb a nest or handle wild bird eggs. Instead, they simply look at the size, shape, color and other features of the eggs to determine the species.
National Geographic notes that a bird’s ability to fly can also influence the shape of its eggs. The study found that the best fliers tended to have more asymmetric or elliptical egg shapes. This group included penguins, which the research team reasoned could still count as fliers since that was the best way to describe how they moved through the water.
A Universal Formula for All Types of Bird Eggs
Visual description aside, researchers have lacked a simple mathematical way to describe egg shapes. The closest scientists got to describing the types of bird eggs in terms of numbers used three measurements and only covered the more uniform shapes, such as rounded or ovoid. Much to their concern, pyriform or conical eggs eluded mathematical description.
However, in August 2021 a paper published in the Annals of the New York Academy of Science revealed the missing equation. Science News describes how researchers found that adding in a fourth measurement could encompass the tricky pear-shaped wild bird eggs. Standard vital statistics relied on the length, breadth and diameter of the spot where the pointed end terminates, but until recent times this formula couldn’t adequately describe all wild bird eggs.
The research team found that adding one extra measurement, where the egg hits its maximum diameter in relation to the midpoint of its length, was the final piece of the puzzle. The resulting equation is now a universal formula that can mathematically describe all types of bird eggs.
Why Reduce an Egg to Numbers?
Having a universal equation of this kind means eggs can be categorized more easily in situations involving species identification, packaging design and conservation. For example, having the egg numbers at their fingertips helps materials scientists create better egg boxes that protect their precious cargo — no more broken shells in the grocery store.
A universal formula can also help conservation efforts. Using the formula, conservation scientists can determine egg fragility and ease of breakage, which may help with the reintroduction of species back into the wild and better predicting which sites would allow eggs to survive.
Egg shape is also a result of nest site stability, and both Science and Phys.org note that better stability helps eggs survive. The species most often mentioned here is the guillemot, a seabird that lays extremely pointy pyriform eggs. They nest on cliffs, so ornithologists assumed that the shape helped the egg stay on the narrow ledges of the sheer cliffs where guillemots nested. In theory, the egg should roll around in a circle and so avoid cliff diving. However, Hakai Magazine reports on a study that takes the guillemot egg shape theory a step further, postulating that the extremely pointed shape helps eggs in other ways.
By having an extremely pointed shape, guillemot eggs rest with more shell surface area in contact with the nest or the ground. The added friction resists movement, making them less likely to roll. The study also theorized that the point helps keep the rounded end clear of any detritus in the nest site, which could help egg hygiene since most gas exchange takes place at this end.
Using math to categorize the shape of wild bird eggs might not be the most colorful part of studying birds, but it will open the door for researchers to more accurately talk about nature’s talented singers.
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