Values of Riparian Habitat to Wildlife

by Tim Cullinan

All wild animals need food, water, and protection from predators and unfavorable weather.  Riparian zones provide all of these.

The riparian zone is a bridge between the river and upland habitats.  Its combination of high moisture, rich soils, and diverse vegetation makes it an exceptionally productive area for wildlife.  Because riparian zones have more habitat niches than any other plant community type in western Washington, they support not only a greater abundance of wildlife, but a greater variety as well.

Riparian zones are important to wildlife for the following reasons:

1. They provide water, and a richer source of food than upland habitats.

2. They provide hiding cover, shelter from the weather, and safe places to nest.

3. They have a more favorable microclimate - i.e. they are warmer in winter and cooler in summer.

4. They serve as safe travel corridors for many wildlife species.

Food and Water

The presence of free water in riparian areas attracts thirsty animals.  The moist, deep soils and moderate temperatures contribute to greater and more diverse plant growth than in upland sites.  This greater plant productivity and diversity in riparian zones provide greater abundance and variety of fruits, nuts, and herbaceous vegetation, all of which provide a food source for herbivorous wildlife.  Predators, in turn, are attracted by the abundance of prey species. 

The riparian vegetation in often dominated by woody, deciduous trees and shrubs such as alder, cottonwood, willow, salmonberry, oceanspray, elderberry, and snowberry.  These deciduous plants support much higher insect populations that conifers in the uplands.  Consequently, they are much more valuable as feeding areas for songbirds, especially during the nesting season.  The riparian vegetation also contributes to stable water temperatures, water quality, and inputs of energy and nutrients to the water.  All these promote a healthy river, which in turn provides food (aquatic invertebrates, fish, etc.) to wildlife like otters, kingfishers, dippers, and harlequin ducks. 

Cover

As noted above, riparian zones have both more vigorous plant growth and greater plant variety than upland areas.  The dense vegetation of riparian zones provides many wildlife species with escape, hiding, and resting cover, as well as cover for nesting that may not exist in the adjacent uplands.  The plant community in riparian zones is also very complex, with many “layers” of plants, from the herbs on the forest floor, up through the brushy understory, to the tops of the highest trees.  This complexity (called “structural diversity” by ecologists) creates many niches, which offers homes to a great variety of wildlife species.

Microclimate

The local conditions in riparian zones are more humid and milder than in upland areas.  They are generally a bit warmer in winter, but more important, they are cooler in summer.  Because of this, they provide an environment that is more favorable to many species, especially large mammals during periods of hot, dry weather or severe winters, and amphibians year-round.

Connectivity

Riparian zones are also important because they provide secure travel corridors for many wildlife species.  The dense vegetation acts as a screen that allows animals to move through the landscape unnoticed by humans and predators.  This not only allows individual animals to move safely between feeding and resting areas, but it plays a more important role in conserving populations.  Animals that can move about safely can disperse more easily into new areas of habitat.  Such movement also ensures gene flow between populations, which is critical for long-term conservation of local wildlife populations.  This is particularly important in places where the natural habitat has been severely fragmented by human disturbance, such as the lower Dungeness Valley.

Use of riparian habitat by wildlife

Eighty percent of Washington’s amphibian species are restricted to riparian zones.  Frogs and most salamanders need access to water for breeding.  Because they must keep their skin moist to absorb oxygen, they must remain in an environment with high humidity.  Most amphibians have limited mobility, so all of their life requirements—food, water, and cover—must be in close proximity.  Riparian zones provide all of these in a relatively small space.  Some Olympic Peninsula amphibians associated with riparian habitats include the rough-skinned newt, Northwest salamander, Van Dyke’s salamander, and the Pacific tree frog.

No Olympic Peninsula reptiles are entirely restricted to riparian zones, but several, like garter snakes, are found there in greater abundance due to the better supply of prey and cover.

Many species of birds find habitat in riparian areas, because of the rich insect populations and dense cover.  During the breeding season, nearly all songbirds subsist on insects.  Birds such as swallows, swifts, and flycatchers catch insects over or near water.  The lush riparian vegetation attracts terrestrial insects, which in turn provide a food source for vireos, warblers, thrushes, and tanagers.  Birds also feed on aquatic plants (waterfowl), aquatic invertebrates (dippers and shorebirds), and amphibians and fish (mergansers, herons, kingfishers).  Higher on the food chain, owls, accipiters, and falcons (e.g. merlin) may occur in relatively high densities in riparian areas due to the abundance of prey.

The dense vegetation typically associated with riparian zones makes them desirable as nesting sites.  The risk of nest predation is lower in places where the cover is more dense and complex. Birds such as the red-eyed vireo, warbling vireo, yellow warbler, black-capped chickadee, spotted towhee and Bullocks oriole build their nests in dense deciduous vegetation. 

Small mammals don’t travel far and therefore need all of their life requirements in a small area.  Because riparian zones contain such a wealth of food, water, and cover, they are ideal places for mice, voles, shrews, and moles.  One species, the marsh shrew, is found only in riparian areas.  Among larger mammals, otters and minks depend heavily on riparian habitat.  Other carnivores, such as raccoons, weasels, bears, and foxes prefer riparian areas because of the abundance of prey.  Large animals such as deer and elk use riparian zones as travel corridors, and especially for relief during hot weather.

Riparian habitats are extremely important to bats.  Like swifts and swallows, bats subsist on flying insects, which are found in greatest abundance over water and in moist habitats.  Bats also need the open water for drinking, and they frequently roost in the dense foliage of riparian trees.