Effects of Prescribed Burning on Avian Foraging Ecology and Arthropod Abundance in Sagebrush- Grassland Brian Mark Winter Iowa State University
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Iowa State University Capstones, Theses and Retrospective Theses and Dissertations Dissertations 1984 Effects of prescribed burning on avian foraging ecology and arthropod abundance in sagebrush- grassland Brian Mark Winter Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/rtd Part of the Ecology and Evolutionary Biology Commons, Natural Resources and Conservation Commons, and the Natural Resources Management and Policy Commons Recommended Citation Winter, Brian Mark, "Effects of prescribed burning on avian foraging ecology and arthropod abundance in sagebrush-grassland " (1984). Retrospective Theses and Dissertations. 331. https://lib.dr.iastate.edu/rtd/331 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]. Effects of prescribed burning on aV1an foraging ecology and arthropod abundance in sagebrush-grassland by Brian Mark Winter A Thesis Submitted to the Graduate Faculty in Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE Department: Animal Ecology Major: wildlife Biology Signatures have been redacted for privacy Iowa State University Ames, Iowa 1984 1508849 ii TABLE OF CONTENTS Page GENERAL INTRODUCTION . 1 Explanat ion of Thesis Format 2 SECTION I. EFFECTS OF PRESCRIBED BURNING ON AVIAN FORAGING ECOLOGY IN SAGEBRUSH-GRASSLAND 3 ABSTRACT .. 4 INTRODUCTION 5 STUDY AREA 7 METHODS 8 RESULTS AND DISCUSSION 14 Hab itat Charac terist ics 14 General Foraging Behavior 19 Activity Budgets 20 Feeding Rates and Prey Load Sizes • 24 Forag ing Pat terns 24 Foraging Arenas and Territories 28 Hab itat and Subst rate Usage 29 MANAGEMENT IMPLICATIONS 35 LITE~TURE CITED . 37 SECTION II. ARTHROPOD ABUNDANCE IN BURNED AND UNBURNED PATCHES OF SAGEBRUSH-GRASSLAND RANGE 39 ABSTRACT .. 40 INTRODUCTION 41 STUDY AREA AND METHODS . 43 RESULTS AND DISCUSSION 46 Hab itat Charac terist ics 46 iii Page Total Arthropods in Burned and Unhurned Patches . 46 Order and Family Differences in Burned and Unburned Patches 53 Seasonal Abundance 59 Arthropods Associated with Sagebrush 62 CONCLUSIONS 67 LITERATURE CITED 69 SECTION III. PRESCRIBED BURNING AFFECTS PLACEMENT OF SAGE SPARROW NESTS 72 INTRODUCTION . 73 STUDY AREA AND METHODS . 74 RESULTS AND DISCUSSION 75 LITERATURE CITED . 78 SUMMARY 79 ADDITIONAL LITERATURE CITED 81 ACKNOWLEDGMENTS 82 l.V LIST OF FIGURES SECTION I: Figure 1. Percentage occurrence of sagebrush plants within 5 condition classes, preburn and post burn. Verticle lines are 90% confidence intervals . 15 Figure 2. Postburn habitat (unburned, burned, edge) selection by male and female Brewer's and sage sparrows. Ninety percent confidence intervals (vertical lines) were determined using the Bonferroni method (see Neu et al. 1974) .... 30 SECTION II: Figure 1. Map of the burn pattern on a portion of the study area. Sampling stations within patches are marked as LUB (large unburned), SUB (small unburned), LB (large burned), and SB (small burned) . .. ........... 47 Figure 2. Seasonal abundance (mean+SE) of arthropods sampled with sweep nets ~nd pitfall traps l.n unburned (solid line) and burned (dashed line) patches. Means denoted by a square are significantly different (P<0.05) based on ANOVA. See Study Area and Methods for sample slzes . 51 Figure 3. Seasonal distribution of major taxa collected with sweep nets and pitfall traps in unburned and burned patches . 60 Figure 4. Seasonal distribution of major taxa associated with sagebrush . 64 v LIST OF TABLES SECTION I: Table 1. Vegetation characteristics (mean±SE) for the preburn year and postburn habitats . .... 18 Table 2. Activity budgets of male and female Brewer's and sage sparrows before prescribed burning and during the first postburn year. Values (X±SE) represent minutes per hour . .. ..... 21 Table 3. Mean (±SE) values of foraging ecology parameters of male and female Brewer's and sage sparrows before prescribed burning and during the first pos tburn year . .. ........... 25 Table 4. Correlations between foraging site characteristics and usage index values (see Methods) of male and female Brewer's and sage sparrows before prescribed burning and during the first postburn year . 32 SECTION II: Table 1. Mean (±SE) numbers of arthropods collected per sample with sweep nets and pitfall traps. ...... 49 Table 2. Mean (±SE) numbers of individuals per 100 samples for major arthropod taxa collected with sweep nets and pitfall traps in unburned (UB) and burned (B) patches . ..... 54 Table 3. Seasonal abundance (mean±SE) of arthropods per 100 g of sagebrush foliage . 63 1 GENERAL INTRODUCTION Prescribed burning in western sagebrush-grasslands has been used primarily to eradicate sagebrush (Artemisia spp.) and, consequently, increase the growth of herbaceous vegetation. Although fire has been used commonly, little is known about its effects on nongame birds breeding 1n sagebrush-grasslands. Furthermore, the effects of sagebrush removal on arthropod abundance and composit ion are unknown. The sage sparrow (Amphispiza belli) and Brewer's sparrow (Spizella breweri) are two of the most abundant nongame birds breeding 1n the shrub steppe of southeastern Idaho, and both spec1es are dependent on sagebrush for breeding (Braun et al. 1976). Changes in the density of both sparrows after sagebrush alteration have been recorded (Best 1972, Pyrah and Jorgensen 1974, Olson 1974, Schroeder and Sturges 1975, McGee 1976, Reynolds 1978, Castrale 1982), but effects of shrub removal on their foraging ecology have not been reported. To assess the effect of prescribed burning on the foraging ecology of sage and Brewer's sparrows, intensive preburn and postburn data were collected. My objectives were: (1) to document effects of prescribed burning on the general feeding behavior, activity budgets, feeding frequency, and foraging patterns of sage and Brewer's sparrows during the nestling period; (2) to evaluate effects of preburn and postburn foraging strategies on nestling growth and development; (3) to determine foraging preferences in relation to preburn and postburn vegetation and associated arthropods; and (4) to assess arthropod abundance in burned and unburned patches of sagebrush-grassland. 2 Explanation ~ Thesis Format My thesis adheres to the guidelines specified for the alternate format and consists of three sections. Section I reports the effects of prescribed burning on activity budgets, foraging ecology, and habitat usage by both sparrow spec~es. A large part of the discussion in section I is related to section II, which exam~nes the composition and abundance of arthropods in burned and unburned patches. Section III focuses on effects of prescribed burning on sage sparrow nest placement; these data were collected incidental to the stated objectives. Each section was written for publication following the requirements of the journal for which it was intended. 3 SECTION I. EFFECTS OF PRESCRIBED BURNING ON AVIAN FORAGING ECOLOGY IN SAGEBRUSH-GRASSLAND 4 ABSTRACT Effects of a prescribed burn on Brewer's sparrow (Spizella breweri) and sage sparrow (Amphispiza belli) foraging ecology were studied in a sagebrush-grassland of southeastern Idaho. Sparrows were observed during the nestling period from tower-blinds to document general feeding behavior, activity budgets, feeding rates, foraging patterns, and habitat selection before and after burning. After the fire, sage sparrows spent more time brooding and shading the nestlings and less time foraging, and males spent more time singing and defending their territories. Activity budgets of Brewer's sparrows did not change after the burn. Feeding rates (frequency and prey load size) of both species were unaffected by the fire. Brewer's sparrows flew farther from the nest to forage postburn, but feeding bout duration did not change. Sage sparrow feeding bout duration decreased after burning. Brewer's sparrows preferred to forage in areas with greater sagebrush (Artemisia spp.) coverage both preburn and postburn; male sage sparrows selected areas with greater grass and green rabbitbrush (Chrysothamnus viscidiflorus) coverage before but not after burning. I conclude that when prescribed burning results in a fine-grained mosaic with good interspersion of burned and unburned patches, both sage and Brewer's sparrows can continue to breed in burned areas, but fires that burn large patches would be detrimental to both species because of their feeding requirements. 5 INTRODUCTION Sagebrush (Artemisia spp.) is a conspicuous feature of rangelands in the western United States, and sagebrush-grassland covered more than 100 million ha (Beetle 1960). Braun et al. (1976) conservatively estimated that at least 10% of all sagebrush rangelands has been altered to control sagebrush and increase livestock forage production. Historically, sagebrush was controlled by natural fires that occurred about once every 50 years (Wright et al. 1979). As the rangelands were settled, however, they were protected from fire by land managers with training influenced by European philosophy (Wright 1974). Managers now accept prescribed burning as an economical, effective, and ecologically sound management tool (Wright et al. 1979). Although effects of prescribed burning on range vegetation has been comprehensively studied