why birds sit on their eggs

As we’re still in nesting season in Southern California, it’s the perfect time to discuss the wonders of the bird egg cycle. And with Mother’s Day just around the corner, it’s a fitting way to pay tribute to all the mothers out there, both bird and human. From egg laying to incubation to hatching, the bird egg cycle is a fascinating display of both nature’s tenderness and tenacity. Here’s the egg cycle process explained, from start to finish:

Bird Egg Cycle Phase #2: Incubating

why birds sit on their eggs

For a certain amount of time, birds must keep their eggs warm in order to promote the healthy development of the hatchling. They achieve this by sitting on their eggs and using the heat from their bodies to maintain a comfortable temperature (between 85 and 104° F). The length of this time, known as the incubation period, differs among species. Generally speaking, though, the longer the incubation period, the larger the bird. For example, the incubation period for a songbird is 12–15 days, but it’s double that or longer for most duck species. For approximately 18 days, robins incubate their eggs for 13 days, and bald eagles for about 40 days. The Megapode, which is primarily found in the Western Pacific Islands, has the longest incubation period on record at ninety days, while the Laysan Albatross has one of the longest at sixty-six days!

Certain bird species begin incubating as soon as the clutch’s first egg is laid, while others hold off until the second or third egg And before starting the incubation process, songbirds wait until they have laid all of their eggs. The incubation process will involve one or both of the bird parents. It’s typical for parents to take “shifts” when caring for their children. For instance, the mother will typically take over during the day after the father of a Northern Flicker completes the night shift. Similar shared incubation behaviors are shared by woodpeckers, starlings, pigeons, and doves, but in other species (such as hummingbirds and some raptors), the mother serves as the only incubator. However, in more recent instances, the father frequently assists by providing food for the mother and guarding the nest from intruders.

The loggers, which captured data continuously for as long as seven days, unveiled a few surprises. Although the median egg-turning rate was twice an hour, the birds varied in their rates. They all continued to rotate throughout the night, which surprised Shaffers team as they had anticipated that only the nocturnal auklet would be active after dusk. Perhaps more surprising was how they rotated the eggs. The most impressive motion involved moving them side to side within the nest rather than rolling them on their sides, as one might anticipate. By using their feet rather than their beaks, the birds are presumably able to turn the eggs without having to get up and run the risk of the egg losing heat or becoming visible to predators.

Shaffer’s next goal is to compare related species in different environments, such as sub-Antarctic cousins of Hawaii’s albatrosses, “to see if habitat temperature influences turning rates, egg attendance, and egg temperatures.” Additionally, he anticipates that the egg loggers will contribute to the solving of other enigmas, such as how an adult being flushed off the nest disturbs the developing chick. Whatever he discovers, one thing is certain: maintaining an egg’s appearance requires a lot of work.

If youve ever seen a bird nudge its eggs with its beak, you may have wondered what all the fuss is about. Turns out, the behavior is a critical part of incubation, and each species may have its own egg-turning recipe to hatch a healthy chick, a new study shows.

According to scientists, most birds rotate their eggs to make sure the embryo receives enough albumen, which is a protein and water mixture that forms the “egg white” portion of an embryo and gives nutrients to the growing chick. Research on domesticated birds reveals that an underdeveloped and typically sickly chick results from an inadequate amount of albumen. Because the adults are in the way by nature, not many studies have looked into egg turning in wild birds. “It’s difficult to observe what’s happening when albatrosses shuffle their feet in the nest,” notes Scott Shaffer, a biologist from San José State University in California.

Shaffer and his group secretly placed the fake eggs inside the nests of three different kinds of seabirds. They secretly placed 17 laysan albatross nests at Kaena Point, Oahu; another 17 laysan albatross nests among western gull eggs on California’s Año Nuevo Island; and 35 laysan auklets burrows on Southeast Farallon Island.

Bird Egg Cycle Phase #1: Laying

why birds sit on their eggs

The majority of bird species lay an egg within a day or two of fertilization. Nevertheless, some bird species may require more time than that to lay eggs following copulation. For example, it could take five to ten days for Bald Eagles, like our own Jackie and Shadow. After mating, lovebirds can lay their eggs five to twelve days later. Furthermore, some species’ egg-laying periods can be weeks or even months.

Usually, birds will lay multiple eggs; these eggs are referred to as a clutch when they are laid during a single nesting season. Bird species differ in their clutch sizes, as do individuals within the same species. A clutch can occasionally consist of just two or three eggs, or it can contain up to 20 eggs or more (like those of the Gray Partridge). Certain birds, such as thrushes, robins, and bluebirds, nest twice, three, four, or even more times a year, while other birds only nest and lay eggs once.

why birds sit on their eggs

why birds sit on their eggs

why birds sit on their eggs

Left to right: crow eggs, goldfinch eggs, and robin eggs.

Like the features of various bird species, there can be wide variations in the color, shape, and size of their eggs. Here’s a list of bird species and their egg characteristics:

Bird species Egg size Egg color Egg markings
Bald Eagle L: 2.3-3.3 in. W: 1.9-2.5 in. Dull white/tan Light brown blotches
Blue Jay L: 1.0-1.3 in. W: 0.7-0.9 in. Blue/pink Brown spots
Blue Tit L: 0.6 in. W: 0.5 in. Cream Brown spots
Crow L: 1.4-1.9 in. W: 1.0-1.2 in. Bluish/olive green Brown and gray blotches
Goldfinch L: 0.6-0.7 in. W: 0.5 in. White/cream Reddish-brown spots
House Finch L: 0.6-0.8 in. W: 0.5-0.6 in. Blue/white Black or lavender spots
House Sparrow L: 0.8-0.9 in. W: 0.6 in. White Black or gray spots
Jackdaw L: 1.4 in. W: 1.0 in. White/pale blue Gray or brown spots
Mourning Dove L: 1.0-1.2 in. W: 0.8-0.9 in. White Smooth
Robin L: 1.1-1.2 in. W: 0.8 in. Blue Light brown spots