Table 2: Truncation distance (w), number of detections (n), detection probability beyond 300 m, fitted detection model, goodness of fit assessment (see Methods), detection probability (P, with its % CV), and difference in density estimates and coefficient of variation between 300 m and 1000 m wide line-transects, by survey type, species and behavior group for data collected during five seabirds at-sea surveys in the Gulf of St. Lawrence in 2009 and 2010. Goodness of fit statistics were classified as poor (α < 0.05) and good otherwise.
Survey type |
Species |
Behavior |
w |
n |
Detection Probability (300 - 1000 m) |
Model1 |
Goodness of fit |
P |
%CV (P) |
Diff. in estimated density (birds/km2) with untruncated data |
Diff. in coefficient of variation with untruncated data |
Line- transect |
Aerialists |
Fly |
1000 |
2497 |
0.082 |
HN Cos (2) |
Poor |
0.23 |
21 |
|
|
Swim |
1000 |
553 |
0.058 |
HR SP |
Good |
0.19 |
12 |
|
|
Alcids |
Fly |
1000 |
830 |
0.093 |
HR SP |
Good |
0.17 |
14 |
|
|
Swim |
1000 |
414 |
0.023 |
HR SP |
Good |
0.17 |
14 |
|
|
Point- transect |
Aerialists |
Fly |
1000 |
2497 |
0.084 |
HN Cos |
Poor |
0.13 |
11 |
|
|
Swim |
1000 |
429 |
0.061 |
UNI SP |
Marginal (p=0.072) |
0.15 |
14 |
|
|
Alcids |
Fly |
1000 |
830 |
0.264 |
HN Cos + Observer |
Good |
0.19 |
17 |
|
|
Swim |
1000 |
326 |
0.024 |
UNI SP |
Poor |
0.10 |
9 |
|
|
Line- transect |
Aerialists |
Fly |
300 |
1841 |
- |
HN Cos (2) obs + wind |
Good |
0.52 |
2 |
0.190 |
-0.006 |
Swim |
300 |
427 |
- |
HN Cos (2) obs + wind |
Good |
0.49 |
46 |
0.005 |
-0.140 |
Alcids |
Fly |
300 |
594 |
- |
HN Cos (2) obs + wind |
Good |
0.43 |
40 |
-0.041 |
-0.087 |
Swim |
300 |
364 |
- |
HN Cos (2) obs + wind |
Good |
0.55 |
51 |
-0.002 |
-0.009 |
Point- transect |
Aerialists |
Fly |
300 |
949 |
- |
HN Cos (2) obs |
Poor |
0.47 |
2 |
0.373 |
-0.211 |
Swim |
300 |
248 |
- |
Uniform |
Poor |
1.00 |
0 |
0.019 |
-0.015 |
Alcids |
Fly |
300 |
306 |
- |
UNI Cos |
Poor |
0.76 |
12 |
-0.051 |
0.066 |
Swim |
300 |
225 |
- |
HN Cos (2) obs + wind |
Marginal |
0.59 |
44 |
0.137 |
0.089 |
1 Abbreviations describe key functions uniform (UNI), half-normal (HN), and hazard-rate (HR) and expansion terms cosine (Cos), simple polynomial (SP), and hermite polynomial (HP). Covariates that were selected in MCDS models included: observer (obs), seastate (following Beaufort scale), and wind speed in knots (wind).