Structure, Cover, & Shelter

Photo © Ed Bierman

Structure can mean a lot of things, but at its most basic, it means the plant structures, like trees, shrubs, logs, snags, cactuses, or grasses, that are used to support animal life. Structure provides birds and other animals places to hide from predators, to search for food or nesting material, to perch while looking for mates or prey, and to build nests or dens. In many ways, it’s so obvious that it’s odd to point out: of course birds need trees! What might come as a surprise, however, is the need for structural diversity.

High, Mid, and Low-level

Birds need a variety of vegetation heights to maximize their opportunities for safe feeding and breeding. Canopy structure, like trees in different heights and shapes, mid-level vegetation, such as shrubs, and structure close to the ground in the form of rock piles, leaf litter, or ground cover all fulfill slightly different purposes. A diversity of cover promotes healthy habitat. Look around your yard. Do you see high, mid, and low-level structure? Are they placed next to one another to promote seamless movement between structural types?

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More Structure, More Birds

Adapted from The Audubon Society Guide to Attracting Birds by Stephen W. Kress.

Photo © Cornell University Press

Steve Kress, in his book, The Audubon Society Guide to Attracting Birds, suggests “song bird borders” which tier the highest vegetation at the edge, and then transition to a shrub layer, followed by herbaceous plants and grasses. There are many ways to create such effects: circles with tall vegetation in the middle, with rings of shrubs and herbs as you move out, or pie-shaped arrangements that cascade from a corner outwards. Find one that works well in your yard, or take advantage of naturally existing features like big, native trees and work towards a diversity of structure over time.

Embrace Your Structural Profile

The visual profile of structural diversity varies significantly by ecoregion. Some ecoregions are dominated by big trees, others by grass. Use the “My resources” section on the Explore Page to learn what ecoregion you live in, and read on to learn about the beautiful variety of plants in your area.

Broadleaf Forest Structure

High: sugar maple (Acer saccharum), Midlevel: thimbleberry (Rubus parviflorus), and Low: ferns (leptosporangiates)

Photo © Vlad Tuchkov, Christoph Diewold, & TB2011

Forested Ecoregions

Forested ecoregions have recognizable structural diversity with abundant high trees, a shrub layer, and lush ground cover. In some ecoregions the dominant tree might be a conifer, while in others a broadleaved tree. Find a wild place, get to know it, and think about ways to mimic the structure and plant diversity you found there.

Desert Structure

High: Sahuaro cactus (Carnegiea gigantea), Mid-level: desert scrub (eg. manzanita, Arctostaphylos pringlei or bitterbrush, Purshia tridentata), and Low: Mormon Tea (Ephedra viridis)).

Photo © informedmindstravel, arbyreed, & Brent Miller

Desert Ecoregions

Desert ecoregions contain dramatic tall structures like sahuaro cactuses, joshua trees, or acacias, an abundance of midlevel shrubs, like manzanita, and dynamic low-level vegetation.

Grassland Structure

Rare trees, hidden thickets (American plum, Prunus americana), and short (Schizachyrium scoparium) and tall grasses (Andropogon gerardi)

Photo © Will Merydith, Bryant Olsen & Ken Rachynski

Grassland Ecoregions

Even though grasslands are dominated by abundant grasses, they also contain the occasional tree and important shrubby areas in the creases between hills, or in gullies. Even amongst grasses you find amazing diversity – tall and short native prairie grass – each with their own important ecological roles.