Friday, December 23, 2016

Not quite home: Nests and Avian Architecture

Woven nests: Village Weavers (Rwanda)

Birds are consumers in their environments beyond food; they use space, plant material, mud, spider silk, mammal hair, rocks, and other materials to construct their nests. In some cases birds construct other structures, like bowers or food stores.

Tufted Titmouse with nesting material (they nest in holes per Cornell University)

According to Avian Architecture, by Peter Goodfellow, the vast majority of birds do not live in their nest, although there are exceptions. The primary function of the nest is to contain eggs for protection and incubation, and then for many species, for raising the young until they can fledge (defined by the book as growing feathers and being able to fly). For many other species, the young are born from the egg with feathers and without a need for parental care. Nests are then often abandoned or perhaps reclaimed the following breeding season.

Cup nest: Chipping Sparrow (Kansas, USA)

Avian Architecture is divided into 12 chapters, with ten nest types (1-10), courts and bowers (11), and edible nests and food stores (12). The ten nest types are: scrape nests, holes and tunnels, platform nests, aquatic nests, cup-shaped nests, domed nests, mud nests, hanging/woven/stitched nests, mound nests, and colonial/group nests. While there is overlap in some nest types, such as Common terns making scrape nests in colonies, the categories are useful to show the wide variety of structures that birds make.

Scrape nest (with some added grasses): Common Tern (Great Gull Island,
New York, USA)

Cavity nests: Pied Kingfishers (Murchison Falls National Park, Uganda)

Platform nest: the aerie of Bald Eagles (Squaw Creek National Wildlife Refuge,
Missouri, USA)

Domed nest: Rufous-naped Wren (near Carara National Park, Costa Rica)

Mud nest: Barn Swallows (Kansas, USA)

Woven nest: Thick-billed (Grosbeak) Weaver (Lake Muhazi, Rwanda)
According to the book, weavers and some icterids (oropendolas, orioles,
caciques, etc.), make identifiable knots and stitches. 

Colonial nesting: a heronry of Great Blue Herons, (Kansas, USA)

The nests that impressed me most were the mounds, built mainly by megapodes, but also by American Flamingos,  Horned Coots, Wandering Albatross, and others. Of the megapodes, some species, like the Malleefowl, dig pits, line them with decaying vegetation, deposit their eggs, and cover them with soil and sand. The eggs are incubated by the heat generated by the decomposing matter. The Malleefowl check the temperature with their bills, and remove or add vegetation to keep a consistent temperature. Yes, you read that correctly, these birds are managing decomposition to meet their goals, which is what humans call composting.

Horned Coots build a totally different mound nest. By depositing stone after stone, they build a cone in the shallows of Andean lakes that extends from the underwater lake bed to just above the water, where the eggs are kept. The nest is thus isolated from land predators on its own little island. Yes, you read that correctly, these birds make islands.


Other than knowing of the bowerbirds from bird books, the only mention of bower I knew was from the Led Zeppelin song, "Gallows Pole," as in "Sister... take him to some shady bower." Merriam-Webster presents three definitions of bower, 1) an attractive dwelling or retreat, 2) a lady's private apartment in a medieval hall or castle, or 3) a shelter (as in a garden) made with tree boughs or vines twined together. All three are relevant to bowerbirds. The males construct and maintain the bowers in mainly forests of New Guinea and Australia to attract female birds; depending on the species, the male builds one of three types of bowers, columns of sticks and grasses in an avenue, columns with a central maypole perch, or a well-arranged platform. Some bowers are decorated extensively with colored objects. Females arrive to the center of the bower and watch the male display, before deciding whether to mate with him or not. I don't have any pictures but an Internet search will turn up plenty (or see Bird Families of the World here). Bowerbirds also construct a separate nest for the eggs.

Two species of swiftlet build nests from their own saliva, which are a favored addition to soup in some regions. Other birds, like woodpeckers, alter their environment to either store food or access food not readily available.

Yellow-bellied Sapsuckers drill holes to drink sap and it insects that feed on
sap (Central Park, New York, USA).

A resource for educators

Avian Architecture presents case studies, diagrams, measurements, text, illustrations, and pictures in a palatable manner that would satisfy a serious birder but also be accessible by non-birders. It is probably, vocabulary-wise, appropriate for middle-school age children and above. However, any educator, even those in elementary school could make use of this book in designing hands-on, minds-on lessons. Students, for example, could pick a nest type and construct it using only the types of materials a bird might have available. Strength tests could be run (How many eggs does the nest hold? How much weight can be added to a small nest, based on the different number of support twigs the nest is attached to? Etc.). Measurements of scale could be calculated (we recreated the nest of a red-winged blackbird at twice the size and its size is now x). Questions could be generated about how birds without use of hands can build or where nests of common backyard birds tend to be located. All kinds of inquiry-based learning could come from this book.

The book certainly inspired me to look back through my pictures and find the nests I had photographed over the years, some of which are shown above. One of the fundamental things I love about nature is the layers that are always present but only become apparent as one learns to sense them. I have now been birding for years but this was the first book I have read entirely about nests (and other bird "builds"). I have seen Hamerkop, oropendolas, weavers- all serious builders- but I paid scant attention to their nests. This book helped peel back another layer of the natural world, in this case how, where, when, and why birds construct.

White-browed Sparrow-weaver nest (Ngorongoro Crater, Tanzania)

No comments:

Post a Comment