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Peter Goodfellow is a retired English teacher and lifelong birdwatcher. His books include Birds as Builders and A Naturalist's Guide to the Birds of Britain and Northern Europe.

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AVIAN ARCHITECTURE

Princeton University Press

Contents

Foreword......................................................6Introduction..................................................8Chapter 1 Scrape Nests........................................10Chapter 2 Holes & Tunnels.....................................22Chapter 3 Platform Nests......................................34Chapter 4 Aquatic Nests.......................................46Chapter 5 Cup-Shaped Nests....................................56Chapter 6 Domed Nests.........................................70Chapter 7 Mud Nests...........................................84Chapter 8 Hanging, Woven & Stitched Nests.....................94Chapter 9 Mound Nests.........................................108Chapter 10 Colonies & Group Nests.............................122Chapter 11 Courts & Bowers....................................132Chapter 12 Edible Nests & Food Stores.........................144Resources.....................................................154Glossary......................................................156Index.........................................................157Acknowledgments...............................................160

Chapter One

The builders of scrape nests are the minimalists of the avian architecture fraternity. Faced with the challenge of an open habitat with limited materials, they literally scratch out an existence by gouging a shallow nest out of the ground. The scrape nest is exactly as it sounds: a scrape or depression in the earth, sometimes with material added to create a lining. Primarily an area for eggs and their incubation, the ground-level scrape offers quite limited defenses. Camouflage is therefore essential, and the scrape nest, eggs, and young are adapted to blend with the ground.

To start constructing a scrape, usually the hen will lower herself onto her breast at the chosen site and rotate and shuffle with her feet to form a shallow depression in the sand, shingle, or vegetation. Many birds line their scrapes, the amount of lining varying with the species and individual, and two building methods are used. First, as a pair moves away from or around the scrape site they pick up nest material—bits of vegetation, small pebbles, shell fragments—and use a technique called "sideways throwing" to toss the objects to the side of or beneath them. Second, the sitting bird pulls at the material and tucks it alongside or beneath her—this is "sideways building."

Some of the simplest scrapes are those of shore-nesting plovers. Wildfowl make more elaborate scrapes and add a layer of down. The Common Eider (Somateria mollissima) builds in the shelter of rock or vegetation and plucks feathers and down from her breast to establish a thick lining.

Despite its simplicity, the scrape nest demonstrates a degree of precision to effectively shelter the eggs and incubating bird, especially in cold, damp habitats. The scientist Jane Reid and her colleagues found that the scrape of the Arctic-breeding Pectoral Sandpiper (Calidris melanotos) was made to an optimal cup depth to result in the minimum heat loss for the eggs; too deep and the cold ground affected incubation, too shallow and wind chill was a problem.

Vulnerable to predators, the eggs in scrape nests demonstrate excellent camouflage. The eggs of sandy-shore species such as plovers generally have a light base color, finely speckled with gray or black. Waders that nest on grasslands, tundra, or marshes lay eggs with a darker base color, as befits the nest site. Ducks' eggs are plainly colored and rely on being hidden by undergrowth and down.

Various features aid the chicks' survival. They often leave the nest soon after hatching, and are precocial (able to walk almost immediately), and nidifugous ("nest flyers"—they flee the nest to seek food, guided by the parents). Their camouflaged plumage protects them when a parent's alarm call makes them crouch stock still.

BLUEPRINTS

Scrape Nest Structures

The architectural blueprint for a scrape nest includes the shallow indentation on a ground site; precise depth to achieve optimal egg temperature; simple lining materials; and strong camouflage features. Species with scrape nests include game birds (pheasants, grouse, partridges); ducks; waders (shore-nesting plovers); the Short-eared Owl (Asio flammeus); and, the Ostrich (Struthio camelus).

VARIETIES OF STRUCTURE

Sites include open ground, boggy ground hidden by growing vegetation, and slightly elevated platforms. The Short-eared Owl makes a scrape in heather moors, tall grass, dead reeds, and marram grass on dunes. Scrapes are sometimes lined with materials including plant stems, leaves, grass, shell fragments, and pebbles. Eggs may be camouflaged or buried for protection.

MATERIALS AND FEATURES

Courser Nest

The coursers form a special subfamily of waders that has evolved into a group of eight species. They inhabit semi-desert or other almost bare ground in Africa and India. The most widespread is the Cream-colored Courser (Cursorius cursor), which is found in barren country bordering the north and south of the Sahara in North Africa. All except one species are mostly sandy colored. The courser's scrape nest is little more than a scratching in the sand, and normally two eggs are laid directly onto the ground. This minimalist architecture in fact provides the nest's primary defense, because the lack of structure together with the superb camouflage of eggs and chicks can make it virtually invisible. If it is disturbed, the courser has long, strong legs that enable it to run well (cursor means "a runner" in Latin). It runs in a hunched manner, then stops suddenly and stands tall, with neck stretched up for a view of the intruder.

Invisibility

The courser nest uses camouflage as its primary defense. The nest structure is inconspicuous, and the eggs are camouflaged by a pale buff color finely spotted with brown. When the adult lands, as British Museum scientist David Bannerman wrote, "the bird will almost fade from view," so closely does it match the ground color. The chicks are even better camouflaged; their pale sandy-rufous down is lightly speckled with white and gray and they lack the adults' striking head pattern. The combined effect is a cloak of invisibility.

Temperature control

This Temminck's Courser (Cursorius temminckii) is photographed in the Gambia, West Africa, where temperatures remain high all year. Due to the exposed nature of the nest, scrape-nesting birds in desert habitats need to prevent their eggs overheating. Panting, ruffling their feathers, and standing over their eggs or chicks to provide the nest with an improvised sunshade, instead of incubating or brooding, help to solve the problem. Double-banded Coursers (Rhinoptilus africanus) of East and South Africa share standing over the egg, and later the chick, to protect them from the sun's direct heat as well as radiated heat from the sand.

Additional camouflage

Many courser scrapes are constructed with no added material beyond the ground that they are built on. Some, however, like the main nest illustration here, have been found to feature an ingenious additional piece of architectural design. A ring of animal dung is constructed around the eggs to provide an extra layer of camouflage. This adds to the concealment and disguise of the scrape.

CASE STUDY

Killdeer

The scrape of the Killdeer uses camouflage to disguise a shallow nest on open ground. Found widely across North America, except Alaska, from southern Canada southward, the Killdeer winters in the southern states and as far south as northern South America. The Killdeer uses noise and display to distract intruders when the nest is threatened.

Habitat and nest

The Killdeer nests in a variety of sites where grass is short or absent—farm fields, golf courses, city parks, sports fields, roadsides, airports, and even backyards. The nest is usually sited on a bare, sandy, or gravelly area, and the Killdeer's four eggs are laid pointed ends inward in a shallow scrape or depression. The scrape is commonly unlined, or sparsely lined with a few plant fragments, wood chips, or pebbles, all of which are gathered nearby.

Nest defense

The Killdeer offers an excellent example of how some ground-nesting species have adapted to the problem of a nest with visible eggs or chicks. Both parents are particularly noisy when disturbed by people or animals. If the incubating bird sees an advancing intruder, it will slip off the eggs, run, and then give the alarm. If surprised, the bird will flounder and stagger away, beating the ground with its wings, calling madly in order to attract the attention of the potential predator. This technique is the "broken-wing trick." When the intruder has been led far enough away, the bird suddenly flies free to join its equally noisy partner. In its haste to flee, the bird occasionally disturbs the eggs; on its return the incubating bird rearranges them before it settles down.

Eggs and young

The male and female share the 24-day incubation of the eggs. The chicks are precocial, leaving the scrape soon after hatching. Their parents guard their young and lead them to insect-rich feeding grounds so they can feed themselves.

Classification

ORDER Charadriiformes

FAMILY Charadriidae

SPECIES Charadrius vociferus

RELATED SPECIES Other plovers, sandpipers, curlews

NEST TYPE Scrape

SPECIES WITH SIMILAR NESTS Terns, game birds, nightjars

NEST SPECIALIZATION Minimal nest material

CASE STUDY

Ostrich

The nest of the Ostrich answers the challenge of protecting eggs in a harsh environment not architecturally but socially. The male commonly forms a harem with three hens to maximize the number of eggs, all laid in one simple pit-like scrape. This improves the chance of a successful hatching. The Ostrich is found south of the Sahara, north of the tropical forest belt, and in southwest Africa.

Habitat and nest

Ostriches live in a wide variety of habitats—semidesert, open savanna, and dry wadis, avoiding ground where trees and shrubs are frequent. The nest is, therefore, created on open ground. It consists of a shallow depression scraped mostly by the male. Its overall diameter is about 9ft (2.7m), and it is 1–2ft (30–61cm) deep.

The shared nest

Ostriches are social birds throughout the year, sometimes in flocks of up to several dozen. Within each flock are dominant males and females. In the breeding season, a dominant female (the major hen) will initiate pair formation with a dominant male. She will allow minor females to join the harem, and all of the hens lay in the one nest. The major hen usually lays 4–8 eggs first; then the other females add to the clutch until there are about 20–25 eggs in total. She drives the minor hens from the scrape once they have laid.

Nest defense

It's normal for the major hen to incubate by day and the male by night. The nest is usually so clearly in the open that the daytime incubating bird often lies with its neck stretched out along the ground in order to be less conspicuous. The chicks begin calling one or more days before hatching, thus establishing close contact with their parents, who care for them for up to a year after hatching. To protect the chicks from predators, the male in particular has an elaborate distraction display, flapping its wings, dropping to the ground, and running about erratically.

Classification

ORDER Struthioniformes

FAMILY Struthionidae

SPECIES Struthio camelus

RELATED SPECIES No close relatives, but other ratites (i.e. flightless, running birds) are the Emu, cassowary, and rhea

NEST TYPE Scrape

SPECIES WITH SIMILAR NESTS Emu; rhea

NEST SPECIALIZATION Nest used by several females

CASE STUDY

Arctic Tern

Constructed in tightly packed groups, the scrape nests of the Arctic Tern demonstrate the defensive capability afforded by nest building in colonies. A summer visitor to the Northern Hemisphere, the Arctic Tern breeds mostly within the Arctic Circle, but also as far south as the British Isles, and Labrador, Nova Scotia, and Massachusetts in North America. They winter at sea in the Southern Ocean.

Habitat and nest

The Arctic Tern's scrape is constructed on a grass-covered islet, a sandy or gravel beach, or even inland on heathland or tundra. The nest is shallow, with or without a little lining. Both sexes work, often alternately, to scrape the depression, in which two eggs are commonly laid.

Breeding

Arctic terns do not breed until they are at least three years old. They breed in solitary pairs, small groups, and often dense, large colonies, the largest of which may number hundreds or even thousands of pairs. In the case of the largest colonies, the scrape nests are likely to be only a few yards apart. The territory of each pair then comprises only the roughly circular area around the nest. This space is just large enough for the pair's courtship and greeting displays, the scrape, and the young.

Nest defense

Arctic Terns are aggressive in defense of their vulnerable ground nests, particularly when they have chicks, and here the colony of nests affords mutual protection. On sight of a predator, the colony will fly up in a "dread," often started by birds in the densest part. Neighbors and wandering chicks are driven away. Predators that may have discovered the nests' location are mobbed and chased. These include gulls, skuas, and crows. Peregrines (Falco peregrinus) and White-tailed Eagles (Haliaeetus albicilla) are mobbed aggressively. Animals and humans are "dive-bombed" with excreta, and even struck with the bill, in defense of the colony's nests.

Classification

ORDER Charadriiformes

FAMILY Laridae

SPECIES Sterna paradisaea

RELATED SPECIES Gulls and skuas

NEST TYPE Scrape

SPECIES WITH SIMILAR NESTS Other "sea terns"

NEST SPECIALIZATION Colony defense

CASE STUDY

Common Eider

The scrape nest of the Common Eider is lined with a bed of the female's down. Eiders nest together for protection and the ducklings are cared for in groups. Breeding along the northern coasts of North America, the shores of Greenland, and the coasts of northwest Europe, the Common Eider generally nests by the shore or on offshore islands.

Habitat and nest

In the breeding season, the Common Eider is usually colonial, with as many as a few thousand nesting together, often as closely as two nests per square yard. The female builds the scrape, often in the shelter of a rock or well hidden in thick herbage. On coasts, the nests can be sited on turf or in a dune, where they are more exposed.

Nest lining

The nest is thickly lined with grass, seaweed, and an abundant amount of the female's own breast feathers and down. The down feathers insulate the wintering bird at sea, but the female is able to sacrifice some of her own insulation because it is spring and the weather is improving. The eggs are also covered with a layer of down when the duck leaves the nest. Old Common Eider nests are reused, causing their architecture to develop into a permanent cup.

Eggs and young

Drakes guard their incubating mates but take no further part in family life. The ducklings hatch after four weeks and are cared for by the female, who leads them to a feeding area, usually near the nest. The ducklings leave the comfort of the nest as soon as they are dry, and are able to feed themselves. At this point the parent-young relationship weakens as the adults go off to feed and gain strength after losing weight during incubation. The ducklings, meanwhile, join those of other families, often forming groups of a hundred or more, which are tended by several ducks known as "aunties." The ducklings become independent after eight or nine weeks.

Classification

ORDER Anseriformes

FAMILY Anatidae

SPECIES Somateria mollissima

RELATED SPECIES King Eider, Steller's Eider, Spectacled Eider NEST TYPE Hollow in the ground, well lined

SPECIES WITH SIMILAR NESTS Most other wildfowl

NEST SPECIALIZATION Thick lining of down

Chapter Two

Hole and tunnel nesting answers the challenge of nest defense by exploiting the relative safety of such refuges as tree holes and rock crevices. Such nests are widespread, constructed by species from within some 50 percent of bird orders. In addition to providing protection from predators, holes and tunnels also offer shelter from the weather, allowing the nesting bird to conserve energy. Not surprisingly, such prime architecture is the subject of intense competition, and it is not uncommon for latecomers to aggressively hijack the new build of another bird or species.

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Excerpted from AVIAN ARCHITECTUREby Peter Goodfellow Copyright © 2011 by Ivy Press Limited. Excerpted by permission of Princeton University Press. All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
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