Vertebrate Response to a Tidal Marsh Restoration In
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VERTEBRATE RESPONSE TO A TIDAL MARSH RESTORATION IN HUMBOLDT BAY, CALIFORNIA by Sandra L. Jacobson A Thesis Presented to The Faculty of Humboldt State University In Partial Fulfillment of the Requirements for the Degree Master of Science December, 1986 VERTEBRATE RESPONSE TO A TIDAL MARSH RESTORATION IN HUMBOLDT BAY, CALIFORNIA by Sandra L. Jacobson Approved by the Master's Thesis Committee Paul F. Springer Stanley W. Harris Director, Natural Resources Graduate Program Date 86/W-59/05/22 Natural Resources Graduate Program Number Approved by the Dean of Graduate Studies Alba M. Gillespie ABSTRACT A 5.5-ha abandoned log pond (originally salt marsh) at the end of Park Street, Eureka, California was chosen as the off-site mitigation area for the destruction of 6.8 ha of wildlife habitat during the construction of the Woodley Island marina. Passive saltmarsh restoration was attempted by breaching a dike separating the log pond from Freshwater Slough (an estuary of Humboldt Bay) in December 1980, thus allowing the periodic tidal intrusion of salt water into 3.8 ha of the area. This study measured the response of amphibians, reptiles, birds, and mammals to the change in vegetation and other habitat conditions brought about by the reestablishment of tidal action. Previously, in August 1979 an interior dike had been constructed within a portion of the mitigation area to enhance an existing 0.7-ha freshwater marsh, and the effect of this change on the vertebrate life also was appraised. Frogs disappeared and snakes declined in numbers within the tidal portion of the mitigation area after the dike was breached. Savannah Sparrows (Passerculus sandwichensis) were the most common birds in the grassland of the dried log pond before breaching, and declined after breaching. Several species of shorebirds and the Snowy Egret (Egretta thula) increased their use of the tidal portion of the mitigation area after breaching. Small mammals such as California Vole (Microtus californicus), Vagrant Shrew (Sorex vagrans), and Western Harvest Mouse (Reithrodontomys megalotis) were common before breaching, iii iv but declined in numbers in the first month after breaching. Use of the area by the most common large mammal, the Domestic Dog (Canis familiaris), increased after breaching because people used the flooded marsh to train retrievers. Within the freshwater marsh five species of birds showed significant increases in numbers during subsequent corresponding seasons, whereas one species showed a significant decrease in numbers. The success of the restoration after breaching was not fully known at the end of 1.5 years of study, but the trend was towards a renewed, vigorous salt marsh. In addition, the interior dike construction enhanced the freshwater marsh. In the interim the tidal and freshwater marshes provided valuable foraging areas for many species of wetland birds, and the freshwater marsh also served as a nesting area for certain bird species. ACKNOWLEDGEMENTS I wish to acknowledge the great deal of help provided to me throughout this project. Financial support was provided by the U. S. Fish and Wildlife Service through a contract with the Humboldt State University Foundation, which, in turn, administered the study through the Wildlife Research Field Station. Special thanks go to Dr. Paul Springer, whose advice and expert professional help went a long way toward making the project a success. I especially acknowledge his editorial help; without it I would have missed an important step in my education. My other committee members, Drs. Stan Harris and John Sawyer, also contributed their time and expertise for my benefit. I appreciate not only the professional help but also the moral support. Dr. Dave Craigie helped me with the statistical analyses and interpretations. Pat Collins introduced me to the SPSS analysis and helped me to learn the seemingly thousands of details needed to successfully work with a computer. Dana Base, John Sterling and John Kelly helped with the field work on those days I was unable to work. Jan Kastler expertly typed the thesis, and Laura Montagna prepared the figures. The final person instrumental to the success of the project contributed neither professional expertise nor field time. He did contribute love, encouragement, moral support, and gas for the many vi trips I took from my summer job sites to the study sites. He is my husband, Chris, and without his contributions I would have had a much more difficult, if not impossible, task in finishing the project. So to Chris I address my deepest appreciation and thanks. TABLE OF CONTENTS Page ABSTRACT iii ACKNOWLEDGEMENTS LIST OF TABLES xi LIST OF FIGURES xii INTRODUCTION 1 STUDY AREAS 6 METHODS 13 Amphibians and Reptiles 13 Birds 13 Mammals 19 RESULTS 23 Amphibians and Reptiles 23 Birds 25 Saltmarsh Breeding Bird Counts 27 Saltmarsh Year-round Bird Counts 30 Snowy Egret 30 Black-shouldered Kite 32 Shorebirds 32 Vaux's Swift and Swallows 41 Marsh Wren 43 Emberizids 48 vii viii TABLE OF CONTENTS (continued) Page Western Meadowlark 53 American Goldfinch 55 Freshwater Marsh Breeding and Year-round Bird Counts . 55 Mammals 61 Salt Marsh 61 Freshwater Marsh 64 DISCUSSION 66 Salt Marsh 66 Amphibians and Reptiles 66 Birds 66 Snowy Egret 67 Black-shouldered Kite 68 Shorebirds 68 Vaux's Swift and Swallows 69 Marsh Wren 70 Emberizids 70 Western Meadowlark 72 American Goldfinch 73 Mammals 73 Freshwater Marsh 75 Amphibians and Reptiles 75 Birds 75 Mammals 77 CONCLUSIONS 78 MANAGEMENT RECOMMENDATIONS 80 REFERENCES CITED 82 ix TABLE OF CONTENTS (continued) Page APPENDIXES A. Common and Scientific Names of Amphibians and Reptiles Mentioned in the Text or Tables 88 B. Common and Scientific Names of Birds Mentioned in the Text, Tables or Appendixes 89 C. Common and Scientific Names of Mammals Mentioned in the Text or Tables 94 D. Common and Scientific Names of Plants Mentioned in the Text 95 E. Mean Number (and Standard Error) of Birds per Visit in Salt Marsh at the Mitigation Area, Eureka, California by Season 97 F. Mean Number (and Standard Error) of Birds per Visit in Salt Marsh at the Control Area, Eureka, California by Season 106 G. Mean Number (and Standard Error) of Birds per Visit in Freshwater Marsh at the Mitigation Area, Eureka, California by Season 112 H. Approximate Territorial Boundaries of Birds during the Breeding Bird Counts in 1979 at the Mitigation Area, Eureka, California 120 I. Approximate Territorial Boundaries of Birds during the Breeding Bird Counts in 1980 at the Mitigation Area, Eureka, California 121 J. Approximate Territorial Boundaries of Birds during the Breeding Bird Counts in 1981 at the Mitigation Area, Eureka, California 122 K. Approximate Territorial Boundaries of Birds during the Breeding Bird Counts in 1982 at the Mitigation Area, Eureka, California 123 L. Approximate Territorial Boundaries of Birds during the Breeding Bird Counts in 1980 at the Control Area, Eureka, California 124 M. Approximate Territorial Boundaries of Birds during the Breeding Bird Counts in 1981 at the Control Area, Eureka, California 125 x TABLE OF CONTENTS (continued) Page APPENDIXES (continued) N. Approximate Territorial Boundaries of Birds during the Breeding Bird Counts in 1982 at the Control Area, Eureka, California 126 LIST OF TABLES Table Page 1 Breeding Bird Count Dates at the Mitigation and Control Areas, Eureka, California 15 2 Number and Frequency of Occurrence of Amphibians and Reptiles Observed at the Mitigation Area, Eureka, California before and after Dike Breaching, 1979-1982 24 3 Species of Birds with Significant Differences in Numbers between at Least 2 Years at a Given Season in Salt Marsh at the Mitigation and/or Control Areas, Eureka, California, 1979-1982 . 26 4 Numbers of Breeding Bird Territories during Breeding Bird Counts in Salt Marsh at the Mitigation and Control Areas, Eureka, California, 1979-1982 28 5 Species of Birds with Significant Differences in Numbers between at Least 2 Years at a Given Season in Freshwater Marsh at the Mitigation Area, Eureka, California, 1979-1982 57 6 Species of Birds with Significant Differences (P<0.05) in Numbers in Fall in Freshwater Marsh at the Mitigation Area, Eureka, California, 1980-1981. 60 7 Number of Small Mammals Caught and the Calculated Density (No. animals/ha), Eureka, California, 1979-1981 62 8 Number and Frequency of Occurrence of Large Mammal Sign Observed at the Mitigation Area before and after Dike Breaching, Eureka, California, 1979-1982 63 9 Number and Frequency of Occurrence of Large Mammal Sign Observed in Salt Marsh at the Control Area before and after Dike Breaching, Eureka, California, 1980-1982 65 xi LIST OF FIGURES Figure Page 1 Location of Woodley Island Marina Site, Park Street Mitigation Area, and Bay Street Control Area on Humboldt Bay, Eureka, California 3 2 Habitat Types in 1979-80 before Dike Breaching and Bird Count Route in 1979 before Dike Construction at the Park Street Mitigation Area, Eureka, California 7 3 Habitat Types in 1981 after Dike Breaching and Bird Count Route in 1979-1982 after Dike Construction at the Park Street Mitigation Area, Eureka, California 9 4 Habitat Types and Bird Count Route at Bay Street Control Area, Eureka, California, 1980-1982 11 5 Small Mammal Trapping Grid Locations at the Mitigation Area, Eureka, California, in 1979, 1980 and 1981 20 6 Small Mammal Trapping Grid Locations at the Control Area, Eureka, California, in 1980 and 1981 21 7 Mean Number of Snowy Egrets in Salt Marsh at the Mitigation and Control Areas, Eureka, California, June 1979 to