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
Yellow Bittern
T. Shears
White-throated Ground-Dove
J. Yue
Collared Kingfisher
Mariana Fruit-Dove
T. Pete
Micronesian Myzomela
The Birds
A. Leishman
Rufous Fantail
E. VanderWerf
S. Vogt
Nightingale Reed-Warbler
T. Pete
Golden White-eye
Bridled White-eye
E. VanderWerf
Micronesian Starling
The Birds
S. Vogt
Micronesian Megapode
T. Rosell
Island Collared-Dove
E. VanderWerf
Micronesian Swiftlet
L. Kee
Eurasian Tree Sparrow
T. Pete
Orange-cheeked Waxbill
Sampling
• 1982 (Engbring et al.)
• 1997 (USFWS)
• 2007 (USFWS)
• Standard pointtransect 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
35
30
25
20
15
10
5
0
1980
B
B
A
Density
Density
A
1985
1990
1995
2000
2005
140
120
100
80
60
40
20
0
1980
2010
A
1985
1990
Year
1980
2005
2010
White-throated Ground-dove
A
300
B
250
Density
Density
A
2000
Year
Yellow Bittern
700
600
500
400
300
200
100
0
1995
B
A
B
C
200
150
100
50
1985
1990
1995
Year
Micronesian Myzomela
2000
2005
2010
0
1980
1985
1990
1995
Year
Micronesian Starling
2000
2005
2010
Density
Increasing Densities
60
Density
50
8
7
6
5
4
3
2
1
0
A
1980
A
B
B
1985
1990
B
1995
B
2000
2005
2010
Year
40
Eurasian Tree Sparrow
30
20
10
0
1980
1985
1990
1995
2000
2005
2010
6
Year
Density
Island Collared-dove
5
A
A
B
4
3
2
1
0
1980
1985
1990
1995
2000
Year
Orange-cheeked Waxbill
2005
2010
Stable Densities
60
Density
50
A
B
A
40
30
20
10
Density
0
70
60
50
40
30
20
10
0
1980
A
1980
A
1985
1990
A
1995
2000
2005
2010
Year
Collared Kingfisher
1985
1990
1995
2000
2005
2010
Mariana Fruit-dove
Density
Year
70
60
50
40
30
20
10
0
A
1980
A
1985
1990
1995
Year
Bridled White-eye
A
2000
2005
2010
Decreasing Densities
Density
1000
A
800
B
C
10%
600
1985
1990
A
B
1000
23%
500
47%
0
1980
1500
41%
400
200
2000
Density
1200
45%
0
1995
2000
2005
2010
1980
1985
1990
Year
Year
Rufous Fantail
Golden White-eye
Density
1995
80
70
60
50
40
30
20
10
0
1980
A
B
C
30%
61%
1985
1990
1995
44%
2000
Year
Nightingale Reed-Warbler
2005
2010
C
29%
2000
2005
2010
Other Birds
500
Micronesian Megapode
•
•
•
•
Very rare species
Detected 5 1 0
Saipan population declining
Although more common on
other Mariana Islands
Density
400
A
A
B
300
200
100
0
1980
1985
1990
1995
2000
2005
2010
Year
Micronesian Swiftlet
• 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
• Introduced Forest
100
Percent
80
– 27%
60
• Secondary Forest
40
20
0
Forest
Secondary Agroforest
Vegetation
Nonforest
– 30%
• Agroforest
Land Class
– 11%
Saipan
100
• Minimum Disturbed
Percent
80
60
– 68%
40
Falanruw et al. 1989
20
0
Introduced
Limestone
Forest Type
Casuarina
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
Less Development
More Development
a
1982
b
c
2007
b
1997
b
2007
2007
a
1997
1997
0.5
b
1982
b
b
a
2007
a
b
a
1997
a
b
1982
a
b
2007
a
1982
a
2007
a
1997
1
1997
1.5
Suicide
Tanapag
1982
0
1982
NIRW Density (SE) .
2
Garapan
Kagman
Year and Region
Susupe
Fadang
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
• Year & Habitat effects
• Large-scale habitat change
• Imminent new predator –
brown tree snake
• Saipan Upland Mitigation
Bank (2002)
• Surveying frequency
• Surveying effort
• Demographic studies
Habitat 1982 2007
Suitable Densities
Open 37
22
SF
31
25
TT
40
27
Less Suitable
GC
38
4
LF
18
8
Res
60
5
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