Monitoring Migrating Shorebirds at the Tofino Mudflats in British Columbia, Canada: is Disturbance a Concern?

Abstract

The Tofino Wah-nah-jus Hilth-hoo-is Mudflats on Vancouver Island, British Columbia, Canada, include both pristine areas and sites with residential and resort development. Shorebird counts were conducted at six sites around these mudflats in 2011 and compared with historical counts from 1988, 1989, and 1995. Temporal trends of counts did not vary among sites with different levels of disturbance. Over the entire mudflats, counts of Dunlin (Calidris alpina) moving northward had a negative trend over time (βyr = -0.04), as did counts of Western Sandpiper (Calidris mauri; βyr = -0.04), Least Sandpiper (Calidris minutilla; βyr = -0.03) and Short-billed Dowitcher (Limnodromus griseus; βyr = -0.04) moving southward. In contrast, counts of Black-bellied Plover (Pluvialis squatarola; βyr = 0.03) and Semipalmated Plover (Charadrius semipalmatus; βyr = 0.02) moving northward increased over time. Counts of Dunlin and Short-billed Dowitcher were lower at disturbed sites relative to non-disturbed sites, indicating that disturbance may be displacing birds away from some sites. Further, counts of northward migrating shorebirds were negatively correlated with the presence of people and dogs at the most disturbed site (Chesterman Beach). Monitoring and precautionary actions to address effects of disturbance at this important stopover site are warranted.

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Monitoring Migrating Shorebirds at the Tofino Mudflats in
British Columbia, Canada: is Disturbance a Concern?
Author(s): Mark C. Drever , Barbara A. Beasley , Yuri Zharikov , Moira J. F.
Lemon , Paul G. Levesque , Michael D. Boyd and Adrian Dorst
Source: Waterbirds, 39(2):125-135.
Published By: The Waterbird Society
DOI: http://dx.doi.org/10.1675/063.039.0203
URL: http://www.bioone.org/doi/full/10.1675/063.039.0203
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Waterbirds
Journal of the Waterbird society
Vol. 39, No. 2 2016 Pages 125-228
Monitoring Migrating Shorebirds at the Tono Mudats in British
Columbia, Canada: is Disturbance a Concern?
Mark C. Drever1,*, BarBara a. Beasley2, yuri Zharikov3, Moira J. F. leMon1,
Paul G. levesque4, MiChael D. BoyD5 anD aDrian Dorst6
1Canadian Wildlife Service, Environment Canada, 5421 Robertson Road, Delta, British Columbia, V4K 3N2, Canada
2Association of Wetland Stewards for Clayoquot & Barkley Sounds, P.O. Box 927, Ucluelet, British Columbia,
V0R 3A0, Canada
3Pacific Rim National Park Reserve, P.O. Box 280, 2040 Pacific Rim Highway, Ucluelet, British Columbia,
V0R 3A0, Canada
4WildResearch, 2258 Oxford Street, Vancouver, British Columbia, V5L 1G1, Canada
5Amec Foster Wheeler, 111 Dunsmuir Street, Suite 400, Vancouver, British Columbia, V6B 5W3, Canada
6Tofino Birding, P.O. Box 503, Tofino, British Columbia, V0R 2Z0, Canada
*Corresponding author; E-mail: mark.drever@canada.ca
Abstract.—The Tofino Wah-nah-jus Hilth-hoo-is Mudflats on Vancouver Island, British Columbia, Canada, in-
clude both pristine areas and sites with residential and resort development. Shorebird counts were conducted at
six sites around these mudflats in 2011 and compared with historical counts from 1988, 1989, and 1995. Temporal
trends of counts did not vary among sites with different levels of disturbance. Over the entire mudflats, counts of
Dunlin (Calidris alpina) moving northward had a negative trend over time (βyr = -0.04), as did counts of Western
Sandpiper (Calidris mauri; βyr = -0.04), Least Sandpiper (Calidris minutilla; βyr = -0.03) and Short-billed Dowitcher
(Limnodromus griseus; βyr = -0.04) moving southward. In contrast, counts of Black-bellied Plover (Pluvialis squatarola;
βyr = 0.03) and Semipalmated Plover (Charadrius semipalmatus; βyr = 0.02) moving northward increased over time.
Counts of Dunlin and Short-billed Dowitcher were lower at disturbed sites relative to non-disturbed sites, indicating
that disturbance may be displacing birds away from some sites. Further, counts of northward migrating shorebirds
were negatively correlated with the presence of people and dogs at the most disturbed site (Chesterman Beach).
Monitoring and precautionary actions to address effects of disturbance at this important stopover site are war-
ranted. Received 1 September 2015, accepted 21 January 2016.
Key words.—disturbance, migration stopover, Pacific Flyway, predation risk, shorebirds, tourism, trends.
Waterbirds 39(2): 125-135, 2016
Many species of shorebirds in North
America are vulnerable to habitat loss and
degradation, and increased human distur-
bance at key locations throughout their
range – especially at coastal stopovers where
birds congregate in large numbers to rest
and refuel during long migrations between
southern non-breeding grounds and breed-
ing grounds in the north (Myers et al. 1987).
Human recreational disturbance can reduce
foraging opportunities and energy stores if
disturbed birds spend more time vigilant
and fleeing or shifting habitats rather than
foraging (Frid and Dill 2002). Some species
appear to be more tolerant of disturbance
than others (Pfister et al. 1992; Fitzpatrick
and Bouchez 1998), and mathematical mod-
els predict that fitness effects will occur at
threshold levels of disturbance that are spe-
cies-specific (West et al. 2002; Goss-Custard
et al. 2006).
At some migratory stopover sites in the
United States, declining trends in the num-
ber of shorebirds have been correlated with
increased human recreational disturbance,
and, in response, temporary beach closures

126 WaterBirDs
to people and/or pets have been imple-
mented (Pfister et al. 1992; Burger and Niles
2013). As beach closures are not popular
with the general public (Goss-Custard et al.
2006; but see Burger and Niles 2013), reli-
able evidence of habitat use and trends in
stopover counts with respect to disturbance
levels is needed to substantiate the need for
closures.
This paper summarizes bird counts and
trends at an important coastal stopover site
for migrating shorebirds in British Colum-
bia, the Tofino Wah-nah-jus Hilth-hoo-is
Mudflats (Tofino Mudflats; Fig. 1). Surveys
conducted in the late 1980s and mid 1990s
(Butler and Kaiser 1988; Butler et al. 1992;
Butler and Lemon 2001) showed the area
was an important stopover site on the Pacific
Flyway of North America, and served as a
feeding and resting area for migrating West-
ern Sandpiper (scientific names are given
in Table 1), Whimbrel, dowitchers spp., and
other shorebird species moving northward
and southward. Since that time, human
populations around the town of Tofino have
grown and recreational use has increased,
prompting conservation concerns (Dodds
2012). The effects of increased development
and recreational use on shorebirds are ex-
pected to be negative (Pfister et al. 1992), but
have never been assessed for the different
sites within the Tofino Mudflats. The spatial
variation in frequency and intensity of dis-
turbance within the study area permitted us
to evaluate whether disturbance affected the
abundance and distribution of shorebirds
within the different sites.
This study had several objectives. First,
we compared shorebird diversity and popu-
lation counts made in 1988-1989, 1995 and
2011 to evaluate any overall trend in the
number of migrants at the Tofino Mudflats.
Second, we looked for patterns of temporal
and spatial shifts in the distribution of shore-
birds between disturbed and relatively un-
disturbed sites within the Tofino Mudflats.
We predicted a reduction in the number
of birds using disturbed sites compared to
Figure 1. Map of the Tofino Wah-nah-jus Hilth-hoo-is Mudflats on Vancouver Island, British Columbia, Canada.

shoreBirDs at toFino MuDFlats 127
undisturbed sites. Third, we examined one
site at the Tofino Mudflats area, Chesterman
Beach, which had very high levels of human
recreational use, to evaluate whether the
number of people and dogs (on- and off-
leash) were negatively associated with shore-
bird counts.
MethoDs
Study Area
The Tofino Mudflats are composed of 1,634 ha (16
km2) of intertidal mudflats and beaches located near
the town of Tofino (49° 9' 8.8" N, 125° 54' 9.0" W) on
Vancouver Island, British Columbia, Canada (Fig. 1).
The Tofino Mudflats were designated as a Wildlife Man-
agement Area under the British Columbia Wildlife Act
in 1997 (Eggen et al. 2002), an Important Bird Area in
2000 (Eggen et al. 2002), and as a site within the Western
Hemisphere Shorebird Reserve Network in 2013 (West-
ern Hemisphere Shorebird Reserve Network 2016).
Six tidal sand flats and mudflats occur in the sheltered
area between the Esowista Peninsula and Meares Island
(Fig. 1). The sheltered flats are known locally as Arakun
Flats, Ducking Flats, Doug Banks Flats (part of Jensen’s
Bay), Maltby Slough, South Bay and Grice Bay (Fig.
1). Chesterman Beach is a wave-washed sand beach on
the exposed outer west coast of the peninsula that lies
within 400 to 1,000 m of the mudflats. We considered
Chesterman Beach and Doug Banks Flats as disturbed
sites. Chesterman Beach has a relatively high residential
Table 1. Maximum daily total counts of shorebirds during six migration seasons at the Tofino Wah-nah-jus Hilth-
hoo-is Mudflats on Vancouver Island, British Columbia, Canada. n = number of daily surveys in each migration
period.
Common Name Scientific Name
Northward Southward
1988
n = 11
1995
n = 16
2011
n = 24
1988
n = 5
1989
n = 16
2011
n = 20
American Avocet Recurvirostra americana 0020 00
Black Oystercatcher Haematopus bachmani 0 0 8 0 11 82
Black-bellied Plover Pluvialis squatarola 21 83 123 2 18 24
American Golden-Plover P. dominica 1000 20
Pacific Golden-Plover P. fulva 0010 00
Semipalmated Plover Charadrius semipalmatus 109 81 127 0 42 35
Killdeer C. vociferus 0050 00
Spotted Sandpiper Actitis macularius 3061 21
Wandering Tattler Tringa incana 0010 00
Greater Yellowlegs T. melanoleuca 45 0 20 3 5 1
Lesser Yellowlegs T. flavipes 0040 30
Unidentified Yellowlegs T. sp. 0 19 0 0 0 0
Whimbrel Numenius phaeopus 249 276 1,327 49 10 1
Long-billed Curlew N. americanus 0010 00
Marbled Godwit Limosa fedoa 1170 08
Ruddy Turnstone Arenaria interpres 2210 00
Black Turnstone A. melanocephala 0 0 17 0 42 42
Red Knot Calidris canutus 2060 20
Surfbird C. virgata 0 0 19 0 0 79
Stilt Sandpiper C. himantopus 0000 21
Sanderling C. alba 0 16 10 12 86 19
Dunlin C. alpina 2,664 2,631 3,138 0 9 4
Baird’s Sandpiper C. bairdii 0020 41
Least Sandpiper C. minutilla 1,630 885 1,163 200 4,440 93
Pectoral Sandpiper C. melanotos 0000 36
Semipalmated Sandpiper C. pusilla 0020 05
Western Sandpiper C. mauri 12,295 13,915 51,527 3,812 42,934 11,622
Unidentified Sandpiper C. sp. 0 0 3,050 0 0 820
Short-billed Dowitcher Limnodromus griseus 0 0 1,451 0 0 38
Long-billed Dowitcher L. scolopaceus 0090 00
Unidentified Dowitcher L. sp. 2,398 5,970 305 140 130 0
Wilson’s Snipe Gallinago delicata 0080 10
Red-necked Phalarope Phalaropus lobatus 0010 09

128 WaterBirDs
density, and it is a very popular recreational site where
many people take their dogs. Doug Banks Flats has a
low residential density, and sections of gravel beaches
are used for walking, dog-walking and interpretive
hikes. The other sites were less disturbed: Grice Bay lies
within the Pacific Rim National Park Reserve, and its
shoreline is completely forested. Maltby Slough/South
Bay has only one or two houses, and Arakun and Duck-
ing Flats have completely forested shorelines and no
road access.
Shorebird Population Counts
Surveyors used binoculars or a spotting scope to
count the total number of shorebirds observed within
the boundaries of each survey site during the north-
ward and/or southward migration periods of 1988,
1989, 1995 and 2011. Northward migration periods oc-
curred in April and May, and southward migration oc-
curred from early August to mid-October of each year.
Observers used a small boat to count birds within the
entire area of Arakun Flats, Ducking Flats, and Grice
Bay by traveling along the outer edge of the mudflats,
and by stopping at standardized vantage points on
land. They also used a boat to survey Maltby Slough
and South Bay from the openings to each of these bays.
Doug Banks Flats was surveyed from various vantage
points on land in Browning Passage. Surveyors walked
the entire length of Chesterman Beach including the
tombolo to Frank Island. We assumed counts represent-
ed total numbers of birds present at each site. Vantage
points covered the site within 750 m, and we used notes
from previous years to ensure sites were surveyed in the
same way. For the northward migration period in 2011,
surveyors also recorded the number of people and dogs
during each shorebird survey at Chesterman Beach.
Surveys were conducted one to seven times a week
at each site, with the exception of southward migration
in 1988 when surveys were done intermittently during
the season. Data from the 1988 southward migration
were not used in these analyses as sampling effort was
not comparable to other years. Most boat surveys began
at low tide when mudflats were exposed, and contin-
ued on the rising tide. Road accessible sites were usually
surveyed during the hour before high tide or at high
tide in 2011. Surveyors counted birds individually when
they were within flocks of less than 200 birds. They es-
timated the size of larger flocks by counting 50 or 100
individuals and then estimated how many similar-sized
groups made up the entire flock. Distant flocks were
recorded as small or large shorebirds and assumed to
have the same species composition as those closer to
shore in 1995 (Butler and Lemon 2001), or identified
to species group and recorded as either “dowitchers” or
“peeps” in 2011.
Temporal Trends
For the seven most abundant species (Black-bellied
Plover, Semipalmated Plover, Whimbrel, Dunlin, Least
Sandpiper, Western Sandpiper, and Short-billed Dow-
itcher), we tested for trends in abundance using a mod-
eling approach (R Development Core Team 2015) that
allowed us to estimate temporal trends of each species
over the study period, while accounting for spatial dif-
ferences in abundance over the six sites and for season-
al variation in abundance over the migration period.
For northward migration, a mixed effects model was
fit with log-transformed count (where Y = loge(Count +
1)) as the response variable, and with Site (as a categori-
cal variable), and Year, day of the year (DOY), and DOY2
as continuous fixed effects. We also included random ef-
fects that included DOY and DOY2 as slopes and year as
an intercept, such that the relationship between mean
counts and DOY was allowed to vary by year as would oc-
cur with a chronology of migration related to yearly varia-
tion in weather and other factors. DOY was centered on
day 123 (3 May or 2 May in leap years) for modeling of
temporal trends. In this model, the fixed effect param-
eter for Year serves as the trend estimate that accounts
for within-season variation over the migration period. We
used a Likelihood Ratio Test to compare this model to
one with the identical random effects, but also included
an interaction between Site and Year, as we would expect
if trends varied among sites. If the interaction was non-
significant (P > 0.10), then it was removed, and infer-
ence was based on the simpler model. We used a signifi-
cance threshold of P = 0.10 in all statistical tests to lessen
probability of Type II error given the small size of our
dataset. If the interaction term was significant, indicating
different trends over time at each site, then we tested for
differences in the average trend at sites with high distur-
bance against trends at sites with low disturbance using
a t-test. Disturbance levels were assigned as ‘disturbed’
for Chesterman Beach and Doug Banks Flats, and ‘non-
disturbed’ for Maltby Slough/South Bay, Arakun Flats,
Ducking Flats, and Grice Bay. Mixed effects models were
fit using package lme4 in statistical program R (Bates et
al. 2014).
For southward migration, the mixed effects model
did not reliably converge, and we therefore used a gen-
eral linear model with log-transformed count as the re-
sponse variable, and with Site, Year, DOY, and DOY2 as
continuous fixed effects. DOY was centered on day 250
(7 September or 6 September in leap years) for model-
ing of temporal trends. This model did not allow the
migration schedule to vary among years. We again com-
pared this model to one that included an interaction
between Site and Year, as would occur if trends varied
among sites. If the interaction term was significant, we
tested for differences in the average trend at sites with
high disturbance against trends at sites with low distur-
bance using a t-test (Zar 1984).
Correlations of Shorebird Counts with Site Size
We reasoned that the number of birds counted at
each site was correlated with the size of the site (Butler
and Lemon 2001), and, therefore, if disturbance were
resulting in site abandonment or reduced use, then dis-
turbed sites would have lower numbers of birds than
would be expected given their area. We used a linear
mixed effects model to regress the mean number of
birds seen at each site/year as a function of site size (ha)
and whether the site was classified as low or high distur-

shoreBirDs at toFino MuDFlats 129
bance. Mean shorebird counts were loge-transformed,
and Year was included in the models as a categorical
random effect to account for year-to-year fluctuations
in overall abundance of shorebirds. A model with pa-
rameters for effects of both site size (Area) and Distur-
bance was first fit, and if the effect of Disturbance was
insignificant, then it was removed and inference based
on the simpler model.
Correlations of Shorebird Counts with Human and Dog
Use at Chesterman Beach
We evaluated effects of human recreational use on
shorebirds counted at Chesterman Beach by testing for
a negative correlation between total numbers of people
and dogs (on- and off-leash) and the numbers of shore-
birds counted at this site during the northward migra-
tion in 2011. Only the three most common species were
considered (Semipalmated Plover, Dunlin, and West-
ern Sandpiper). Initially, each measure of disturbance
(numbers of people, numbers of dogs on-leash, num-
bers of dogs off-leash) was considered separately, but all
three measures were strongly correlated and gave the
same qualitative answer, so only the total numbers of
dogs and people were used in analyses.
The numbers of shorebirds can be expected to vary
over the field season. Therefore, a Poisson general lin-
ear model was fit, with shorebird counts as the response
variable and a quadratic function of DOY to allow for
non-linear changes over the migration period, to which
we then added a term for the total numbers of people
and dogs. We then evaluated the potential effect of hu-
man and dog traffic on shorebird numbers at Chester-
man Beach by refitting each species’ model under two
scenarios of traffic volume. The high traffic scenario
was based on the 75th percentile of numbers of people
and dogs observed during the 2011 shorebird surveys
(83 people and dogs), whereas the low traffic scenario
was based on the 25th percentile (10 people and dogs).
results
Species Diversity and Composition
Observers recorded a cumulative tally
of 30 species of shorebirds over all sites and
years (Table 1). There were 29 species mov-
ing northward, including seven species that
were seen only on the northward migration:
American Avocet, Pacific Golden-Plover, Kill-
deer, Wandering Tattler, Long-billed Curlew,
Ruddy Turnstone, and Long-billed Dowitch-
er. A total of 23 species was detected moving
southward, with only one unique southward
species, the Stilt Sandpiper (Table 1).
Western Sandpiper was the most abun-
dant species, followed by Short-billed Dow-
itcher, Dunlin, Least Sandpiper, Whimbrel,
Semipalmated Plover, and Black-bellied Plo-
ver (Table 1). These seven species were the
most ubiquitous across all sites during the
northward migration (Frontispiece), and all
but Dunlin (which migrate southward later
in the year) were present at most sites on the
southward migration (Fig. 2).
Temporal Trends
Trends in shorebird abundance among
1980s, 1995, and 2011 differed by species
and by migration period (Table 2): during
northward migration, Dunlin counts across
all sites had a significant negative trend, in
contrast to Black-bellied and Semipalmated
plovers that had positive trends over time.
Two species (Whimbrel and Least Sandpip-
er) showed evidence of trends that differed
among the six sites, although trends at more
disturbed sites did not differ significantly
from the undisturbed sites (Table 2). Dur-
ing southward migration, trends between
1989 and 2011 did not differ among sites,
and counts of Western Sandpiper, Least
Sandpiper and Short-billed Dowitcher had
significant negative trends (Table 2). Semi-
palmated Plover also had a negative trend at
Chesterman Beach (Table 2).
Correlations of Shorebird Counts with Site
Size
Numbers of birds counted during north-
ward migration were significantly and posi-
tively associated with site size (Area) for five
of the seven focal species (Table 3). The Area
parameter was not significant for Whimbrel,
largely due to large numbers of Whimbrel
seen at Grice Bay, a site of intermediate size.
Evidence for an effect of disturbance on the
spatial distribution of shorebirds was found
for Dunlin and Short-billed Dowitcher. For
these two species, the parameter value for
Disturbance was significantly negative (Ta-
ble 3), indicating relatively lower counts
were found at sites classified as disturbed
sites than at non-disturbed sites, consistent
with predictions that disturbance may be dis-
placing shorebirds away from some sites. In
contrast, the Disturbance parameter was sig-

130 WaterBirDs
nificantly negative for Semipalmated Plover,
contrary to predictions, resulting from high
counts of Semipalmated Plover at Chester-
man Beach, the most disturbed site.
Correlations between numbers of birds
and site size were generally weaker dur-
ing southward migration, with only Least
Sandpiper and Western Sandpiper having
significant positive relationships (Table 3).
Parameter values for Disturbance were not
significant for any of the seven focal species
during southward migration.
Correlations of Shorebird Counts with Hu-
man and Dog Use at Chesterman Beach
The number of people and dogs on
Chesterman Beach varied widely during
the northward migration period in 2011.
Each day, we observed between 0 and 95
people (mean = 34), 0 to 6 dogs on-leash
(mean = 1), and 0 to 19 dogs off-leash
(mean = 5). The number of shorebirds var-
ied between 0 to 89 Semipalmated Plovers
(mean = 21), 0 to 141 Dunlin (mean = 13),
Figure 2. Total counts of shorebirds during southward migration at the Tofino Wah-nah-jus Hilth-hoo-is Mudflats (at
six sites) in 1988, 1989 and 2011. Note different scales on y-axes. Day of Year (Day 1 = 1 Januar y).

shoreBirDs at toFino MuDFlats 131
and 0 to 843 Western Sandpipers (mean =
92). Abundances of all three species tend-
ed to be highest in late April and early May
(Fig. 3).
For all three species, daily counts of birds
seen at Chesterman Beach were negatively
correlated with the total number of people
and dogs. In each case, the parameter for
the total number of people and dogs was
significantly negative (Table 4), indicating
fewer shorebirds were observed at Chester-
man Beach when large numbers of people
and dogs were present. When each species’
model was used to estimate shorebird abun-
dance under two different traffic scenarios,
smaller abundances of birds were pre-
dicted with high traffic volume (83 people
and dogs) than with low traffic volume (10
people and dogs), and differences varied by
species (Fig. 3). For Semipalmated Plovers,
Table 2. Temporal trends in mean counts at six sites during northward and southward migration at the Tofino
Wah-nah-jus Hilth-hoo-is Mudflats on Vancouver Island, British Columbia, based on surveys conducted in 1988,
1989, 1995, and 2011. Likelihood Ratio Test (LRT) evaluates whether trends differed significantly among sites. If
LRT was not significant, an overall trend was estimated. Trends in bold are considered significant (P < 0.10). Trend
indicates overall trend. If Trend (disturbed) is shown, then Trend refers to value calculated only from sites with
low disturbance. Significance refers to t-test between trends at sites with high and low disturbance. Semipalmated
Plover during southward migration only occurred in sufficient numbers at Chesterman Beach, and no Likelihood
Ratio Test was conducted.
Species
Likelihood Ratio Test Trend Trend (disturbed) Significance
∆LL DF PBeta SE Beta SE t P
Northward
Black-bellied Plover 7.43 5 0.19 0.02 0.01
Semipalmated Plover 5.85 5 0.32 0.02 0.01
Whimbrel 19.49 3 < 0.001 -0.02 0.01 0.005 0.02 -0.29 0.76
Dunlin 7.34 5 0.20 -0.04 0.02
Least Sandpiper 13.57 5 0.02 0.02 0.11 0.070 0.07 -0.33 0.74
Western Sandpiper 4.47 5 0.48 0.01 0.02
Short-billed Dowitcher 6.11 4 0.19 0.01 0.02
Southward
Semipalmated Plover -0.04 0.02
Least Sandpiper 18.40 4 0.11 -0.03 0.01
Western Sandpiper 18.13 4 0.53 -0.04 0.02
Short-billed Dowitcher 1.82 4 0.48 -0.04 0.02
Table 3. Parameter values for linear mixed effects models explaining spatial variation in shorebird counts at six
sites in the Tofino Wah-nah-jus Hilth-hoo-is Mudflats on Vancouver Island, British Columbia, as a function of site
size (ha), and whether the site was classified as disturbed or non-disturbed. A negative value for the Disturbance
parameter indicates lower counts were observed at disturbed sites, whereas a positive value indicates higher counts
were observed at disturbed sites, contrary to predictions. Significant parameter values (P < 0.10) noted in bold font.
Species
Northward Migration Southward Migration
Parameter Value SE Parameter Value SE
Black-bellied Plover Area 0.003 0.001 Area -0.0002 0.0007
Semipalmated Plover Area -0.002 0.001 Area -0.0030 0.0014
Disturbance 0.995 0.431
Whimbrel Area -0.002 0.003 Area -0.0003 0.0004
Dunlin Area 0.005 0.001
Disturbance -0.809 0.453
Least Sandpiper Area 0.007 0.003 Area 0.0040 0.0013
Western Sandpiper Area 0.006 0.001 Area 0.0040 0.0021
Short-billed Dowitcher Area 0.005 0.003 Area 0.0020 0.0020
Disturbance -1.510 0.895

132 WaterBirDs
numbers of birds predicted under the high
traffic scenario were 63.5% of numbers pre-
dicted under the low traffic scenario. Larger
reductions were predicted for Western Sand-
piper and Dunlin, where numbers predicted
under the high traffic scenario were small
fractions of Western Sandpiper (16.5%) and
Dunlin (1%) numbers predicted under the
low traffic scenario (Fig. 3).
DisCussion
The peak counts of Western Sandpiper
and Short-billed Dowitcher indicate the To-
fino Mudflats continue to meet the popula-
tion criteria for inclusion as a site of regional
importance within the Western Hemisphere
Shorebird Reserve Network (Western Hemi-
sphere Shorebird Reserve Network 2016).
Peak counts of > 40,000 Western Sandpiper
and 1,526 Short-billed Dowitcher at the Tofi-
no Mudflats comprise more than 1% of their
total flyway populations (Andres et al. 2012).
A peak count of 411 Whimbrel exceeds the
conservation threshold of 0.5% used by
Wilke and Johnston-González (2010), who
specified the Tofino Mudflats as one of 18
important stopover/staging sites in the con-
servation plan for the western population of
Whimbrel. The Fraser River Delta supports
much larger numbers of northward migrat-
ing Western Sandpipers (600,000 birds, or
14 to 21% of the total flyway population of
3.5 million) and Pacific Dunlin (200,000
birds, or 30 to 50% of the total flyway popu-
lation of 550,000) (Drever et al. 2014), but
lower counts of Short-billed Dowitcher (≤
1,000 individuals) and Whimbrel (flocks of
up to 80) (Butler and Campbell 1987; Butler
and Lemon 2001). Thus, the Tofino Mud-
flats are a particularly important stopover
site for these two large-bodied shorebirds in
British Columbia.
We found mixed results in assessing
whether increased disturbance affected the
numbers of shorebirds stopping over at the
Tofino Mudflats. We found a negative rela-
tionship between the number of people and
dogs and the number of small shorebirds
using the most frequently disturbed site,
Chesterman Beach, during day-to-day sam-
pling in 2011. Further, lower counts than
expected relative to site size were found for
northward-bound Dunlin and Short-billed
Dowitcher at disturbed sites compared to
undisturbed sites. These negative correla-
tions, however, were not reflected in greater
declines in counts at Chesterman Beach and
Doug Banks Flats. We had a limited ability
to detect trends due to a small sample with
3-4 years of data over the 23-year period of
Figure 3. The number of Semipalmated Plover, Dunlin,
and Western Sandpiper observed at Chesterman Beach,
Tofino, British Columbia, during northward migration,
2011. Lines indicate the numbers of birds predicted
from species’ models (Table 4) to occur under two sce-
narios (high and low) of human and dog traffic on the
beach. Day of Year refers to the number of days since
January 1. Day 115 = 25 April, and Day 130 = 10 May.
Not shown in the figure are counts of 141 Dunlin and
843 Western Sandpiper on Day 123 (3 May 2011).

shoreBirDs at toFino MuDFlats 133
shorebird counts that can fluctuate widely
from year to year (Warnock et al. 2004; Ross
et al. 2012). Nonetheless, these results sug-
gest that while disturbance may displace
birds away from sites, it may not necessarily
result in long-term abandonment or popula-
tion declines.
Tolerance to disturbance varies among
shorebird species across sites (Koch and Pa-
ton 2014). Short-billed Dowitchers and Dun-
lin are disturbance-sensitive species (Pfister
et al. 1992; Peters and Otis 2007; Koch and
Paton 2014), and we found lower densities
of both at disturbed sites. Black-bellied and
Semipalmated plovers have been among the
least sensitive to disturbance at some sites
(Pfister et al. 1992; Murchison 2014) but not
others (Yasué 2005; Koch and Paton 2014).
These two species were the only ones in our
study with increasing trends. We found high
counts of Semipalmated Plover at Chester-
man Beach, the site with the highest dis-
turbance, which is consistent with other
studies that indicate this species continues
to use sites with high human traffic (Koch
and Paton 2014; Murchison 2014). Finding
high numbers of shorebirds at Chesterman
Beach despite frequent disturbance may also
reflect the ease with which birds move be-
tween this site and nearby Doug Banks Flats
and Maltby Slough. These sites are less than
500 m apart (Fig. 1); hence, birds displaced
by disturbance could readily return to Ches-
terman Beach after having a short reprieve
at a less disturbed site.
The likelihood of species being perma-
nently displaced by recreational activities
depends on the number of people and fre-
quency of disturbance (Pfister et al. 1992; Ya-
sué 2006; Tarr et al. 2010; Murchison 2014).
Negative relationships between site-specific
disturbance and annual counts of certain
species can occur when disturbance levels
are high enough (Peters and Otis 2007;
Martin et al. 2015). Therefore, different
thresholds of disturbance lead to declines of
shorebird counts at different temporal scales
(Peters and Otis 2007; Navedo and Her-
rera 2012). Disturbance frequency at Tofino
Mudflats may not have reached a threshold
level to have a long-term effect of abandon-
ment, although it may affect distributions of
species and clearly influences daily counts of
shorebirds at Chesterman Beach.
We detected several significant tempo-
ral trends in shorebird counts at the Tofino
Mudflats. These trends partly matched the
direction of trends observed at other sites
along the Pacific Flyway. Northward migrat-
ing Pacific Dunlin declined at the Fraser Riv-
er Delta and at migratory and overwintering
sites in the Strait of Georgia, Washington,
Oregon, and California, although in some
of these other places, declines occurred over
Table 4. Parameter values for general linear model relating the number of shorebirds counted during northward
migration to Day of Year (DOY) as quadratic function, and the number of people and dogs observed on Chester-
man Beach, Tofino, British Columbia, April/May 2011, n = 15.
Parameter Estimate SE Z P
Semipalmated Plover
Intercept -177.69 36.09 -4.92 < 0.001
DOY 2.79 0.570 4.92 < 0.001
DOY2 -0.011 0.002 -4.82 < 0.001
Total People/Dogs -0.006 0.002 -3.49 < 0.001
Dunlin
Intercept -294.45 80.33 -3.67 < 0.001
DOY 4.73 1.27 3.73 < 0.001
DOY2 -0.019 0.005 -3.75 < 0.001
Total People/Dogs -0.060 0.007 -8.17 < 0.001
Western Sandpiper
Intercept -336.21 23.24 -14.46 < 0.001
DOY 5.41 0.37 14.75 < 0.001
DOY2 -0.021 0.001 -14.79 < 0.001
Total People/Dogs -0.025 0.001 -20.57 < 0.001

134 WaterBirDs
only part of the same time period covered by
our counts (Crewe et al. 2012; Drever et al.
2014). We saw a decline in counts of West-
ern Sandpiper during the southward migra-
tion. Declines in Western Sandpiper popu-
lations happened from the mid-1990s to
2000 at a wintering site in Ecuador (O’Hara
et al. 2007), as well as at smaller northward
stopover sites at Bolinas Lagoon, Califor-
nia, from 1972 to 2004, and at Totten Inlet,
Washington, from the mid-1980s to 2011
(Drever et al. 2014). No declines in north-
ward migrating Western Sandpipers were
detected at the Fraser River Delta from 1991
to 2013 (Drever et al. 2014). Trends for Pa-
cific Flyway populations of Least Sandpipers
were found to be stable, and those for Short-
billed Dowitchers are unknown (Andres et
al. 2012), whereas we found decreases in
both species during southward migration be-
tween 1989 and 2011. The increasing trends
for northward migrating Semipalmated and
Black-bellied plovers match the increasing
and stable trends, respectively, reported for
these species by Andres et al. (2012).
Spatial distribution patterns of shore-
birds differed between migration periods
at the Tofino Mudflats, such that shorebird
densities were better predicted by site size
during the northward migration than south-
ward migration. Miller (2012) found similar
results at estuaries in Oregon and suggested
different pressures act on the birds during
the different time periods. During north-
ward migration, adult birds are under selec-
tive pressure to arrive early at the breeding
grounds (Clark and Butler 1999), experi-
ence greater predation pressure from fal-
cons (Lank et al. 2003), and move in relative-
ly large flocks to mitigate predation risk. The
trade-off is that being in a large flock likely
increases aggression and reduces foraging
efficiency, which is especially energetically
stressful in conditions of poor weather and
decreased food availability as birds fly north
(O’Reilly and Wingfield 1995). Thus, north-
ward birds traveling in large flocks over a
concentrated period of time may choose to
spread out across sites to distribute them-
selves more evenly with respect to food re-
sources. Alternatively, shorebirds during
northward migration may have less time to
adequately assess food availability, and their
distribution is more random. In contrast,
southward migration occurs at a slower rate,
and migrants generally experience favorable
weather, ample food, travel in smaller flocks,
and, depending on age class and timing, en-
counter variable rates of predation (Lank
et al. 2003). These factors may cause birds
to choose sites for different reasons on the
southward journey. A combination of these
factors is likely acting on shorebirds that mi-
grate through the Tofino Mudflats.
aCknoWleDGMents
Funding was provided by the Canadian Wildlife Ser-
vice, Environment Canada. Jason Komaromi prepared
Figure 1. We thank Rob Butler (Pacific WildLife Foun-
dation), Pete Clarkson (Parks Canada), Dan Harrison
(Raincoast Education Society), and Josie Osborne (Dis-
trict of Tofino) for support, and Mark Hobson, Avery
Bartels, and Emily Gonzales for assistance in the field.
We thank Jamie’s Whaling Station for providing a berth
for the zodiac, and Doug Banks for allowing access
through his property. Careful reviews by B. Andres and
an anonymous reviewer improved the manuscript.
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