What do you know about nests?
- Mecklenburg Audubon
- Apr 25
- 8 min read
We are in the height of breeding season. Resident birds started nesting back in March while our friends for the south have finally gotten here and have set up housekeeping. So, what do you really know about bird nests? Here is an excerpt from The Birdwatcher’s Companion to North American Birds by Christopher W. Leahy. I think you will find it very informative.
Since some species construct no enclosure whatever for their eggs, it can be argued that nests are not, strictly speaking, necessary. However, it is clear from their elaborate evolution and general prevalence that nests have aided survival by protecting eggs and young from weather and predation and perhaps by increasing the efficiency of the rearing process.
Like most other functions of avian life, the nesting urge is tied to a bird’s hormonal cycles. The earliest manifestation of this urge – prospecting for a suitable site – coincides with the mating and copulation period and at least in some species, nest building parallels the development of the fertilized ovum. Hormonal triggers are in turn set off by external phenomena such as temperature and precipitation, so that site selection, for example, may be prolonged due to bad weather.
SITE SELECTION: Once a pair has mated, choosing a place to lay the eggs becomes a high priority. Either or both partners may undertake this responsibility, according to the habits of their species, but the female dominates the process in the majority of cases. Birds that return to old nest sites in successive years are, of course, relieved of this responsibility. For some species, such as many colonial seabirds, choosing a site is mostly ritual, with the final selection apparently quite arbitrary. Most species, however, ‘shop around’ for a while. The process may include ‘fitting’ the body into prospective tree forks or patches of ground. This period varies in length from species that seem to take the first site they see and immediately start construction, to tits and others that inspect sites year-round. For the majority of species site selection probably consumes a few days.
NEST BUILDING: On superficial observation nest construction seems to be clear proof of a highly sophisticated avian brain. However, we need to recognize individual birds are not inventing original works of art or specialized craftsmanship from scratch when they set out to make their first nest. It is evident that many nest building skills are ‘hard-wired’ genetically. Through observation we know that birds use a lot of stereotyped motions in building nests, and it has been shown experimentally that captive-reared birds can make decent facsimiles of finished nests without ever seeing one built. It is also true that abnormal nests are not uncommon and young birds are often less skilled engineers than their elders, so some learning of the ‘practice makes perfect’ kind most also occur.
The effort that goes into nest building also varies among species. Many species forgo the process altogether and simply lay their eggs on a bare surface or take over an abandoned nest without making alterations. Eagles return each year to old nest sites apparently never lose the urge to build. Bald Eagles add many new sticks each year, creating an enormous edifice over decades. Male wrens build a series of dummy nests. In some species, young from a first brood will help in the construction of its parents’ second nest of the season, which benefits all concerned.
NESTING PATTERN & TIMING: Most birds build a new nest for each brood they rear, even when double- or triple- brooded, but less time and energy are expended each time in nest construction. Gnatcatchers often transport old nest materials to a new site. Whether a species is single- or multiple-brooded depends on both the inherent nature of the species and the climate in which it lives. Most North American birds are single-brooded, but a significant percentage of song birds rear a second brood and a few (e.g. Mourning Dove, House Finch, and Song and Field Sparrows) are typically treble-brooded in the southern parts of their range.
The time required to build the nest is also highly variable. Most song birds do the job in 3-9 days, though the period may be prolonged by cold or otherwise bad weather; this is especially true of some swallows, which can take over a month to build a nest. The complexity of the nest structure is also a factor: the long, pendulous sack of the Altamira Oriole may take 3 weeks or more.
SEX ROLES: Site selection and nest building tend to be dominated by the female but males are rarely exempted entirely from these duties. The Red Phalarope may be the only North American species in which the male alone is responsible for nest construction. Among all hummingbirds; most tits, icterids, tanagers, and finches; and some flycatchers, swallows, vireos, and wood warblers, the female alone builds the nest. In most species nest building is shared in a variety of ways. Pairs of woodpeckers, waxwings, gnatcatchers and some swallows divide responsibility equally. In Mourning and other dove species, the female builds while the males brings materials. In some cases, the male will build certain parts of the nest and the female will do the rest. Male wrens of some species build a series of nest ‘shells’ and the female selects one and lines it for occupation. However, in House Wrens the female does all the real work, with the male reduced to ineffective and ritualistic stick-carrying.
MATERIALS: In general, birds of a given species will use similar materials in making their nest; however, there is considerable variation, depending on the availability of materials and individual ‘taste’. Though most nests are made with a small number of ‘basic’ components – mostly plant material – in some cases held together with a binding substance, a few species characteristically incorporate an ‘odd’ item. Great Crested Flycatcher nests, for example usually contain snakeskin – though not for protective purposes, as is sometimes supposed. Some species like to ‘decorate’ their nests with flowers or man-made materials, such as paper (Blue Jay), rags (Northern Mockingbird, American Robin), or yarn (Baltimore Oriole). Materials commonly used for basic external nest structure include sticks, grasses, cattail, sedges, rushes, Spanish moss, seaweed, wet decaying aquatic plants, bark, lichens, paper, string/yarn, and mud. All song birds and many other species line their nests; some ground nesters make no external nest but simply line a scrape or hollow in the earth. Lining is the last stage in the construction of complex nests and materials used are much finer than those used in the ‘walls’. Typical lining materials are leaves (dead or fresh), fine grasses, lichens, fungal fibers, moss, plant down, bark fibers, pine needles, contour feathers, down feathers and animal hair/fur.
LOCATION: Bird’s nests are found in virtually every conceivable situation except in midair, on the surface of the sea, and underwater. Placement ranges from 3 or more feet below the earth’s surface (Burrowing Owl) to over 100 feet in trees (Marbled Murrelet at 148 feet). Particular species tend to nest within a characteristic range of heights, which may be quite broad and span two or more niches. Ground nesters never nest in treetops and treetop species do not nest on the ground, but some ground nesters will also build in low shrubs, or the lower branches of trees and treetop species may descend to within a few feet of the ground. This variation may be seasonal and geographic as well as individual. Eastern Towhees and Song & Field Sparrows often build their first nest of the season on the ground then move up into the shrubbery for successive broods.
Requirements as to the kind of situation in which the nest is built are also very generalized in many cases. Some cavity nesters like the House Wren, will appropriate virtually any hole of the right size regardless of the substance in which it occurs. Many species have come to regard man-made structures as acceptable nest sites and a few, like the Barn Swallows, phoebes, House Sparrow, and Chimney Swift, have come to prefer them to what nature offers.
Some birds enhance nesting security by nesting close to other, more aggressive bird species. For example, several species of songbirds have nested among the twiggy interstices of a raptor’s nest, and birds nesting within tern or gull colonies doubtless derive some bene t from the latter’s no-nonsense approach to nest defense.
TYPES OF NESTS: Given the great diversity in bird forms, habitats and habitat preferences, a comparable variety in nesting styles is hardly surprising. It is entirely appropriate that the tiny Calliope Hummingbird should build a nest measuring 1.5 inches in diameter, 7/8-inch high, and weighing perhaps an ounce; equally so that a Bald Eagle’s nest accumulated over decades should attain a diameter of 9 feet, a depth of 20 feet and eventually weigh a ton or two.
The type of nest a species makes is less variable than the materials it uses or the location it chooses. However, many species build similar structures.
Example of the many different types of nests birds construct.
Who Builds What, Where
NO NEST: Vultures, loons, boobies, falcons, grouse, oystercatchers, plovers, terns, skimmers, nightjars
LINED SCRAPES: (little or no external nest structure, but with a substantial lining) geese, ducks, sandpipers, some gulls, some sparrow (Savannah & Grasshopper)
MOUNDS: (on open ground or in shallow water) loons; grebes; pelicans, cormorants, swans, some ducks
FLOATING NESTS: grebes, some ducks, Forster’s and Black Terns
GROUND HOLES (BURROWS, BANK HOLES AND CREVICES IN ROCKS): Burrowing Owl, kingfishers, Bank & Rough-winged Swallows, wrens, waterthrushes
TREE HOLES: some ducks, owls, woodpeckers, Kestrel, Merlin; Great Crested-flycatcher, Tree Swallow, Purple Martin, chickadees, titmouse, creepers, nuthatches, wrens, bluebirds, staling, Prothonotary Warbler
STICK PLATFORMS: (in trees or lower vegetation): anhinga, most herons, Wood Stork, ibises, raptors, pigeons, doves, large owls, cuckoo
CUP NESTS (THE ‘CLASSIC’ BIRDS NEST IN A TREE): cuckoos, hummingbirds, most flycatchers, crows, jays, thrushes, gnatcatchers, waxwings, shrikes, many warblers (Yellowthroat, Yellow-breasted Chat, Hooded, American Redstart), some blackbirds, tanagers, cardinals, grosbeaks, many sparrows
GROUND CUPS: rails, Sanderling, many warblers (Black and white, Worm-eating, Palm, Kentucky, Canada), most sparrows
DOMED OR ENCLOSED NESTS: Carolina Wren, Ovenbird, Common Yellowthroat, meadowlarks, House Sparrow
SUSPENDED NESTS (ATTACHED TO AND HANGING FROM A BRANCH OR OTHER SUPPORT): Acadian Flycatcher, kinglets, vireos, orioles, Northern Parula, Yellow-throated Warbler (where there is Spanish moss)
MUD NESTS: swallows, phoebes
NESTS IN/ON MAN-MADE STRUCTURES: Osprey, Kestrel, gulls, killdeer and terns (flat gravel rooftops), owls, nighthawks, swifts, phoebes, some swallows, wrens, Purples Martins, some wrens, robins, Starlings, grackles, House Sparrows, House Finchs
FINDING & IDENTIFYING: The laws that prohibit the collection of most native birds also protect their nests and eggs. This does not, however, prevent the dedicated birdwatcher from both adding to our knowledge of birdlife and having fun with nests. Countless details of nest construction, site preferences, frequency of renesting, and the degree of variation shown by any given species remain to be recorded. Properly identified off-season nests can be used in confirming the presence of a particular species.
Looking for nests in winter when the absence of most leaves makes the beginner’s efforts reasonably rewarding, can add a lot to a stroll through your neighborhood or a nearby wilderness. There are now several good field guides to help with identification, and most people over twelve will probably not be very disappointed at not being able to bring these treasures home. Watching nesting activities ‘live’ is also rewarding – once you’ve seen an oriole stitching its distinctive bag together, you may find yourself addicted to this benign form of voyeurism.
Take care not to disturb an active nest. Most birds will abandon their nest without a pang given what they regard as due cause, and some species are much more skittish than others. Birds are particularly liable to disturbance during the early phases of the cycle. Whole colonies of terns, for example, may abandon a site they’ve used for years for reasons that seem (to us at least) whimsical at best. On the other hand, most birds are quite tolerant of observation and once your presence has been found innocuous you can often count on being ignored. If a bird flushes off eggs or stops feeding young at your approach, back off; you’re too close.
If you are the kind of person who wants to fondle, sniff, and eyeball each of life’s little wonders, restrain yourself. Stand back, watch from the sidelines, you will learn just as much and be equally rewarded for your efforts.
Additional Resources
Identifying Nests & Eggs (NESTWATCH) https://nestwatch.org/learn/how-to-nestwatch/identifying-nests-and-eggs/
Nests, Eggs, and Nestlings of North American Birds: Second Edition (Princeton Field Guides), by Paul J. Baicich.
Peterson Field Guide: Eastern Birds’ Nests, by Hal H. Harrison
Nests: Fifty Nests and the Birds that Built Them, by Sharon Beals.
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