OVERVIEW

During the spring breeding season, more than a

hundred songbird species conduct a birds-eye

assessment of the Mid-Atlantic highlands to determine

suitable habitat for mating and raising young.

Different bird species require different habitats for

food , shelter and breeding. Some species need

extensive areas of dense forest. Others prefer fringe

areas with a mix of trees, shrubs, grasses, and farmland. Still others are adapted to more developed

urban and suburban landscapes. This brochure

explains that the types of birds found in an area are an

indication of its ecological condition; it also demonstrates the linkages between bird communities and

land use/land cover. (See the graphic on the back

cover as an example of the types of birds indicative of

various ecological conditions and the types of land

cover they represent.)

The types of birds found in an area indicate the

ecological condition of that area. Bird communities and ecological condition are also linked to

land cover. As the land cover of an area

changes, so do the types of birds in that area

(See Figure 1).

The quality of our environment affects our health,

our economy, and the future of our children.

Environmental scientists have long suspected that

ecological condition is linked to changing landuse patterns brought on by increasing population

and economic development.

The U.S. Environmental Protection Agency and

the Penn State Cooperative Wetlands Center

have found associations among songbirds, where

they live, and environmental health or condition in

the Mid-Atlantic highlands area (65,000 square

miles; see Figure 2).

We can now measure how the distribution of

various birds changes as land use is altered.

This association allows birds to be used in

United States Office of Research and EPA/620/R-00/003

Environmental Protection Development June 2000

Agency Washington, DC 20460 www.epa.gov

MAIA Project Summary

Birds Indicate Ecological Condition

of the Mid-Atlantic Highlands

The Mid-Atlantic Integrated Assessment

(MAIA) is an interagency, multi disciplinary research,

monitoring and assessment program to develop

high-quality scientific information on the region’s

natural resources: current condition, stressors, trends,

and vulnerabilities. MAIA results and information are

intended to satisfy a broad group of stakeholders’

needs, convey important information relevant to their

assessment questions and issues, and be useful in

making management decisions.

General Information on the Mid-Atlantic Integrated Assessment can be found through the World Wide Web at

http://www.epa.gov/maia. The research supporting this document was funded by the U.S. EPA Office of Research

and Development under Interagency Agreement Number DW14936411-01-2 with the U.S. Fish and Wildlife Service. It

has been subjected to EPA’s peer and administrative review. The management recommendations were developed by

EPA Region 3. The full research report, The Bird Community Index: A Tool for Assessing Biotic Integrity in the

Mid-Atlantic Highlands, Report Number 98-4, the Penn State Cooperative Wetlands Center, can be obtained at

www.wetlands.cas.psu.edu.

Photo by: G. Bradley

Figure 1. Relationship between birds, land cover, and

ecological condition.
conjunction with other indicators to estimate ecological

condition.

The presence or absence of particular birds across the

study area indicates that:

• 16% of the highlands is in excellent ecological

condition;

• another 27% is in good condition;

• 36% is in fair ecological condition; and

• a total of 21% (5% urban and 16% rural) is in

poor condition.

It was also found within the 200-acre survey sites that

ecological condition was closely associated with the amount

and age of forest and other land-cover. For example:

• Sites in good or excellent ecological condition

were usually associated with an average of 87%

forest cover.

• Sites in excellent condition had a taller and more

closed tree canopy (a mature forest) than sites in

good condition.

• Sites in poor ecological condition were usually

associated with less than 28% forest cover.

• Sites in poor ecological condition were also

observed when agricultural/non-woody-plant

cover exceeded 61%, or urban/residential cover

exceeded 29%.

Most of the Mid-Atlantic highlands is

forested. A forest is an area thickly

covered with trees and distinguished by

the types of trees and plants, their

density, and the soil type. Forests are

also divided into vertical layers: the

canopy, the shrub layer, and the forest

floor. Clearing forests not only removes

the trees, but also the crucial habitat

needed by non-woody plants, insects,

birds, and other wildlife in each forest

layer. Forest clearing also degrades

aquatic systems and water quality by

increasing erosion and light penetration.

In the absence of human activity, the

geology, climate, rainfall, and frequency

of natural disturbances in the MidAtlantic highlands support naturallyoccurring forests. Therefore, mature

forests represent the highest ecological

condition potentially attainable in the

region. Human activity creates habitats such as lawns,

agricultural fields, forest edges, and forests with only a

few species of trees. These areas represent a lower

ecological condition than a mature forest.

Obviously, the entire Mid-Atlantic highlands cannot be

returned to its highest ecological condition. This would

require destruction of many human amenities and, in

some cases, take hundreds of years to accomplish.

However, areas can be identified that are moving

toward a lower level of ecological condition. See the

APPLICATIONS section on page 7 for what can

be done to lessen the impact of this decline.

ECOLOGICAL INDICATORS

Our understanding of how living things interact and

how these interactions contribute to healthy surroundings is limited. To better understand these interactions

and improve efforts to protect the environment, we

need to measure characteristics which reflect the

condition of ecological resources and the impacts

which adversely affect them. These characteristics

are called ecological indicators.

BIRDS ARE SENSITIVE ECOLOGICAL

INDICATORS

Birds exhibit numerous traits that make them good

ecological indicators at regional and national scales.

Figure 2. The songbird study surveyed 126 sites that were

randomly distributed across the highlands (65,000 sq. mi.).

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They are everywhere, and different species vary in

their sensitivity to physical, chemical, and biological

threats. Each species also exhibits life history traits

(e.g., ground nester – nests on the ground; temperate

migrant – migrates south of the Mid-Atlantic highlands, but within North America; omnivore – feeds

on both animal and plant material) that link to multiple

environmental characteristics. Recording bird species

within a designated area is relatively easy and inexpensive; birds have strong public appeal; bird species

are well known; there are many trained field observers available; and no laboratory analysis is required.

Additionally, survey methods harm neither birds nor

the survey sites, and long-term records and ongoing

programs are available to provide or augment data.

Because of the unique role of every bird species in its

habitat, the composition of the birds in an area is a

multi-faceted indicator of ecological condition.

The authors of this study have analyzed and combined

information on the variety of species of birds present

in the Mid-Atlantic highlands area to create a regional

indicator of ecological condition. This indicator was

developed and tested here as part of EPA’s Environmental Monitoring and Assessment Program

(EMAP).

It is important to recognize that both the highest

ecological condition and the bird species that indicate

that condition may differ in other regions. Therefore,

the bird based ecological indicator for the MidAtlantic highlands is intended for use solely in this

study area. It is anticipated that a similar indicator

can be developed for almost any region, based on the

region’s birdlife.

PROCEDURE

In the early 1990s, 34 sites in central Pennsylvania

were selected and ranked according to their degree

of ecological decline or degradation (human disturbance gradient). The degree of degradation was

based on an intensive study of soil type; amount of

soil deposited by erosion; plant, amphibian, and

wildlife communities; and where each site fits into the

general landscape pattern. Sites were ranked from

nearly pristine to severely degraded.

Next, an independent ranking of these sites using only

bird species data was developed. Birds were surveyed at each of the sites, thus determining the bird

composition (community) at each site. The bird

community at each site is comprised of multiple life

history groups (species that require similar habitat,

food, nest location, or other elements for survival) that

also reflect condition. The separate rankings of the

sites based on the original human disturbance gradient

and the bird communities were compared. This

comparison satisfactorily demonstrated that ecological

condition, as indicated by the bird community, closely

matched the ecological condition determined previously by other physical and biological characteristics

of each survey site.

Sixteen specific groups of bird species, such as omnivores, bark probers, residents, migrants, shrub nesters,

etc., were ultimately selected as representative of the

mostly forested Mid-Atlantic highlands area (Table 1).

Of the 16 groups, nine were “specialists” and seven

INDICATORS:

• An indicator is a sign that relays a

complex message in a simplified and

useful manner.

• An ecological indicator is a measure that

describes the condition of an ecosystem or

one of its critical components.

Example – The presence of trout in a stream

indicates cool, well-oxygenated water, with

 lots of aquatic life; therefore, the presence

 or absence of trout is an indicator of

 stream condition.

EPA’s EMAP develops indicators and

other research tools to track status

and trends in the condition of the

nation’s ecological resources. These

resources include estuaries, wetlands,

inland lakes and streams, forests, and

mixed landscapes.

Photo by: USGS BRD

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were “generalists”; for example, insectivores are

specialists and omnivores are generalists. Placement of

specific bird species within each group was based on a

review of scientific publications. Species may be

assigned to several groups as well as to both specialist

and generalist groups simultaneously. In general, a high

proportion of birds with specialized requirements

indicates healthy natural habitat that provides ecological

benefits at local and larger scales.

Birds and vegetation were surveyed across the entire

Mid-Atlantic highlands within sites sufficiently large

(200 acres) to represent most of the habitat elements

that are required by breeding birds. Use of EPA’s

EMAP survey design guaranteed that data from the

126 sample sites were representative of the entire

highlands area.

MAJOR FINDINGS

ECOLOGICAL CONDITION IS LINKED TO

BIRD COMMUNITY ATTRIBUTES

Five levels of ecological condition (Figure 3) were

clearly distinguishable across the study region from

the types of birds found at each site. Examples of

these birds are listed on page 6 and in the figure on

the back cover.

Highland areas in excellent condition are dominated

by birds that, among other traits:

• eat insects exclusively,

• seek food on the ground and in tree bark,

• reproduce only once per year, and

• migrate from distant wintering grounds.

Such characteristics tell us that these areas also support

upper levels of the food chain, structurally complex

habitat, relative protection from non-native predators

and competitors, and continental-scale lifecycles. In the

Mid-Atlantic highlands, an extensive mature hardwood

or mixed-hardwood forest provides the maximum

amount of these ecological features and benefits.

Many of the same bird species occur in areas of good

ecological condition. However, they do not dominate

the community as fully, while other species appear that

are less specialized, for example, in what and where they

eat. The bird community in these areas still reflects forest

habitat, but it is not as physically or biologically complex.

These distinctions in the bird data were supported by

vegetation measurements: Areas in excellent condition

support a taller (~80 feet) and more closed (~61%)

tree canopy than areas in good condition (~65-foot

canopy height and ~47% canopy closure). The

forests are no bigger at the sites in excellent condition,

but the trees are.

The bird community in areas of fair ecological condition

indicates a significant decline in the provision of protective ground cover as well as upper-canopy feeding and

nesting habitats. At the same time, non-native species

begin to appear, signaling aggressive competition with

native birds for food and shelter. With increasing shrub

and grassland species, this community signals a shift from

the native ecosystem to a mix of forest and the introduced habitats of agricultural and residential areas.

Analysis separated areas of poor condition into two

classes — rural and urban — based on the distinct

bird groups observed in each landscape type. In both

cases, highland areas in poor ecological condition

have birds that:

• are non-native

• do not have specialized diets

• reproduce multiple times per season

• parasitize or prey on the nests of other birds.

This is a classic profile of opportunistic behavior, and

is observed in both plant and animal species when

Figure 3. The bird community indicator classified

the highlands area into five categories of ecological

condition.

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habitats are simplified or otherwise disturbed by

human or other events. Habitats supporting these

bird groups are generally not sustainable. They are

maintained by intensive vegetation control, the

addition of nutrients, and other manipulations. These

activities halt the process of plant succession, disrupt

the natural food chain, and render these areas

inhospitable to many native species.

BIRD COMMUNITIES ARE LINKED TO

LANDSCAPE PATTERN

The term “landscape” refers to the spatial pattern or

structure of a land area and the repeating patterns

associated with dominant land uses. The relative

proportion of forest, agriculture and urban land cover

contained in an area also defines a landscape as does

the interrelationship between them. The MAIA

landscape ranges from wilderness areas to major

cities, yet the patterns and processes of human and

natural activity within the landscape are interconnected

in many different ways and at many different scales.

The five categories of ecological condition as defined

by the bird communities were highly related to the

configuration ofland cover in the 200-acre sites.

Figure 4 provides examples of these landscape patterns, which were characterized from aerial photography.

“Excellent ecological condition” conveys the sense of an

undisturbed, self-sustaining natural area. In the MidAtlantic highlands, most undisturbed areas develop into

mature forest communities. Therefore, it is not surprising

that this study finds ecological condition, as indicated by

bird composition, to be positively correlated with

percent forest cover and measures of mature forest

vegetation. What may be surprising is that less than

one-fifth of the Mid-Atlantic highlands remains in

excellent condition, and that labels of fair to poor

describe more than half of the region.

This study begins to define the critical thresholds of landcover change where shifts in ecological condition take

place. At the 200-acre scale, both good and excellent

ecological condition were associated with an

average of 87% forest cover. Poor ecological

condition was observed when agricultural/nonwoody-plant cover exceeded 61%, or urban/

residential cover exceeded 29%.

 One interpretation of these results is to consider areas in

good ecological condition as desirable by society, and to

manage them so as to maintain current land cover.

Longer rotation sequences in forested areas of good

condition could create more areas with the potential to

support excellent condition. Many of the areas in poor

condition are also justified by societal requirements for

agricultural and urban land uses. Community planning

efforts may focus instead on those marginal landscapes in

fair condition, guiding development such that they are not

transformed beyond critical land-cover thresholds into

areas of poor ecological condition.

The results further demonstrate that bird community

composition is related to land-cover pattern at spatial

scales of at least 200 acres. To mitigate the spread of

poor-integrity environments, planners and managers

must consider the landscape-scale consequences of

localized land-cover transformations. Similarly, a

landscape framework should drive restoration activities to increase the percentage of the region in good

to excellent ecological condition.

Figure 4. Ecological condition, as indicated by

songbird communities, is highly correlated

with land-cover composition.

5
BIRD COMMUNITIES

The following species belong to Mid-Atlantic bird

communities shown to indicate levels of ecological

condition at the landscape scale. While a full community profile is necessary to apply the bird community indicator, these examples illustrate the use of bird

characteristics to determine ecological condition.

The black-and-white warbler is an insectivore, a

neotropical migrant, a forest ground nester, and an

interior forest obligate (must have interior forest to

survive). If this species and other interior forest

obligates, such as ovenbirds, scarlet tanagers, and

worm-eating warblers, comprise more than 35% of

the species in your bird community, it is likely an area

of excellent or good ecological condition.

The grasshopper sparrow is an omnivore, a shortdistance migrant, a double-brooded species, and an

open-ground nester.

You may be in an area of fair ecological condition

for the Mid-Atlantic highlands, if grassland species

such as this are found in mixed communities with

forest generalists, such as the tufted titmouse.

These areas contain fewer omnivores, nest predators,

residents, and exotics; and significantly more uppercanopy foragers, single-brooded species, and forestground nesters than areas of low ecological condition.

The European starling is an omnivore, a year-round

resident, a non-native (exotic) species, and a nest

predator (preys on eggs or young of other birds). If

this species and other nest predators such as the

American crow or the blue jay, or nest parasites

(lays its eggs in other birds’ nests), such as the

brown-headed cowbird, comprise more than 15% of

the species in your bird community, it is likely an area

of poor ecological condition.

(Refer to the graphic on the back cover as an example of the types of birds indicative of various

ecological conditions and the types of land cover they

represent.)

Tufted Titmouse

Photo by: 

©Tom Vezo/VIREO

Black-and-White Warbler

Photo by: 

©Gerard Bailey/VIREO

Grasshopper Sparrow

Photo by: 

©Tom Ulrich/VIREO

European Starling

Photo by: 

©R. and S. Day/VIREO

6
* These groups of species have similar life history traits; that is, they require similar habitat, food, or other elements for survival.

Omnivore (eats both animals Trophic (Diet) X

and plants)

Bark Prober Insectivore Foraging Behavior X

Ground Gleaner Insectivore Foraging Behavior X

Upper-Canopy Forager Insectivore Foraging Behavior X

Lower-Canopy Forager Insectivore Foraging Behavior X

Nest Predator/Brood Parasite Population Limiting X

Exotic (introduced species) Origin X

Resident Migratory X

Temperate Migrant Migratory X

Single-Brooded Number of Broods X

Canopy Nester Nest Placement X

Shrub Nester Nest Placement X

Open-Ground Nester Nest Placement X

Forest-Ground Nester Nest Placement X

Forest Generalist Primary Habitat X

Interior Forest Obligate (must Primary Habitat X

have interior forest to survive)

LIFE HISTORY BIRD GROUPS* CATEGORY SPECIALIST GENERALIST

TABLE 1: SUMMARY OF THE LIFE HISTORY BIRD GROUPS* USED IN THE STUDY

APPLICATIONS

Public and private agencies, organizations, and

individuals can help improve ecological conditions in

the Mid-Atlantic region in the following ways:

• Protect and maintain existing forests that are in

good or excellent condition.

• Restore areas in fair condition (e.g. marginally

productive agricultural land).

• Guide development away from areas in good and

excellent condition. Work to avoid further degradation of areas in fair condition.

• Focus development in areas that show poor

ecological condition.

The land uses in the Mid-Atlantic and how they are

distributed across the area affect the quality of the

natural environment (see An Ecological Assessment

of the United States Mid-Atlantic Region – A

Landscape Atlas, EPA/600/R-97/130, November,

1997).

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For More Information, Please Contact

Funded by the U.S. Environmental Protection Agency

Laura Jackson

U.S. Environmental Protection Agency

Office of Research and Development

Research Triangle Park, NC 27711

jackson.laura@epa.gov

Timothy O’Connell / Robert Brooks

Pennsylvania State University

Cooperative Wetlands Center

University Park, PA 16802-4703

tjo111@psu.edu / rpb2@psu.edu

Tom DeMoss

U.S. Environmental Protection Agency

Region 3

Environmental Science Center

Ft. Meade, MD 20755-5350

demoss.tom@epa.gov

Birds in the Mid-Atlantic Highlands as Indicators of Ecological Condition