TBC Full Report

Tucson Bird Count:

Results and Analysis

by Will Turner

The Tucson Bird Count has so far been a great success. Volunteers from the Tucson community have counted birds at over 1000 sites throughout the Tucson basin in spring surveys since 2001, and monitored birds in 20 parks on a quarterly basis. More than 215 species have been recorded to date. Many studies have used TBC data to date (see the TBC Press Room), and TBC data have been used to inform land-use decisions. Additional studies using TBC data are underway, and much more will be done as other data sets (for example, land cover) are collected and as the TBC continues through time. The TBC exists because of the efforts of scores of committed birders, and the project's continuation into the future will depend on their ongoing participation and the commitment of individuals and institutions to put TBC results to good use.

The Tucson Bird Count currently consists of two programs. The Route Program surveys hundreds of preselected sites across the Tucson basin each spring, while the Park Monitoring Program provides year-round data focused on particular parks, washes, neighborhoods, or other areas of interest.

Route Program Results & Analysis, 2001-2002

In the Route Program (overview), volunteers survey birds using 5-minute point counts at preselected sites in and around Tucson. Data from this program let us create local distribution maps for all species found, allow comparisons of bird communities in different areas in and around Tucson, and track changes in Tucson-area birds through time. In designing the Route Program, the study area is divided up into a grid of 1 km2 cells, and one site is placed randomly within each cell. Adjacent sites are linked together into "Routes", with each route taking about one morning for a volunteer(s) to survey.

By all measures the TBC Route Program's first two years have been a success. More than 80 birders participated each spring. In 2001, observers surveyed 674 sites. In 2002, the count grew to 724 sites. In these two years observers reported about 44,000 individual birds representing 138 species (see current Species Summary Table). The first scientific paper based on the Tucson Bird Count will be published in the journal Landscape and Urban Planning in 2003, and more are in the works. Below are some key findings presented in this first paper (a preprint of the full paper can be viewed online).

2001 Species Distribution Maps
The large number of sites surveyed in the Route Program lets us make Tucson-area distribution maps for bird species encountered. These maps show some interesting and often distinct patterns, with many species falling into one of a few general distribution types, discussed below. Although more detailed analyses will follow, the fact that simply inspecting species maps can reveal such pronounced patterns indicates just how powerfully habitat dictates where birds reside in the Tucson area.

Black-throated Sparrow
Some species show donut-shaped distributions around Tucson. For example, Gambel's Quail is one of the most common species in the Tucson area, yet is almost completely absent from most of Tucson proper. Many other native desert birds, for example Ash-throated Flycatcher, Black-throated Sparrow, and others, show similarly donut-shaped patterns.

Rock Dove
In contrast, another group of species show the opposite pattern, reaching their highest abundance near Tucson's urban core and decreasing toward less-developed areas. These include 3 non-native species — Rock Dove, European Starling, and House Sparrow — 3 species that have recently expanded their ranges — Anna's Hummingbird, Great-tailed Grackle, and Inca Dove — and a few native species, including Northern Mockingbird and Western Kingbird.

Bewick's Wren
Several bird species were observed most frequently in more wooded areas, which in present-day Tucson are now generally restricted to the northeast part of town. Each of the species showing this distribution pattern — Phainopepla, Brown-crested Flycatcher, Bewick's Wren, Northern Cardinal — generally prefers more densely vegetated streamside habitats in the arid southwestern United States.

Common Yellowthroat
Last (and least, it turns out), are species characteristic of southwesten riparian habitats. Due to decreased groundwater levels and direct removal of forests, riparian habitats are currently less extensive than they had been around Tucson as recently as 100 years ago. Only two riparian species — Abert's Towhee, Yellow Warbler — were found at any appreciable number of sites. Although neither species was found at more than 15 sites, the distribution of these sites is informative: each lies within meters of a major wash. Other riparian species showed up once or twice — Common Yellowthroat and Song Sparrow — or not at all — Summer Tanager and Yellow-breasted Chat.
Yellow-billed Cuckoo
Yellow-billed Cuckoo, a native riparian species that is currently a candidate for federal endangered status, arrives on its breeding grounds only well after the TBC's spring count and thus is not expected in spring data. It has been recorded during its breeding season in the TBC Park Monitoring Program (see cuckoo), although even these observations are relatively distant from urban Tucson. Although current conditions for riparian species around Tucson are bleak, several new attempts to restore riparian areas may provide more habitat for these species in the future. In springs to come, the TBC will track the impacts of these efforts on birds in riparian areas and surrounding landscapes.

2001 Land Use Analysis
Distribution maps give us some insight into how birds respond to development, but we can go a step further by using mapped information on land use. I condensed various local zoning codes into 4 land use classes: Commercial/Industrial (CI), High-density Residential (RH; min. lot size < 8000 sq ft), Low-density Residential (RL), and Open Space (OS; includes the large natural parks but not city parks or golf courses). Using this map, I analyzed the TBC bird data to discern the land-use class(es) that each species appeared to either excel or fare poorly in (see Table 4 in the TBC Paper Preprint). I also calculated a Sensitivity Index (SI) for each species, with higher SI values indicating greater drop-offs in occurrence from preferred land use class to other classes (greater sensitivity).

A few native species, such as Mourning Dove, were found equally often in all land use classes (low SI of 0.08). Other species, such as Curve-billed Thrasher (SI=0.24), and Gambel's Quail (SI=0.51), were most common in the less-developed classes (OS and RL), but were also found at higher development intensities (albeit less frequently). In contrast, many native desert species were most common in OS or RL, and rare or nonexistent at higher development intensities. These sensitive species show higher SI values.

Table: Native Sonoran upland and xeroriparian species most sensitive to Tucson development as indicated by zoning code


Ash-throated Flycatcher OS 1.29
Bell's Vireo OS 1.68
Black-tailed Gnatcatcher OS 1.05
Black-throated Sparrow OS 1.39
Brown-crested Flycatcher OS/RL 1.08
Canyon Towhee OS 1.47
Canyon Wren OS 1.70
Gilded Flicker OS 1.10
Lucy's Warbler OS/RL 1.06
Phainopepla RL 1.40
Purple Martin OS/RL 1.16
Future development is likely to affect most strongly those species that prefer classes of lower development intensity (OS and RL) and also show high SI values. This analysis reveals a list of 11 such species (table at right), all of which depend on either upland Sonoran habitats or densely vegetated washes. While it is safe to say that all of these species are strongly influenced by development, this is not a complete list. In particular, this analysis does not reveal sensitive species that either (1) are rare or have already become rare and thus not enough data could be collected to detect statistically significant results, or (2) depend on less-common habitat types, such as riparian habitat (e.g., Abert's Towhee) or mixed Sonoran upland-grassland (e.g., Rufous-winged Sparrow).

These findings have several implications. First, they show the importance of natural habitats (OS in the above analysis) in sustaining populations of many native bird species. Second, the finding that some native species appear to persist in some developed areas offers some hope that we may be able to successfully sustain birds near the places we spend our lives. A small number of native species may be able to persist in developed areas as they are currently structured. As for the others, sustaining them will

Bell's Vireo
require rethinking development practices. TBC results suggest that restoring and retaining parcels of natural habitat in the metropolitan landscape will be necessary to revive and sustain our native bird community. Additionally, developed areas should retain as much of the structural and vegetative character of natural habitats as possible over a substantial part of the landscape.

Can birds and people coexist?
Why should we bother to sustain birds in urban/suburban areas? First, the world is becoming more urban (percentage of humans worldwide in urban areas passes 50% this decade, 70-80% in N America and Europe). Simply put, the land left over is not enough to sustain the world's biodiversity. Second, having nature near the places we live enhances human quality of life. Third, bringing people in contact with nature where they live, work, and play can increase appreciation for all nature, wherever it may be. The Tucson Bird Count comes in again here: using TBC and mapped data on human population from the US Census, we can actually put numbers on the bird community that exists near where people live. Of the roughly 520,000 people living in the area surveyed by the Route Program, three out of four live where the number of bird species is below the TBC average. If bird diversity is any indication of nature in general, that translates to billions of people worldwide with reduced opportunities to interact with and benefit from nature.

TBC results suggest that we can change this unfortunate situation. We know that a few places, even in the heart of Tucson, appear to help sustain diverse native bird communities. Ongoing work is investigating TBC data in conjunction with high-resolution land cover maps to determine what it is, exactly, about places with high bird diversity that makes them special. Because "put a natural park the size of Saguaro East in the middle of Tucson" is generally not an option, we need the details. For example, what is the minimum area of upland Sonoran vegetation required for Black-tailed Gnatcatchers to show up? Is clustered or dispersed development better for sustaining bird species? What species are most vulnerable to development, how can we make future development easier on them, and what important areas should we avoid developing entirely? The Tucson Bird Count's Route Program will help answer these and other important questions.

Park Monitoring Program Results, 2001-2002
The Tucson Bird Count's second program is the Park Monitoring Program, in which volunteers select a park, wash, neighborhood, or other area of bird/birding interest to monitor four times per year. The Park Monitoring Program serves a number of uses, including (1) providing initial bird inventory data on parks for which no rigorous inventory has been done; (2) collecting data at more focused spatial scales than is possible in the more extensive Route Program; (3) monitoring changes in a park's bird community through time as the park and surrounding landscape change or as management/restoration actions are taken; (4) surveying Tucson's bird community year-round. At the time of this writing individuals and groups have adopted 13 parks and recorded data on 165 species.

Be a part of the Tucson Bird Count
The TBC is important to science and conservation, is vital to Tucson's livability for both birds and people, and is unprecedented worldwide. The most important part of the TBC, bar none, is the committed individuals who participate in the counts. To find out how you can help, contact us or see the TBC's Participation Page.