Tucson’s Birds:Why Scale Matters

Rachel McCaffrey

In developed areas, factors controlled by humans are important to determining whether native bird species persist

• Vegetation– Volume– Composition– Diversity

• Land-use – Types– Arrangement– Intensity

Bird• Occurrence• Abundance• Diversity• Composition

• Volunteer-based bird survey program

• Abundances and distribution

• Annual, citywide count~ 1,000 sites, 1/km2

• Quarterly, “Park” count~ 200 sites at 30 locations

Annual Survey Sites10 km ±

Park Monitoring Sites

Research Focus

Birds and habitat features in residential developments: an issue of scale

What we know:• Urban areas have less diverse groups of birds• ↑ in non-native species• Some types of development support more

native birds

Scale is important!

urban areas = heterogeneity and disturbance(Hostetler 1999)

(Hostetler 1999)

Local vs. landscape features

Individual yards Surrounding area

Species Dependent!

Why is this important?

which features @ which scale

=

species and scale-specific

management guidelines• homeowners

• neighborhoods• planners

Study Design

Randomly selected 300 sites

Bird surveys

• 5-minute point count, 40 m radius• Each site surveyed 4 times, March 15 – June 15• 10 species

Habitat features - Local

• 0.5-ha circular plot (40 m radius)

– Represents typical residential lot– On-site measurements

• Features measured based on known habitat requirements of species

Habitat features - Local

• Number of: – cholla cacti (> 1m)– saguaro cacti (> 2m)– mesquite and palo verde trees (> 3m)– native thorn trees (> 2m)– large “roost” trees (> 5m)– palm trees (> 5m)– homes

• Presence of:– desert mistletoe– wash

• Percent of vegetation that is native

Habitat features - Landscape

• 50-ha circular plot (399 m radius)– Represents typical neighborhood/development– Used digitalized aerial photographs & GIS

• Features measured based on habitat requirements and management potential

• number of washes• percent of area in open space• percent of area covered by lawn• presence of natural area > 5 ha

Habitat features - Landscape

Regression analyses:

Which features are most important for each species at each scale?

Variance decomposition:

Was a species most influenced by features at the local or landscape scale?

Data Analysis

Results

Average of 5.5 species/site

21.6% of sites 87.8% of sites

Results – Local Scale

• number of thorn trees• number of cholla• number of mesquite and palo verde trees • overall percent native vegetation• number of homes

Results – Landscape Scale

• number of washes (4)• percent of area in open space (6)• percent of area covered by lawn (3)

Results - Scale

Species most influenced by local scale features:• Cactus wren

• Curve-billed thrasher

• Phainopepla

Cactus wren

0

20

40

60

80

100

0 1-3 4-6 7-9 10-12 13-15 16-18 19+Number of cholla

Per

cent

of

site

s w

ith

cact

us

wre

ns

Results - Scale

Species most influenced by

landscape scale features:• Ash-throated flycatcher

• Lesser goldfinch

Ash-throated flycatcher

0

10

20

30

40

0 1 2 3 4+

Number of washes

Percent of sites withAsh-throated Flycatchers

Results - Scale

Species most influenced by shared associations: • Gambel’s quail

• Gila woodpecker

• Northern cardinal

• Pyrrhuloxia

• Verdin

Pyrrhuloxia

• Influenced most by shared associations across scales……• Local: % native vegetation• Landscape: % open, % lawn (-)

E.J. Peiker

The Influence of Scale

• Importance of habitat features varied by species and scale

• Cross-scale interactions

Need scale-specific

management strategies!

Local scale implications

Individual homeowners can have an impact!

• plant thorn trees, cholla, native trees

Landscape scale implications

Neighborhood groups and developers of master-planned communities can take broader actions:

• ban/limit lawns

• promote native landscaping

• incorporate open space

• restore riparian areas

A multi-scale approach

Homeowner plants thorn trees

Development incorporates open space

Regional planning efforts to maintain riparian networks

In Conclusion…..

The persistence of many native birds in urban areas will depend on:• Identifying key habitat features • Understanding the relevant scales • Targeting management efforts