A Survey of Nesting Colonial Waterbirds in the Hells Canyon Study Area Von R. Pope Wildlife Technician Technical Report Appendix E.3.2-13 January 2001 Revised July 2003 Hells Canyon Complex FERC No. 1971 Copyright © 2003 by Idaho Power Company Idaho Power Company Nesting Colonial Waterbirds TABLE OF CONTENTS Table of Contents............................................................................................................................. i List of Tables ................................................................................................................................. iii List of Figures................................................................................................................................ iii Abstract............................................................................................................................................1 1. Introduction.................................................................................................................................2 2. Study Area ..................................................................................................................................3 2.1. Location .............................................................................................................................3 2.2. Physiography......................................................................................................................4 2.3. Land Features and Geology ...............................................................................................4 2.4. Soils....................................................................................................................................5 2.5. Climate...............................................................................................................................5 2.6. Vegetation..........................................................................................................................6 2.7. Land Use ............................................................................................................................8 3. Plant Operations..........................................................................................................................8 4. Methods.......................................................................................................................................9 4.1. Survey Design....................................................................................................................9 4.1.1. Rookeries ..................................................................................................................9 4.1.2. Shoreline Surveys .....................................................................................................9 4.2. Survey Methods ...............................................................................................................10 4.2.1. Rookery Counts ......................................................................................................10 4.2.2. Shoreline Surveys ...................................................................................................10 4.3. Data Analysis...................................................................................................................11 5. Results.......................................................................................................................................11 Hells Canyon Complex Page i Nesting Colonial Waterbirds Idaho Power Company 6. Discussion.................................................................................................................................12 7. Summary and Conclusions .......................................................................................................13 8. Acknowledgments.....................................................................................................................14 9. Literature Cited .........................................................................................................................14 Page ii Hells Canyon Complex Idaho Power Company Nesting Colonial Waterbirds LIST OF TABLES Table 1. Maximum number of adult colonial waterbirds observed by species and rookery, Hells Canyon Study Area, 1996–1998. .................................................. 19 Table 2. Maximum number of occupied nests by species and rookery, Hells Canyon Study Area, 1996–1998.................................................................. 19 LIST OF FIGURES Figure 1. Areas surveyed for nesting colonial waterbirds in the Hells Canyon area, 1996–1998............................................................................................................. 21 Figure 2. Köppen climate diagrams for the Weiser, Richland, Brownlee Dam, and Lewiston weather stations, Hells Canyon Study Area, Idaho–Oregon border. ................................................................................................................... 23 Figure 3. Location of the Powder River rookery in the Hells Canyon Complex, 1997−1998............................................................................................................. 25 Figure 4. Location of the Peep Island rookery in the Hells Canyon Complex, 1996−1998............................................................................................................. 27 Figure 5. Number of occupied nests by species (DCCO−double-crested cormorant; GBH−great blue heron, and BCNH−black-crowned night-heron) at each rookery, Hells Canyon Complex, 1996–1998....................................................... 29 Hells Canyon Complex Page iii Nesting Colonial Waterbirds Idaho Power Company This page left blank intentionally. Page iv Hells Canyon Complex Idaho Power Company Nesting Colonial Waterbirds ABSTRACT Surveys for nesting colonial waterbirds were conducted in the Hells Canyon Complex from 1996 through 1998. The objectives of this study were to locate existing colonies and estimate the maximum number of adults and occupied nests for each species present. Two colonial waterbird nesting colonies were located and monitored within the study area. The first, the Powder River Rookery, is located at the confluence of Eagle Creek and the Powder River with Brownlee Reservoir near Richland, Oregon. The second, Peep Island Rookery, is on an island complex in an unimpounded reach of the Snake River above Brownlee Reservoir. The Powder River Rookery was monitored from 1996 through 1998 and the Peep Island Rookery, in 1997 and 1998. Occupancy counts were conducted during the spring when adults were incubating or when juveniles were present. Three species of colonial waterbirds were documented to nest in the study area: the great blue heron (Ardea herodias), black-crowned night-heron (Nycticorax nycticorax), and double-crested cormorant (Phalocrocorax auritus). At the Powder River Rookery, only great blue herons nested. A maximum of 16 occupied great blue heron nests was documented here in 1998. All three species were observed nesting at the Peep Island Rookery. In 1998, 43 occupied double-crested cormorant nests were recorded at Peep Island, while the black-crowned night-heron and great blue heron occupied a maximum of 5 and 4 nests, respectively. Hells Canyon Complex Page 1 Nesting Colonial Waterbirds Idaho Power Company 1. INTRODUCTION Colonial waterbirds are bird species that feed predominantly in aquatic systems and often nest close together (Speich 1986). The precarious status of colonial waterbirds indicates that most species occur in a few colonies and that available habitat is limited. Past persecution of many of these species for their feather plumes pushed many species toward extinction (Erwin et al. 1993). Surveys and censuses of colonial waterbirds are important to state and federal agencies because these species, being at the top of the food chain, are sensitive to the health of aquatic ecosystems. Therefore, numbers and reproduction of colonial nesting waterbirds can serve as indicators of the presence of artificial contaminants in the environment (Trost 1985, Speich 1986). The importance of colonial waterbirds as indicator species in Idaho justifies a census program. The Snake River and its impoundments provide resources necessary to support a variety of nesting colonial waterbirds. In fact, from Swan Falls Dam to Farewell Bend, there are over 100 islands in the Snake River. In this section, 94 of the islands are part of the Deer Flat Wildlife Refuge. A variety of colonial waterbirds successfully nest on many of these islands. Species nesting on islands in the Snake River include the double-crested cormorant (Phalocrocorax auritus), great blue heron (Ardea herodias), black-crowned night-heron (Nycticorax nycticorax), and California gull (Larus californicus) (Trost and Gerstell 1994). Trost and Gerstell (1994) reviewed the status of 18 colonial waterbird species in southern Idaho during 1993. Eight of the 18 species reviewed are listed as species of local or special concern. Six species are on the Blue List of the National Audubon Society (Tate 1986), including the American white pelican (Pelecanus erythrorhynchos), black tern (Chlidonias niger), double-crested cormorant, great blue heron, black-crowned night-heron, and common tern (Sterna hirundo). Birds on the Blue List are considered declining by experienced bird observers. However, the Audubon Society considers all of these species except the black tern