Since earliest history, eggs have served as evocative symbols of new life and rebirth. We humans turn to the avian world to describe our own “broodiness,” our urge to save up a “nest egg,” and how, when our children leave, we have “empty-nest syndrome.” When June, and eggs, are bustin’ out all over, we’re filled with joy and wonder. And questions.
Q The song says, “Birds do it. Bees do it. Even educated fleas do it.” But what exactly is it that birds “do”?
A Before mating, birds often court one another with ritualized displays. For example, a pair of Whooping Cranes will face each other and dance, leaping into the air, bowing, and flapping their wings. Red-tailed Hawks may grasp one another’s talons in flight and spiral together toward the ground. Male songbirds sometimes present their mate with a choice insect or berry. Mallards bob their heads up and down, the pair moving their heads in opposite directions so that one is bobbing up while the other bobs down.
When ready to mate, in most cases, the male bird alights on the female’s back. The birds twist their tails so that their cloacae (the common chamber where the urinary, intestinal, and genital tracts open) meet. The sperm pass from the male’s cloaca to the female’s. As the fertilized egg works its way down the female’s oviduct, the cells along the way secrete the proteins that make up the albumen, and then secrete the calcium that will form the shell. Usually by early the next morning, the female lays the egg. Females have one functional ovary and in most species ovulate once every day or two, so the laying period lasts at least as many days as there are eggs in a clutch.
During the days or weeks between starting nest building and finishing laying a clutch of eggs, a pair of birds may mate several or many times, and sperm can remain viable inside a female often for more than a week. If her mate is killed, she may be able to raise young on her own, though normally she replaces her lost mate with another male within a day or so. In recent decades, ornithologists have been discovering that many species have “extra pair copulations.” Even when female birds are socially bonded to their mate, they sometimes mate with another male once or twice, and often the young birds in a single brood have more than one father.
Q Why do birds have such elaborate and varied courtship rituals?
A Courtship rituals are a form of communication, enabling birds to signal their willingness to mate. They also give the birds an opportunity to assess their partner. A female bird invests a great deal, physiologically and energetically, in producing eggs, incubating them, and raising the young. Courtship displays can help her select a mate who is most likely to produce healthy young. She may look for clues about his health, vigor, or ability to provision the young, based on his appearance, his display, or his song.
For example, a male bird may show off his brightly colored plumage because bright colors indicate his health or ability to find good food. A male Snail Kite offers his mate a stick or a snail, perhaps a sign of his ability to provide materials for a nest and his superior hunting skills. Male songbirds may sing repeatedly to advertise their vigor or experience. Female Northern Mockingbirds may prefer males that sing the most song variations. Since older males typically sing more songs, a larger repertoire may indicate longevity and experience in raising young.
The male Eastern Bluebird displays at his nest cavity to attract a female. He brings nest material to the hole, goes in and out, and waves his wings while perched above it. Only the female builds the actual nest and incubates the eggs, but he shares the work in feeding the nestlings.
Q Why do Blue-footed Boobies have blue feet?
A Blue-footed Boobies, fish-eating relatives of pelicans, breed in tropical and subtropical islands in the Pacific Ocean, most notably the Galápagos. They have large webbed feet ranging in color from pale turquoise to a deep aquamarine. Males flaunt these feet in courtship dances, holding them up and stamping them on the ground. Males with the most brilliant feet are the most attractive to females. Booby foot color is brightest when birds are well fed on nutritious fish — in captivity when deprived of a good diet, the foot color grows noticeably duller within 48 hours. So this is an excellent cue for females to use to determine a male’s ability to find food, a direct signal about how well he will provide for young. Interestingly, if a scientist dulls the color of a male booby’s feet with paint after his mate has laid her first egg, her second egg will be small, perhaps to reduce the food resources necessary to raise that chick.
Although the male Blue-footed Booby dances, showing off his blue feet conspicuously in a courtship ritual, the blue foot color is present on both males and females throughout the year, not just during the breeding season. Both sexes use their feet to incubate their eggs and to keep the chicks warm, but the color doesn’t enhance those functions.
Western Grebes, grassland grouse, Calliope Hummingbirds, manakins, tropical wrens — the vast array of spectacular courtship displays fills humans with wonder even as they set bird libidos on fire.
Many people have seen film footage of a pair of Western Grebes (elegant, long-necked, black-and-white diving birds from the American West) dancing in synchrony on the surface of a lake. In these spectacular dances, called the “rushing display,” two birds turn to one side and lunge forward with their bodies completely out of the water and run rapidly across the surface side by side. Occasionally one or more other birds join them. After “rushing” back and forth for 5 to 20 minutes, the birds lower their wings and dive into the water. They don’t call during this dance, but the pattering of their feet on the water is distinctive and thrilling to witness.
Greater Sage-Grouse, Greater and Lesser Prairie-Chickens, and Sharp-tailed Grouse — all large chicken-like birds of the American West through the northern plains — have wonderful displays. Males gather together on a breeding ground called a lek, inflating brightly colored air sacs, stomping their feet, erecting some body or head feathers, and opening their wings. Females wander through and choose the males with the best displays to mate with. These grouse form no pair bond: the females build their nests and care for eggs and chicks entirely on their own. They’ll fly in from several miles away to a lekking ground to choose the finest males.
Many species of manakins, from Central and South America, have amazing displays, from the “moonwalking” Red-capped Manakin (see page 162) to the White-collared and Orange-collared Manakins. In these, males clear a patch of ground as a lek and leap back and forth between thin upright bare sticks, giving a loud wing snap with each jump. When a female is present males jump together, crossing each other above the bare display court. They erect their throat feathers to form a beard during displays.
Many male hummingbirds have spectacular courtship flights to attract females. For example, the male Calliope Hummingbird, the tiniest North American species, living in the mountainous West, makes a spectacular dive: climbing to about 100 feet (30 m) and then plunging at high speed and braking abruptly, then climbing again, following a U-shaped trajectory. During this, the flight feathers make a buzzy hum.
Many tropical wrens have an auditory rather than a visual courtship display, singing elaborate duets so seamlessly integrated that it can be difficult to discern that more than one bird is singing.
Q I was watching birds at the feeder and noticed a male Rose-breasted Grosbeak feeding either its mate or a fledgling, which was perched very close by waiting for the male to bring it seed. Why wasn’t the female or fledgling going to the feeder itself?
A During courtship, males sometimes offer food to females — the females may use this to determine how good a provider each of her suitors could be. After the babies fledge, it takes them a while to figure out what foods are appropriate to eat, and they may still be clumsy fliers. So it is probably safer for a young bird to sit in the relative shelter of a shrub while the adult flies through the open to and from the feeder bringing it food.
Q Why do robins lay blue eggs? Is it possible to tell males and females apart?
A No one knows why robins lay blue eggs, but the eggs of most thrush species are blue. The blue doesn’t seem to camouflage the eggs, but it doesn’t make them particularly conspicuous either. Pigments usually add some structural strength to tissues, and this particular blue pigment may give the eggshells just the right thickness and hardness to protect the embryo while allowing it to finally break out.
Robins flock year-round except during the breeding season. The mother remains at or near the nest site all the time when she has eggs or nestlings, but after the first brood of young fledge, the father takes them at nighttime to a communal roost. When he leaves them after 12 or 14 days to help raise the next brood, they remain together and with other young robins.
After the pairs have finished raising young, they also join these flocks. During fall and winter, robins can sometimes be found in flocks numbering in the thousands, ten thousands, or even hundred thousands, though most flocks seem to number a dozen or two. These flocks break up in spring when males and females appear restless and territorial squabbles erupt more frequently.
The differences between male and female robins are very subtle. Females are overall paler than males, especially on the head, which is almost black on males. The white eye crescents and throat striping are a bit more dramatic on males, too. But when robins from other areas join together, especially in winter flocks, sometimes you’ll notice that bright females from one area are as intense as dull males from another area. It’s easiest to see the differences between a pair that you’re regularly watching, especially during the breeding season. Also, if you hear a robin singing (not just making the peek! or tut-tut-tut calls), it’s a male for sure.
The male and female of some species of birds, especially those that mate for life, such as jays, crows, ravens, cranes, eagles, geese, and swans, are identical or differ only in size. In other species, the male and female may bear dramatically different plumage, such as cardinals, waxwings, finches, and many ducks. This is called sexual dimorphism.
Females are often fairly cryptically colored, which helps camouflage them on the eggs, though male Rose-breasted Grosbeaks, despite their brilliant color and pattern, also incubate. Males are bright, which helps them attract a mate and aids in their territorial defense. For example, female Red-winged Blackbirds and female Baltimore Orioles tend to prefer males with the most brilliant colors, and these males tend to defend the best territories.
For many birds, the name of the species really describes only the male. Female Scarlet Tanagers are never scarlet, female Red-winged Blackbirds do not have red wings, and female Ruby-throated Hummingbirds do not have ruby throats.
Q Do male American Goldfinches change color in winter in the Midwest? Or do they migrate and leave the females here?
A Winter male American Goldfinches, like females, are dully colored. The difference between winter and summer plumages is the most striking in its family, and the spring molt is unique among finches. Across the continent, migratory activity peaks in mid-April to early June during the spring molt, and in late October to mid-December after the fall molt. There is a great deal of variation in individual birds — some may migrate some years and not others. Goldfinches associate in flocks that include both sexes, and individuals of both sexes migrate or remain residents in the Midwest as they please.
Q In my local park, I saw two mockingbirds fighting, but I couldn’t tell what they were fighting over. It seemed like there was plenty of space for both of them.
A When it’s time to nest, many birds establish and defend territories, and fight for mates. To successfully raise young, birds need a safe place for their nest and adequate food to feed their family. Many bird species defend an area around their nest site, chasing away other birds that might compete with them for food. They may also chase intruders away to prevent rivals from mating with their partners. A Northern Mockingbird’s territory may range in size from about 1 to 6 acres (0.4–2.4 ha). Some songbirds have relatively tiny territories — Ovenbirds and Song Sparrows may require less than half an acre. But songbirds that require specialized food or food from higher up the food chain require more space. Scarlet Tanagers can require 5 to 30 acres (2.0–12 ha) or more, depending on the quality of the habitat. Loggerhead Shrikes may require 75 acres (30 ha) or more, and Gray Jays average about 250 acres (101 ha).
In nonsongbirds, too, the size of a territory is affected by the abundance and distribution of food and nest sites. Bald Eagles in sparsely vegetated Saskatchewan defend territories at least 1½ square miles (3.9 square km) in size; the minimum size of their territories on Kruzof Island in Alaska, where food resources are more abundant, is only 1/5 square mile (0.5 square km). Some eagles may fly quite a distance from their nest to fish, so if there are abundant fishing waters in one area, eagles can be somewhat concentrated where large trees provide good nesting. Once an eagle catches a fish, other eagles sometimes aggressively fight to take it, so even though they can share fishing areas, they need at least some space between one another. Red-winged Blackbirds, by contrast, vigorously defend their nesting territories but feed peaceably, almost shoulder-to-shoulder, away from the nesting area.
Q How many pairs of wrens can live peaceably in my backyard? Are they extremely territorial? I’d like to put up several wren houses.
A Wrens are extremely territorial. You’ll get one male at most, but he may build stick nests in each of your wren houses, and may attract more than one mate. Each female will choose one box to nest in.
Q Do all birds defend territories?
A No. Some birds are extremely sociable even during the nesting season. For example, thousands of Cliff Swallows may build their gourd-shaped mud nests side by side in a single dense colony. One reason they live in close proximity is because the specific sites where they can find mud of the right consistency and suitable structures on which to build their nests are limited. Each pair defends the area right where they’re building, but once the nest is built, they don’t seem to mind if other swallows perch on the nest itself as long as they don’t enter. After they finish building, they defend just the area immediately beneath their nest to prevent other birds from building a nest that might block the entrance to their own nest.
Great Blue Herons also nest in colonies, constructing their stick nests in a stand of dead trees. Adults may fly several miles to and from good fishing spots, and they tend to be rather territorial around their fishing grounds, but at the nest sites they are gregarious.
Emperor Penguins don’t defend territories either. They stand side by side while incubating their eggs and raising their chicks. What do Cliff Swallows and Emperor Penguins have in common? They can both find areas with concentrated food distant from their nesting site. Cliff Swallows chase after swarms of insects. Penguins leave the nesting area to fish in the ocean. Both of these sources of food would be hard to defend.
By nesting closely together, the birds can benefit from better protection from predators; while some birds are off searching for food, other adults are nearby to detect and drive away marauders. Great Blue Herons build the kinds of structures that eagles or osprey like to take over, but it’s difficult for these large raptors to take over a nest in a heronry, and the presence of so many large herons tends to keep the raptors away. Penguins get a special benefit from nesting in tight colonies during cold weather: They can crowd together, keeping each other warm.
Whooping Cranes in northern Canada defend territories that vary widely in size, from just a half of a square mile to 18 square miles (46 square km), depending on the resources available to them.
Q Our dog, a 10-pound rat terrier/miniature pinscher who doesn’t bark, is getting swooped quite frequently by a couple of aggressive blackbirds. They have actually nicked him while he’s in our yard. We have a number of evergreen trees on our property. Is it possible there is a nest? We’ve never had the issue before. We have also noticed, as have our neighbors, that we have at least one hawk in the area. If it’s a nesting/protecting thing, how long is it going to last? Our dog is terrified!
A I suspect the blackbirds are Common Grackles, which nest in conifers. They may well have been there in past years, too, but this year the hawk may well have added to their stress levels. When your dog was the only perceived danger, they could go about their business while merely keeping an eye on it. Now that there is a much huger danger to them and their young, their rising stress levels may be making them act more aggressive in general. If it’s a Cooper’s Hawk, they don’t dare mob it, so they’re taking out all their frustrations on your poor little dog.
Grackles incubate their eggs for 11 to 15 days, and then the nestlings remain in the nest for 10 to 17 days. So, worst-case scenario, they’ll be harassing your dog for a full month. But they don’t re-nest, so when the babies at long last fledge and the families move on, your dog will be left in peace.
A bird’s diet and nesting habits determine what kind of territory it will defend. A suburban robin prefers moist lawns with earthworms and berry-bearing plants to provide food, and good tree limbs or house eaves for a secure nest site. A Barn Swallow looks for a bridge, culvert, barn, or other building that provides struts, eaves, or other supports for its heavy mud nest, near a pond or open field rich with flying insects.
Both species require mud for nest construction, so the best territories for each will also contain wet, muddy shorelines or good puddles. In good swallow areas, insects are far more abundant than the birds require, so many may nest close to one another without it hurting each other’s ability to find food for their own young. Robins could much more easily deplete the supply of worms and other food on their territories if other robins nested too closely, so they defend their territories far more vigorously than do swallows.
Most hummingbirds seem to prefer territories with plenty of spider webs and lichens because they use these materials to build their nests. An ideal territory might also include nesting sapsuckers. Before flowers open and produce nectar in spring, Ruby-throated Hummingbirds can drink sap from wells in trees drilled by Yellow-bellied Sapsuckers. Birds that nest in cavities but do not excavate their own, such as bluebirds and wrens, search out these structures in suitable habitat that will supply their food needs.
Males of a few species, including tropical manakins, birds-of-paradise, bowerbirds, and cocks-of-the-rock, defend territories just so they can display to females there. Dozens or even hundreds of male Sharp-tailed Grouse or other grassland grouse species, including prairie-chickens, gather on large display areas called leks. These spots may look like any others to the human eye, but the grouse may return to them year after year, ignoring other similar-looking spots nearby.
At the lek, males display by inflating colorful air sacs, erecting their tails, and stomping their feet. Competing males, especially those on the periphery of the lek, may come to blows, pecking, biting, feather-pulling, wing-beating, and clawing at one another, especially when females enter the lek. Females may visit a lek several times during the early nesting stages, but they build their nest and raise their chicks completely independently of the males, sometimes more than a mile from the lek.
SEE ALSO: page 238 for more on lek displays.
Q If robins make a nest in a bush close to the house one season, what are the chances they will go back to the same place the next season to build their nest?
A If the female survives the winter, and if she successfully reared young the first year, the chances are excellent that she will return to the same place the next year. If the nest failed for any reason, she will usually find a new place to build.
Q Do all birds sleep in nests?
A No. Nests aren’t designed to serve as beds for adult birds. They’re really just incubators for eggs and hatchlings, and cribs for nestlings. Chicks of many birds, including ducks, geese, and relatives of chickens such as grouse, leave their nest within a few hours of hatching, never to return. Others remain in their nest until they can hop or fly.
Woodpeckers and other birds that nest in cavities often sleep in cavities even when they’re not nesting. Cavities protect birds from excessive cold and heat and, even more important, from rain and snow and wind. But cavities aren’t absolutely safe. Raccoons, cats, and some other predators can reach into cavities to pull out sleeping birds, which have no other way out. And cavities can foster parasites. Some birds roost in cavities only on very cold nights; otherwise, they roost on branches. As soon as young woodpeckers leave the nest, they move into abandoned cavities or excavate new ones for sleeping, and switch to new cavities fairly often.
This is why it’s so important for birds to have both good nest sites and good roost sites in their habitats.
Q One day I looked out on my porch and a little bird was plucking fur from my golden retriever! Why was it harassing my dog?
A The bird wasn’t trying to bother your dog; it was just taking advantage of a convenient source of fur to gather soft insulation for its nest. Many birds, including Chipping Sparrows and Tufted Titmice, pluck fur from dead and sleeping animals. They also pluck tail hairs from horses. Once I saw a Tufted Titmouse pulling hairs from the tail of a raccoon. The tail was sticking out of a big cavity, and the raccoon was apparently sleeping inside. It hardly moved at all as the titmouse collected hairs; suddenly it rolled over, its tail slowly twisting around as the titmouse clung to it, finally flying off with a beakful of hairs.
The largest documented individual nest is that of a Bald Eagle in Florida; it was 20 feet (6 m) deep, almost 10 feet (3 m) wide, and weighed almost 3 tons. The largest nest on record built by social birds was a nest made by African social-weavers. The nest had 100 chambers. It was 27 feet (8.2 m) across and 6 feet (1.8 m) high.
When building a nest for the first time, most birds seem to instinctively know what materials to use and how to build it without having observed nest building before, perhaps from having been raised in a particular kind of nest, but their skills improve with age and experience. Some species, including turkeys, nighthawks, and Killdeer, make a simple scrape in the ground, using their bellies to shape it. Others, such as orioles, construct elaborately woven nests using hundreds of strands of grasses or fibers. There are hundreds of ways in which birds construct their nests! Here are a few examples:
Peregrine Falcons nest on ledges, cliffs, and inside special nest boxes with a gravel bottom set out to attract them. The female doesn’t bring any materials or make any serious efforts at construction; she merely lowers her belly and hollows out a little impression where she can lay her eggs, to keep them from rolling off.
Woodpeckers build some of the most ecologically important nests, because they provide roosting and nesting accommodations for many other animals after the woodpeckers are done using them. A Pileated Woodpecker can hammer a hole about 2 inches (5 cm) deep into hard wood with its bill. It can’t hammer with any kind of power deeper than that, because it can’t align its body to have leverage, so Pileated Woodpeckers seek out trees with healthy outer wood that are rotten on the inside. Male and female both hammer a round hole wide enough to pass through, and then reach in to grab mouthfuls of the rotted woody matter and spit them out to excavate a nesting chamber inside. During the nesting season, both parents incubate the eggs and then care for and feed the young throughout the daytime; the male stays inside the nest with the eggs or chicks at night.
Wood Ducks also depend on cavities but cannot excavate their own. Wood Ducks occasionally use old Pileated Woodpecker holes, but more often prefer holes formed when a rotten branch falls off a tree and heart rot creates a nest chamber. Wood Ducks don’t collect nesting materials, but the female does line the bottom with down feathers she pulls from her breast and belly; they grow loose during the breeding season so this is easy for her to do.
Black-capped Chickadees can use an old Downy Woodpecker cavity or bird house; or they can excavate their own cavity in a rotten section of a birch, aspen, or other soft-wooded tree. Once the cavity is excavated, usually by both the male and female, the female builds the nest inside. She starts out using moss to form the bottom and sides, and then lines it with softer material such as rabbit fur.
House Wrens nest inside old Downy Woodpecker or chickadee cavities, inside bird boxes, and inside all manner of other small spaces. Wrens have successfully nested inside old boots, overall pockets, truck axles, fish creels, and cow skulls. The male chooses as many potential nest cavities as he can find, covering the bottom of each with a platform of small sticks. The female chooses the one most to her liking and finishes building the actual nest in a depression in the stick platform; she lines this cup with soft materials.
Tree Swallows nest in old tree cavities or bird boxes. Females build the nest, which they line with feathers, mostly brought by the males.
Common Loons build their nests along a shoreline or on a mass of floating vegetation. Experienced pairs prefer floating masses or floating artificial nest platforms because they rise with water levels and aren’t as readily flooded as a shoreline nest. Both adults work fairly equally on the nest, pulling or retrieving vegetation adjacent to the nest or from the lake bottom, and then tossing it sideways onto the nest. They both shape the nest by sitting and contouring the materials to their body shape. While sitting on the nest, they may pull materials from their surroundings to add to the nest. Early in the season, it usually takes more than a week for a pair of loons to build a nest, but later on it may take only a single day. This may be partly because they’re more hormonally primed later on, partly because more vegetation is available further into the spring, and partly because late nestings may be replacement nests when the birds are in a bigger hurry to finish.
The Baltimore Oriole female builds her complicated hanging nest in three stages. First, she constructs the outer bowl of flexible plant, animal, or human-made fibers that can be very coarse — these provide the structural support. After she’s put together the basic skeleton, she often works from inside the nest adding more fibers, especially as she moves onto the next stage. At that point, she begins weaving more springy, flexible fibers into an inner bowl, which fills in spaces and maintains the nest’s shape. Finally, she adds downy fibers to line the nest. It usually takes her about a week to build the nest.
Barn Swallows work together to build their nest, though the female seems to take a leading role. Both birds collect mud in their beaks, often mixing it with grass stems to form rounded pellets, the basic “bricks.” As soon as they form a new pellet, they fly to the nest site and attach it, first to a wall or other vertical structure, or to the top of a beam, eave, or other horizontal support.
Little by little they construct a narrow mud shelf, just big enough for them to sit on, and then build up the sides to form the inner bowl. If it’s attached to a vertical wall, the nest is a semicircular half-cup shape. If it’s built atop a beam or other bottom support, the nest will be more circular. The female spends a lot of time shaping it with her belly. Once the basic mud nest is constructed, they line it with grasses and then feathers. If things go well, they may complete the nest in three days, but sometimes it takes as long as two weeks, especially when the weather is unfavorable for gathering mud.
American Dippers, birds of gushing mountain streams in the West, nest on cliff faces or ledges, sometimes behind noisy waterfalls. Males may help with nest construction, but in some pairs the female does it all. They seem to prefer using wet materials for building. In 1908, D. Gale described the process for one female, who rejected her mate’s “desultory contribution” to help. She built the nest “from the bottom up … the walls raised on all sides by forcing the building material into the wall from below…. (F)ibers on the outside … lie loose, plush-like, to lead the water from the dome roof as from a hay-cock. As this work on the walls dries, the insertion of other plugs … knits the whole densely.… by working from below, the lips or edges of the walls from all sides are closed up…. while working on the lower side the bird lay flat on the floor, spread her wings for a purchase and seemed to push with all her strength to ensure a well-caulked seam.” All this took just one hour.
Bald Eagles usually begin building a nest together months before producing eggs, though in one case nest construction took only four days. Both mates gather fairly large sticks, though the female usually takes the lead in placing them. Grasses, mosses, and even cornstalks are used as fillers. Once the basic structure is in place, they’ll add finer materials, such as Spanish moss, and then feathers. Pairs work on the nest throughout the nesting period and, especially, after their young have fledged each year and before the next nesting season. A single Bald Eagle nest may remain in use for several decades. As one bird dies, its mate will take a new mate, so what appears to be the same pair year after year may actually be different ones.
Q Last spring I watched prairie-chickens from a blind. Later in the morning when the chickens started leaving, suddenly Tree Swallows came in, flying back and forth just above where the prairie-chickens had been dancing. Do prairie-chickens have lice or were they stirring up bugs that the swallows were feeding on?
A The swallows were picking up little feathers that had gotten stuck in the prairie grasses while the prairie-chickens were preening, displaying, and fighting. Swallows line their nests with feathers, and after they’ve discovered that grassland grouse and prairie-chickens leave a lot of down feathers after their morning activities, the swallows make it a regular practice to check out the area every morning as the chickens leave.
Q Are any martin houses guaranteed to attract Purple Martins?
A No. Purple Martins are declining over much of their range, making it difficult for people to attract them to a new nest site. You’ll increase the likelihood of success by following recommendations from the Purple Martin Conservation Society. If you do set out a martin house, please make sure to evict any House Sparrows before they complete their nests. Do this by tossing out nest materials and closing the holes until martins appear. House Sparrows are a serious competitor with Purple Martins and are one of the major reasons for Purple Martin declines.
Purple Martin houses built as “apartment buildings” should not have ledges that connect one apartment to another. If a chick from one chamber wanders out and into the next apartment, its parents won’t follow it there for feedings. Meanwhile, the parents nesting in that chamber may end up feeding the wanderer rather than their own nestlings if the wanderer is larger and appears hungrier. There are overall higher mortality rates in these kinds of martin boxes than in ones with dividers completely separating chambers, or in gourds.
Q Help! We used to have a lot of Purple Martins, but they’ve been dwindling and this year there’s just one pair left. House Sparrows took over the rest of the martin house, and all we ask is that they leave the one hole alone for the Purple Martins, but they’re being so aggressive! I’m afraid we’ll lose our Purple Martins for good. Is there anything we can do?
A House Sparrows are one of the worst problems facing Purple Martins. Having even one pair in a martin house is eventually going to eliminate the martins. Every year, the entry holes should be closed or blocked until martins return.
For the most current suggestions for dealing with House Sparrows in Purple Martin houses, visit the Purple Martin Conservation Association’s website at www.purplemartin.org.
A “COMPOST” NEST THAT WARMS THE EGGS
Australian Brush-Turkeys have unusual nests that actually give off enough heat to incubate the eggs without the parents. The male uses his oversized feet to scratch together a pile of dead leaves, branches, and other fallen vegetation, constructing a huge nest, sometimes 12 feet (3.6 m) in diameter and 3 feet (1 m) deep. The nest looks like a messy pile of leaves but works as a compost pile to keep eggs warm. Female brush-turkeys mate with the males whose nests seem to provide the best incubation environment in which to lay their eggs. After the chicks hatch, they dig their way out of the nest and move on, ready to lead independent lives immediately.
It’s illegal to collect nests — both state and federal laws protect birds and their feathers, eggs, and nests from being collected. Nests sometimes harbor mites, lice, and botfly larvae, so they probably aren’t a good choice for keeping indoors anyway.
PROVIDING SAFE HOUSING FOR BIRDS
Unlike human housing, birdhouses don’t have to meet any building codes and, sadly, many birdhouses on the market are made of metal or cheap plastic, both of which can get excessively hot or cold. And many houses have inappropriate hole sizes for the birds they are intended for. When a wren or chickadee house has a hole larger than 1 1/8 inch (2.9 cm), House Sparrows can enter and kill the babies. When a bluebird box has a hole larger than 1 9/16 inch (3.9 cm), starlings can get in and kill them.
If the wood inside the box is too smooth below the entry hole, young bluebirds, ducklings, and other baby birds often cannot get the traction they need to get out of the box. Rough cut plywood is a good choice, or you can score the inside or add rough material below the hole.
Many people like the looks of a bird house with a little perch below the entrance hole. But birds accustomed to natural cavities and woodpecker holes don’t need that perch, which is an open invitation to House Sparrows. If you buy a birdhouse that has a dowel or other perch below the entrance, break or cut it off.
Birds don’t care about adorable designs. Keep designer birdhouses indoors, and set out birdhouses conforming to plans produced by authoritative sources such as the Cornell Lab of Ornithology (www.nestwatch.org), state departments of natural resources or conservation, and organizations such as Audubon and the National Wildlife Federation.
Many birds never enter cavities or birdhouses — only a relatively small number of species do nest in birdhouses. The ones people are usually most interested in providing housing for include:
American Kestrel (nest box)
American Robin (nest platform)
Barred Owl (nest box with very large entrance)
Bluebirds (nest box)
Chickadees (nest box or tube)
Common Loon (nest platforms)
Eastern Phoebe (nest platform)
Flycatchers, Ash-throated and Great Crested (nest box)
House Wrens (nest box or tube nest)
Oak and Tufted titmice (nest box)
Osprey (nest platform)
Peregrine Falcon (gravel-covered ledge or open box)
Prothonotary Warbler (nest box)
Purple Martin (gourds or nest box with multiple compartments)
Screech owls (nest box — same size as for Wood Ducks)
Swallows, Tree and Violet-green (nest box — same size as for bluebirds)
Wood Duck (nest box)
Wrens (nest box or nest tube)
Q Birds seem so devoted to one another, courting and raising their young together. How many species mate for life?
A There is a great deal of variation among species, and even among individuals, with regard to mating systems. Swans, geese, and cranes may migrate long distances between nesting and wintering grounds, pairs remaining together throughout. Eagles and falcons may also migrate long distances and nest with the same partner year after year, but there is little or no evidence that they remain together except during the breeding season.
Florida Scrub-Jays are not the least bit migratory — birds spend their entire lives within a very small area — and pairs remain together as long as they both survive. Tropical wrens that remain on the same territory throughout the year not only mate for life but learn to sing complex duets, some so perfectly synchronized that it may sound like a single bird unless the listener stands between them.
There may be some randomness about other birds pairing for life. Chickadees tend to select mates from across the dominance hierarchy within their winter flock: the highest-ranking female mates with the highest-ranking male, the second-most dominant female with the second-most dominant male, and so on. Flocks are fairly stable from year to year, so some of these pairings may last several years. But when a high-ranking bird of one sex dies and the rankings shift upward, a shift in pairings usually occurs. Some birds that return to the same general nesting area year after year can end up with the same mate. With robins, this tends to occur more often when they were successful raising young the previous year. And for many species, there is little or no tendency to select the same mate in subsequent years.
Many species remain together for an entire season, but some only remain together for a single nesting and then both birds find new mates. After a pair of House Wrens fledges a brood, the female often finds a new mate while the male continues to rear the fledglings and attracts a new mate. In contrast, many ducks remain together during nest-building and egg-laying, but then males move on when the female starts incubating.
Some species don’t remain together for long. Ruby-throated Hummingbirds don’t form a pair bond at all. The male contributes to the survival of the young by driving away other birds and many large insects from nearby flowers, ensuring that the nectar supply won’t be depleted when the larger, dominant female flies in to feed. This minimizes the amount of time she must spend away from eggs and chicks.
Male gallinaceous birds, such as turkeys and prairie-chickens, produce a display which attracts females. The most successful males may mate with many females. The females nest and care for the young without male assistance. In some cases, such as in turkeys, the males most likely to be selected as mates are also the most aggressive, and so females must try to keep their young ones away from these males until the young can protect themselves.
Whether birds of a pair stay together for a lifetime or for a nest period, there is also a great deal of variation in whether birds mate with birds other than their social partners. Ornithologists used to believe that the vast majority of bird pairs were faithful during a nesting, but DNA tests have revealed that more than one male has fathered many broods in more than 90 percent of all species tested. “Extra-pair paternity” is extremely common in ducks and some swallows, but extremely rare in Florida Scrub-Jays.
Teasing out the reasons why different species, sometimes closely related, have entirely different mating systems can keep amateur and professional ornithologists engaged for years.
Q Many species of birds share parenting duties after the eggs hatch. Do males help with the incubating process?
A In some species yes, and in others no. Male and female Rose-breasted Grosbeaks share incubation duties. Some male Barn Swallows incubate a great deal and others don’t, and only the males that do incubate develop a brood patch — a bare spot on the belly where the heat of the adult is transferred to the eggs. Loons take turns during the day but only the female incubates at night. Woodpeckers take turns during the day but only the male incubates at night.
In some species, such as hawks, owls, jays, and crows, the male hunts and brings food to the female, who remains on the nest virtually all the time, especially during bad weather. In some shorebirds, especially phalaropes (delicate birds that spin like tops as they swim to stir up food), only the male incubates and cares for the babies. In these cases, the female is the one who defends the territory.
There are almost as many reasons for differences among incubation strategies as there are species. Sandhill Crane females incubate while males guard. In the unrelated but superficially similar-looking Great Blue Heron, both sexes develop a brood patch and both take turns incubating.
Hummingbird and raptor females are larger than males, and in both groups the female incubates. But relative size cannot be the explanation because in geese and most blackbirds, the male is significantly larger than the female, yet again the female is the one who incubates. Red-winged Blackbird males are brilliantly colored; in this species only the cryptically colored female incubates. But both the dully colored female and the conspicuous male Northern Cardinal and Rose-breasted Grosbeak incubate, and both sexes occasionally even sing from the nest.
NOT AS EASY AS IT LOOKS
Incubating takes a tremendous amount of energy, especially in cold environments. A female Snowy Owl, for example, begins incubating the moment she lays her first egg, and if her mate is able to get enough food, she won’t leave the nest at all for many days at a time. Although they look like they’re not doing anything, incubating birds often lose weight during this period, especially if their mates are unable to bring them sufficient food.
Q There is a Wood Duck house on the river near my cabin, low enough that I can peek inside while I’m canoeing. Last year I watched the mother sitting on 12 eggs for weeks — she always sat tight whenever I looked in. But then one day she was gone and all the eggs were broken and looked like they’d been cleaned out. She never came back. What predator would have done this?
A It sounds like your ducklings all hatched out! Ducklings call inside their eggs to synchronize their hatching, and then when all the babies are dried off, they jump from the nest and follow their mother to water, never to return unless one of them, as an adult, chooses that box to nest in. If a predator had found them, you’d have found signs of blood and at least a few broken but unemptied eggs.
Q A female cardinal nesting in our yard died by flying into a window. What will happen to the eggs? Will her mate take care of them?
A Male cardinals can incubate eggs, although the female typically incubates much more. This male may take over entirely and raise the young on his own. Some cardinals in this situation, however, will abandon the nest and move on to find a new mate with which to start over. This approach can actually allow a bird to raise more young that summer. If the male tries to hatch out and raise the original nest of eggs, he’s almost certain to lose at least some of the babies in the nest because it’s hard for a single bird to find enough food for four or five nestlings. If the cardinal does abandon the nest, a chipmunk, jay, crow, or squirrel may come in and eat the eggs. It’s heartbreaking, but somehow birds muddle through.
KEEPING AN EYE ON THINGS
If birds are nesting near you in an accessible spot, it’s hard to resist checking on the eggs and the chicks. It’s okay to watch discreetly, but too much attention could cause the parents to abandon the nest. It’s best to peek in on nests in midafternoon (when parents are feeding young the least often), for a very brief time, and not every single day.
If you enjoy finding and watching bird nests, consider joining the NestWatch citizen-science project, coordinated by the Cornell Lab of Ornithology and Smithsonian Migratory Bird Center. Visit www.nestwatch.org to find out how to watch nesting birds safely and to record your observations. The information you gather is valuable to scientists studying nesting birds and the factors that lead to their failures or successes.
Q Why don’t I ever see baby pigeons?
A Pigeons make their loosely constructed cup nests in crevices and on ledges. They lay two eggs, which hatch after 18 days, and the babies, called squabs, tend to sit tight for more than two weeks. By day 18 after hatching, they can walk and may wander a bit along their ledge, but they don’t open their wings and fly down from it until they’re completely feathered and able to fly, sometime between day 25 and 32. By this time, they are as large as adults, but they’re still dependent on their parents for protection and food.
Q Last summer after a storm we found a tiny baby robin that had fallen from its nest. I put it back in the nest, but my neighbor told me the parents would reject it if it smelled like human hands. I’m not sure, but it looked like the parents were still feeding it after I put it back. Can birds really smell our hands?
A Probably not, and they don’t reject young birds after people touch them. Most birds have a sense of smell that is as poor as ours, or poorer, and they identify their babies the same ways we do — by how the babies look and sound. If you find a nestling — a baby bird that can’t yet hop, walk, or fly — and if you know where the nest is, the best thing you can do is return the little bird to the nest.
Q I had a Mourning Dove nest in my hanging basket. I couldn’t resist the temptation and tried to feed the nestlings some millet, but they got scared and flew away. Will they ever come back to the nest? Can their parents find them? I am upset that I came that close to them. They did have full feathers, and I believe that they were about two weeks old. It seemed like the parents were staying away for longer periods of time. This morning I heard the cooing of an adult near my house and felt sad — was that the parent looking for its young?
A Don’t feel bad. The startle response that causes nestlings to flee when they recognize danger doesn’t kick in until they are mature enough to survive. Their parents will search for them and will almost definitely find them. Mourning Doves usually fledge between 12 and 14 days, so these may well have been ready to go anyway.
The young will never return to the nest — they’ll be roosting on branches now, exactly as they would if they had fledged on their own without being startled. The parents may or may not reuse this plant for a nest site next time — we never know what will lead them to make that decision. The adult singing is part of getting revved up for the next breeding period, because they will renest after these babies are no longer dependent.
While birds are still nestlings, they usually have a special diet, so “help” from people isn’t generally helpful. Mourning Doves feed their babies “pigeon milk,” which is surprisingly similar to mammalian milk, though it’s manufactured in a part of the bird’s digestive system called the “crop.” As baby doves grow, the parents’ bodies start mixing the pigeon milk with a slurry of regurgitated seeds, so when the babies do start feeding on their own, they’ll be able to digest seeds.
Q Someone told me it’s illegal to take care of baby birds. Is this true?
A Yes. This may sound cruel when we find a desperate little bird barely clinging to life. But in this event, enforcement is usually lenient if you do your best to keep the bird alive while you find a licensed wildlife rehabilitator to take the bird. Native birds are protected by state and local laws, especially the Migratory Bird Treaty Act, and cannot legally be kept as pets.
Every species of baby bird has specific dietary and care needs, and it’s very easy to accidentally injure them. And even if we can keep them alive, it’s critical to a bird’s survival and quality of life to be educated by its natural parents or surrogates. Sometimes when young birds leave the nest prematurely and cannot yet fly, people try to raise them. But if these birds are well-feathered and can hop, they quickly become skilled at hiding, and their parents can usually find them and continue to feed them raise them.
Rehabilitation facilities usually know what to do to provide at least some of the skills wild birds need to survive and thrive, but baby birds have a much better prognosis for a long, natural life if they are raised by their parents.
Individual baby birds, even in the same family, may have very different “personalities.” One day I spent hours watching two young female Pileated Woodpeckers learning to feed with their parents. One would try half-heartedly to probe at a dead tree as her father pointed out the best spots, but she’d quickly start to whine and flap her wings, begging for him to feed her. Meanwhile, the other daughter was with the mother at a different stump that looked no richer in bugs. This daughter probed busily, sometimes pulling out a big grub and toying with it before eating it. The mother offered her a couple of grubs, but this youngster just ignored her, reminding me of trying to dress my daughter when she was a toddler — she’d refuse my help, insisting, “NO! Katie do!”
Q Why do birds leave the nest before they can fly?
A It’s to any young bird’s advantage to leave the nest as soon as it safely can. People tend to think of nests as safe, cozy little homes, but predators have an easy time locating and raiding a nest of calling baby birds, and the warmth and high humidity of nests make them breeding grounds for dangerous avian parasites.
Some species don’t remain in the nest more than a matter of hours. These babies follow one or both of their parents, learning what to eat and how to avoid danger and where to hide while resting or when in danger. But being flightless does put ducklings, Killdeer chicks, and other “precocial chicks” at risk from all kinds of predators, so most of the birds that raise young this way must produce a lot of eggs in a single clutch to have a reasonable expectation that over their lifetime, at least two babies will survive to replace them.
Baby birds that remain in nests and have a fairly long helpless stage cost their parents’ significant time and energy. Parent hawks, herons, songbirds, and other types of birds work from sunrise to sunset every day to get their young fed and out of the nest as quickly as possible. After fledging, the young birds are more spread out, and the parents can lead them to different spots every night, enhancing each one’s chances of survival.
Some species, such as swallows, woodpeckers, and other cavity nesters, nest where there are no nearby branches for young to grab onto when they first leave the nest. Unless startled by a predator, young of these species tend to remain in the nest until they are strong fliers.
Q How many eggs do birds lay?
A This depends on the species. Some species, such as albatrosses and some penguins, lay just one egg each time they attempt to raise young. Despite their difference in body size, Ruby-throated Hummingbirds and Common Loons lay two. Many songbirds lay four or five eggs, but chickadees and House Wrens usually lay six to nine and the even tinier kinglets may lay even more! Ducks and grouse can lay a dozen or more in a single clutch. If something destroys the nest early in the season, most birds can start over, but if it’s too late, they give up for the year.
Many birds are indeterminate layers, meaning if their eggs are removed one by one, they’ll continue laying more for a long time. People take advantage of this with domestic poultry, but indeterminate laying is also present in wild birds. In one experiment, an egg was removed each day from a Northern Flicker nest (a species that normally lays 6 to 9 eggs in a clutch), and the female produced a total of 71 eggs in 73 days.
Q How long does it take for eggs to hatch?
A It depends on the species. Small songbird eggs can hatch in just 11 days, Ruby-throated Hummingbirds in 12 to 14 days, Common Loons and many ducks in about 28 days, Bald Eagles in about 35 days, and Emperor Penguins in about 65 days.
On average, clutch sizes are smaller in the tropics, where adults are long-lived, than in the temperate zone, where birds live fast and die young.
Q What part of the egg turns into the chick?
A The yolk is a single giant cell that divides to form the chick. Of course, the whole yolk doesn’t split in half — the cells that divide from it are very tiny and grow to surround the yolk as it shrinks, providing the nourishment for the growing chick.
Q My Cockatiel lays eggs all the time, but there isn’t a male in sight. I thought you needed two parents to make a baby.
A You do need two parents to make a baby bird. But during the breeding season (which for Cockatiels is much of the year), females ovulate whether or not they mate. Unfertilized eggs, like store-bought chicken eggs, have a yolk and albumen but can’t produce a chick.
It may be a good idea to let her build a nest and lay the eggs in there. Once she has a full clutch, she’ll start incubating them and will stop ovulating. If you remove the egg every day, she’ll keep laying eggs. Producing eggs requires calcium, so if she’s continually laying eggs, she may suffer from calcium deficiency.
Q While at our family cabin in Michigan, I found a Cooper’s Hawk egg on the ground, about a hundred yards from where the nest was. It was cold to the touch, but I picked it up and kept it warm, just in case. I’d like to know if there’s a way to find out if the chick inside is still alive.
A To see the chick inside, people candle eggs; that is, they hold them up so they’re backlit by a bright light. But please don’t try to hatch this egg. If it was dropped, it’s very likely the embryo was killed. It’s even likely that the parents tossed it out when it didn’t hatch after other nestlings did hatch. If something else happened and a live egg was dropped by a predator or fell out of the nest in a storm or accident, its chances of hatching into a healthy chick are low. Being shaken, the impact of falling, and being significantly cooled after the onset of incubation could each be problematic.
LET SLEEPING BIRDS LIE
Water birds sometimes sleep in the water. Some sleep on tree branches or in cavities, too. Some birds can be literally half asleep — they close one eye and allow one half of their brain to sleep while the other eye and half of the brain are engaged in watching for predators.
Most songbirds find a secluded branch or a tree cavity, fluff out their down feathers beneath their outer feathers, turn their head to face backward, tuck their beak into their back feathers, and close their eyes.