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State of the Birds Report

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Aridlands

Aridland birds will be susceptible to warmer and drier habitats.


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                      Noteworthy

More than 40% of airidland bird species show medium or high vulnerability to climate changes.

Aridlands, already drier and more variable than other habitat types, are predicted to get even drier, warmer, and more variable.

Most aridlands will be altered by increased invasion of trees, shrubs, and other woody plant species, which will decrease their quality as habitat for bird species that prefer aridlands dominated by grasses and other desert vegetation.

Aridlands ecosystems are highly susceptible to invasion by nonnative species. Facilitated by climate change, invasion by nonnative species could alter the type and quantity of food for birds. 
 

Image: Sonoran Desert courtesy USFWS   
It is highly likely that species that are either very rare or nonexistent in the U.S. at present will expand their ranges into our country from the south, thus increasing
bird species diversity in some geographic areas.


Observations and Predictions

Aridlands of the United States, already subject to some of the highest extremes of climate variability in the country, are at great risk from climate change. The major predicted effects of climate change on all types of aridlands suggest that they will become warmer and drier. Associated with this will be increasingly variable precipitation, particularly in areas such as deserts, where summer and winter precipitation patterns help determine plant and animal distribution.

Linked to these climatic changes, aridlands will be highly susceptible to changes in plant species composition, particularly increasing tree cover in areas now dominated by shrubs (such as the vast expanses of sagebrush in the Colorado Plateau) and increasing density and surface area of shrubs in regions now dominated by grasses and other desert plants.

Invasion by nonnative species is expected to be exacerbated by changes in climate, which could promote devastating changes in fire frequency as well as alter the type and quantity of food for birds.

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Crested Caracara by Melissa Meadows

Bird Species Vulnerability

Compared with other habitat types, relatively few aridland bird species are vulnerable to climate change, though vulnerable species are found in all major aridlands types. Examples include Greater and Gunnison’s sage-grouse of sagebrush habitats of the Colorado Plateau and Great Basin, Costa’s Hummingbird and Gilded Flicker of the Sonoran Desert, Bendire’s and Crissal thrasher of the Chihuahuan Desert, Black-capped Vireo of the Edwards Plateau, and Wrentit of the coastal California chaparral. Aridland birds are primarily vulnerable because of their exposure: the probability that their habitats will undergo major changes due to climate change.

Fifty aridland species are considered vulnerable due to habitat exposure. A significant number are obligate breeding species of aridlands, which contributes to their vulnerability. Fourteen aridland species show medium or high vulnerability, but are not currently considered of conservation concern. These should be considered at much higher risk in the future and should be given special attention. Of these, the Lesser Nighthawk, Common Poorwill, Lucifer Hummingbird, and Phainopepla deserve special attention. The nighthawk and poorwill have increased vulnerability because of their dependency on large flying insect prey and their low reproductive potential. Lucifer Hummingbird and Phainopepla are dependent on seasonal flower and fruit resources and are only found in aridlands, thus increasing their vulnerability.

 

AridlandsPie_p14.jpg Of 79 aridlands species, 44% have medium or high vulnerability to climate change.

 

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Phainopepla by
John Bedell
Potential Impacts

Climate change could decouple the availability of food resources such as flowers and seeds from the time that they are needed by various aridlands species. A great unknown for aridlands birds is the extent to which extreme climatic events, especially heat waves and drought, will push different species’ physiological tolerances for heat and dehydration to or above their limits, resulting in increased mortality. Some evidence already exists that these events can stress smallbodied species such as hummingbirds and Verdin and there is evidence of reproductive failure and catastrophic mortality from heat waves in the United States and elsewhere.

Birds associated with riparian systems in aridlands, such as Phainopepla and Lucy’s Warbler, will be especially affected due to changes in water availability and vegetation of these systems. Aridlands, especially those in the Southwest, also provide important wintering habitat for numerous species from grasslands and other habitat types. If aridlands undergo the changes predicted, their suitability for a large number of these wintering species will decline.

Most aridland birds are adapted to the dry and variable climates in which they live, so it is expected that many will adjust their behavior, distribution, or movement patterns in response to climate change. It is expected that many aridlands species and the habitats they use should be able to expand to the north, east, and to higher elevations. Significant northward range expansions have already been observed for some aridlands species such as Cactus Wren, Cave Swallow, and White-winged Dove. Examples of species that are currently rare or of restricted distribution in the U.S., but are likely to expand, include Bronzed Cowbird, Crested Caracara, and Northern Beardless-Tyrannulet.

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Allen's Hummingbird courtesy USFWS

 Key Steps

Given the nature of aridlands and the predicted effects of climate change, we need to preserve additional airidland habitats so birds can move as change occurs, particularly to the north, east, and up in elevation; barriers that prohibit this movement should be identified and removed or minimized. Riparian areas will increase in their importance for aridland birds. They need to be protected and restoration efforts implemented to increase the quantity and quality of this generally scarce habitat type.

Management tools such as prescribed burning can be used to reduce shrubs and promote grasses in areas susceptible to woody plant invasion. Analyses of current and predicted climate change must be conducted to identify areas within the subtypes of aridlands that are less likely to show temperature increases or higher variability; these areas could serve as refuges for aridlands birds in the future. special attention and monitoring must be paid to nonnative invasive plants; if they are not controlled, they may spread so rapidly that they become impossible to control.

Conservation in Action

The San Pedro River National Conservation Area, designated by Congress as a Riparian National Conservation Area, is home to more than 100 species of breeding birds and an additional 250 species of migratory and wintering birds occur in the area. In cooperation with state and local conservation planning partners, the Bureau of Land Management is maintaining and restoring sagebrush landscapes on public lands in 11 western states to conserve sage-grouse populations. 

 

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