1) The study tracked surf scoters in the Salish Sea using satellite transmitters to determine their nocturnal habitat use and movements between diurnal and nocturnal areas. 2) It found that surf scoters traveled farther on average in the South Puget Sound region and moved offshore at night to deeper waters compared to their diurnal foraging areas nearshore. 3) Logistic regression modeling revealed that minimum distance to shore, water depth, tidal current, and vessel traffic density were significant predictors of surf scoter nocturnal habitat preference, with preferences for deeper, more offshore areas with less vessel traffic.

1. Nocturnal Habitat Selection of Surf Scoters in the Salish Sea
Melanitta perspicillata
By L. Hamiltonƚ, J. R. Evensonŧ, and D. L. Robertsƚ
ȽGraduate Program on the Environment, The Evergreen State College, Olympia, WA, email: hamlin06@evergreen.edu
Ŧ Waterfowl Survey and Sea Duck Specialist, WDFW, email: joseph.evenson@dfw.wa.gov
Introduction
Surf Scoters are sea ducks that utilize the
Salish Sea during all annual life stages
except breeding. They are present all year,
but most common from August through
May. They are most often observed
foraging for mussels, clams and herring
eggs along the shoreline. Surf Scoters are
one of the least studied of all North
American duck species and populations
indicate a declining trend since 1955.
Winter estimates from the Puget Sound
indicate a 77 percent decline since 1979.
Research Objectives
1) Determine Surf Scoter nocturnal habitat use area characteristics
2) Determine what factors influence the selection of identified resting
areas through resource selection probability analysis
3) Develop predictive models to estimate likely nocturnal resting areas
across the Salish Sea.
As is true for most marine bird species, all Surf Scoter surveys have
been conducted during diurnal periods, resulting in distribution data that
lacks a nocturnal component. These data are what currently guides
conservation and management decisions in the Salish Sea. Without a
nocturnal component, our knowledge on winter habitat requirements for
Surf Scoters is incomplete and planning efforts are insufficient.
Determining nocturnal use area habitat characteristics fills an important
data gap within Surf Scoter winter habitat requirements and overall
ecology.
To identify influencing factors Washington
Department of Fish and Wildlife (WDFW),
with funding from the Sea Duck Joint
Venture, implanted surf scoters with Platform
Terminal Transmitters (PTT’s) during
winters of 2003-2006 to document the
ecology of their annual life stages.
Methods
To determine how far Surf Scoters will travel between diurnal foraging
areas and nocturnal resting areas, we measured distance traveled
between diurnal and nocturnal locations when both were present within
one Argos duty cycle. We compared distances traveled between four
regions within the Salish Sea with analysis of variance and means
comparisons for all pairs (ANOVA, Tukey-Kramer HSD; JMP®,
Version 11. SAS Institute Inc., Cary, NC, 1989-2007).
We investigated nocturnal habitat preferences with a use vs. pseudo-
non-use resource selection design. We generated 5,100 random
locations within the Salish Sea Study area using ArcMap. For each
nocturnal satellite location and random pseudo-non-use location we
measured minimum distance to shore, water depth, tidal current,
exposure of nearest shoreline and vessel traffic density using various
spatial layers in ArcMap. We compared measurements between use and
pseudo-non-use points with t-tests (JMP®, Version 11).
We determined which habitat variables were the best predictors of
nocturnal presence using logistic regression (JMP®, Version 11) and
evaluated competing models with Akaike’s information criterion
adjusted for small sample sizes and AICc weights. Through the subset
model selection approach we evaluated 4 predictor variables; minimum
distance to shore, water depth, root-mean square tidal current, and
vessel traffic density.
Results
From the original filtered
data sets from 34 Surf
Scoters, we measured 233
movements between diurnal
and nocturnal locations
throughout the Salish Sea
resulting in an average
distance traveled of 3,967m.
ANOVA revealed variation
between regions (F3 = 5.22,
Data Preparation
Removed:
- Low Accuracy Data
- Civil Twilight
Locations
- Diurnal Locations
- Flightless Moult
Locations
- Auto correlated
Locations
Use
Pseudo-non-
use F
Range of
nocturnal use
Variable 𝑋 SE 𝑋 SE
Min Dist to Shore (m) 1388 33 3605 49 -37.14*** 2 - 8415
Water Depth (m) -34 41 -115 1.42 42.83 ˗251 - 0
Tidal Current (RMS) 0.09 0.002 0.22 0.003 -33.15*** 0.01 – 0.87
Shoreline ExposureA 2.40 0.60 3.1 0.01 0.09***(U) 1-4
Vessel Traffic Density 0.22 0.02 0.54 0.03 -8.23*** 0 – 9.12
A signifies that difference was evaluated with chi squared likelihood statistic.
*** signifies P < 0.0001 at 95% confidence.
Table 1. Mean comparisons for 5 habitat variables.
𝒑 = 0.1257 + 0.0131*Depth + -4.9350*Tidal + -0.0519*Vessel +
-4.48E-05*MinDistShore
Of the 15 candidate nocturnal presence prediction models, the full
model best fit the data, accounting for 71% of the AICc weight and was
3.5 times more likely to explain habitat preference than the next best
fitting model. This is strong but not unequivocal (w>0.90) support for
the best AICc model, so model averaging (Burnham and Anderson 2002)
was conducted. Only the 4 confidence set models were averaged as they
accounted for 99% of the AICc weight. This resulted in our nocturnal
presence model below:
Discussion
We provide a quantitative analysis that shows that Surf Scoters utilize nocturnal habitats that differ from documented diurnal distributions. Our
nocturnal location data has confirmed that Surf Scoters move offshore to deeper water to rest in comparison to diurnal foraging areas. The longer
distances traveled in the South Puget Sound region reinforces the importance of the characteristics that are selected. This region is almost entirely
comprised of narrow passages and inlets and demonstrates that Surf Scoters balance utilizing preferred nocturnal habitat, with minimizing distances
from food resources These findings set a precedent for future studies regarding a variety of marine birds displaying similar movement and behavior
characteristics and identifies a need to consider nocturnal distribution when assessing the conservation status of marine bird species in general.
Habitat in deeper and more open water is accompanied by threats (e.g. vessel traffic) that are different than those Scoters face in nearshore habitats.
Washington State waters see ~ 230,000 transits annually, including nearly 8,000 deep draft vessel movements. Our nocturnal data demonstrated a
strong avoidance of high vessel traffic in the Salish Sea. As rest periods are critical for conserving energy during winter months, vessel disturbance
would be detrimental during nocturnal periods. This suggest the possibility of night time vessel traffic limiting available nocturnal habitat for Surf
Scoters.
In addition to vessel traffic being a direct daily disturbance, bird distributions that overlap or occur in close proximity to oil transportation are at
greater risk of contamination. Many small oil spills (1000 L or less) go undetected or unreported. These small-scale oil discharges are more widely
distributed and happen more frequently, causing a greater ecological impact and potentially have cumulative effects on seabird populations. Also,
determination of important nocturnal use areas will improve catastrophic oil spill response plans, which do not currently account for nocturnal bird
use areas in Washington.
Figure 3. Map showing nocturnal locations in
purple, diurnal locations in yellow and current
tanker vessel traffic density in the Salish Sea.
3967
3629
3854
3218
6066
0 1000 2000 3000 4000 5000 6000 7000
ALL REGIONS
STRAIT OF GEORGIA
NORTH PUGET SOUND
CENTRAL PUGET SOUND
SOUTH PUGET SOUND
Means comparisons between 1,064 nocturnal use locations and 5,002
pseudo-non-use locations revealed differences in minimum distance to
shore, root-mean-squared tidal current, exposure of nearest shoreline and
vessel traffic density (Table 1).
Figure 2. Average distance traveled (m) by Surf Scoters
between diurnal and nocturnal locations within a 24
hour period within the Salish Sea.
P = 0.0017) and a post hoc Tukey test showed a difference in mean
distance traveled between the South Puget Sound and the Central Puget
Sound region (q = 2.59, P = 0.0008) (Figure 2).
Distance (in meters)
Figure 1. Flow chart of data manipulation
conducted in preparation for analysis.