Status and Trends of the Land Bird Avifauna on Saipan

Transcription

1 Status and Trends of the Land Bird Avifauna on Saipan 28 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

2 Outline Introduction Sampling Population estimation Trend estimation Estimates Threats Focal Species Nightingale Reed-Warbler

3 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?

4 The Birds B. Kumiu E. VanderWerf T. Shears Yellow Bittern White-throated Ground-Dove Mariana Fruit-Dove J. Yue Collared Kingfisher T. Pete Micronesian Myzomela

5 The Birds A. Leishman E. VanderWerf S. Vogt Rufous Fantail Nightingale Reed-Warbler Bridled White-eye Golden White-eye T. Pete E. VanderWerf Micronesian Starling

6 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

7 Sampling 1982 (Engbring et al.) 1997 (USFWS) 27 (USFWS) Standard pointtransect sampling 14 transects stations 242 resampled

8 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

9 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

10 Increasing Densities A B B Yellow Bittern A A B White-throated Ground-dove A A B A B C Micronesian Myzomela Micronesian Starling

11 Increasing Densities A B B Island Collared-dove A B B Eurasian Tree Sparrow A A B Orange-cheeked Waxbill

12 Stable Densities A A A Mariana Fruit-dove A B A Collared Kingfisher A A A Bridled White-eye

13 Decreasing Densities A B C 1% 41% 47% A B C 23% 29% 45% Rufous Fantail Golden White-eye A B C 3% 61% Nightingale Reed-Warbler 44%

14 Other Birds Micronesian Megapode Very rare species Detected 5 1 Saipan population declining Although more common on other Mariana Islands A A B Micronesian Swiftlet numbers a magnitude smaller no movement assumption violated preferentially record near point distances biased low > overestimates

15 Rapid human development 429% increase between 198 & 2; subsequent decline Coastal plain, southern plateau, Kagman peninsula (7%)

16 Land class & disturbance Saipan Percent Forest Secondary Vegetation Land Class Saipan Agroforest Nonforest Introduced Forest 27% Secondary Forest 3% Agroforest 11% Percent Minimum Disturbed 68% Falanruw et al Introduced Limestone Casuarina Forest Type

17 Nightingale Reed-Warbler Regional Comparisons Habitat Associations Photo by CNMI-DFW

18 NIRW Regional Comparisons Little development Suicide Tanapag More development Garapan Kagman Susupe Fadang Repeated measures ANOVA

19 NIRW Regional Comparisons 2 Less Development More Development NIRW (SE) a a a a a b b b a b b a a b a b b a b c Suicide Tanapag Garapan Kagman Susupe Fadang and Region

20 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

21 NIRW Habitat Associations 58 to 22 birds/km2 & Habitat effects Large-scale habitat change Imminent new predator brown tree snake Saipan Upland Mitigation Bank (22) Surveying frequency Surveying effort Demographic studies Habitat Suitable Densities Open SF TT 4 27 Less Suitable GC 38 4 LF 18 8 Res 6 5

22 Acknowledgements Funding: CNMI Division of Fish and Wildlife U.S. Fish and Wildlife Service U.S. Geological Survey PIERC Thanks to: M. Gorresen, J. Hatfield, R. Holden, S. Kremer, & L. Mehrhoff Data Sets 1982: Engbring, Ramsey & Wildman 1997: USFWS Bird Observers C. Aguon, F. Amidon, P. Ashman, J. Engbring, J. Lepson, A. Marshall, G. Martin, P. Pyle, N. Shema, P. Radley, M. Reynolds, & L. Williams