Iowa State University Capstones, Theses and Retrospective Theses and Dissertations Dissertations

1992 Species composition and abundance, and nest density and fate of birds in roadsides adjacent to Iowa rowcrop fields Martha Camp Iowa State University

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This Thesis is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Retrospective Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. Species composition and abundance, and nest density and fate of birds in

roadsides adjacent to Iowa rowcrop fields

by

Martha Camp

A Thesis Submitted to the

Graduate Faculty in Partial Fulfillment of the

Requirements for the Degree of

MASTER OF SCIENCE

Major: Animal Ecology

Approved:

Signatures have been redacted for privacy

Iowa State University Ames,Iowa 1992 11

TABLE OF CONTENTS Page

GENERAL ThITRODUCTION 1

Explanation of Thesis Fonnat 2

PAPER I. BIRD ABUNDANCE AND SPECIES RICHNESS IN ROADSIDES ADJACENT TO IOWA ROWCROP FIELDS 3

ABSTRACT 4 INTRODUCTION 5 STUDY SITES 7 MElHODS 12

Vegetation measurements 12

Bird Census 13

Statistics 13 RESULTS AND DISCUSSION 15 Vegetation Characteristics--Roadside 15 Comparisons between Roadside Types, Treatments, and Years 15

Seasonal Changes 16

Vegetation Characteristics--Field 19

Bird Species Composition and Abundance--Roadside and Field 19 Vegetation Type and Treatment 25 Vegetation Characteristics in Roadsides 25 Coverage of Habitats Adjacent to Roadsides 27 Seasonal Changes of Bird Species Abundance in Roadsides 28

MANAGEMENT IMPLICATIONS 31 LITERATURE CITED 33 iii

PAPER II. NESTING OF BIRDS IN ROADSIDES ADJACENT TO IOWA ROWCROP FIELDS 40

ABSTRACf 41

INTRODUCTION 42

STUDY SITES 44

MEIHODS 45

Roadside Vegetation Measurements 45

Nest Site and Nest Vicinity Measurements 45 Nest Searching and Monitoring 46

Nest Fate Calculations 47 Statistical Analysis 48

RESULTS AND DISCUSSION 50

Vegetation Characteristics 50

Composition and Density of Nesting Species 50

Influence of Roadside and Nest Site Characteristics on Nest Placement 53

Red-winged blackbird 53 Vesper sparrow 54 Gray partridge and ring-necked pheasant 54

Nesting Success 59

Causes of Nest Failure 60 Roadside and Nest Site Characteristics Influencing Redwing Nest Fate 60 MANAGEMENT IMPLICATIONS 63 LITERATURE CITED 66

GENERAL SUMMARY 73

ADDITIONAL LITERATURE CITED 75

ACKNOWLEDGMENTS 77 1

GENERAL INTRODUCTION

Agricultural practices in the Midwest have intensified as a result of technological advances such as the increased use of machinery, single cropping systems, and agricultural chemicals. These advances have enabled farmers to till more land than in the past and consequently, large rowcrop farms now dominate the Midwest landscape. As farm size has increased most of the native grassland and wetland habitat in the Midwest has been

destroyed. Nearly 100% of the wetlands and pre-settlement prairie have been lost in Iowa alone (Bishop 1981, Smith 1981).

Native grasslands and wetlands once sustained a variety of bird species (Laubach 1984,

Herkert 1991) but the cropfields that replaced these native habitats are not, in most cases,

suitable habitat for birds (Rodenhouse and Best 1983, Basore et al. 1986, Frawley 1989).

Some linear habitats (e.g., fencerows, grassed waterways, and roadsides) are relatively

undisturbed by farming and contain native prairie vegetation. These areas may provide

much needed habitat for some native birds (Best 1983, Bryan and Best 1991, Warner

1992). The increasing farm size, however, has begun to encroach on these areas as well, a

trend which is exemplified by the removal of fencerows (Vance 1976).

In recent years, the potential value of roadsides to birds has received considerable

attention (Montag 1975, Varland 1985, Ryan 1986, Alt. Roadside Steer. Comm. 1989,

Warner 1992). A number of studies have documented ring-necked pheasant (Phasianus

colchicus) and gray partridge (Perdix perdix) use of and nesting in roadsides in agricultural

areas (Joselyn et al. 1968, Warner et aI. 1987, Nelson et al. 1990), and nongame birds use

of highways (Oetting 1971, Machan 1975, MichealI980). Although an average township

in Iowa may contain about 270 km of roadsides associated with gravel roads (M. Masteller,

Iowa Dep. Trans., pers. commun.), no studies had assessed the value of such roadsides to

nongame birds in Iowa. My study not only answers questions concerning bird use of and 2

nesting in roadsides adjacent to gravel roads, but also provides some recommendations concerning the management of these areas for avian wildlife. Explanation of Thesis Format

This thesis is composed of two papers written for publication in scientific journals.

Paper I deals with the relative abundance and species composition of birds using roadsides.

Paper II discusses the nest density and success of birds nesting in roadsides. A general introduction precedes the two papers and a general summary follows them. The literature cited in the general introduction and summary is referenced in the section entitled

"Additional Literature Cited." Data acquisition, statistical analysis, and the preparation of the text for both sections were the responsibility of the candidate; guidance and editorial advice were supplied by Dr. Louis B. Best. 3

PAPER I. BIRD ABUNDANCE AND SPECIES RICHNESS IN ROADSIDES ADJACENT TO IOWA ROWCROP FIELDS 4

ABSTRACT

Bird use of roadsides adjacent to rowcrop fields in central Iowa was studied from May through August, 1990 and 1991. Thirty-five bird species were seen in roadsides, compared with 26 species in rowcrop fields. Red-winged blackbird (Agelaius phoeniceus), brown­ headed cowbird (Molothrus ater), vesper sparrow (Pooecetes gramineus), western meadowlark (Stumella magna), and dickcissel (Spiza americana) were the most abundant bird species in roadsides. Total bird abundance in roadsides averaged 1,670 birdS/l 00 ha, compared to 49 birds 1100 ha in crop fields. Few bird species showed a preference for roadsides with native versus exotic grasses or for burned versus unburned roadsides, but the abundance of some birds was related to vegetation height and density in roadsides. The abundance of 5 bird species, as well as total bird abundance, was greater in 1990 than in

1991. Dickcissel abundance increased throughout the summer in roadsides, whereas common grackle (Ouiscalus qui scala) abundance peaked in early June and then declined.

Native prairie vegetation and prescribed burning mayor may not be appropriate for the conditions found in many gravel roadsides. Fences should be retained along gravel roadsides.

o 5

INTRODUCTION

Before agriculture dominated the Midwest plains, a variety of native prairie grasses and forbs characterized the landscape (Dick-Peddie 1953, Smith 1981). Throughout the 1800's, this grassland was brought under cultivation (Nat!. Res. Council 1970), and since the

1930's large rowcrop farms (com and soybean monocultures) have replaced the early, small farms that produced a variety of crops (Mohlis 1974, Vance 1976, Taylor et al. 1978).

The original prairie and later small farms with interspersed crops supported a number of grassland bird species (Dambach and Good 1940, Wiens and Dyer 1975). Habitat for many avian species has been lost, however, as pastures and hay and oat fields have been eliminated. The remaining habitats (e.g., fencerows, grassed waterways, railroad rights-of-way, and roadsides) are, therefore, gaining importance as potential refuges for grassland birds (Braband 1979, David and Warner 1979, Best 1983, Bryan and Best 1991).

Because of their linear nature, these habitats lack the area needed by some avian species

(Samson 1980), but other species thrive in corridor and edge environments (Kroodsma I 1984, Bryan and Best 1991).

Roadsides adjacent to gravel roads are prevalent in many rowcrop systems. An average township in Iowa, for example, may contain about 270 km of roadsides associated with gravel roads (M. Masteller, Iowa Dept. Trans., pers. commun.). Studies of roadside use

by avian wildlife have dealt mainly with the ring-necked pheasant (Phasianus colchicus)

(e.g., Joselyn et al. 1968, Warner et al. 1987, Nelson et al. 1990). Optimal pheasant nesting cover, a mix of alfalfa (Medicago sativa) and smooth brome (Bromus inermis)

(Snyder 1974, Warner et al. 1987, Nelson et al. 1990), is not the best habitat for all birds

(Skinner et al. 1984). In addition, most studies of roadside use by birds have been conducted along highways (e.g., Oetting 1971, Machan 1975, Clark and Karr 1979,

MichealI980), which comprise less than 0.5% of the total land area in Iowa (M. Masteller.

Iowa Dept. Trans., pers. commun.). 6

In the past few years, many counties in Iowa have re-examined their roadside vegetation management strategies (Alt. Roadside Steer. Comm. 1989). Efforts are under way to replace the exotic grass smooth brome with native prairie grasses. Smooth brome, commonly planted in roadsides, creates a relatively homogeneous habitat where all the vegetation is about the same height and density and, therefore, attractive to only a few bird species (Wasser and Dittberner 1986). Roadsides with a variety of native grasses and forbs provide a more heterogeneous habitat that may be attractive to many grassland bird species

(Wiens 1969, Skinner et al. 1984, Kahl et al. 1985). Historically, the hardiness and heterogeneity of the native prairie vegetation was maintained, in part, by periodic prairie ftres (Owens and Myres 1973, Vogl1974). The reestablished native vegetation also must be burned periodically to maintain its vigor and diversity and to prevent encroachment by woody vegetation (Towne and Owensby 1984, Collins 1987).

The objectives of our study were (1) to document the abundance and composition of bird species using roadsides and adjacent rowcrop ftelds and (2) to evaluate the influence of roadside vegetation type (native vs. exotic) and controlled burning on bird use of roadsides. 7

STUDY SITES

Eighteen roadsides in Story and Boone counties in 1990 and 16 roadsides in Hardin

County in 1991 were chosen for study. The topography of these counties is nearly flat to gently rolling (DeWitt 1984, Voy 1986). The average daily maximum temperature from

April through August is 29 C, and the mean midday relative humidity is 60% (Table 1).

Normal annual rainfall is about 85 cm, with about 62 cm falling from April through

September (DeWitt 1984, Voy 1986).

Boone, Story and Hardin counties were chosen for several reasons. Each is typical of the central Iowa cash-grain region where intensive rowcrop farming makes suitable wildlife habitat scarce (U.S. Dep. Agric. 1990). All counties have active Integrated Roadside

Vegetation Management (IRVM) programs whose personnel cooperated to burn some of the roadsides studied. IRVM surveys, conducted in each county, also enabled us to locate roadsides with remnant native prairie tracts.

All studied roadsides were associated with gravel roads and were adjacent to cornfields or soybean fields. Roadsides near other habitats were excluded to avoid confounding effects. All roadside plots had a fenceline characteristic of many roadsides in Iowa.

Roadsides with woody plants were avoided because most roadsides are sprayed, mowed or burned to eliminate woody vegetation (Wasser and Dittberner 1986). Furthermore, the presence of woody vegetation significantly increases bird abundance and diversity in farmland habitats (Shalaway 1985, Best et al. 1990). Roadside plots were 500 m long, about 6 m wide (the width of the roadside), and about 0.8 m deep at the center. Field plots, which were 100 x 500 m, were established 50 m from the field edge and parallel to the roadside study plots. Thus bird use of fields and roadsides could be compared. The total area covered by the 34 roadsides and field plots was 10.2 and 170 ha, respectively.

Ten roadsides chosen in 1990 and eight in 1991 contained warm-season, native prairie grasses; the dominant species were big bluestem (Andropogon gerardii) and Canada wild 8

rye (Elymus canadensis) (Table 2). Native prairie remnants with relatively low native grass coverage were used as study plots because IRVM programs to seed roadsides with native prairie vegetation had just begun, thus no seeded stands were well established. Each year, eight roadsides also contained predominantly the exotic, cool-season grass smooth brome.

Half of the native prairie roadsides each year were burned in April, and half of the exotic grass roadsides were burned in March 1990. No smooth brome roadsides were burned in

1991 because of weather delays. Roadsides usually were assigned randomly to the bum treatment, although sites with metal fence posts were preferred for burning to avoid possible damage to wooden fence posts. Because burning is used as a management technique to maintain vigorous stands of all types of grass (Vogi 1974), both native and exotic grasses were burned to compare the effects of fire on the two vegetation types. 9

Table 1. Climatological data for Story, Boone and Hardin counties, Iowa, April-August

1990-91a and averages from 1957-1978b (normal).

Temperature (daily maximum C) Total precipitation (cm)

Month 1990 1991 Normal 1990 1991 Normal

April 15 16 15 8.5 19.9 8.7

May 19 23 22 20.8 24.4 11.0

June 27 30 27 22.5 14.2 13.7

July 27 30 29 30.5 6.4 10.4

August 27 28 28 7.9 11.2 11.0

aSource: Department of Geological and Atmospheric Science, Iowa State University,

Ames, Iowa.

bSources: DeWitt 1984, Voy 1986. 10

• (16)

3.3

3.4 1.0 2.9 1.2

S.E.

1.7 0.9 0.5

0.6

x

1991

7.8 3.6

4.7 4.4

1.7

5.7

73.9

42.5 a

Year

*

** *

I

** **

years.

(18)

1.8

3.7 1.2

3.4 1.2 S.E.

and 0.7

x

1990

2.4

5.7 4.7

2.1

0.2 0.4 0.7 0.0

60.6

40.3

treatments,

(21)

4.0

4.0 1.5 2.0

0.7 S.E.

0.7 0.3

0.7 0.9 0.4 0.4

types,

x

5.8 0.2 6.6 3.0

0.4 1.0 2.2

73.3

45.6

Unburned

vegetation

Treatment

(13)

3.8 3.6 1.0

2.3 1.5

S.E.

0.8 0.3 1.0

0.9

x

1.7

5.9

2.6

3.4

0.4

Burned 2.1 2.0

comparing

68.2

42.2

(16)

2.9

4.4 2.4

0.4 S.E.

1.3 0.5 0.4 roadsides,

0.7

x

Exotic

Iowa

4.0 1.6 0.7 0.0

1.5 0.5 3.7

type 77.4

62.8

in

*

**

** **

b

**

1.2

3.5 Roadside 2.9 3.3 0.7 S.E. 1.1 1.0

0.7 0.8

x

Nativtiill 1.5

4.5

5.9 2.4 1.5

characteristics 3.6

62.1 11.6

21.1

vegetative

gerardii)

S.E.)

repens) C

rye (±

grass

inermis) pectinata)

canadensis) arundinacea)

bluegrass

brome

wild pratensis)

cordgrass

Mean

canary

Coverage

bluestem

2.

(Bromus (~

(~spp.)

(Spartina (Andropo~on

(Elymus (AgrQpyron

(Phalaris

Kentucky Smooth Prairie Big

Sedge

Canada

Quackgrass

Reed

Grass

Table

Canopy Canopy coverage

Forb 3.8 0.8 * 2.0 0.6 2.7 0.8 * 0.7 0.5 1.6 0.6 2.5 0.7 Litter 5.5 2.5 3.7 1.6 0.5 2.6 ** 22.0 7.0 10.5 4.5 4.2 3.5 Bare ground 22.2 2.7 18.8 2.7 25.2 3.3 ** 2.6 1.4 13.0 2.4 17.6 2.8 Structure

Density (index value)d 13.6 0.9 ** 17.1 0.8 14.2 0.9 ** 17.8 0.9 13.2 0.9 ** 17.3 0.8 Height (cm) 47.3 2.1 ** 54.1 2.0 47.1 2.1 ** 56.1 2.1 45.4 2.0 ** 53.7 1.8

aA verage values were determined for each roadside and then used as sample units to calculate means and standard errors. bNumber of roadsides sampled...... COnly species with coverages ~ 1% are listed. Species found in roadsides with a coverage < 1 % were prairie drop seed ..... (Sporobolus heterolepis), little bluestem (Andropogon scoparius), porcupine-grass (Stipa spartea), Chinese foxtail (Setaria faberi), switchgrass (Panicum virgatum), field horsetail (Equisetum arvense), Scribner's panic grass (£. scribnerianum), side oats grama

(Bouteloua curtipendula), broad-leaved cat-tail (~latifolia),orchard grass (Dactylis glomerata), bird's-foot violet (Viola pedata) , common dandelion (Taraxacum officinale), common milkweed (Asclepias syriaca), common vetch (Vicia sativa), hoary vervain (Verbena stricta), multiflora rose (Rosa multiflora), hedge-nettle (Stachys palustris), Canada thistle (Cirsium arvense), wild strawberry (Fragaria virginiana), ground cherry ( Physalis spp.), lady's thumb (Polygonum persicaria), self-heal (Prunella vulgaris), meadow rue (Thalictrum spp.), common morning glory (Ipomoea purpurea), and giant ragweed (Ambrosia trifida). Source of scientific and vernacular names: Great Plains Flora Association (1986). dCalculated by summing the individual interval readings from the density pole. * P s 0.05, ** P s 0.01; Student's t-test. 12

METHODS Vegetation and Landscape Measurements

The height, density, and composition of the vegetation were measured at one randomly chosen sample site along each 100 m of a roadside. At each site, measurements were taken on the foreslope (nearest the road), bottom, and backslope of the roadside. Height and density were measured every 2 weeks; composition was measured monthly. All measurements were taken between mid-May and late July. Measurements taken at the foreslope, bottom, and backslope of a roadside were found to be strongly correlated (£ ~

0.(01) and thus were combined for data analysis. Only measurements taken in May and

June were analyzed because July measurements were strongly correlated (£ ~ 0.001) with those in May and June. May and June vegetation was considered most likely to influence bird use of roadsides during the breeding season.

Vegetation density was measured with a 1.5-m tall and 2.5-cm diameter pole graduated at

100cm intervals. At each sampling point, the pole was viewed from four directions at a height of 1 m and a distance of 1.5 m. The proportion of each interval obscured by vegetation was categorized as 0-20, 21-40, 41-60, 61-80, or 81-100% and recorded as 1,2,

3,4, or 5, respectively. A density index was calculated by averaging the measurements from the 4 directions at each interval and then summing over all intervals (Basore et al.

1986). The height of the highest pole interval touched by vegetation (alive or dead) was taken to represent vegetation height. The composition of the vegetation in roadsides was determined by estimating percent canopy coverage of plant species within a 0.1 m2 circular quadrat. Individual plant species coverages were estimated on an overlapping basis, so the sum of the coverages could exceed 100% (Daubenmire 1959). The coverage of herbaceous growth forms (i.e., grasses and forbs) was calculated by summing the coverages of individual species. Plant litter and bare ground coverages also were recorded. 13

Crop residue type (com or soybean) was identified, and residue coverage was estimated visually (1-25, 26-50,51-75,76-100%) in mid-April in each field plot. Crop height was measured every 2 weeks from mid-June through late July once every 100 m along the length of each field plot.

To determine if differences between years in bird abundances were correlated with differences in the coverage of habitat types adjacent to the studied roadsides, the land within a O.5-mile (0.8-km) zone of each study site was cover-mapped. Agricultural Stabilization and Conservation Service (ASCS) aerial photographs in combination with ground-truthing, were used to delineate habitat types. The habitat types were rowcrop, hayfield, pasture, scrubland (hills and sparse trees, usually near a river), farmstead sparse «25% tree coverage), and farmstead moderate-to-dense (>25% trees). The average percent coverage of each habitat type near roadsides was determined for each year.

Bird Census

To estimate relative bird abundance, the length of each roadside shoulder was walked between 06:00 and 08:00, and all birds observed in roadsides or foraging in the air above roadsides were recorded. Each roadside was censused weekly from mid-May through early

August. Censuses of each roadside were alternated between 2 observers to reduce observer bias. For comparison, the fields were censused by walking the length of the field plot mid­ line, and birds observed within 50 m of either side of the line were recorded.

Statistics

The influence of vegetation type (exotic vs. native grass), treatment (burned vs. unburned), year (1990 vs. 1991), and adjacent crop type on bird abundance and species richness in roadsides was determined by using the General Linear Models (GLM) procedure. Least-squares means (LSMEANS) were generated to eliminate biases caused by differences in sample sizes. When variances within groups were unequal, the observations were weighted so that variances were proportional to the size of the mean (SAS Inst. Inc. 14

1988). Pearson's product-moment correlation coefficients were used to determine relationships between bird species richness and abundance, and vegetation characteristics in roadsides. Seasonal changes in vegetation height, bird species richness, and abundance were evaluated according to five periods (16-31 May, 1-15 June, 16-30 June, 1-15 July, and 16-31 July), and the periods were regarded as repeated measures (Cochran and Cox

1957:293). Statistical significance was set at P < 0.01 for correlational analyses to reduce possible spurious correlations given the number of comparisons made and at P < 0.05 for all other analyses. 15

RESULTS AND DISCUSSION Vegetation Characteristics--Roadside

Eighteen grass and 16 forb species were found in the 34 studied roadsides (10.2 ha)

(Table 2). Grass was the dominant plant growth form, consisting primarily of smooth brome and Kentucky bluegrass (Poa pratensis). Forbs were extremely sparse in roadsides; no species had a coverage> 1 %. Forbs are not planted in roadside seeding mixtures and do not become easily established as invaders because they are actively prevented from encroachment by spraying and mowing (Gabiou 1974, Nelson and Berner 1988). The average vegetation height from 15 May through 30 June was 51.0.:t 1.7 (SE) em, and the average vegetation density index value was 15.6.:t 0.8. Grass coverage in roadsides was similar to that in grassed waterways, another linear habitat associated with Iowa rowcrop fields (Bryan and Best 1991). Forb coverage and vegetation density and height, however, were greater in waterways than in roadsides.

Comparisons of Roadside Types, Treatments, and Years

Native-grass roadsides had less grass and greater forb coverage than did exotic-grass roadsides (Table 2). The coverage of smooth brome was greater in exotic grass roadsides, whereas the coverages of big bluestem, sedge (Carex spp.), and Canada wild rye were greater on native grass roadsides. Native tallgrass prairie is dominated by bluestem grasses

(Andropogon spp.) and has a sparse forb component (Ehrenreich 1958, Tester and Marshall

1963). The height and density of the vegetation in native grass roadsides were less than those in exotic grass roadsides (see Seasonal Changes for discussion).

Plant species composition did not differ greatly between burned and unburned roadsides.

In other studies (Tester and Marshall 1963, Collins and Barber 1985, Collins 1987), it has been reported to increase, decrease or remain the same after burning. Increased species richness after a fire has been attributed to the germination of dormant seeds in the soil

(Hassan and West 1986). Roadside soils, which are disturbed from road construction and 16

grading, may have no such viable seed bank (Gabiou 1974). There was greater forb coverage, less plant litter, and more bare ground in burned than in unburned roadsides

(Table 2). Burning tends to increase forb coverage in grasslands by eliminating accumulated litter which inhibits forb growth (VogI1974, Collins 1987). Vegetation height and density, which are typically greater after burning in native prairies (Tester and Marshall

1963, Vog11974), were less in burned than in unburned roadsides. Our results may have occurred because we measured the height and density of both alive and dead vegetation, and because we analyzed only measurements taken early in the growing season (see Methods).

Grass coverage and vegetation density and height were greater in roadsides in 1991 than in 1990 (Table 2). April rainfall, which was greater in 1991 than in 1990 (Table 1), may have increased vegetation growth in May and June of 1991. In grasslands, increased precipitation is correlated with greater plant growth (Lauenroth 1979).

Seasonal Changes

Vegetation height and density in roadsides were strongly correlated in 1990 and 1991 (r

= 0.96, n = 34, £ < 0.001); thus only height, the more commonly taken measurement, was evaluated. Similar vegetation growth patterns occurred in roadsides both years (E = 2.1 ;

4,96 df; £ = 0.08; Fig. 1). In 1990, vegetation in exotic grass roadsides was taller than that in native grass roadsides from mid-May through mid-June (1.::: 1.9, 16 df, £.::: 0.04; Fig.

1). Exotic grasses, which are cool season plants, attain their maximum height by early summer, whereas warm-season prairie grasses continue to grow until fall (Pohl 1966). The similar (£ = 0.76) vegetation growth patterns in roadsides with native and exotic grasses in

1991 may be because of the greater than normal rainfall in April of 1991 (Table 1, see also

Lauenroth 1979) or the variation in vegetation height observed within each roadside type o that year. Vegetation (alive and dead) in unburned roadsides was taller than that in burned roadsides from mid-May through mid-June in 1990 (1'::: 2.2, 16 df, £.::: 0.02) and from mid through late May in 1991 (1'::: 2.6,6 df, £.::: 0.02) (Fig. 1). Typically, plants grow more 17 Fig. 1. Mean height of (A) native vs. exotic roadside vegetation, (B) burned vs. unburned roadside vegetation, and (C) crops adjacent to roadsides in central Iowa at approximately 2- week intervals from 16 May through 31 July. 18

80 A 70 e-- / 60 / / 50 / tI 40 ... 1990 - Native • 1991 -- Exotic 30

80 B 70 -E 0 60 - / ..c // -C) 50 ~/ :r:Q) /7t'" 40 ,/./ ... 1990 - Unburned ~/' • 1991 -- Burned 30 ,y/'

200 C 1990-91 150 - Corn 100 -- Soybeans

50 - - - - 0 - May June June July July 16-31 1-15 16-30 1-15 16-31 19

rapidly after burning, which clears away plant litter and allows the sun to warm the soil

(VogI1974, Hassan and West 1986). A fire on abused soils, at the wrong season, or under

adverse weather conditions, however, can have negative effects on plant growth (Vogi

1974). Vegetation Characteristics--Field

Average soybean residue coverage was significantly less in 1990 than in 1991 (1990: X = 26%, S.B. = 4.4, 1991: X = 60, S.E. = 9.4; 1 = 3.10, 18 df, £ = 0.01). The difference in com residue coverage between years approached significance (1990: X = 33 %, S.E. = 5.7, 1991: I = 56%, S.B. = 13.1; 1 = 1.80, 18 df, £ = 0.09). The amount of residue coverage in 1990 for both crops was similar to that found by Bryan and Best (1991)

and was more typical of reduced tillage systems (Best 1986) than the residue coverage in

1991. Average soybean or com heights did not differ between years (1990: £ = 0.85,

1991: £ = 0.65), nor did the seasonal growth of either crop differ (1990: £ = 0.67, 1991:

£ = 0.37) (Fig. 1). Bird Species Composition and Abundance--Roadside and Field

Thirty-five bird species were seen in roadsides (10.2 ha), compared with 26 species in

rowcrop fields (170 ha) (Table 3). The major species seen in roadsides were the red­

winged blackbird, brown-headed cowbird, vesper sparrow, western meadowlark,

dickcissel, gray partridge, song sparrow, American robin, bam swallow, and common

grackle (see Table 3 for scientific names of bird species). The most common species in

rowcrop fields were the brown-headed cowbird, homed lark, vesper sparrow, killdeer, and

red-winged blackbird. Sixteen species were seen only in roadsides, whereas 6 species were

seen only in fields. o There was no significant difference between the mean number of bird species seen per

roadside in 1990 and in 199(£ = 0.52). In 1990, an average of 12 species was seen per

roadside (range 5-16), whereas in 1991 the average was 7 species (range 4-12). More Table 3. Mean (S.E.) bird abundance (birds/census/IOO ha) in Iowa roadsides and rowcrop fields in 1990 and 1991.

Roadsides Fields

Species 19901n = 18)a 1991 (n =16) 1990 (n = 18) 1991 (n = 16) x S.E. x S.E. x S.E. x S.E.

Red-tailed hawk 0.0 5.2 2.8 0.0 0.0 (Buteo jamaicensis) American kestrel 0.0 3.5 3.5 0.0 0.0 (Falco sparverius) Ring-necked pheasant+b 11.5 10.5 5.2 2.4 0.1 0.1 0.1 0.1 (Phasianus colchicus) Gray partridge+ 61.6 22.3 22.5 8.1 3.0 1.4 0.2 0.2 tv (Perdix perdix) 0 Lesser golden plover 0.0 0.0 0.0 3.9 3.7 (Pluvialis dominica) Killdeer 1.4 1.4 0.0 6.0 2.0 3.3 0.8 (Charadrius vociferous) Solitary sandpiper l.7 1.7 0.0 0.0 0.0 (Tringa solitaria) Upland sandpiper 3.4 3.4 0.0 1.1 0.7 0.0 (Bartramia longicauda) Semipalmated sandpiper 0.0 0.0 0.0 0.8 0.8 (Calidris pusilla) Rock dove 0.0 1.7 1.7 0.0 0.0 (Columba livia) Mourning dove 9.6 4.1 3.5 2.3 0.0 0.0 (Zenaida macroura) Chimney swift 0.0 0.0 -- 0.6 0.5 0.0 (Chaetura pelagica) Table 3. cont.

Roadsides Fields

Species 1990 (n = 18)a 1991 (n = 16) 1990 (n = 18) 1991 (n = 16) x S.E. x S.E. x S.E. x S.E.

Red-headed woodpecker 6.5 4.9 3.4 2.3 0.0 0.0 (Melanerpes erythrocephalus) Downy woodpecker 1.4 1.4 0.0 -- 0.0 0.0 (Picoides pubescens) Eastern kingbird 25.1 8.7 10.4 5.6 1.7 0.7 0.1 0.1 (Tyrannus tyrannus) -- 12.8 3.2 7.0 Homed lark 10.2 7.6 0.0 * 1.8 N (Eremophila alpestris) ...... Bam swallow 30.3 12.2 27.7 19.3 3.6 1.4 0.1 0.1 (Hirundo rustica) Cliff swallow 0.0 0.0 -- 0.1 0.1 0.0 (H. pyrrhonota,) American crow 0.0 3.5 3.5 0.0 0.0 (Corvus brachyrhynchos) House wren 0.0 -- 1.7 1.7 0.0 0.0 (Troglodytes aedon) Marsh wren 7.7 6.2 1.7 1.7 0.0 0.0 (Cistothorus palustris) Brown thrasher 16.3 5.5 * 3.4 2.4 0.0 0.0 (Toxostoma rufum) American robin 83.3 30.9 ** 13.5 4.9 2.2 0.9 0.4 0.3 (Turdus migratorius) Eastern bluebird 0.0 -- 0.0 0.3 0.3 0.0 (Siala sialis) Table 3. cont.

Roadsides Fields

Species 1990(n= 18)a 1991 (n = 16) 1990 (n = 18) 1991 (n = 16) x S.E. x S.E. x S.E. x S.E.

Loggerhead shrike 3.5 2.4 0.0 0.0 0.0 (Lanius ludovicianus) European starling 3.2 2.2 1.7 1.7 0.7 0.5 0.0 (Sturnus vulgaris) Common yellowthroat+ 7.9 4.6 ** 0.0 0.0 0.0 (Geothlypis trichas) House sparrow 18.6 9.7 38.1 28.1 0.3 0.2 0.0 (Passer domesticus) Western meadowlark+ 92.0 17.9 105.5 87.2 1.0 0.4 0.9 0.8 tv (Sturnella magna) tv Yellow-headed blackbird 0.0 0.0 -- 0.0 0.1 0.1 (Xanthocephalus xanthocephalus) Red-winged blackbird+ 688.5 138.6 841.1 197.0 4.9 1.7 2.8 0.7 (Agelaius phoeniceus) Common grackle 19.1 4.0 29.5 10.6 1.3 0.5 2.4 1.3 (Quiscalus quiscula) Brown-headed cowbird+ 463.6 73.3 ** 192.5 51.0 14.4 3.1 ** 3.4 1.0 (Molothrus ater) Indigo bunting 1.7 1.7 0.0 -- 0.0 0.0 (Passerina cyanea) American goldfinch 15.5 7.3 3.4 2.3 0.5 0.5 0.0 (Carduelis tristis) Dickcissel+ 76.5 26.9 27.7 13.9 1.5 1.1 0.5 0.3 (Spiza americana) Table 3. cont.

Roadsides Fields

Species 1990 (n = 18)a 1991 (n = 16) 1990 (n = 18) 1991 (n = 16) x S.E. x S.E. x S.E. x S.E.

Savannah sparrow 22.4 10.3 1.7 1.7 1.2 0.9 0.0 (Passerculus sandwichensis) Grasshopper sparrow 1.7 1.7 0.0 0.0 0.0 (Ammodramus savannarum) Vesper sparrow+ 218.2 23.3 **104.1 27.2 10.9 1.4 ** 3.9 0.8 N (Pooecetes gramineus) w Chipping sparrow 10.5 6.4 0.0 0.0 0.0 N (Spizella passerina) .J:>.. Song sparrow+ 43.7 22.2 31.2 9.1 0.3 0.2 0.2 0.2 (Melospiza melodia) Unknown sparrow 49.0 10.5 3.4 2.4 1.6 0.4 0.0

Total 2058.9 213.3 **1280.4 185.8 68.4 8.2 ** 30.3 6.1

aNumber of roadsides and fields sampled.

bBirds recorded nesting in roadsides.

* P ~ 0.05, ** P ~ 0.01; Student's t-test. 25

Vegetation ~ and Treatment

The relative abundance of very few bird species in roadsides di ffered as a result of vegetation type or treatment Dickcissels were more abundant in roadsides with exotic vegetation (K = 81.4 birds/census/1oo ha, S.E. = 23.3) than in those with native plants (X = 25.0, S.E. = 12.8) (t = 2.6, 26 df, £ = 0.01). Dickcissel abundance was not correlated with any individual vegetation characteristic (see below), thus possible explanations for dickcissel preference for exotic roadsides will be discussed in this section. Dickcissels are known to prefer areas with forbs for perching and as nest sites (Zimmerman 1971, Skinner et al. 1984, Kahl et al. 1985), so their abundance in exotic grass roadsides, which had lower forb coverage than native areas (Table 2), was unexpected. The exotic grass roadsides, however, did have the tallest, most dense vegetation, which is preferred by dickcissels (Harrison 1974, Zimmerman 1982) and may have influenced their abundance in exotic grass roadsides where fencelines and utility poles and wires could be used as perching sites. Brown-headed cowbirds and vesper sparrows were more abundant in burned (BHC: X = 439.2 birds/censusllOO ha, S.E. = 82.7; VS: X = 228.7, S.E. = 30.7) than in unburned roadsides (BHC: X = 222.7 birds/census/IOO ha, S.B. = 82.7; VS: R =

121.9, S.E. 30.7) (BHC: t = 2.1,22 df, £ = 0.05; VS: 1 = 2.8, £ = 0.01). Vegetation Characteristics in Roadsides

Numerous studies (e.g., Cody 1968; Wiens 1973, 1974; Balda 1975) have related the density, height, and coverage of grasses and forbs to the abundance of individual bird species in grasslands. Brown-headed cowbird, vesper sparrow, and American robin abundance was inversely related to the height and density of vegetation in roadsides (Table

4). Brown-headed cowbirds are thought to locate nests for parasitizing through active searches and watching the nesting activities of host species (Norman and Robertson 1975,

Thompson and Gottfried 1981). Thus cowbirds may have been attracted to roadsides with scant vegetation because host nests were most easily detected in those areas. Vesper 26

Table 4. Significant (P ~ 0.01) relationships between bird numbers (birds/censuS/IOO ha) and vegetation characteristics in roadsides in central Iowa in 1990-1991 (n = 34).

Structure Coverage

Height Density Grass Forb Bare

Brown-headed cowbird -0.41a

Vesper sparrow -0.62 -0.59 0.48

American robin -0.55 -0.50 -0.42 0.51

Homed lark 0.72

Number of species -0.54 -0.48

aValues presented are Pearson's product-moment correlation coefficients. 27

sparrows are known to prefer habitats with short grass and bare ground (e.g., Best and

Rodenhouse 1984, Reed 1986). Given the vegetative characteristics selected by these two species, their greater abundance in burned roadsides (see earlier discussion) is not surprising. American robins prefer short, sparse vegetation for foraging (Eiserer 1980).

The greater abundance of cowbirds, vesper sparrows, and robins in roadsides in 1990 than in 1991 (Table 3) may be due to the lower density of vegetation in roadsides in 1990 (Table

1). Horned larks, which are attracted to areas with sparse vegetation (e.g., Wiens 1973,

Kahl et al. 1985), were more abundant in roadsides with greater forb coverage. Forb coverage was negatively correlated with vegetation height (r = -0.37,!l = 34, £ = 0.03) and positively correlated with the coverage of bare ground (r = 0.41, £ = 0.02); thus horned larks choosing areas with more forbs also were using areas with sparser vegetation.

The number of species seen in a roadside was inversely related to grass coverage (Table

4). Other studies have reported that grasslands with short, scattered plant growth support more (Owens and Myres 1973) or fewer (Kantrud 1981, Renken and Dinsmore 1987) bird species than do densely vegetated areas. Wiens (1969) reported that the number of bird species did not differ between the two habitat types.

Coverage of Habitats Adjacent to Roadsides

Rowcrop fields made up at least 92 % of the land surrounding each studied roadside; no other habitat type had a coverage>2.0%. The coverage of moderate-to-densely wooded farmsteads near roadsides was greater in 1990 (R = 2.0%, S.E. = 0.2) than in 1991 (X =

0.5%, S.B. = 0.1) (t = 3.8, 32 df, £ < 0.001). No other habitat differed in abundance between years. Of the bird species whose abundances differed between 1990 and 1991

(Table 3), none were correlated with the coverage of nearby farmsteads. Thus the relatively

minor differences between years in the habitats adjacent to roadsides evidently did not

influence bird abundance in roadsides. 28

Seasonal Changes of Bird Species Abundance in Roadsides

The number of species seen and the abundance of some individual species probably were influenced by factors such as vegetation height that changed over time. Data from 1990 and

1991 were combined to evaluate seasonal changes in bird abundance in roadsides because vegetation growth was similar both years (see earlier discussion).

The number of dickcissels in roadsides increased throughout most of the summer

(E = 5.8; 4,96 df; £ ~ 0.001; Fig. 2). The greatest increase in dickcissel abundance in roadsides occurred during June. Almost 50% of the first alfalfa crop had been harvested by

15 June both years (Iowa Crop and Livestock Rep. Servo 1990, 1991), and dickcissels were thus forced out of a preferred nesting habitat in Iowa (Frawley and Best 1991, IgI

1991). At the same time, the tall vegetation in roadsides (Fig. 1) created a habitat attractive to dickcissels (e.g., Zimmerman 1982, Skinner et al. 1984). Dickcissels that have nested successfully begin flocking in mid-July in Iowa (IgI, pers. commun.); this behavior may explain the decrease in their abundance in roadsides during the last half of July.

Common grackle abundance reached a peak in mid-June before declining during July

(E = 2.9; 4,96 df; £ = 0.03; Fig. 2). Common grackles nest from mid-May through early June in the Midwest (Maxwell and Putnam 1972, Howe 1976) and form large roosting flocks in mid-summer (Caccamise et al. 1983). Thus the peak in grackle abundance in roadsides in June may have resulted from local fledging and flocking activities. Post fledging dispersal and the declining size of roosting flocks during late summer (Caccamise et al. 1983) may account for the July decrease in grackle abundance in roadsides. Laubach

(1984), who documented seasonal patterns similar to ours, observed common grackles only from April through June in an Iowa prairie. 29 Fig. 2. Mean abundance (birds observed/censuS/lOO ha) of birds in 34 roadsides in central

Iowa at approximately 2-week intervals from 16 May through 31 July. 30

140

120 Dickcissel / "- Q) / , ..... (,) 100 Common Grackle / " c: /' «S , '"C / ' c: 80 / ::l ..c /'

MANAGEMENT IMPLICATIONS

Most gravel roadsides in Iowa, like those we studied, contain little or no native prairie vegetation. At present, therefore, the impact of well-established native vegetation on bird use of gravel roadsides cannot be assessed. Roadsides adjacent to gravel roads in Iowa are periodically dredged and reseeded to eliminate built-up sediment from wind and water erosion. Efforts are underway to seed native prairie species in recently dredged gravel

roadsides, but it may not be economically practical, or even possible, to establish pure

prairie stands in roadsides subject to frequent dredging and other disturbances. To reduce

the need for frequent dredging, some roadside managers encourage landowners to plant

permanent field bortders and practice conservation tillage techniques. We observed many

bird species using smooth brome roadsides. Smooth brome thrives in the harsh roadside

environment (Wasser and Dittberner 1986), and it may be the best vegetation type for gravel

roadsides.

Mowing smooth brome, preferably in mid-to-Iate August to minimize any negative

impacts on avian use of an area (Bryan and Best 1991), has been recommended to maintain

healthy vegetation (Wasser and Dittberner 1986). The contour of most gravel roadsides in

Iowa, however, is too steep to permit mowing except on the road shoulder. Prescribed

burns, done every 3-5 years in the spring before the seeds come out of dormancy or adult

vegetation emerges, are also beneficial to grasses (Vogi 1974) and may be used in place of

mowing in such areas. Because changes in the species composition and vigor of vegetation

as a result of fire occur slowly (Vogl 1974), we were unable to evaluate the long-term

effects of fire on roadside vegetation. Fire can be detrimental in roadsides where the

vegetation is not well established (VogI1974), however, and should be used with caution.

Many farmers are removing fencelines from gravel roadsides, and they should be

encouraged to retain them. Roadsides with fences are less susceptible to agricultural

encroachment (i.e. cultivation and herbicide spraying) and, therefore, are wider than those 32

without fences, creating more wildlife habitat. Furthermore, fencelines are used by birds for perching and singing in roadsides where few forbs are available to support these activities.

Some bird species that typically use grassland habitats (i.e., bobolink [Dolichonyx oryzivorus], grasshopper sparrow [Ammodramus savannarum], savannah sparrow

[Passerculus sandwichensis], and upland sandpiper [Bartramia longicauda]) were conspicuously absent from the studied roadsides. These species may have minimum area requirements (see Samson 1980) and therefore are not attracted to linear roadside habitats. The studied roadsides were chosen, in part, for their isolation from blocks of grassland bird habitat.

Roadsides that contain vegetation preferred by grassland birds, adjacent to similarly vegetated blocks of grassland habitat (i.e., Conservation Reserve Program fields) may, however, attract nesting birds. Such roadsides also may serve as corridors between blocks of grassland habitat for non-migratory birds such as pheasant and partridge.

o 33

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PAPER II. NEST DENSITY AND FATE OF BIRDS IN ROADSIDES ADJACENT TO IOWA ROWCROP FIELDS 41

ABSTRACT

One hundred and twenty nests of 8 species were found in 34 roadsides (10.2 ha), with a total nest density of 1,147 nests/100 ha. The Mayfield method was used to determine nest success for the red-winged blackbird (26%) and the vesper sparrow (Pooecetes gramineus)

(5.5%). Predation was responsible for 76% of all red-winged blackbird nest failures; 46% of all redwing nests were parasitized by the brown-headed cowbird (Molothrus ater). Red­

winged blackbird nest density and success were greatest in areas with tall, dense vegetation;

whereas vesper sparrow nests were most dense in areas of sparse vegetation. Gray

partridge and ring-necked pheasant (Phasianus colchicus) nest densities were greatest in

roadsides with the most residue coverage. Partridge nests were placed at sites with sparse

vegetation, whereas pheasants preferred to nest at sites with few forbs. Red-winged

blackbirds most often placed their nests in the bottom and at the fence of a roadside; all

vesper sparrows nested in the short vegetation of the foreslope. Neither partridge nor

pheasants nested preferentially in any roadside position. The placement of a red-winged

blackbird nest at a roadside position did not influence nest success, although predation was

greatest on red-winged blackbird nests placed in the bottom and the fence. Blackbird nests

placed in forbs, shrubs, and the fence were more successful than those built in grasses other

than reed canary grass. Seeding mixes of smooth brome (Bromus inermis) and alfalfa

(Medicago sativa), and native grasses and forbs in roadsides may increase the attractiveness

of these areas to birds that use such substrates for nesting. Fences are used by many birds

in place of vegetation for nesting and should be retained in roadsides. Prescribed burns

would increase the vigor and structural heterogeneity of roadside vegetation; mowing

roadsides should be discouraged except at the roadside shoulder. 42

INTRODUCTION

Before agriculture dominated the Midwest plains, tallgrass prairie characterized the landscape (Dick-Peddie 1953, Smith 1981). Throughout the 1800's this grassland was brought under cultivation (Nat!. Res. Counci11970), and since the 1930's, large rowcrop farms (com and soybean monocultures) have replaced the early, small farms that produced a variety of crops (Mohlis 1974, Vance 1976, Taylor et al. 1978).

Several grassland bird species nested both in the original prairie and, later, in the fields and field borders of the small farms (Dambach and Good 1940, Wiens and Dyer 1975), but nesting habitat for many avian species has been lost as pastures, and hay and oat fields have been eliminated. High densities of nesting birds have been documented in some of the remaining habitats such as fencerows, grassed waterways, and roadsides (Snow and

Mayer-Gross 1967, Basore et al. 1986, Warner et al. 1987, Bryan 1990). High nest

density, however, is not necessarily synonymous with high reproductive output (e.g.,

Gates and Gysel 1978). In agricultural areas, disturbance from farming practices often

decreases nesting success dramatically (Rodenhouse and Best 1983, Warner et al. 1987,

Frawley 1989, Bryan 1990). In the linear habitats available to nesting birds in agricultural areas, high predation rates also may reduce nesting success (e.g., Shalaway 1985, Basore et

al. 1986, Bryan 1990) because predators are thought to actively search these areas or to use

them as travel lanes (Davison 1941, Fritzell 1978).

Roadsides adjacent to gravel roads are common in many rowcrop systems (see paper I),

and most are not mowed because their side slopes are too steep. In addition, many Iowa

counties are attempting to make roadsides more attractive to wildlife (Alt. Roadside Steer.

Comm. 1989) by planting native grasses and forbs, and maintaining their vigor through

prescribed bums (Vogl 1974). Thus, roadsides may provide valuable, relatively

undisturbed habitat for nesting birds in predominantly rowcrop environments. Most studies

of roadside nesting have dealt mainly with the ring-necked pheasant (Phasianus co1chicus) 43

and gray partridge (Perdix perdix) (Warner et al. 1987, Nelson et al. 1990, Carroll and

Crawford 1991), although Warner (1992) recently documented roadside nesting by passerines in Illinois. In Iowa, the importance of roadsides to nesting passerines and game birds had not been studied. The objectives of our study, therefore, were to 1) document the bird species nesting in roadsides and their nest densities, 2) determine nesting success and causes of nest failure, and 3) assess the influence of different vegetation and structural characteristics in roadsides and at nest sites on nest density and success.

o 44

STUDY SITES

Eighteen roadsides in Story and Boone counties in 1990, and 16 roadsides in Hardin

County in 1991, were chosen for study. All 3 counties are typical of the central Iowa cash­ grain region where intensive rowcrop farming makes suitable wildlife habitat scarce

(U.S.Dep.Agric. 1990). The topography of these counties is nearly flat to gently rolling

(DeWitt 1984, Yoy 1986). The average daily maximum temperature from April through

August is 29 C, and the mean midday relative humidity is 60%. Normal annual rainfall is about 85 cm, with about 62 cm falling from April through September (DeWitt 1984, Voy

1986).

All studied roadsides were associated with gravel roads and were adjacent to cornfields or soybean fields. Roadsides near other habitats were excluded to avoid confounding effects. Roadside plots were 500 m long, about 6 m wide (the width of the roadside), and about 0.8 m deep at the center (Fig. 1). The total area covered by the 34 roadsides was 10.2 ha. All roadside plots had a fence, like many roadsides in Iowa. In a few instances, the shoulder of the roadside had been mowed, but no roadsides were entirely mowed.

Roadsides with woody plants were avoided because most roadsides are sprayed, mowed, or burned to eliminate woody vegetation (Wasser and Dittberner 1986). Furthermore, the presence of woody vegetation significantly increases the diversity of nesting birds in farmland habitats (Shalaway 1985). Half of the roadsides contained the cool-season grass smooth brome (Bromus inermis) and half contained warm-season, native prairie vegetation; half of the roadsides of each vegetation type were burned each spring (see paper I for details). 45

METHODS

Roadside Vegetation Measurements

The height, density, and composition of the vegetation were measured at one randomly

chosen sample site along each 100 m of a roadside. At each site, measurements were taken

in the foreslope (nearest the road), bottom, backslope, and fence of the roadside. Height

and density were measured every 2 weeks; composition was measured monthly. All

measurements were taken between mid-May and late July.

Vegetation density was measured with a 1.5-m tall and 2.5-cm diameter pole graduated at

10-cm intervals. At each sampling point, the pole was viewed from the 4 cardinal directions

at a height of 1 m and a distance of 1.5 m. The proportion of each interval obscured by

vegetation was categorized as 0-20,21-40,41-60,61-80, or 81-100% and was recorded as

1 - 5, respectively. A density index was calculated by averaging the measurements from the

4 directions at each interval and then summing over all intervals (Basore et al. 1986). The

height of the highest pole interval touched by vegetation (alive or dead) was taken to

represent vegetation height The composition of the vegetation in roadsides was determined

by estimating percent canopy coverage of plant species within a 0.1 m2 circular quadrat.

Individual plant species coverages were estimated on an overlapping basis; thus, the sum of

the coverages could exceed 100% (Daubenmire 1959). The coverage of herbaceous growth

forms (i.e., grasses and forbs) was calculated by summing the coverages of individual

species. Plant litter and bare ground coverages also were estimated.

Nest Site and Nest Vicinity Measurements

Nest height and nest placement within a roadside (foreslope, bottom, backslope, fence)

were recorded for all nests. The height, density, and composition of the vegetation were o measuredboth at the nest and, to characterize the nest vicinity, 1 m from the nest in the 4

cardinal directions. Vegetation measurements were taken at passerine nests when a nest was

found if it contained at least I egg or had already been preyed upon or abandoned. To 46

reduce abandonment, passerine nests found before egg laying were monitored until at least 1 egg had been laid, then measurements were taken. Ring-necked pheasant and gray partridge nests were not measured during incubation unless the hen was away from the nest. Nest Searching and Monitoring

Nest searches were made by 2 observers, once a week, in all roadsides from mid-May through early August 1990-1991. Observers walked abreast 1 m apart along the length of a roadside, parting the vegetation with a stick as they progressed, similar to the technique used by Joselyn et al. (1968). Repeated passes were made over the length ofthe roadside plot until the entire area had been traversed Once found, nests with at least 1 egg were marked by placing numbered flagging on the fence at least 5 m from the nest to reduce predation (Picozzi 1975, Ramas 1984).

Passerine nests were checked every 2-4 days until either the young fledged or the nest failed To minimize desertion, ring-necked pheasant and gray partridge nests were observed from a distance without flushing the hen. A nest was considered successful if it fledged at least 1 host young. Nests were considered lost to predators if the nest contents (eggs or young) had been removed from the nest; the type of predator was identified when possible by assessing the nest contents and condition of the nest and nest vicinity (Rearden 1951,

Best and Stauffer 1980). Nest failure was attributed to weather when nests were found empty or destroyed after a storm. Failures were attributed to parasitism by the brown­

headed cowbird (Molothrus ater) when the nest fledged only cowbird young or was abandoned after cowbird eggs were deposited in it. Nests deserted by the adults, but whose contents remained unchanged from the previous visit, were considered to be abandoned due

to unknown causes. Losses also were attributed to mowing and to vegetation that tipped as a result of growth or the weight ofthe nest. Finally, nest failure was attributed to

researchers when on 1 visit we flushed a female or damaged a nest, and on the next visit the

nest was deserted. 47

Nest Fate Calculations

Of the 120 nests located, 98 were used in analyzing nest fates because they were active

(i.e., contained at least 1 host egg or young and attended by an adult bird) when found and were not destroyed by an observer. The remaining 22 nests were used only in nest density and nest site selection analyses; 5 were destroyed by observers, and 17 were inactive when found.

Although 8 active gray partridge nests were found, 5 nests also were found after having been preyed upon, and 3 were found after abandonment, none of which could be included in calculations of nest success. Using only the active nests would not, therefore, give an accurate estimate of nest success; thus, nest success was not calculated for the partridge.

Nest success was calculated for the red-winged blackbird and vesper sparrow, species with n ~ 5 active nests, by using the Mayfield method (Mayfield 1975, Johnson 1979) and

MICROMORT (Heisey and Fuller 1985). (See Table 1 for scientific names of bird species.) These methods were used to determine daily survival rates and, for the redwing, mortality rates for specific causes of nest failure. The vesper sparrow sample size was too small for mortality rate calculations. The percentage of successful nests and of nests that failed as a result of each cause of mortality were computed from the daily rates. Intervals of

3, 11, and 11 days were used for the red-winged blackbird egg-laying, incubation, and nestling periods (Case and Hewitt 1963, Robertson 1972, Dolbeer 1976, Besser et al.

1987). If nestlings were observed in the nest at 7-8 days of age and were missing at the

next visit, they were considered to have fledged successfully if no evidence of mortality was

noted (Dolbeer 1976, Besser et aI. 1987). Too few vesper sparrow nests were found to

estimate interval survival rates; 24 days was used to estimate survival rates for the entire

nesting cycle (Rodenhouse and Best 1983). 48

Statistical Analysis

Roadside vegetation types and treatments were combined during analysis to increase the sample size, although plant species composition and burning influenced the vegetation structure, which, in tum, influenced nest density and success. Nest densities of only 3 species were significantly different (gray partridge 1990: X = 314 nestsll 00 ha, SE = 434,

1991: X= 62, SE = 134, £ = 0.03; ring-necked pheasant: 1990: K = 130 nests/100 ha, SE = 232, 1991: K= 0; £ = 0.03) or nearly significantly different (dickcissel: 1990: R= 56 nests/loo ha, SE = 128, 1991: K = 0; £ = 0.09) between the 2 years of the study. Total nest densities and nesting outcomes for each species did not differ between years.

Consequently, nest data from the 2 years also were combined for analysis.

Only the red-winged blackbird, gray partridge, ring-necked pheasant, and vesper sparrow (species with n ~ 5 nests) were used to determine the effects of roadside characteristics on nest densities and to compare nest site characteristics with roadside characteristics. Differences in the number of nests found between years and among positions (foreslope, bottom, backslope, fence) on roadsides were determined for each species by using the General Linear Models (GLM) procedure (SAS Inst. Inc. 1988). All

34 roadsides were combined in the comparisons among roadside positions. The roadside positions were considered linear habitats, and the differences in their area were deemed secondary to other char~cteristics (e.g., slope, proximity to the road or crop field) in attracting nesting birds. Therefore, the numbers of nests at each position, rather than nest

densities, were compared. Pearson's product-moment correlation coefficients were used to

determine relationships between nest densities and vegetation characteristics in all 34 roadsides. Mean nest site values for vegetation height, density, and composition values

were computed for each roadside where nests occurred and then were compared to the

roadside vegetation characteristics by using paired t-tests. The frequency with which red­

winged blackbird nests were placed in various growth forms was compared with the 49

frequency of occurrence of those growth fonns in the roadside sampling quadrats. This was done by Chi-squared tests with roadsides as experimental units.

Daily survival and predation rates were analyzed relative to roadside positions and vegetation characteristics, and nest site vegetation characteristics for the red-winged blackbird, the only species with n > 20 nests (Hensler and Nichols 1981). Nest fate was analyzed relative to the height, density, and composition of roadside and nest site vegetation by ranking roadsides and nest sites on the basis of the values of each vegetation characteristic considered. Two groups of roadsides and nest sites were formed for each characteristic (one with low values, one with high values), with approximately equal numbers of nests in each group, where possible. Daily survival and predation rates were then calculated for each group. Statistical comparisons of daily rates between our study and other studies, and among roadside characteristics within our study, were made by using 2- tailed Z-tests. 50

RESULTS AND DISCUSSION

Vegetation Characteristics

Eighteen grass and 16 forb species were found studied roadsides (see paper I for details). Grass was the dominant plant growth form, consisting primarily of smooth brome and Kentucky bluegrass (Poa pratensis). Forbs were extremely sparse in roadsides; no species had a coverage greater than 1 %. Forbs are not planted in roadside seeding mixtures and do not become established as invaders because of active management to prevent their encroachment (Gabiou 1974, Nelson and Berner 1988). The average vegetation height from 15 May through 31 July was 57.7 ± 1.0 (SE) cm, and the average vegetation density was 18.4 ± 0.5. Species composition and grass coverage in roadsides were similar to those in Iowa grassed waterways, another linear habitat associated with rowcrop fields (Bryan and Best 1991). Forb coverage and vegetation density and height, however, were greater in waterways than in roadsides.

Grass coverage and vegetation density and height were greater in roadsides in 1991 than in 1990 (see paper I for details). April rainfall was greater in 1991 than in 1990, which may have increased vegetation growth in May and June of 1991. In grasslands, increased annual precipitation is correlated with greater plant growth (Lauenroth 1979).

Composition and Density of Nesting Species

One hundred and twenty nests of 8 species were found in the 34 roadsides (10.2 ha), resulting in a computed total nest density for all species combined of 1,147 nests/1 00 ha

(Table 1). This estimate is similar to the 1,104 nests/l00 ha of 10 species reported in Iowa grassed waterways by Bryan (1990), although gray partridge did not nest in waterways, and dickcissel nest densities were much greater in waterways than in roadsides. The total nest density we documented greatly exceeds the 328 nests/1 00 ha observed in rural 111 inois roadsides (Warner 1992) and the 383 nests/1oo ha found by Basore et a1. (1986) for 14 species using strip cover in agricultural areas. The difference may come, in part, from the 51 Table 1. Densities (nestS/l00 ha) and fates (n)a of nests found in 34 roadsides (10.2 ha) in central Iowa from 15 May through 4 August 1990-1991.

Cause of nest failure

Nest Active Tipped Cowbird Species densities nests (n) Successful Predation Abandoned Mowing Weather vegetation b parasitismc

Ring-necked pheasant 69 2 1 0 0 0 1 0 0 (Phasiaous colchicus) Gray partridge 196 8 5 1 1 1 0 0 0 (Perdix~) Common yellowthroat 10 1 0 0 0 0 0 0 1 (Geothlypis trichas) Western meadowlark 29 3 0 3 0 0 0 0 0 (Stumella mat:na) Red-winged blackbird 745 73 20 40 3 1 4 2 3 (At:elaius phoeniceus) Dickcissel 29 3 0 3 0 0 0 0 0 (.sIDzaamericana) Vesper sparrow 69 6 1 3 1 0 0 0 1 (Pooecetes gramineus) Song sparrow 29 2 0 1 0 0 1 0 0 (Melospiza melodia) Total 1147 98 27 51 5 2 6 2 5

aIncludes only nests that were active when found, whose cause and timing of failure could be determined, and that were not destroyed by the observer. blncludes vegetation that tipped during growth, or as a result of the weight of the nest. CJncludes only those nests that failed because of cowbird parasitism (i.e., removal of all host eggs, induced desertion, or starvation of host young). VI N 53

intensive nest searching technique used in our study and by Bryan (1990). Nest densities found in roadsides a1so were much greater than those reported for no-till and tilled crop fields (Basore et al. 1986), and grazed and ungrazed pastures (Skinner 1974, George et al.

1979). Influence of Roadside and Nest Site Characteristics on Nest Placement

Red-winged blackbird

In roadsides, red-winged blackbird nest densities were positively correlated (r = 0.56, n

= 34, £ > 0.001) with the coverage of reed canary grass (Phlaris arundinace) and with vegetation height (r = 0.47, £ = 0.005) and density (r = 0.37, £ = 0.03). In addition, redwing nest sites had taller, more dense vegetation and fewer forbs than the roadside overall (Tables 2, 3). Although they are habitat genera1ists, redwings require tall, dense vegetation for nest support and concealment (Harrison 1974, Albers 1978, Buhnerkempe

1979).

The overall average nest height CK = 0.58, SE = 0.06 m) was within the range (0.2 - 1.4 m) reported in other studies of upland nesting blackbirds (Holcomb and Twiest 1968,

Krapu 1978, Ducey and Miller 1980). A large proportion (25 out of 76) of red-winged blackbird nests were placed in fence wires. The remaining nests were placed in both live and dead vegetation: 16 were in reed canary grass, 14 in field horsetail (Equisetum arvense), 10 in all species of forbs, 7 in grass species other than reed canary grass, and 4 in shrubs. The nesting frequency in fences could not be tested, but reed canary grass and shrubs were used in proportion (X2 ~ 0.4, 1 df,£ ~ 0.50) to their abundance in roadside quadrats. Horsetail (X2 = 6.9, £ = 0.01), all species of forbs (X2 = 5.3, £ = 0.02), and grasses other than reed canary grass (X2 = 5.3, £ = 0.02) were used less often than would be expected, based on their frequency of occurrence in roadsides. If a greater abundance of tall, strong forbs had been available in roadsides, red-winged blackbirds would probably have chosen to nest in them; redwing nest densities usual1y are greatest in areas with high 54

forb coverage (Buhnerkempe 1979, George et al. 1979, Bryan 1990). Ducey and Miller

(1980) reported that 83 % of all redwing nests in roadsides were placed in forbs, compared with only 6% in fences.

The bottom of the roadside was the widest, most flat position, whereas the foreslope was the same width as the backslope but had a steeper contour (Fig. 1.). The fence was the most narrow position, and the ground surface at the fence was lower than that of the foreslope. More red-winged blackbird nests were found in the bottom and the fence than in the foreslope of roadsides (Fig. I.;!.?: 1.98, 3 df, £ ~ 0.05). Many roadside bottoms were fIlled with water much of the summer both years and contained emergent stands of tall vegetation, which simulated the marsh habitats preferred by redwings. Fence wires also were used by redwings for nest support.

Vesper sparrow

Vesper sparrow nest densities in roadsides were positively correlated with the amount of bare ground (r = 0.59, £ < 0.(01) and negatively correlated with vegetation density (r =

-0.36, £ = 0.04) and height (r = -0.37, £ = 0.03). Vesper sparrows are known to nest in xeric, sparsely vegetated areas (Harrison 1974, Best and Rodenhouse 1984, Reed 1986).

Vesper sparrows placed their nests in areas with shorter, more sparse vegetation than what occurred in the roadside as a whole (Tables 2,3) although the immediate nest site contained less bare ground than the nest vicinity (1 m from the nest). Vesper sparrows are known to conceal their nests in or near clumps of vegetation (Rodenhouse and Best 1983). All vesper sparrow nests were on the foreslope (Fig. 1.) where, as a result of mowing and the presence of gravel from the road, the vegetation was most sparse.

Gray partridge and ring-necked pheasant

Gray partridge (r = 0.61, £ < 0.001) and ring-necked pheasant (r = 0.60, £ < 0.00 1) nest densities in roadsides were positively correlated with plant residue coverage. Gray partridge nest densities also were positively correlated (r = 0.40, £ = 0.02) with Kentucky 55

Table 2. Mean (S.E.) vegetation structure and percent coverage values at nest sitesa and in nest vicinitiesb for bird species with n > 5 nests in roadsides in Iowa, 1990-1991.

Density (index value) Height (cm) Grass Forb Bare ground

Nest Vicinity Nest Vicinity Nest Vicinity Nest Vicinity Nest Vicinity

Species X SE x SE x SE X SE x SE x SE x SE x SE x SE x SE

Gray partridge (ll)C 14.4 1.8 14.7 1.2 49.7 4.0 54.1 4.2 76.5 8.4 82.5 5.2 1.8 1.8 2.1 1.0 8.6 6.5 4.4 2.7

Ring-necked pheasant (4) 19.9 2.0 31.0 15.8 58.5 8.7 54.4 7.2 63.8 21.9 34.8 20.8 2.5 2.5 1.3 1.3 0.0 0.0 3.1 3.1

Red-winged blackbird (15) 32.1 2.2 27.2 2.1 92.0 6.5 80.6 7.1 81.7 6.5 83.0 5.7 22.8 7.6 5.6 2.7 0.6 0.5 4.1 1.3

Vesper sparrow (6) 4.1 1.7 5.1 1.3 32.5 5.7 20.7 3.8 52.1 11.4 40.0 7.9 13.3 13.3 3.2 3.2 31.2 7.8 55.0 83.0

aMeasured in a 0.1-m2 quadrat centered at the nest.

bMeasured in 0.1-m2 quadrats, poisitioned 1 m from the nest in the 4 cardinal directions.

cMeans were calculated for each species for each roadside where nests were present, and the values were then used to derive an overall mean.

The numbers in parentheses represent the number of roadsides used to calculate the tabled values. Table 3. Paired t-test comparisons of vegetation characteristics at nest sitesa (N), nest vicinitiesb (V), and within the roadside overall (R). Only significantly different comparsions are shown.c

Percent coverage

Density Height Grass Forb Bare

Ring-necked pheasant (4)d R> V**

Gray partridge (11) R> V**

Red-winged blackbird (15) N> R*** N> R*** N> R** R> N***

V> R** V>R** N> V** R>V* VI 0'1 N> V*** N> V*** V> N**

Vesper sparrow (6) R> N*** R>N**

R> V*** R> V*** R> V*** V> R** V>N**

aMeasured in a 0.1 m2 quadrat centered at the nest. bMeasured in 0.1 m2 quadrats positioned 1 m from the nest in the 4 cardinal directions. cNumber of roadsides used in the paired t-test comparisons. * £ = 0.05, **£ = 0.01, *** £ 2: 0.001. 57 Fig. 1. Mean roadside (n = 34) contour and total number of nests of 4 species in each roadside position in central Iowa, 1990-1991. 58

~------6 m ------i.~ .83 ,• m Roadside Profile

Foreslope Bottom Backslope Fence

5 ~------~ Ring-necked Pheasant

5

o L...-Z.oI~ 30 t5 25 Q) Z '020 en ~ Q) .0 15 E :::::J Z 10

5

o

5 Vesper Sparrow

o Foreslope Bottom Backslope Fence 59

bluegrass coverage and negatively correlated (r = -0.37, £ = 0.03) with the amount of bare ground. Other studies (Linder et al. 1960, George et al. 1979, Carroll 1987, Carroll and

Crawford 1991) have reported high nest densities of both pheasant and partridge associated with greater residue coverage and less bare ground. Gray partridge nests were placed in areas where the vegetation was less dense, and ring-necked pheasant nests were placed in areas with less forb coverage, than the roadside overall. McCrow (1982) also reported that partridge selectively nested in sites with sparser vegetation than in the rest of the roadside.

Pheasants prefer to nest in sites with greater grass coverage over areas with an abundance of forbs (Warner et al. 1987). As reported by others (Warner et al. 1987, Carroll and

Crawford 1991), neither ring-necked pheasants nor gray partridge exhibited preferences for nesting in a particular roadside position (Fig. 1.; 1 ~ 1.2, 3 df, £ ~ 0.19). Nesting Success

As a result of the low daily nest survival rate (DSR) (0.8864 ± 0.0477 [SED, vesper sparrow nest success was only 5.5%. This was similar to the DSR (0.8611 ± 0.0574, !l = 5), and nest success (2.8%) of vesper sparrows in grassed waterways (Bryan 1990), although these estimates may be unreliable because of the small sample sizes in both studies.

No differences were found in red-wing blackbird DSR among the egg-laying (0.9489 ±

0.0222), incubation (0.9541 ± 0.0086), and nestling periods (0.9333 ± 0.0141). Thus, the

DSR during the entire nesting cycle (0.9471 ± 0.0071) was used in computing redwing nest success in roadsides (26%). The DSR of this species in roadsides was not significantly different (Z = 1.54, £ = 0.12) from that in grassed waterways (0.9019 ± 0.0283) (Bryan

1990), but nest success in waterways was only 8.4%. The apparent nest success of redwings has ranged from 13 to 46% (Best and Stauffer 1980, Ducey and Miller 1980,

Basore et al. 1986) in other linear upland habitats, and from 4 to 35% in block upland habitats (Case and Hewitt 1963, Robertson 1972, Blakely 1976, Dolbeer 1976, Krapu

1978, Besser et a1. 1987). 60

Causes of Nest Failure

The major cause of nest loss was predation (Table 1), which accounted for 76% of all red-winged blackbird nest failures (calculated by using MICROMORT). Ninety percent of the predation on redwing nests was attributed to birds or snakes; the remaining 10% was attributed to mammalian predation. Predation was responsible for 72 % of the nest failures of all species combined. Others (Best and Stauffer 1980, ShaIaway 1985) have reported

similar rates of predation in linear habitats in midwestern farmlands. Lower predation rates

(45 - 57%) have been reported, however, in some linear habitats associated with

midwestern crop fields (Basore et al. 1986, Warner et al. 1987, Bryan 1990) and these are

similar to the predation rates found in block grassland habitats (Wray et al. 1982, Basore et al. 1986, Frawley 1989).

Other causes of nest failure, calculated for the red-winged blackbird by using

MICROMORT were weather, brown-headed cowbird parasitism, vegetation tipping,

abandonment, and mowing, which accounted for 7,6,3,2, and 2% of all nest losses,

respectively. Cowbird parasitism did not always cause nest failure. Forty-six percent of all

redwing nests were parasitized; 17% of the parasitized nests were successful. Fifty percent

of the nests of all species combined were parasitized; 14 % of these were successful.

Although Johnson and Temple (1990) reported lower incidence of parasitism in grassland

habitat away from wooded edges, rates similar to those in our study have been observed in

other block grassland habitats (Elliot 1978, Krapu 1978, Blankespoor et al. 1982),

roadsides (Hergenrader 1962, Linz 1982), and grassed waterways (Bryan 1990). Others

(Shalaway 1985, Wray et al. 1982) have reported no cowbird parasitism in linear and block

grassland habitats.

Roadside and Nest Site Characteristics Influencin~ Redwin~ Nest Fate

Red-winged blackbird DSR were highest in roadsides with the greatest grass coverage (Z

= 2.26, £ = 0.02) and vegetation height (Z = 2.05, £ = 0.04) and were nearly significantly 61

higher where roadside vegetation was most dense (2 = 1.77, £ = 0.08). Daily nest

predation rates were greatest in roadsides with lowest grass coverage (2 = 2.18, £ = 0.03) and vegetation density (2 = 2.16, £ = 0.03), and were nearly significantly greater where roadside vegetation was shortest (Z = 1.71, £ = 0.09). Others (Johnson and Temple 1990, Mankin and Warner 1992) have reported that tall, dense vegetation in grassland habitats may

restrict the activity of nest predators and conceal nests better than sparse vegetation,

resulting in greater nest success.

There were no differences in redwing DSR among roadside positions. Daily nest predation rates in both the bottom (0.0373 ± 0.0004 (SE], Z = 2.12, £ = 0.03) and along

the fence (0.0594 ± 0.0291, Z = 3.05, £ = 0.002) were greater than in the foreslope (0.0093 ± 0.0092); predation rates in the backslope (0.0319 ± 0.0128) were not different than in the other positions. The soil surfaces in both the bottom and fence are relatively flat

(Fig. 1.) and may be easier for mammals and snakes to traverse than the sloped banks of the

foreslope. Predators also may avoid foreslopes because of disturbance from vehicular

traffic.

Red-winged blackbird DSR were greatest (Z = 2.18, £ = 0.03) at nest sites with the

most forb coverage. In addition, the DSR of nests placed in forbs (Z = 1.92, £ = 0.05) and

shrubs (Z = 1.99, £ = 0.05) were greater than those of nests built in grasses other than reed

canary grass. Predation rates were lowest (Z = 2.27, £ = 0.02) at nest sites with the most

forb coverage and predation rates on nests placed in forbs were less than on nests placed in

grasses other than reed canary grass (Z = 3.79, £:$; 0.001). Predation rates on nests in reed

canary grass were less than on nests in fences (2 = 1.90, £ = 0.05). Predation rates on

nests placed in shrubs were less than on nests in all other nest substrates (2 ~ 2.13, £ :$;

0.03). Other studies (Robertson 1972, Krapu 1978, Besser et al. 1987) have reported the

greatest success rates for red-winged blackbirds nesting in thick stands of tall. strong 62

vegetation. As documented elsewhere (Francis 1973, Krapu 1978), nest height was not related to nesting success in roadsides. 63

MANAGEMENT ThfPLICATIONS

The density of bird nests in roadsides is greater than that in cropfields (Basore et al. 1986,

Frawley 1989). In addition, nests in cropfields often are destroyed by mowing, cultivation, or other farming activities (Rodenhouse and Best 1983, Frawley 1989) whereas roadsides are relatively undisturbed by farming practices. Thus, birds that nest in roadsides may be able to produce more young than those nesting in cropfields. To increase the attractiveness of roadsides to nesting birds and to enhance bird productivity in roadsides, several measures can be taken.

Traditionally, roadsides in the Midwest have been planted to smooth brome that is mowed and sprayed to maintain healthy vegetation and to prevent weed encroachment (Wasser and

Dittberner 1986). In our study, as in other studies (Warner et al. 1987, Carroll and Crawford

1991), pheasants and partridge nested in smooth brome grass and residue in roadsides.

Adding a legume such as alfalfa (Medicago sativa), which was not present in our roadsides, may increase the density of game birds nesting in roadsides (Warner et al. 1987, Nelson et al.

1990, Frawley 1989) while not diminishing nest success rates (Warner et al. 1987), thereby increasing the total number of birds fledged in these areas. The seeding of legumes is sometimes discouraged because legumes are short-lived, leaving bare spots exposed to erosion

(U.S.Dep.Agric. 1960), although alfalfa can be interseeded periodically as its production decreases. Roadsides adjacent to gravel roads in Iowa are periodically dredged and reseeded to eliminate built-up sediment from wind and water erosion.

Although roadsides adjacent to gravel roads in Iowa traditionally are not completely mowed, the roadside shoulder often is mowed for the safety of drivers. In our study, this created a swath of short, sparse vegetation that attracted nesting vesper sparrows and western meadowlarks. Mowing of the roadside shoulder should be restricted to early spring and late

fall to reduce nest losses directly from mowing while providing nesting habitat for these bird

species. 64

Recently, new roadside management strategies have been implemented in many counties in

Iowa (Alt. Roadside Steer. Comm. 1989). Native prairie grasses and forbs are being seeded in roadsides, often following dredging, to recreate the original habitat that supported native wildlife. To reduce the need for frequent dredging, roadside managers encourage landowners to plant permanent field borders, and to practice conservation tillage techniques adjacent to roadsides where native vegetation has been seeded. Prescribed burns also are carried out every

3-5 years in the spring before grass seeds germinate or growing vegetation emerges. These bums simulate the original prairie fires and maintain the vigor of the native vegetation (Vogl

1974). Finally, farmers are being encouraged to retain the fences in their roadsides to prevent farming practices from encroaching upon roadsides.

In our study tall, strong grasses and forbs, and fences were preferred by red-winged blackbirds for nest sites. Seeding tall, strong native vegetation in roadsides and preventing the elimination of fences would attract redwings and other birds that use such substrates for nesting (e.g., Buhnerkempe 1979, George et al. 1979). In early summer, many birds in our

study nested in the smooth brome residue that was left from the previous year. The residue

from native vegetation, which often remains standing throughout the winter, would provide a

more robust nesting cover than smooth brome residue for such birds (see Holcomb and Twiest

1968, Albers 1978). In grasslands, structurally diverse habitats attract a variety of species of

nesting birds (Skinner et al1984, Johnson and Temple 1986, Nelson et al. 1990). Prescribed

bums produced areas of sparse vegetation in our otherwise densely vegetated roadsides,

creating a structurally diverse habitat that attracted many species of nesting birds.

Some bird species that typically nest in grassland habitats (i.e., bobolink [Dolichonyx

oryzivorusl, grasshopper sparrow [Ammodramus savannarum1, savannah sparrow

[Passerculus sandwichensis), and upland sandpiper [Bartramia 10ngicaudaD were

conspicuously absent from the studied roadsides. These species may have minimum area

requirements (see Samson 1980) and therefore are not attracted to linear roadside habitats. The 65

studied roadsides were chosen, in part, for their isolation from blocks of grassland bird habitat.

Roadsides that contain vegetation preferred by grassland birds, adjacent to similarly vegetated blocks of grassland habitat (i.e., Conservation Reserve Program fields) may, however, attract nesting birds. Such roadsides also may serve as corridors between blocks of grassland habitat for non-migratory birds such as pheasant and partridge. 66

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o 73

GENERAL SUMMARY

Thirty-five bird species were seen in roadsides, compared with 26 species in rowcrop fields. Red-winged blackbirds (Agelaius phoeniceus), brown-headed cowbirds (Molothrus ater), vesper sparrows (Pooecetes gramineus), western meadowlarks (Sturnella magna), and dickcissels (Spiza americana) were the most abundant bird species in roadsides. Total bird abundance in roadsides averaged 1,670 birdS/l 00 ha, compared to 49 birdsll 00 ha in crop fields.

Few birds showed a preference for roadsides with native versus exotic grasses or for burned versus unburned roadsides, but the abundance of some birds was related to vegetation height and density in roadsides. The abundance of 5 bird species, as well as total bird abundance, was greater in 1990 than in 1991. Dickcissel abundance increased throughout the summer in roadsides, whereas common grackle (Quiscalus quiscala) abundance peaked early in June and then declined.

Eight species were observed nesting in roadsides; red-winged blackbirds and gray partridge (Perdix perdix) were the most common. One hundred and twenty nests were

found of all species combined, with a nest density of 1,147 nests/loo ha The Mayfield

method was used to detennine nest success for the red-winged blackbird (26%), and the vesper sparrow (5.5%). Predation was responsible for 57.8% of all red-winged blackbird

nest failures; 46% of all blackbird nests were parasitized by the brown-headed cowbird.

Red-winged blackbird nest density and success were greatest in roadsides and at nest

sites with taIl, dense vegetation. Gray partridge and ring-necked pheasant (Phasianus

co1chicus) nest densities were greatest in areas of high residue coverage. Vesper sparrow

nests were most dense in areas of sparse vegetation. Red-winged blackbirds most often

placed their nests in the bottom and at the fence of a roadside; all vesper sparrows nested in

the short vegetation of the foreslope. The placement of a red-winged blackbird nest in a

roadside position did not influence nest success, although predation was greatest on 74

redwing nests placed in the bottom and at the fence. Blackbird nests placed in forbs,

shrubs, and the fence were more successful than those built in grass.

Native prairie vegetation and prescribed burning mayor may not be appropriate for the

conditions found in many gravel roadsides. If native grasses and forbs could be

successfully introduced into roadsides, they may attract birds that use such substrates for

territorial song perches and nesting substrates. Fences, which are used by many birds in

place of vegetation for these activities, should be retained in roadsides. Adding a legume

such as alfalfa (Medicago saliva) to smooth brome (Bromus inermis) dominated roadsides

also may increase the attractiveness of these areas to many nesting birds. Mowing roadsides

adjacent to gravel roads should be discouraged except at the roadside shoulder.

In agricultural lands, birds are concentrated into small fragments of suitable habitat (e.g.,

grassed waterways, fencerows, roadsides). Although similar in many respects, each of

these habitats has unique characteristics (see Best 1983, Bryan 1990), and proper

management for each area is necessary to best fulfill the needs of the avian community in

agricultural areas. 75

ADDITIONAL LITERATURE CITED

Alternate Roadside Steering Committee. 1989. Integrated roadside vegetation policies for

planting and management. George Butler Assoc., Ames, Ia. 37pp.

Basore, N. S., L. B. Best, and 1. B. Wooley. 1986. Bird nesting in no-tillage and tilled

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gray partridge brood habitat in roadsides and managed grasslands. Pages 103-119 in 76

K. E. Church, R. E. Warner, and S. J. Brady, eds. Perdix V: gray partridge and ring­

necked pheasant workshop. Kans. Dep. WildI. and Parks, Emporia, Kans.

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183.

Ryan, D. R. 1986. Nongame management in grassland and agricultural ecosystems.

Pages 117-136 in J. B. Hale, L. B. Best, and R. L. Clawson, eds. Management of

nongame wildlife in the midwest: a developing art. Bookcrafters, Chelsea, Mich.

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10.

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Wildl. Soc. Bull. 4:11-15.

Varland, K. 1985. Why roadsides for wildlife? Minnesota Volunteer 48:3-7.

Warner, R. E., G. B. Joselyn, and S. L. Etter. 1987. Factors affecting roadside nesting

by pheasants in Illinois. Wildl. Soc. Bull. 15:221-228.

Warner, R. E. 1992. Nest ecology of grassland passerines on road rights-of-way in central

Illinois. BioI. Conserv. 59:1-7. 77

ACKNOWLEDGMENTS

I thank D. Drynan and V. Polton for their dedicated assistance in field work and data compilation. S. Lekwa, D. Webber, J. Kooiker of the Story County Conservation Board, and D. Sheeley, Hardin County Engineer, burned roadside vegetation for me. I am indebted to the farmers in Story, Boone, and Hardin counties who graciously allowed me to work on their land I appreciate, too, the statistical insight and expertise given by P. Hinz and K. Koehler.

Drs. Louis Best, James Dinsmore, and Richard Cruse contributed time and energy to this project by serving on my committee and reviewing earlier drafts of this thesis, for which I am grateful. I am particularly indebted to my major advisor, Dr. Best, for his instruction in research design, his infinite patience in answering my questions, and his painstaking editing of my writing.

My housemates, Anjeanette and Kathy, deserve medals for their loving support and encouragement, and for continuing to live in the same house with me during this process. I am grateful, too, for my family's unceasing support in thought and prayer. Finally, I thank

God, with Whom everything is possible.

This project was supported by the Iowa Agriculture and Home Economics Experiment

Station, Iowa Department of Natural Resources, Iowa Department of Transportation, Iowa

Science Foundation, Leopold Center for Sustainable Agriculture, and Max McGraw

Wildlife Foundation.