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Effects of Roadside Transect Width on Waterfowl and Wetland Estimates

Tables


Table 1.  Basin densities (mean ± SE) and bias (mean ± SE; range in parentheses) for 40-km² plots and 800-m and 400-m wide transects, for 45 plots in North Dakota using NWI data.  Bias is calculated as the difference between basin density on transect and that on the plot.  Biases with 95% confidence intervals not including zero are highlighted in bold.
Basin Water Regime Sample Basin Density (No./Ha) Bias
No./Ha % Plot Densitya
Temporary Plot 0.0647 ± 0.0085    
  800 m 0.0657 ± 0.0085 0.0010 ± 0.0007 1.5 ± 1.1
400 m 0.0657 ± 0.0083 0.0011 ± 0.0014 1.7 ± 2.2
Seasonal Plot 0.0694 ± 0.0065    
  800 m 0.0735 ± 0.0069 0.0041 ± 0.0012 5.9 ± 1.7
400 m 0.0842 ± 0.0078 0.0148 ± 0.0022 21.3 ± 3.2
Semipermanent Plot 0.0094 ± 0.0011    
  800 m 0.0096 ± 0.0012 0.0001 ± 0.0002 1.1 ± 2.1
400 m 0.0096 ± 0.0014 0.0002 ± 0.0004 2.1 ± 4.3
All basins Plot 0.1435 ± 0.0135    
  800 m 0.1487 ± 0.0138 0.0052 ± 0.0017 3.5 ± 1.2
400 m 0.1597 ± 0.0146 0.0161 ± 0.0028 11.2 ± 2.0
a Bias (no./ha) expressed as a percentage of plot density.

 

Table 2.  Basin densities (mean ± SE) and bias (mean SE; range in parentheses) for 40-km² plots and 800-m and 400-m wide transects, when excavated seasonal and temporary wetlands are excluded, for 45 plots in North Dakota, using NWI data.  Bias is calculated as the difference between basin density on transect and that on the plot.  All 95% confidence intervals for biases included zero.
Basin Water Regime Sample Basin Density (No./Ha) Bias
No./Ha % Plot Densitya
Temporary Plot 0.0639 0.0085    
  800 m 0.0646 0.0084 0.0007 0.0007 1.1 1.1
400 m 0.0641 0.0082 0.0001 0.0013 0.2 2.0
Seasonal Plot 0.0618 0.0062    
  800 m 0.0622 0.0064 0.0004 0.0012 0.6 1.9
400 m 0.0652 0.0069 0.0034 0.0019 5.5 3.1
All basins Plot 0.1257 0.0124    
  800 m 0.1268 0.0124 0.0010 0.0017 0.8 1.4
400 m 0.1292 0.0145 0.0035 0.0027 2.8 21.8
a Bias (no./ha) expressed as a percentage of plot density.

 

Table 3.  Basin density (mean ± SE, range) on inner and outer transect widths, and difference between the inner and outer transect widths (mean SE; range in parentheses) for 45 plots in North Dakota, using NWI data.  Differences highlighted in bold indicate those differences with 95% confidence intervals that do not include zero.
Basin Water Regime Inner Transect Width Outer Transect Width Mean Difference (Inner-Outer) No. Plots
Inner > Outer Outer > Inner
Temporary 0.0657 ± 0.0083 0.0571 ± 0.0078 0.0086 ± 0.0024 33 12
(0.0026, 0.2644) (0, 0.2629) (-0.0290, 0.0565)
Seasonal 0.0843 ± 0.0078 0.0532 ± 0.0059 0.0311 ± 0.0037 43 2
(0.0032, 0.2340) (0, 0.2205) (-0.0030, 0.0977)
Semipermanent 0.0096 ± 0.0014 0.0084 ± 0.0010 0.0012 ± 0.0008 26 19
(0.0006, 0.0422) (0, 0.0295) (-0.0089, 0.0208)
All basins 0.1597 ± 0.0146 0.1188 ± 0.0118 0.0409 ±0.0049 43 2
(0.0084, 0.4335) (0.0029, 0.3374) (-0.0131, 0.1069)

 

Table 4.  Mean γ (mean ± SE), a correction factor that takes into account variation in basin densities and area, for 800-m and 400-m transects and for the outer transect width, and difference between inner (400-m transect) and outer transect widths (mean ± SE; range in parentheses) for 41 plots in North Dakota, 1995.  Significant (P < 0.05) differences are highlighted in bold.  N = number of plots.
   γ   No. Plots
Species 800-m Transect 400-m Transect (Inner Transect Width) Outer Width Mean Difference (Inner-Outer) Inner > Outer Outer > Inner
Mallard
   (N = 38)
2.5071 ± 0.4685 2.5718 ± 0.5149 2.5705 ± 0.5250 0.0013 ± 0.5078 13 22
      (-4.9130, 14.8349)
Pintail
   (N = 38)
1.8884 ± 0.4535 2.0308 ± 0.5114 1.7809 ± 0.5246 0.2499 ± 0.6382 16 17
      (-7.9660, 15.9057)
Gadwall
   (N = 39)
1.4332 ± 0.2626 1.3978 ± 0.3397 1.6520 ± 0.3474 -0.2542 ± 0.2856 18 14
      (-7.9637, 3.3007)
Blue-winged teal
   (N = 39)

1.1380 ± 0.1382 1.2610 ± 0.1479 0.8468 ± 0.1524 0.4142 ± 0.1512 23 9
      (-1.1076, 3.2672)
N. Shoveler
   (N = 41)
1.7498 ± 0.3575 1.9999 ± 0.3428 1.0977 ± 0.3554 0.9023 ± 0.4352 27 7
      (-2.0593, 15.1808)

 

Table 5.  Adjustment index for visibility of ducks counted on inner and outer transect widths during 2 periods, and difference between the inner and outer transect widths (mean ± SE; range in parentheses; n) for 45 plots in North Dakota, 1995.  Differences whose 95% confidence intervals do not include zero are highlighted in bold.  For inner and outer transect widths, N = total number of basins observed; for difference, N = number of plots.
Count Basin Water Regime Outer Transect Width Inner Transect Width Mean Difference (Inner-Outer)
1-15 May
Temporary 2.94 ± 0.40 2.44 ± 0.34 -1.60 ± 0.96
  (1.05, 28.57) (1.05, 200.00) (-18.95, 10.43)
N = 184 N = 670 N = 32
Seasonal 3.31 ± 0.87 2.04 ± 0.11 -1.87 ± 0.99
  (1.05, 200.00) (1.05, 28.57) (-29.20, 1.81)
N = 245 N = 1308 N = 35
Semipermanent 2.99 ± 0.57 4.28 ± 1.27 0.27 ± 0.90
  (1.05, 50.00) (1.05, 200.00) (-10.52, 21.63)
N = 108 N = 225 N = 29
All basins 3.12 ± 0.44 2.39 ± 0.18 -4.33 ± 1.21
  (1.05, 200.00) (1.05, 200.00) (-30.43, 5.73)
N = 537 N = 2203 N = 38
16 May-5 June Temporary 6.23 ± 0.88 4.09 ± 0.29 -3.03 ± 1.51
  (1.05, 200.00) (1.05, 66.67) (-29.34, 9.50)
N = 241 N = 668 N = 33
Seasonal 7.34 ± 1.75 3.04 ± 0.21 -5.20 ± 2.11
  (1.05, 400.00) (1.05, 100.00) (-63.88, 4.89)
N = 310 N = 1313 N = 35
Semipermanent 10.72 ± 0.58 6.14 ± 0.88 1.82 ± 1.57
  (1.05, 400.00) (1.05, 400.00) (-8.09, 35.01)
N = 105 N = 240 N = 25
All basins 7.47 ± 1.17 3.69 ± 0.23 -0.24 ± 0.95
  (1.05, 400.00) (1.05, 400.00) (-9.91, 31.72)
N = 656 N = 2221 N = 37

 

Table 6.  Proportion of wetland basins that had to be replaced from the sample of 800-m transects, proportion replaced for inner and outer transect widths, and the difference in proportion of basins dropped between inner and outer transect widths (mean ± SE; range in parentheses) for 45 plots in North Dakota, 1995.  Inner transect width is the same as the 400-m transect.  Differences were calculated using square-root transformed values.
Basin Water Regime 800-m Transect Inner Transect Width Outer Transect Width Mean Difference (Inner-Outer)
Temporary 22.17 ± 2.94 12.21 ± 2.18 12.56 ± 2.15 -2.98 ± 4.43
  (0.0-87.50) (0.0-50.00) (0.0-75.00) (-66.67, 70.71)
Seasonal 19.05 ± 1.79 13.65 ± 2.69 10.26 ± 1.43 1.59 ± 3.63
  (0.0-51.67) (0.0-71.43) (0.0-45.23) (-41.60, 51.38)
Semipermanent 20.25 ± 2.67 14.45 ± 3.33 18.34 ± 3.04 -8.10 ± 4.32
  (0.0-66.67) (0.0-100) (0.0-100) (-70.71, 60.30)
All basins 19.35 ± 1.80 12.78 ± 2.40 10.20 ± 1.05 0.31 ± 3.34
  (0.0-52.00) (0.0-62.00) (0.0-33.00) (-32.93, 59.28)

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