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Assessment of Forest Birds on Saipan

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Assessment of Forest Birds on Saipan Status and Trends of the Land Bird Avifauna on Saipan 2008 Hawai`i Conservation Conference Based on a report to the U.S. Fish and Wildlife Service by R.J. Camp, T.K. Pratt, A.P. Marshall, F. Amidon, and L.L. Williams Outline • Introduction • Sampling – Population estimation – Trend estimation • Estimates • Threats • Focal Species – Nightingale Reed-Warbler Introduction • Mariana Islands identified as an Endemic Bird Area by BirdLife International – Increasing human population & rampant habitat transformation – Brown Tree Snake (Bogia irregularis) eliminated most birds on Guam – Brown Tree Snake now reported from Saipan • Faced with large-scale habitat change and an imminent new predator, how are land birds on Saipan fairing? The Birds B. Kumiu E. VanderWerf T. Shears Yellow Bittern White-throated Ground-Dove Mariana Fruit-Dove J. Yue T. Pete Collared Kingfisher Micronesian Myzomela The Birds A. Leishman E. VanderWerf S. Vogt Rufous Fantail Nightingale Reed-Warbler Bridled White-eye T. Pete E. VanderWerf Golden White-eye Micronesian Starling The Birds S. Vogt E. VanderWerf Micronesian Megapode Micronesian Swiftlet T. Rosell L. Kee T. Pete Island Collared-Dove Eurasian Tree Sparrow Orange-cheeked Waxbill Sampling • 1982 (Engbring et al.) • 1997 (USFWS) • 2007 (USFWS) • Standard point- transect sampling – 14 transects – 244-248 stations – 242 resampled Estimation • Fit a species specific detection function to account for birds present but missed • Estimate density and variance by species – Global detection function – Account for covariates (eg weather) – Annual estimates generated Trends • Determine trend with repeated measures ANOVA – Densities were log + 1 transformed – Compound symmetry variance-covariance structure – Kenward-Roger adjustment to df – Tukey’s adjustment for multiple-comparisons • Increasing, stable or declining trends Increasing Densities 40 140 35 A B B 120 A A B 30 100 25 80 20 60 Density 15 Density 10 40 5 20 0 0 1980 1985 1990 1995 2000 2005 2010 1980 1985 1990 1995 2000 2005 2010 Year Year Yellow Bittern White-throated Ground-dove 700 300 600 A A B 250 A B C 500 200 400 150 300 Density 200 Density 100 100 50 0 0 1980 1985 1990 1995 2000 2005 2010 1980 1985 1990 1995 2000 2005 2010 Year Year Micronesian Myzomela Micronesian Starling Increasing Densities 8 7 A B B 6 5 4 Density 3 2 1 0 60 1980 1985 1990 1995 2000 2005 2010 50 A B B Year 40 30 Eurasian Tree Sparrow Density 20 10 0 1980 1985 1990 1995 2000 2005 2010 6 Year 5 A A B 4 Island Collared-dove 3 Density 2 1 0 1980 1985 1990 1995 2000 2005 2010 Year Orange-cheeked Waxbill Stable Densities 60 50 A B A 40 30 Density 20 10 0 1980 1985 1990 1995 2000 2005 2010 70 60 A A A Year 50 40 Collared Kingfisher 30 Density 20 10 0 1980 1985 1990 1995 2000 2005 2010 70 60 Year A A A 50 40 30 Mariana Fruit-dove Density 20 10 0 1980 1985 1990 1995 2000 2005 2010 Year Bridled White-eye Decreasing Densities 1200 2000 1000 A B C A B C 1500 800 600 10% 1000 Density Density 23% 400 41% 500 29% 200 47% 45% 0 0 1980 1985 1990 1995 2000 2005 2010 1980 1985 1990 1995 2000 2005 2010 Year Year Rufous Fantail Golden White-eye 80 70 A B C 60 50 40 30% Density 30 20 44% 10 61% 0 1980 1985 1990 1995 2000 2005 2010 Year Nightingale Reed-Warbler Other Birds 500 400 A A B 300 200 Density Micronesian Megapode 100 • Very rare species 0 • 1980 1985 1990 1995 2000 2005 2010 Detected 5 1 0 Year • Saipan population declining • Although more common on Micronesian Swiftlet other Mariana Islands • numbers a magnitude smaller • no movement assumption violated • preferentially record near point • distances biased low > overestimates Rapid human development • 429% increase between 1980 & 2000; subsequent decline • Coastal plain, southern plateau, Kagman peninsula (70%) Land class & disturbance Saipan 100 • Introduced Forest 80 60 – 27% Percent 40 • Secondary Forest 20 0 – Forest Secondary Agroforest Nonforest 30% Vegetation Land Class • Agroforest Saipan – 11% 100 80 • Minimum Disturbed 60 40 – 68% Percent 20 Falanruw et al. 1989 0 Introduced Limestone Casuarina Forest Type Nightingale Reed-Warbler • Regional Comparisons • Habitat Associations Photo by CNMI-DFW NIRW Regional Comparisons • Little development – Suicide – Tanapag • More development – Garapan – Kagman – Susupe – Fadang • Repeated measures ANOVA NIRW Regional Comparisons 2 Less Development More Development . 1.5 a b b a a b a b b a b c 1 a a a a a b b b 0.5 NIRW Density (SE) 0 1982 1997 2007 1982 1997 2007 1982 1997 2007 1982 1997 2007 1982 1997 2007 1982 1997 2007 Suicide Tanapag Garapan Kagman Susupe Fadang Year and Region NIRW Habitat Associations • Suitable habitat – Open, Secondary forest and Tangantangan thicket • Less suitable habitat – Golf course, Limestone forest and Residential • 2-way repeated measures ANOVA NIRW Habitat Associations • 58 to 22 birds/km2 Habitat 1982 2007 • Year & Habitat effects Suitable Densities • Large-scale habitat change Open 37 22 • Imminent new predator – SF 31 25 brown tree snake TT 40 27 • Saipan Upland Mitigation Less Suitable Bank (2002) GC 38 4 • Surveying frequency LF 18 8 • Surveying effort • Demographic studies Res 60 5 Acknowledgements • Funding: • Data Sets – CNMI Division of Fish – 1982: Engbring, Ramsey & and Wildlife Wildman – U.S. Fish and Wildlife – 1997: USFWS Service • Bird Observers – U.S. Geological – C. Aguon, F. Amidon, P. Survey – PIERC Ashman, J. Engbring, J. Lepson, A. Marshall, G. • Thanks to: Martin, P. Pyle, N. Shema, – M. Gorresen, J. P. Radley, M. Reynolds, & Hatfield, R. Holden, S. L. Williams Kremer, & L. Mehrhoff .
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