Double-Survey Estimates of Bald Eagle Populations in Oregon
The literature on abundance of birds of prey is almost devoid of population estimates with statistical rigor. Therefore, we surveyed bald eagle (Haliaeetus leucocephalus) populations on the Crooked and lower Columbia rivers of Oregon and used the double-survey method to estimate populations and sigh...
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| Veröffentlicht in: | The Journal of wildlife management 1999-07, Vol.63 (3), p.794-802 |
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| container_title | The Journal of wildlife management |
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| creator | Anthony, Robert G. Garrett, Monte G. Isaacs, Frank B. |
| description | The literature on abundance of birds of prey is almost devoid of population estimates with statistical rigor. Therefore, we surveyed bald eagle (Haliaeetus leucocephalus) populations on the Crooked and lower Columbia rivers of Oregon and used the double-survey method to estimate populations and sighting probabilities for different survey methods (aerial, boat, vehicle) and bald eagle ages (adults vs. subadults). Sighting probabilities were consistently |
| doi_str_mv | 10.2307/3802792 |
| format | Article |
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Therefore, we surveyed bald eagle (Haliaeetus leucocephalus) populations on the Crooked and lower Columbia rivers of Oregon and used the double-survey method to estimate populations and sighting probabilities for different survey methods (aerial, boat, vehicle) and bald eagle ages (adults vs. subadults). Sighting probabilities were consistently <1.00, so direct counts were biased estimates of abundance. There was a greater probability of observing adult (0.625) versus subadult (0.494) eagles on the Crooked River for different survey methods, but we did not detect differences in sighting probabilities for adults (0.707) versus subadults (0.683) on the Columbia River. The probability of observing bald eagles from aircraft (0.636) was lower than that from boats (0.758) on the Columbia River, and sighting probabilities from aircraft (0.354) were lower than those from the ground (0.764) on the Crooked River. Precision of population estimates was generally good: most (68%, n = 30) coefficients of variation were <10%, and only 7% were >20%. The results revealed variable and negative bias (percent relative bias = -9 to -70%) of direct counts and emphasized the importance of estimating populations where some measure of precision and ability to conduct inference tests are available. We recommend use of the double-survey method to estimate abundance of bald eagle populations and other raptors in open habitats.</description><identifier>ISSN: 0022-541X</identifier><identifier>EISSN: 1937-2817</identifier><identifier>DOI: 10.2307/3802792</identifier><identifier>CODEN: JWMAA9</identifier><language>eng</language><publisher>Bethesda, MD: The Wildlife Society</publisher><subject>Aircraft ; Animal populations ; Animal, plant and microbial ecology ; Biological and medical sciences ; Birds ; Boats ; Eagles ; Estimation bias ; Estimation methods ; Fundamental and applied biological sciences. Psychology ; General aspects. 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Therefore, we surveyed bald eagle (Haliaeetus leucocephalus) populations on the Crooked and lower Columbia rivers of Oregon and used the double-survey method to estimate populations and sighting probabilities for different survey methods (aerial, boat, vehicle) and bald eagle ages (adults vs. subadults). Sighting probabilities were consistently <1.00, so direct counts were biased estimates of abundance. There was a greater probability of observing adult (0.625) versus subadult (0.494) eagles on the Crooked River for different survey methods, but we did not detect differences in sighting probabilities for adults (0.707) versus subadults (0.683) on the Columbia River. The probability of observing bald eagles from aircraft (0.636) was lower than that from boats (0.758) on the Columbia River, and sighting probabilities from aircraft (0.354) were lower than those from the ground (0.764) on the Crooked River. Precision of population estimates was generally good: most (68%, n = 30) coefficients of variation were <10%, and only 7% were >20%. The results revealed variable and negative bias (percent relative bias = -9 to -70%) of direct counts and emphasized the importance of estimating populations where some measure of precision and ability to conduct inference tests are available. We recommend use of the double-survey method to estimate abundance of bald eagle populations and other raptors in open habitats.</description><subject>Aircraft</subject><subject>Animal populations</subject><subject>Animal, plant and microbial ecology</subject><subject>Biological and medical sciences</subject><subject>Birds</subject><subject>Boats</subject><subject>Eagles</subject><subject>Estimation bias</subject><subject>Estimation methods</subject><subject>Fundamental and applied biological sciences. Psychology</subject><subject>General aspects. Techniques</subject><subject>Methods and techniques (sampling, tagging, trapping, modelling...)</subject><subject>Population estimates</subject><subject>Statistical methods</subject><subject>Survey methods</subject><subject>Vehicles</subject><subject>Wildlife management</subject><subject>Wildlife population estimation</subject><issn>0022-541X</issn><issn>1937-2817</issn><fulltext>true</fulltext><rsrctype>article</rsrctype><creationdate>1999</creationdate><recordtype>article</recordtype><recordid>eNp10NtKw0AQBuBFFKxVfIUgolfRPSWbxStb6wEKFVTwLoyb2ZKyzdbdROjbm9JCQfBqYPj4-WcIOWf0hguqbkVBudL8gAyYFirlBVOHZEAp52km2ecxOYlxQalgrMgH5O7Bd18O07cu_OA6mcS2XkKLMfE2GYGrkgnMHSavftU5aGvfxKRuklnAuW9OyZEFF_FsN4fk43HyPn5Op7Onl_H9NDVC6DZlsipAywwZcCtNJoSQfanNDnSmUSNkBoqqsMIAZ1WFIreC8wqNtBXmYkiutrmr4L87jG25rKNB56BB38WSKSkUU7qHF3_gwneh6buVXEiWS0lZj663yAQfY0BbrkJ_c1iXjJabD5a7D_bychcH0YCzARpTxz0vtJZU7dkitj78m_YLtg948g</recordid><startdate>19990701</startdate><enddate>19990701</enddate><creator>Anthony, Robert G.</creator><creator>Garrett, Monte G.</creator><creator>Isaacs, Frank B.</creator><general>The Wildlife Society</general><general>Wildlife Society</general><general>Blackwell Publishing Ltd</general><scope>IQODW</scope><scope>AAYXX</scope><scope>CITATION</scope><scope>7QG</scope><scope>7QL</scope><scope>7SN</scope><scope>7ST</scope><scope>7T7</scope><scope>7U6</scope><scope>7U9</scope><scope>8FD</scope><scope>C1K</scope><scope>FR3</scope><scope>H94</scope><scope>M7N</scope><scope>P64</scope></search><sort><creationdate>19990701</creationdate><title>Double-Survey Estimates of Bald Eagle Populations in Oregon</title><author>Anthony, Robert G. ; Garrett, Monte G. ; Isaacs, Frank B.</author></sort><facets><frbrtype>5</frbrtype><frbrgroupid>cdi_FETCH-LOGICAL-c339t-14d8a945e1a2f4c533348178a94a959e9ea5ca8d8f3ca21dde36f322dec4fde63</frbrgroupid><rsrctype>articles</rsrctype><prefilter>articles</prefilter><language>eng</language><creationdate>1999</creationdate><topic>Aircraft</topic><topic>Animal populations</topic><topic>Animal, plant and microbial ecology</topic><topic>Biological and medical sciences</topic><topic>Birds</topic><topic>Boats</topic><topic>Eagles</topic><topic>Estimation bias</topic><topic>Estimation methods</topic><topic>Fundamental and applied biological sciences. Psychology</topic><topic>General aspects. Techniques</topic><topic>Methods and techniques (sampling, tagging, trapping, modelling...)</topic><topic>Population estimates</topic><topic>Statistical methods</topic><topic>Survey methods</topic><topic>Vehicles</topic><topic>Wildlife management</topic><topic>Wildlife population estimation</topic><toplevel>peer_reviewed</toplevel><toplevel>online_resources</toplevel><creatorcontrib>Anthony, Robert G.</creatorcontrib><creatorcontrib>Garrett, Monte G.</creatorcontrib><creatorcontrib>Isaacs, Frank B.</creatorcontrib><collection>Pascal-Francis</collection><collection>CrossRef</collection><collection>Animal Behavior Abstracts</collection><collection>Bacteriology Abstracts (Microbiology B)</collection><collection>Ecology Abstracts</collection><collection>Environment Abstracts</collection><collection>Industrial and Applied Microbiology Abstracts (Microbiology A)</collection><collection>Sustainability Science Abstracts</collection><collection>Virology and AIDS Abstracts</collection><collection>Technology Research Database</collection><collection>Environmental Sciences and Pollution Management</collection><collection>Engineering Research Database</collection><collection>AIDS and Cancer Research Abstracts</collection><collection>Algology Mycology and Protozoology Abstracts (Microbiology C)</collection><collection>Biotechnology and BioEngineering Abstracts</collection><jtitle>The Journal of wildlife management</jtitle></facets><delivery><delcategory>Remote Search Resource</delcategory><fulltext>fulltext</fulltext></delivery><addata><au>Anthony, Robert G.</au><au>Garrett, Monte G.</au><au>Isaacs, Frank B.</au><format>journal</format><genre>article</genre><ristype>JOUR</ristype><atitle>Double-Survey Estimates of Bald Eagle Populations in Oregon</atitle><jtitle>The Journal of wildlife management</jtitle><date>1999-07-01</date><risdate>1999</risdate><volume>63</volume><issue>3</issue><spage>794</spage><epage>802</epage><pages>794-802</pages><issn>0022-541X</issn><eissn>1937-2817</eissn><coden>JWMAA9</coden><abstract>The literature on abundance of birds of prey is almost devoid of population estimates with statistical rigor. Therefore, we surveyed bald eagle (Haliaeetus leucocephalus) populations on the Crooked and lower Columbia rivers of Oregon and used the double-survey method to estimate populations and sighting probabilities for different survey methods (aerial, boat, vehicle) and bald eagle ages (adults vs. subadults). Sighting probabilities were consistently <1.00, so direct counts were biased estimates of abundance. There was a greater probability of observing adult (0.625) versus subadult (0.494) eagles on the Crooked River for different survey methods, but we did not detect differences in sighting probabilities for adults (0.707) versus subadults (0.683) on the Columbia River. The probability of observing bald eagles from aircraft (0.636) was lower than that from boats (0.758) on the Columbia River, and sighting probabilities from aircraft (0.354) were lower than those from the ground (0.764) on the Crooked River. Precision of population estimates was generally good: most (68%, n = 30) coefficients of variation were <10%, and only 7% were >20%. The results revealed variable and negative bias (percent relative bias = -9 to -70%) of direct counts and emphasized the importance of estimating populations where some measure of precision and ability to conduct inference tests are available. We recommend use of the double-survey method to estimate abundance of bald eagle populations and other raptors in open habitats.</abstract><cop>Bethesda, MD</cop><pub>The Wildlife Society</pub><doi>10.2307/3802792</doi><tpages>9</tpages></addata></record> |
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| ispartof | The Journal of wildlife management, 1999-07, Vol.63 (3), p.794-802 |
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| language | eng |
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| source | Jstor Complete Legacy |
| subjects | Aircraft Animal populations Animal, plant and microbial ecology Biological and medical sciences Birds Boats Eagles Estimation bias Estimation methods Fundamental and applied biological sciences. Psychology General aspects. Techniques Methods and techniques (sampling, tagging, trapping, modelling...) Population estimates Statistical methods Survey methods Vehicles Wildlife management Wildlife population estimation |
| title | Double-Survey Estimates of Bald Eagle Populations in Oregon |
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