It’s common knowledge that birds periodically turn their eggs when they are incubating them, but have you ever stopped to ask why they do this. One assumes that if this action weren’t critical to the incubation process, it wouldn’t be practiced, and science bears this out. According to Audubon, birds turn their eggs to make sure the embryo gets enough albumen – the white part of the egg that contains water and protein and provides essential nutrients to the developing embryo. Too little albumen leads to an underdeveloped and often sickly chick. (Photo: Canada Goose turning eggs)
Among ground-nesting birds in the Northeast, the American Woodcock, also known as the Timberdoodle, is one of the earliest to lay eggs – usually around mid- to late April. The female shapes a shallow depression in the leaf litter and then incubates her eggs for about three weeks. During this time, if she is sufficiently disturbed, the female will flush and feign injury. She usually lands nearby, runs about with her tail spread, wings drooping and her body quivering, uttering a cat-like sound to distract potential predators.
Upon hatching, the precocial chicks are brooded until their down dries and then leave the nest, usually within hours of hatching. For the first week or so they are dependent upon their mother feeding them, but soon are finding their own food. In a little over a month, the chicks become completely independent. (Thanks to Susan Morse and Phillip Mulligan for photo op.)
In the Northeast, Bald Eagles seek out the tallest trees around in which to build their nests. In certain locations in Alaska, coastal California and northern Canada where there are no trees, Bald Eagles will nest on the ground. When building a nest in a tree, eagles will usually build it in the top quarter of the tree, just below the crown, on limbs capable of supporting a large nest. Sticks from the ground are collected up to a mile away from the nest or are broken off of nearby trees. Additional materials are regularly added to the nest throughout the year, including daily additions during the breeding season (see photo).
Many live eagle cams can be found online (in Minnesota, one chick, one egg – http://mnbound.com/live-eagle-cam/ ; in Georgia, older nestlings: http://www.berry.edu/eaglecam/ ; in Pennsylvania, very young chicks: http://www.ustream.tv/decoraheagles ), giving the viewer a window into the incubation, birth and growth of these raptors. Depending on the location of the nest, one can see every stage of development, from eggs to hatchlings to all-but-fledged nestlings. In New England, eggs are soon to hatch, if they haven’t already. (Thanks to Marianne Blake for photo op.)
Great Horned Owls are said to have the widest range of nest sites of any bird in North or South America. Like other owls and falcons, this raptor does not build its own nest, but rather relies heavily on abandoned stick nests of diurnal birds of prey. Red-tailed Hawk nests are often usurped, as well as those of Bald Eagles, crows, ravens and herons. Nests may be lined with shreds of bark, leaves, downy feathers from the owl’s breast, fur of prey and trampled pellets. In addition to bird nests, Great Horned Owls also raise their one to four nestlings (usually two) in tree cavities and snags, on cliffs, in deserted buildings, in squirrel nests and even on the ground.
The female Great Horned Owl does all the incubating; the male delivers prey to her at intervals throughout the night. These early nesters have incubated eggs successfully when outside temperatures have been as low as -27°F. Hopefully warmer temperatures will welcome the newly hatched owlets in about a month. (photo: mostly hidden Great Horned Owl in Great Blue Heron nest)
Peeps can be heard from inside an egg before the chick starts to crack it open (a process referred to as “pipping”) with its temporary “egg tooth.” The eggs hatch in the order laid, not at the same time. The chicks are covered with sooty black down which is often dry within an hour of hatching. While waiting for the second egg to hatch, the parent loon often takes the firstborn chick for its maiden swim, returning to the nest with the chick to incubate the remaining egg until it hatches. By the third week, the chick’s black down is replaced by brownish-gray down.
Typically Common Loons lay two eggs, each of which is roughly four inches long and olive green to brown in color, with brown or black splotches. The eggs are laid one to three days apart with the 28-day incubation period beginning when both eggs have been laid. Both parents incubate, turning the eggs when they switch places or during long periods of incubation. If the loon on the nest is anxious for relief, it will give a “wail” call, and if its mate does not respond, it continues wailing, even after leaving the nest to find its mate.
Naturally Curious posts for the next four days will be devoted to Common Loons. They are nesting now, eggs are hatching, chicks are swimming, parents are feeding – life is good on ponds and lakes in the north woods, and I would love to share this magical time with you.
Both members of a pair of Common Loons contribute to nest-building in May or June. Their ground nest is often built on the sheltered side of an island, facing the mainland. It is usually within just a few feet of the water, eliminating the necessity for the loons to walk very far. (The position of their legs far back on their bodies is advantageous when it comes to diving and swimming, but makes walking very challenging.) Both male and female share the building of the nest, throwing submerged vegetation from the water onto the nest site or pulling it from the water while sitting on the nest. Material continues to be added to the nest throughout incubation. Nearly two feet in diameter, a nest can take a week or so to build. Successful nests (those that produce chicks) are often re-used from year to year.
Ovenbirds, the warblers responsible for the “teacher–teacher-teacher- TEACHER” song that reverberates throughout deciduous woods at this time of year, are known not only for their distinctive song, but also for their unique domed, ground nests (see dead center of photo). It is the resemblance of their nest to an old-fashioned domed oven that is the source of the Ovenbird’s common name. The materials used to build the nest (bulk of nest is made up of leaves, with additional bits of plant stems, bark, pine needles, rootlets , moss and a lining of deer and/or horse hair), as well as the roofed structure make it all but invisible to most passersby. More often than not the female Ovenbird chooses a site with an especially thick leaf layer on which to build her 6 ½-inch-diameter nest. She enters and exits through a side entrance that is roughly 2 inches wide. The female incubates and broods the young, but both parents feed them, approaching and leaving the nest on foot along a few partially concealed routes. As the nestlings grow, the top of the nest is frequently pushed back, exposing the nest cup. No attempt is made by either parent to reconstruct the roof before the young fledge in about a week to ten days. (Thanks to Tii McLane for photo op.)
Parental care varies according to species, but usually only one sex is responsible for the care of offspring. The exception to this rule is birds, where at least 81% of species exhibit bi-parental care. It may not be shared equally, but both contribute in some way. Fairly typical are Yellow Warblers (pictured). The female Yellow Warbler builds the nest, lays the eggs, incubates the eggs, and broods the young all by herself. The male occasionally feeds his mate while she’s on the nest and when the eggs hatch, shares the delivery of food to the nestlings and the cleaning of the nest. Recent research has shown that the amount of parental care provided by males is directly related to the genetic fidelity of the female. If she’s true blue, then she may well receive a lot more help from her mate.
A Ruffed Grouse’s nest is pretty basic – just a shallow bowl on the forest floor, created by the hen grouse tossing leaves over her shoulder and having them fall on her back, slip down to the ground and form a bowl. Ruffed Grouse lay anywhere from 9 to 14 eggs at intervals of 25 to 30 hours, which means it takes about two weeks for a hen to lay an average clutch of 11 eggs. Each of her eggs weighs about 4 percent of her body weight — the entire clutch will be equal to about half of her weight. Once incubation starts (when the last egg is laid) the hen’s behavior goes from wandering around and feeding voraciously, to sitting on the nest and barely moving. Because of this behavior, as well as her cryptic coloration, an incubating Ruffed Grouse hen is much more likely to see you before you see her. She will stay motionless on her nest, even in the face of danger, hiding her eggs. Once she is certain she has been spotted, she will fly off the nest, exposing her eggs. Foxes, crows, ravens, chipmunks, skunks, bobcats and raccoons are some of the predators responsible for the loss of 25% – 40% of grouse nests each year. After the precocial Ruffed Grouse chicks hatch during the first two weeks of June, they will be led away from the nest site by the hen. Within 24 hours they will be feeding on insects and within a week they may double their weight! (Thanks to Ginny Barlow for photo op.)