Spring migration routes and chronology of surf

scoters (Melanitta perspicillata): a synthesis of

Pacific coast studies

S.E.W. De La Cruz, J.Y. Takekawa, M.T. Wilson, D.R. Nysewander, J.R. Evenson,

D. Esler, W.S. Boyd, and D.H. Ward

Abstract: Understanding interconnectivity among wintering, stopover, and breeding areas of migratory birds is pivotal to

discerning how events occurring in each might have a cross-seasonal effect on another. Such information can guide the location and timing of conservation efforts. Thus, we examined spring migration routes, chronology, and stopover use of 85

surf scoters (Melanitta perspicillata (L., 1758)) marked with satellite transmitters at four Pacific Flyway wintering sites:

San Quintin Bay, Baja California; San Francisco Bay, California; Puget Sound, Washington; and Strait of Georgia, British

Columbia. Eighty-three percent of marked scoters followed two main routes to the breeding area: a Southern Inland route

involving staging in Puget Sound and Strait of Georgia and protracted inland migration, or a Northern Coastal route characterized by short movements along the Pacific coast of British Columbia and southeast Alaska with inland migration initiating from Lynn Canal and surrounding areas. Route choice was related to nesting site latitude in the Canadian Northern

Boreal Forest. Data from birds tracked over 2 years indicated strong migration route fidelity, but altered chronology and

stopover locations between years. Departure date varied by wintering site, but arrival and apparent settling dates were synchronous, suggesting individuals adjusted migration timing to meet an optimized reproductive schedule.

Re ́sume ́ : La compre ́hension de l’interconnectivite ́ entre les zones d’hivernage, d’arreˆt et de reproduction chez les oiseaux

migrateurs est essentielle si l’on veut voir comment les e ́ve ́nements qui se passent dans chacune de ces zones peuvent

avoir un effet lors d’une autre saison dans une autre zone. De telles informations pourraient orienter le choix des sites et

du moment des interventions de conservation. Nous avons ainsi examine ́ les routes printanie`res de migration, leur chronologie et l’utilisation des points d’arreˆt chez 85 macreuses a` front blanc (Melanitta perspicillata (L., 1758)) munies d’e ́metteurs satellites a` quatre sites d’hivernage sur la route de migration du Pacifique, la baie de San Quintin en BasseCalifornie, la baie de San Francisco en Californie, Puget Sound au Washington et le de ́troit de Ge ́orgie en ColombieBritannique. Quatre-vingt trois pourcent des macreuses marque ́es suivent deux voies principales vers la zone de reproduction, une route du sud dans l’inte ́rieur des terres comportant des arreˆts a` Puget Sound et au de ́troit de Ge ́orgie avec une

migration prolonge ́e a` l’inte ́rieur des terres et une route coˆtie`re du nord caracte ́rise ́e par de courts de ́placements le long de

la coˆte de la Colombie-Britannique et du sud-est de l’Alaska et une migration a` l’inte ́rieur des terres de ́butant au canal de

Lynn et les environs. Le choix de route de ́pend de la latitude du site de nidification dans la foreˆt bore ́ale du nord du Canada. Des donne ́es obtenues d’oiseaux marque ́s au cours de deux anne ́es indiquent une forte fide ́lite ́ a` la route de migration,

mais la chronologie de la migration et les sites d’arreˆt peuvent changer d’une anne ́e a` l’autre. La date de de ́part varie en

fonction du site d’hivernage, mais les dates d’arrive ́e et d’installation apparente sont synchronise ́es, ce qui laisse croire

que les individus ajustent la chronologie de leur migration afin d’obtenir un calendrier optimal de reproduction.

[Traduit par la Re ́daction]

Received 8 April 2009. Accepted 17 August 2009. Published on the NRC Research Press Web site at cjz.nrc.ca on 6 November 2009.

S.E.W. De La Cruz.1,2 Graduate Group in Ecology, 2148 Wickson Hall, One Shields Avenue, Davis, CA 95616, USA.

J.Y. Takekawa. U.S. Geological Survey, Western Ecological Research Center, San Francisco Bay Estuary Field Station, 505 Azuar

Drive, Vallejo, CA 94592, USA.

M.T. Wilson. Stillwater National Wildlife Refuge Complex, 1000 Auction Road, Fallon, NV 89406, USA.

D.R. Nysewander and J.R. Evenson. Washington Department of Fish and Wildlife, 600 Capitol Way North, Olympia, WA 98501,

USA.

D. Esler. Centre for Wildlife Ecology, Simon Fraser University, 5421 Robertson Road, Delta, BC 4K 3N2, Canada.

W.S. Boyd. Canadian Wildlife Service, Pacific and YT Region, 5421 Robertson Road, Delta, BC V4K 3N2, Canada.

D.H. Ward. U.S. Geological Survey, Alaska Science Center, 4210 University Drive, Anchorage, AK 99508, USA.

1Corresponding author (e-mail: susan_wainwright@usgs.gov).

2Present address: U.S. Geological Survey, Western Ecological Research Center, San Francisco Bay Estuary Field Station, 505 Azuar

Drive, Vallejo, CA 94592, USA.

1069

Can. J. Zool. 87: 1069–1086 (2009) doi:10.1139/Z09-099 Published by NRC Research Press
Introduction

Recent advances in the study of avian migration have underscored the important linkages between wintering, stopover, and breeding areas (Marra et al. 1998; Gill et al.

2001; Drent et al. 2003; Newton 2006), and the need to

consider this interconnectivity in conservation planning

(Mehlman et al. 2005). It is becoming increasingly clear

that the timing of spring migration and quality of stopover

sites can greatly influence reproductive success and female

annual survival (Drent et al. 2006, 2007; Black et al. 2007),

especially for arctic nesting species. Individuals are hypothesized to alter their migration strategies based upon decisions

to minimize migration duration, maximize energy accumulation at stopovers, or avoid predation risk (Alerstam and

Lindstro ̈m 1990; Farmer and Wiens 1998, 1999; Vrugt et

al. 2007), and ultimately optimize their fitness.

As techniques for studying migration improve (e.g., Webster et al. 2002), so too does our opportunity to examine

individual migration strategies. For example, satellite telemetry has greatly advanced our ability to observe strategies

of individuals under different climatic conditions (Miller et

al. 2005) or across time (Berthold et al. 2002; Alerstam et

al. 2006; Mosbech et al. 2006) at continental spatial scales.

Understanding migration ecology from the basis of individual behavioral strategies allows us a powerful means of predicting the effects of future habitat changes by extrapolating

individual responses to populations (Sutherland 1996; Atkinson et al. 2005). This is particularly important in the case of

rapidly declining sea duck populations, many of which rely

on habitats such as coastal waters and boreal lakes where resources are predicted to be altered dramatically as a result of

climate change (Stewart et al. 1998; Harley et al. 2006).

Surf scoters (Melanitta perspicillata (L., 1758)) are sea

ducks that winter along the Pacific and Atlantic coasts of

North America and breed in low densities across the boreal

forests of Alaska and Canada (Savard et al. 1998; Takekawa

et al. 2010). Based on breeding and wintering area surveys,

surf scoters have undergone long-term declines (Savard et

al. 1998; Trost 2002; Nysewander et al. 2003), particularly

in the western part of their range (Goudie et al. 1994;

Hodges et al. 1996). Until lately surf scoters were one of

the least studied waterfowl species in North America (Bellrose 1980; Savard et al.1998), and this lack of basic knowledge has hindered our ability to determine causes of decline.

Recent work has helped define the breeding range of Pacific coast surf scoters and has shown that birds from different wintering sites co-mingle across this area (Takekawa et

al. 2010). However, little is known about the timing of their

spring migration and the routes that scoters follow from various Pacific coast wintering sites to the breeding grounds

(see Savard et al. 1998). Individuals wintering in separate

regions may experience variation in overwinter conditions

that could differentially influence their subsequent migration

timing or strategies and their breeding success, and this may

ultimately translate into population-level effects (Gill et al.

2001; Newton 2004). Additionally, previous work with

shorebirds has demonstrated how integrated observations of

migratory populations and identification of broad regional

patterns provide a much more complete picture of migration

than do inferences based on observations from small segments of the population (Warnock and Bishop 1998; Farmer

and Wiens 1999). Understanding how individual and regional migration strategies may influence the overall population will ultimately help direct management actions for

conservation of surf scoters (Sea Duck Joint Venture

(SDJV) Management Board 2001).3

We integrated data from satellite telemetry studies conducted at four major Pacific coast wintering sites to examine

the spring migration strategies of individual surf scoters in

western North America. These projects were initiated to examine migration from each wintering site separately; however, the similarities in timing and methodology of each

project provided us with a unique opportunity to compare

the routes and chronology of surf scoters wintering at

different latitudes. Specifically, our objectives were to

(i) establish primary spring migration routes of individuals

from each wintering site; (ii) compare migration chronology

among scoters from each wintering site, including arrival

timing and settling dates at nesting sites in the Northern

Boreal Forest; (iii) evaluate how winter body mass and wintering site departure timing relates to subsequent migration

timing; and (iv) identify important stopover and staging

areas.

Materials and methods

Study area

We compiled migration data from surf scoters marked

with platform transmitter terminals (PTTs) at four sites

within their wintering range along the Pacific coast of North

America (Fig. 1): San Quintin Bay, Baja California, Mexico

(SQ; 116.08W, 30.48N); San Francisco Bay, California, USA

(SF; 122.48W, 37.88N); Puget Sound, Washington, USA

(PS; 122.48W, 47.58N); and Strait of Georgia, British Columbia, Canada (SG; 122.48W, 49.38N). While PS and SG

are geographically close together, radio-marked birds from

these sites tracked over the same time period as PTTmarked birds in the current study had high site fidelity to

marking sites and maintained small home ranges over winter

that rarely overlapped with each other (Kirk et al. 2008; J.R.

Evenson and D.R. Nysewander, unpublished data; D. Esler,

unpublished data). Because birds from these sites remained

largely distinct from each other, our a priori assumption

was that migration strategies could vary between them;

thus, we chose to analyze data from these two marking sites

separately. We examined spring migration chronology and

routes along the Pacific coast from Baja San Quintin north

to southeast Alaska, and through the Canadian provinces of

British Columbia, Yukon Territory, and Alberta to the

Northern Boreal Forest breeding areas of western Canada

and eastern Alaska (Takekawa et al. 2010).

Capture and marking

We captured wintering surf scoters in floating mist nets

using decoys (SQ, SF, PS, and SG; Kaiser et al. 1995) or

3 Sea Duck Joint Venture (SDJV) Management Board. 2001. Sea Duck Joint Venture Strategic Plan: 2001–2006. SDJV Continental Team.

Unpublished Report, c/o USFWS, Anchorage, Alaska, USA, and Candian Wildlife Service, Sackville, N.B., Canada.

1070 Can. J. Zool. Vol. 87, 2009

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Fig. 1. Study site map showing winter marking sites (solid black polygons) and the locations and codes of the Pacific coast migration stopover areas of surf scoters (Melanitta perspicillata) discussed in the text. We divided the spring migration route into these broad biogeographic migration areas to facilitate discussion of routes and to calculate mean stopover length of stay. From south to north the full names

corresponding to the abbreviated codes are as follows: Coastal Migration Areas — San Quintin Bay (SQ), Baja California Coast (BC),

Southern California Coast (SC), Central California Coast (CC), San Francisco Bay (SF), Northern California Coast (NC), Oregon Coast

(OC), Columbia River Mouth (MC), Washington Coast (WC), Puget Sound (PS), Strait of Georgia (SG), Outer Vancouver Coast (VC),

Queen Charlotte Sound (QC), Petersburg Southeast Alaska Coast (PK), Haines Southeast Alaska Coast (HK); Interior Migration Areas —

Southern Inland British Columbia (SB), Central Inland British Columbia (CB), Northern Inland British Columbia (NB), Yukon Territory

(YK), Lesser Slave Lake Alberta (LS), Cariboo Mountains Alberta (CM).

De La Cruz et al. 1071

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from small boats with a netgun (SQ and SF; Coda Enterprises, Inc., Mesa, Arizona, USA). Marking periods ranged

from 8 to 27 February 2005 and 2006 in SQ; from 3 January

to 27 February 2003, 2005, and 2006 in SF; from 20 November to 28 March 2003, 2004, 2005, and 2006 in PS; and

from 1 to 30 November 2005 in SG. We banded, weighed,

and measured each captured bird, used a combination of

plumage characteristics and cloacal examination to determine sex, and estimated bursal depth to determine age

(Mather and Esler 1999; Iverson et al. 2003). Coelomic implant transmitters with external antennas (38 g each, PTT100; Microwave Telemetry, Inc., Columbia, Maryland,

USA) were surgically implanted (Olsen et al. 1992; Korschgen et al.1996; Mulcahy and Esler 1999) in after 2nd year

(ASY) male and female scoters. Implant transmitters are

less disruptive and cause fewer behavioral modifications

than external attachment methods for some wild waterfowl

(Rotella et al. 1993; Hupp et al. 2003) and coelomic implant

transmitters are preferred for scoters relative to other transmitter types when data are collected over a long period of

time (Iverson et al. 2006). Marked birds were released after

a recovery period of between 2 and 6 h. Sex of marked scoters varied at each marking site (Table 1); however, the majority of birds (84%) were adult female. All capture,

handling, and marking of scoters was carried out under the

guidance of the Animal Care and Use Committees at each

investigator’s institution or organization, with permits from

California Department of Fish and Game, Canadian Wildlife

Service, Washington Department of Fish and Wildlife, U.S.

Fish and Wildlife Service, U.S. Geological Survey (USGS)

Bird Banding Laboratory, and Secretarı ́a de Medio Ambiente y Recursos Naturales (SEMARNAT).

Location data

All PTTs were programmed to transmit data for 6–8 h

and turn off for 48–96 h, with the exception of two PTTs

from PS that transmitted for 6 h and turned off for 144 h

during spring migration. Transmitter signals were received

by U.S. National Oceanic and Atmospheric Administration

polar-orbiting weather satellites, and CLS America (Largo,

Maryland) estimated transmitter location on the basis of

Doppler shifts in transmitter frequencies. Location accuracy

classes were determined based on satellite-to-PTT geometry,

the number of transmissions received from the PTT, and the

stability of the PTT transmission frequency during a satellite

pass. For location classes (LC) 3, 2, 1, and 0, CLS America

rated accuracy as <150, <350, <1000, and >1000 m, respectively. Accuracy was not provided for LC A (3 messages received by satellite), LC B (2 messages), and LC Z (latitude

and longitude often provided if >1 message received). Data

from each wintering site were compiled at the USGS Western Ecological Research Center and filtered using systematic

plausibility tests of direction, distance, and rate of movement between locations (Douglas 2006). The filtering program was set to ensure that LC 1–3 locations were always

retained. We used all filtered locations to calculate chronological dates; however, to plot overall migratory routes, we

used a more restrictive filter (Douglas 2006) that chose the

best location from every reporting cycle.

We used ArcMap version 9.2 (Environmental Systems

Research Institute, Inc., Redlands, California, USA) to plot

and analyze the selected locations and delineate migration

routes. We divided coastal and interior routes used by surf

scoters into broad migration stopover and staging areas

(Fig. 1; see legend for full area names) of similar biogeography along a latitudinal gradient. These migration areas were

used to determine the numbers of scoters following identified routes and to facilitate discussion of differences in

migratory strategies among individuals from different wintering sites.

Estimating migration duration and dates

Length of stay (LOS) in a particular migration area was

estimated as the difference between the departure date from

that area and the arrival date in that area plus one to account

for the fact that the bird could have been present in the area

both on the day of arrival and on the day of departure. Following Warnock and Bishop (1998), we defined a 2–7 day

use of a migration area as a stopover event, and >7 days

use of an area as a staging event. Staging areas have been

defined as predictable locations with abundant feeding resources where birds can fatten significantly and have long

lengths of stay (Skagen and Knopf 1994; Warnock and

Bishop 1998); thus, we distinguished between these two

events to identify important staging areas along migration

routes.

We defined the departure date from a wintering site as the

median date between the last location at the wintering site

and the first location in a new migration area (Fig. 1). Similarly, we estimated departure date from coastal to inland

areas as the median date between the last coastal location

and the first interior location. Breeding ground arrival date

was estimated as the median date between last interior location and first location in the breeding range as defined by

the distribution of the marked population (see Takekawa et

al. 2010). We used the median date between arrival in the

breeding area and the first day a bird was located in an apparent nesting area (typically an area <20 km2) where it remained for ‡25 days (following Takekawa et al. 2010) as

the settling (nest initiation) date for females. Paired males

typically leave females about 3 weeks after arriving to

breeding lakes (Savard et al. 1998); thus, we used males in

our calculation of settling date only if they remained in an

apparent nesting area for ‡21 days. For some birds, breeding

area arrival date was the same as the settling date if the first

location in the breeding area was in the apparent nesting

area for that bird. Finally, we estimated total migration duration as the difference between the settling date and the wintering site departure date plus 1 day to include both the

departure day and the arrival day in the calculation. We

present all dates in ordinal, or day of year, format as specified by the International Organization for Standardization.

Statistical analysis

We used linear regression (PROC REG; SAS Institute

Inc. 2005) to model the relationship between body mass at

time of capture and wintering site departure date of scoters

from PS and SF. We did not adjust mass for structural size

to obtain an estimate of body condition, given that recent

work shows using unverified body condition indices provides no improvement over using body mass alone to predict

1072 Can. J. Zool. Vol. 87, 2009

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condition and can actually lead to reduced predictability of

fat stores in some species (Schamber et al. 2009). Therefore,

in the absence of a verified condition index for scoters, we

felt that the best practice was to use body mass for our regression analysis. We also only used birds marked during

January and February and excluded those marked in the

fall, because earlier marked birds may fluctuate substantially

in mass over the winter. Nearly all males were marked during the fall, and we excluded the few males marked in

spring (n = 5) and conducted this analysis only on females.

For all individuals, we used linear regression to model the

relationship between wintering site departure and migration

duration, coastal departure latitude, breeding area arrival

date, and settling date, as well as to examine coastal departure latitude, which marks the beginning of interior migration, in relation to final nesting latitude.

We used one-way ANOVA (PROC GLM; SAS Institute

Inc. 2005) to determine if departure, arrival, and settling

dates, stopover LOS, and migration duration varied by wintering site. We also compared these variables within each

wintering site among birds using different migration routes.

For these analyses, we combined data across years and sexes

because sample sizes were not large enough to permit consideration of these variables (Table 1). Statistical analyses

were performed with SAS version 9.1 (SAS Institute Inc.

2005), and we used the Tukey–Kramer method to make

multiple comparisons among wintering sites while preserving type I error. The significance value for all tests was a <

0.05.

Results

Location data

We used location data from all birds that departed their

wintering sites and progressed in a northward direction (n =

85; see Table 1). As migration progressed, the sample size

decreases owing to transmitter failure or battery drain, as

well as scoter mortality (n = 1 confirmed mortality). Of the

85 birds that left wintering areas, we tracked 74 throughout

the entire breeding season. We received a total of 33 081 locations between 1 February and 15 June from 2003 to 2006,

but 1.6% of these were discarded as outliers by the plausibility filtering program. The remaining locations were categorized as LC 3 (16.7%), LC 2 (16.6%), LC 1 (18.5%),

LC 0 (12.5%), LC A (15.9%), LC B (18.1%), and LC Z

(1.8%).

Migration strategies

Routes

Scoters from all wintering sites used coastal migration

routes (Figs. 2a–2d) and used several areas for stopovers.

North of Puget Sound, most scoters traveled along the interior passages of large coastal islands (Strait of Georgia,

Queen Charlotte Sound, and Hecate Strait, British Columbia; the Inside Passage, Alaska) with the exception of seven

SF scoters that used the western edge of Vancouver Island,

British Columbia.

The majority of scoters from all four marking sites followed two main routes from the point of PS and SG onward.

Forty-two percent of all birds migrating inland followed a

Southern Inland route, in which they began their migration

inland from PS and lower SG areas. Scoters using the

Southern Inland route sometimes staged in PS or SG, and

typically displayed a protracted inland migration. Forty-one

percent of all birds that migrated inland used a Northern

Coastal route, flying along the coast of British Columbia

and southeast Alaska, usually making frequent stops, and

finally departing for inland migration from the northern end

of the Inside Passage of southeast Alaska (Figs. 2a–2d, Table 2). A smaller number used an Intermediate Coastal route

in which they made some coastal stopovers and migrated inland from various river mouths and deltas within the Queen

Charlotte Sound and Petersburg Southeast Alaska migration

areas (13%; Figs. 2a–2d, Table 2). In addition, two scoters

continued farther north and began their interior migration

near the Copper River Delta, Alaska (144.68N, 60.28W) and

from Cook Inlet, Alaska (152.78N, 60.28W; Figs. 2a, 2b).

One SQ scoter migrated interior from the mouth of the Columbia River, Washington (124.28N, 46.78W); however, its

PTT stopped transmitting in Southern Central British Columbia. Routes taken by these three birds were termed Other

(Table 2).

Among wintering sites, mean coastal departure latitude

for inland migration did not vary (F[3,74] = 2.50, P = 0.066).

However, the Northern Coastal route was the single most

common path for scoters marked in SQ (50%), SF (53%),

and SG (50%; Table 2). Fifty-six percent of PS marked

scoters used the Southern Inland route to the breeding area

(Table 2). For scoters from all of the marking sites, coastal

departure latitude was positively related to final nesting latitude (PROC REG: F[1,74] = 57.05, P < 0.0001, r2 = 0.44;

Fig. 3).

Table 1. Summary of surf scoters (Melanitta perspicillata) marked with satellite transmitters (platform transmitter terminal; PTTs) in 2003–2006 from four different wintering sites: San Quintin

Bay, Baja California, Mexico (SQ); San Francisco Bay, California, USA (SF); Puget Sound, Washington, USA (PS); and Strait of Georgia, British Columbia, Canada (SG).

SQ SF PS SG

Year Male Female Male Female Male Female Male Female Total

2003 0 0 0 8. 0 0. 00 8

2004 0 0 0 0. 4 3. 00 7

2005 0 2 0 9. 2 14. 4 4 35

2006 0 3 0 12.(5) 2 8.(5) 0 0 35

Total 0 5 0 34. 8 30. 4 4 85

Note: Numbers represent scoters that departed from wintering areas in each year. The number of birds that

produced 2 years of data during any part of spring migration is shown in parentheses.

De La Cruz et al. 1073

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Individual scoters most commonly initiated inland migration from river mouths and sounds, and interior routes usually followed a north to northeast orientation to nesting sites

(Figs. 2a–2d). All birds following the Southern Inland route

traveled across the Fraser River Plateau in the Central Inland British Columbia migration area (see Fig. 1) and then

through the Lesser Slave Lake or Cariboo Mountain migration areas, en route to nesting sites in the Northwest Territories and Saskatchewan. Scoters following the Northern

Coastal route traveled through the mountains in Northern InFig. 2. Migration routes of surf scoters (Melanitta perspicillata) marked at four Pacific coast wintering sites: (a) Strait of Georgia (SG),

(b) Puget Sound (PS), (c) San Francisco Bay (SF), and (d) San Quintin Bay (SQ). Routes depicted include those of all birds that made a

complete migration from wintering site to the Northern Boreal Forest breeding area. Colored arrows in a represent the Southern

Inland (blue), the Intermediate Coastal (clear), and the Northern Coastal (yellow) routes.

1074 Can. J. Zool. Vol. 87, 2009

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land British Columbia and Yukon Territory to nesting sites

in the Northwest Territories. Fifty-six percent of scoters departing on the Northern Coastal route left from the Taiya Inlet, north of Haines, Alaska. These birds mainly traveled

through Chilcoot and White Pass into Northern Inland British Columbia and across Yukon Territory mountain ranges

to nesting sites at or north of the Great Bear Lake in the

Northwest Territories (Figs. 2a–2b). Scoters departing from

lower latitudes near Haines or from the Queen Charlotte

Sound and Petersburg Southeast Alaska migration areas

traveled through Central Inland British Columbia and the

Cariboo Mountain areas, or through Northern Inland British

Columbia and Yukon Territory to reach their nesting areas.

Chronology

Mean winter departure date was variable among sites, but

was significantly different only between SF and PS (F[3,84] =

4.64, P = 0.005; Figs. 4a–4d, Table 3). Departure dates

ranged from 20 February (SF 2006) at the earliest to 30

May (SG 2005) at the latest (Figs. 4a–4d, Table 3). We

found that body mass was significantly related to female

winter departure date, and lighter birds left wintering sites

later (PROC REG: F[1,44] = 10.62, P = 0.002, r2 = 0.18;

Fig. 5).

Mean departure date from the coast to inland migration

corridors was significantly different only between SF and

PS (F[3,74] = 4.69, P = 0.005; Table 3) such that PS birds

departed earlier than SF birds. Breeding area arrival dates

did not vary significantly among wintering sites (F[3,71] =

2.55, P = 0.063; Table 3). We found no significant difference in settling dates among wintering sites (F[3,70] = 2.01,

P = 0.121). The mean difference between arrival and

Table 2. Percentage and number of surf scoters (Melanitta perspicillata) from each Pacific coast wintering site (San Quintin (SQ), San Francisco Bay (SF), Puget Sound (PS), Strait of Georgia (SG)) that

followed each migratory route to the breeding area.

Wintering site n Southern Inland Intermediate Coastal Northern Coastal Other

SQ 4 25.(1) 0. 50.(2) 25.(1)

SF 30 33.(10) 13.(4) 53.(16) 0.

PS 36 56.(20) 14.(5) 28.(10) 2.(1)

SG 8 25.(2) 12.5 (1) 50.(4) 12.5 (1)

Overall 78 42.(33) 13.(10) 41.(32) 4.(3)

Fig. 3. Scatterplot chart depicting the relationship between coastal

departure latitude and ultimate nesting site latitude of Pacific coast

surf scoters (Melanitta perspicillata). The linear regression equation

describing the fit of the line is y = 0.4544x + 39, r2 = 0.4353.

Fig. 4. Cumulative proportion of surf scoters (Melanitta perspicillata) departing over time for spring migration from four Pacific

coast wintering sites: (a) Strait of Georgia (SG), (b) Puget Sound

(PS), (c) San Francisco Bay (SF), and (d) San Quintin Bay (SQ).

Mean departure dates are represented by vertical black lines and

median dates by vertical gray lines. Departure dates ranged from 20

February to 30 May, and mean departure date from SF was significantly earlier than mean departure date from PS (F[3,84] = 4.64, P =

0.005).

De La Cruz et al. 1075

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Table 3. Wintering site departure, coastal departure for inland migration, breeding area arrival, and settling ordinal dates by wintering site (San Quintin 

Puget Sound (PS), Strait of Georgia (SG)) and migration strategy (Southern Inland, Intermediate, Northern Coastal) for Pacific coast surf scoters (Melan

Winter departure Coastal departure Arrival Settling

Wintering site Route Mean ± SE n Mean ± SE n Mean ± SE n Mean ± SE n 

SQ Southern Inland 111.0 1 144.0 1 149.0 1 151.0 1 

Intermediate Coastal — — — — Northern Coastal 108.5±7.5 2 148.8±3.8 2 154.5±5.5 2 161.8±3.8 2 Overall* 103.8±4.2AB 5 144.6±3.2AB 4 152.7±3.7 3 158.2±4.2 3 

SF Southern Inland 104.8±7.0 10 136.4±2.4 10 145.4±2.1 10 149.0±2.1 10 

Intermediate Coastal 103.3±11.1 4 139.0±3.9 4 142.0±3.3 4 146.5±3.3 4 Northern Coastal 100.1±5.6 16 143.6±1.9 16 145.5±1.7 15 147.5±1.7 15 Overall* 100.5±4.2A 34 140.6±1.5A 30 145.0±1.2 29 147.9±1.2 29 

PS Southern Inland 128.8±3.4a 20 130.9±1.3a 20 142.6±1.3 20 148.2±2.4 19 

Intermediate Coastal 103.8±6.8b 5 134.8±2.6a 5 143.8±2.6 5 148.3±1.9 4 Northern Coastal 112.1±4.8b 10 142.5±1.8b 10 144.8±1.9 9 151.2±3.4 9 Overall* 118.2±3.1B 8 134.8±1.2B 38 143.2±1.0 35 149.8±1.7 34 

SG Southern Inland 144.0±4.4a 2 144.0±3.2 2 149.0±4.0 2 150.0±4.5 2 

Intermediate Coastal 127.0 1 143.0 1 144.0 1 149.0 1 Northern Coastal 109.0±3.1b 4 138.3±2.2 4 139.8±2.9 4 142.5±3.2 4 Overall* 117.5±7.0AB 8 140.4±1.6AB 8 143.1±2.1 8 145.4±2.1 8 

Note: We compared chronology among wintering sites and reported differences in the Overall row using uppercased letters. We also compared chronology by strategy w

differences using lowercased letters under each wintering site. The absence of letters indicates no significant differences.

*Sample size (n) for each Overall category includes birds that began migration but stopped transmitting before beginning inland migration. These birds were never assigned a 

included in calculations of means by strategy. In addition, because of the small sample size (n = 3), we did not calculate means for the Other migration strategy; however, scoterin the calculation of overall means.

Published by NRC Research Press
settling at apparent nesting sites ranged from 2.3 ± 0.7 days

(SG) to 6.4 ± 1.3 days (PS) and did not differ among birds

from all wintering sites (F[3,70] = 2.36, P = 0.078; Table 3).

Wintering site departure date was positively related to

breeding area arrival date and to settling dates (PROC

REG; arrival: F[1,74] = 8.33, P = 0.005, r2 = 0.10; settling:

F[1,73] = 8.58, P = 0.005, r2 = 0.11); however, it was not related to coastal departure date for interior migration (PROC

REG: F[1,77] = 0.75, P = 0.39, r2 = 0.01).

We also compared chronology by migration route within

each wintering site (Table 3). We excluded Other migration

routes because of the small number of birds using them (n =

3). We found significant differences in chronology by route

for PS and SG birds only. Birds from both areas using the

Northern Coastal route departed the wintering area significantly earlier than those using the Southern Inland route or,

in the case of PS, Intermediate Coastal routes (PS: F[2,32] =

7.68, P = 0.002; SG: F[2,4] = 21.11, P = 0.008). PS scoters

using the Northern Coastal route departed the coast for inland migration significantly later than PS birds following

the Southern Inland and Intermediate Coastal routes

(F[2,32] = 13.58, P < 0.0001).

Migration duration and stopover areas

The total duration of spring migration by individuals

ranged from 1.5 days (PS 2006) to 90.5 days (SF 2006)

across all years and wintering sites. The mean total duration

of migration differed significantly only between PS and SF

scoters (F[3,70] = 4.64, P = 0.005); SF scoters took longer to

migrate compared with PS scoters (Table 4). The mean duration of coastal migration was significantly shorter for PS

birds compared with SF birds, but was not different among

any of the other wintering sites (F[3,74] = 9.22, P < 0.0001;

Table 4). The duration of inland migration was significantly

longer for PS scoters compared with birds from SQ, SF, and

SG (F[3,70] = 8.71, P< 0.0001; Table 4). We found positive

relationships between winter departure date and total migration duration (PROC REG: F[1,73] = 381.04, P < 0.0001, r2 =

0.84), marine migration duration (PROC REG: F[1,77] =

443.15, P < 0.0001, r2 = 0.85), and inland migration duration (PROC REG: F[1,73] = 4.74, P = 0.032, r2 = 0.06).

Individuals made between 0 and 9 stopovers at coastal

areas, and between 0 and 5 stopovers at inland areas. The

mean number of coastal migration areas in which scoters

stopped was significantly different among wintering sites

(F[3,75] = 10.41, P < 0.0001), and SQ birds had the greatest

number of stops in migration areas (Table 4, Fig. 6). In contrast, we did not find any difference in the number of stops

in inland migration areas among wintering sites (F[3,70] =

1.99, P = 0.123; Table 4). Mean LOS at coastal migration

areas was significantly longer for SF compared with PS

scoters (F[3,75] = 5.89, P = 0.001; Table 4). There were no

differences in mean LOS at inland migration areas among

scoters from each wintering site (F[3,70] = 1.92, P = 0.134).

Length of stay at coastal migration areas decreased with

later winter departure dates from all wintering sites (PROC

REG: F[1,77] = 82.47, P = 0.0001, r2 = 0.52); however, we

found no relationship between length of stay at inland migration areas and departure dates from all wintering sites

(PROC REG: F[1,73] = 0.00, P = 0.95, r2 = 0.00).

Among migration stopover areas that we defined on the

lower Pacific coast (below Puget Sound; Fig. 1), the largest

number of birds stopped along the Oregon coast (n = 23,

59% of SQ and SF migrants; Fig. 6). Although individuals

stopped in each general migration region that we identified,

SQ birds mainly used three lower Pacific coast areas for

staging (Baja California Coast, San Francisco Bay, Oregon

coast), whereas SF birds staged only in central California

(Fig. 6). Puget Sound and outer Vancouver Coast were used

as staging areas only by SF scoters. Above the Strait of

Georgia, each stopover area was used by scoters from all

wintering areas (Fig. 6), with the exception that PS and SQ

scoters stopped but did not stage in Queen Charlotte Sound.

Of migration areas available to scoters from all winter marking sites, Haines Southeast Alaska had the greatest use (n =

39) and the longest mean LOS (mean ± SE: SQ = 31.5 ±

11.6 days; PS = 13.89 ± 2.46 days; SG = 21.24 ± 1.75

days) for birds from all marking areas except SF. All SF

scoters that staged in PS used the Southern Inland route and

stayed 27.6 ± 6.4 days in PS. SF scoters that used the Northern Coastal route staged in the Haines Southeast Alaska migration area for 19.6 ± 1.89 days. All but two scoters that

arrived in the breeding area made at least one stop at an interior migration area. Overall, Lesser Slave Lake had the

greatest use of any single interior migration area, with 24

(31%) of all inland migrating birds stopping in this area.

Stopover sites on the Fraser River Plateau (Southern Inland

British Columbia and Central Inland British Columbia combined) were used by 34 (44%) of all birds. For scoters using

the Northern Coastal route, Yukon Territory was the most

heavily used stopover site. Twenty-one birds (27% of all inland migrating birds, 66% of birds migrating from Haines

Southeast Alaska) stopped in the Yukon Territory migration

area, but only PS birds staged in this area (Fig. 6).

Route fidelity

We obtained 2 years of migration data for 6 female surf

scoters (SF = 3, PS = 3) in the spring of 2005 and 2006.

All six birds followed very similar routes in both years

(Fig. 7) with some differences in the number of stopover

Fig. 5. Scatterplot chart depicting the relationship between the unadjusted body mass of female surf scoters (Melanitta perspicillata)

and departure date across all wintering sites. The linear regression

equation describing the fit of the line is y = –0.1243x + 227.75,

r2 = 0.1833.

De La Cruz et al. 1077

Published by NRC Research Press
Table 4. Migration duration, number of stops in migration areas, and length of stay (LOS) by wintering site (San Quintin (SQ), San Francisco Bay (SF

Georgia (SG)) and migration strategy for Pacific coast surf scoters (Melanitta perspicillata).

Coastal Inland

Total duration(days) Duration (days) Stops LOS (days) Duration (days) Stops 

Wintering site Route Mean ± SE n Mean ± SE n Mean ± SE n Mean ± SE n Mean ± SE n Mean ± S

SQ Southern Inland 41.0 1 33.0 1 2.0 1 16.5±3.2 1 8.0 1 2.0 

Intermediate Coastal — 2 — — — — — Northern Coastal 54.3±11.3 40.3±11.3 2 5.0±0.0 2 8.1±2.3 2 14.0±0.0 2 2.5±0.5 Overall* 49.8±7.9AB 3 38.1±4.9AB 4 4.0±0.7A 4 10.6±2.2AB 4 12.0±2.0A 3 2.3±0.3 

SF Southern Inland 45.2±6.3 10 31.6±5.8 10 2.6±0.4a 10 15.6±3.0 10 13.7±1.3a 10 2.7±0.2a 

Intermediate Coastal 44.3±10.0 4 35.8±9.1 4 5.0±0.6b 4 7.4±4.8 4 8.5±2.0ab 4 1.8±0.4aNorthern Coastal 49.0±5.2 15 43.5±4.6 16 3.9±0.3b 16 12.3±2.4 16 5.0±1.1b 15 1.3±0.2b Overall* 47.0±3.6A 29 38.5±3.4A 30 3.7±0.3AB 30 12.7±1.8A 30 8.4±1.1A 29 1.8±0.2 

PS Southern Inland 19.7±3.1a 19 1.1±3.0a 20 0.3±0.2a 20 1.2±0.9a 20 18.6±1.8a 19 3.0±0.3a 

Intermediate Coastal 51.1±6.1b 5 31.0±6.0b 5 3.8±0.4b 5 8.1±1.7b 5 20.2±3.6a 5 2.2±0.5b Northern Coastal 42.1±4.5b 9 30.4±4.3b 10 2.8±0.3b 10 10.7±1.2b 10 9.9±2.7b 9 1.2±0.4b Overall* 31.4±3.3B 34 14.7±3.4B 36 1.6±0.3C 36 5.0±1.0B 36 16.3±1.5B 34 2.4±0.2 

SG Southern Inland 7.0±3.7 2 0.0±0.0 2 0.0±0.0 2 0.0±0.0 2 7.0±1.9 2 1.5±0.4 

Intermediate Coastal 23.0 1 16.0 1 1.0 1 16.0±2.6 1 7.0 1 2.0 Northern Coastal 34.5±2.6 4 29.3±1.8 4 2.8±0.2 4 11.0±1.3 4 5.3±1.3 4 1.3±0.3 Overall* 28.9±5.9AB 8 22.9±6.0AB 8 2.1±0.6BC 8 8.8±2.1AB 8 6.0±0.8A 8 1.6±0.3 

Note: We compared durations and stops among wintering sites and reported differences in the Overall row using uppercased letters. We also compared chronology by st

reported differences using lowercased letters under each wintering site. The absence of letters indicates no significant differences.

*Sample size (n) for each Overall category includes birds that began migration, but stopped transmitting before beginning inland migration. These birds were never assigned 

not included in calculations of means by strategy. In addition, because of the small sample size (n = 3), we did not calculate means for the Other migration strategy; howeve

included in the calculation of overall means.

Published by NRC Research Press
areas used and LOS (Table 5). During the 2nd year, transmitters provided fewer locations; thus, we could not be certain that all stopovers were represented. Migration

chronology was different between years for each bird,

although settling dates were remarkably similar for PS birds.

One PS scoter both departed its wintering area and arrived

in the breeding area within a day of the previous year

(Table 5). Additionally, four of the birds arrived and settled

in the breeding area simultaneously during both of the years

they were tracked (Table 5). These four birds represented

both PS and SF wintering areas and both the Southern Inland and the Northern Coastal routes.

Discussion

Use of routes

We integrated satellite telemetry data from surf scoters

marked at four wintering sites on the Pacific coast of North

America to identify spring migration routes and chronology.

We identified Southern Inland and Northern Coastal migration routes used by 83% of surf scoters. The route followed

by an individual had a strong influence on chronology and

stopover sites, and therefore its migration strategy. Use of

these routes, as shown by comparing inland departure latitudes, was independent of wintering sites in which scoters

were marked. However, there was a clear relationship between departure latitude for inland migration and ultimate

nesting site latitude. Given that strong female natal philopatry exists for many sea ducks (Goudie et al. 1994; Eadie et

al. 1995; Pearce et al. 2005), and nesting site fidelity has

been demonstrated for surf scoters (Takekawa et al. 2010),

nesting site may play a large role in determining the migration route used by Pacific Coast surf scoters. Avian migrants

are known to alter their overall migration routes to adjust for

variation in winter and spring resources (Catry et al. 2004)

or regional weather conditions (Alerstam et al. 2006), but in

our study surf scoters with data spanning two consecutive

years showed strong fidelity to overall migration routes and

made slight alterations in chronology at stopover sites.

Energetics and predation risks by route

Factors determining migration strategy selection include

time, energy, and risk of mortality (Alerstam and Lindstrom

1990). Given the short ice-free nesting period in the Northern Boreal Forest breeding area (Takekawa et al. 2010), surf

scoters may be expected to maximize their energy gains during migration (Alerstam and Lindstro ̈m 1990; Farmer and

Wiens 1998, 1999) and migrate with significant capital investment for self maintenance or egg production (Klaassen

et al. 2006). Annual route fidelity such as what we found in

surf scoters may confer advantage to individuals who gain

local knowledge about stopovers that have predictable food

resources and about predators along the route (Rohwer

1992; Bauer et al. 2008). Between the two main migration

routes observed in this study, prey type, value, and predictability, as well as risk of predation, may differ greatly.

Scoters taking the Southern Inland route staged (SQ, SF

birds) or remained (PS, SG birds) in the Puget Sound and

Strait of Georgia until mid-May. During spring, surf scoters

are known to aggregate at spawning sites of Pacific herring

(Clupea pallasi Valenciennes in Cuvier and Valenciennes,

1847), where they consume lipid-rich, energetically profitable roe (Bishop and Green 2001; Sullivan et al. 2002;

Lewis et al. 2007; Anderson et al. 2009). Spawning tapers

off at most sites in mid-April when the first SQ and SF migrants are arriving to the region, although spawning at historically large spawn sites such as Cherry Point, may occur

through the end of June (Stick 2005). Scoters that use the

Southern Inland route could be relying on the once predictable, but now declining (Stick 2005) spawn to accumulate

resources before turning inland. However, in a recent study,

very few radio-marked surf scoters responded to spring herring spawn events within Puget Sound (J.R. Evenson and

D.R. Nysewander, unpublished data), and additional work

Fig. 6. Mean length of stay (LOS) in migration stopover areas by

surf scoters (Melanitta perspicillata) from four Pacific coast wintering sites: (a) Strait of Georgia (SG), (b) Puget Sound (PS),

(c) San Francisco Bay (SF), and (d) San Quintin Bay (SQ). Open

bars represent coastal migration areas and shaded bars represent inland migration areas. Error bars represent 1 SE and numbers above

each bar indicate the number of birds that stopped in that migration

area.

De La Cruz et al. 1079

Published by NRC Research Press
in this area shows that scoters may be in part relying on epifaunal invertebrate prey during late winter and spring (Anderson et al. 2008).

It is unclear why birds that follow the Southern Inland

route choose to stage during inland migration, instead of remaining on the coast for a longer period of time. Depletion

of spawn or alternate benthic and epibenthic prey (Kirk et

al. 2007; Anderson et al. 2008) could be one factor spurring

inland migration. Prey availability in high-latitude freshwater lakes may be less predictable than in coastal waters

because of their ephemeral nature (Piersma 2003). However,

thawing of lower to mid-latitude lakes in areas such as the

Fraser River Plateau occurs as early as March (Calbick et

al. 2004) and emerging aquatic invertebrates could provide

an abundant source of prey for staging scoters migrating

during April and May. Predators encountered inland may be

less predictable than those on the coast. While predation of

scoters and other waterfowl from raptors is prevalent in

coastal waters (Todd et al. 1982; Savard et al. 1998), birds

migrating across land may encounter a more diverse array

of predators including mammalian predators. However, birds

using freshwater lakes may also have more cover from predators available, thereby reducing their risk of predation

(Lind 2004) compared with birds in open coastal waters.

In contrast to the Southern Inland route strategy, there is

some evidence that individuals using the Northern Coastal

route may be following a ‘‘silver wave’’ of herring spawn

resources up the Pacific coast to their final staging site. Lok

(2008) found that the phenology of scoter migration along

some areas of the British Columbia and southeast Alaska

coasts was tied to Pacific herring spawning activity, which

occurs in a northward, latitudinal progression over the

course of spring. Lok (2008) also identified areas farther

from the mainland coast and closer to herring spawns as important habitat for migrating scoters. This may reflect a

strategy of balancing use of sites with highly predictable

prey sources with those that are more protected from aerial

predators (Schmaljohann and Dierschke 2005; Bauer et al.

2008; Pomeroy et al. 2008). If migration routes are predicated on nesting site latitude, then scoters following the

Northern Coastal route may be obliged to obtain all their

capital energy stores from coastal resources such as roe or

benthic prey before turning inland. The most direct inland

path to nesting sites in the northern part of the breeding

area takes individuals over subarctic mountain ranges where

access to thawed, freshwater lakes with abundant prey items

may be limited.

Chronology

To maximize their fitness, migrants time their migration

based on body condition and proximate cues in their environment (Weber et al. 1998). We found that poor individual

condition, as measured by female body mass at time of

marking, did have a significant, although slight, negative influence on departure time from the wintering site. Furthermore, at all wintering sites, individual scoters departing

earliest had longer total migration durations, longer mean

LOS at stopover sites, arrived earliest to the breeding areas,

and settled at nesting sites slightly earlier than later departing birds. Birds that depart late from wintering sites may

have a hard time correcting for poor timing en route to

breeding areas. Studies of barnacle geese (Branta leucopsis

(Bechstein, 1803)) and American redstarts (Setophaga ruticilla (L., 1758)) have also shown that birds departing from

wintering areas earliest are the earliest breeders, suggesting

that optimal reproductive fitness for some species has its basis in the wintering ground (Marra et al. 1998; Prop et al.

2003; Black et al. 2007).

Among wintering sites and migration routes, mean arrival

dates to the breeding area were remarkably similar. Birds

from all wintering sites and using all routes settled at nesting sites less than a week after arrival to the breeding area.

Thus, wintering site and migration route taken did not seem

to confer a greater ability to arrive on time and initiate nesting on the breeding area. However, our results do suggest a

strong selective pressure on timing of arrival. Arrival time is

an important element of competition among migratory birds

(Newton 2006), as individuals who arrive earlier begin

breeding earlier (Nilsson and Persson1994), lay more eggs

(Dalhaug et al. 1996), and show the highest fledging success

(Brinkhof et al. 1993). Surf scoters are one of the most

northerly nesting duck species (Goudie et al. 1994), and re1080 Can. J. Zool. Vol. 87, 2009

Published by NRC Research Press

Table 5. Migration duration, number of stopovers, length of stay (LOS), and chronology for six female surf scoters (Melanitta perspicilCoastal

Stopover

Wintering site PTT No. Year Route* Total duration (days)

Winter departure

(ordinal date; days) No. LOS (days)

SF 55912 2005 SI 27.0 132.0 4 4.8

2006 SI 26.0 115.5 2 8.3

55914 2005 NC 52.0 92.0 4 12.3

2006 NC 27.0 125.5 2 10.5

55919 2005 SI 33.0 125.0 4 5.0

2006 SI 65.0 80.5 1 45.0

PS 43888 2005 NC 14.0 129.0 1 8.0

2006 NC 79.0 64.0 4 19.5

53978 2005 SI 22.0 127.0 0 0.0

2006 SI 37.5 112.0 1 14.5

53980 2005 SI 18.0 126.0 0 0.0

2006 SI 16.0 125.0 0 0.0

*Route names: NC, Northern Coastal; SI, Southern Inland.
production in arctic and subarctic nesting species may be

particularly sensitive to arrival timing given the limited

number of ice-free days available for nesting (Hupp et al.

2006; Takekawa et al. 2010). We could not determine if

marked birds that appeared to be nesting successfully produced broods, thus it is not clear if wintering site or route

use had implications for ultimate reproductive success.

Chronology data for six spring migrants across 2 years

provided additional evidence of the ability of individuals to

adjust their strategy depending on changing conditions.

While in each year these birds followed the same route to

the same nest sites, timing of departure from wintering site

and coast were highly variable. During both years, Southern

Inland migrants had longer inland migrations than scoters

following the Northern Coastal route. Four individuals arrived and settled to nesting areas on the same day, and three

birds did this during both years. Individuals may have been

able to adjust their migration timing in relation to weather or

variable foraging conditions en route to arrive at the breeding area within the same narrow breeding window each year

(Farmer and Wiens 1999; Drent et al. 2003).

Stopover ecology

Individually marked birds in our study made short ‘‘hops’’

or slightly longer ‘‘skips’’ (Piersma 1987) between stopover

sites along the coast. Individuals that migrated along the

coast used at least one stopover site, but this increased with

distance traveled. Making series of short flights such as this

is energetically cheaper than covering the distance in long

flights, and may indicate the availability of good stopover

habitat resources (Piersma 1987). North of their wintering

sites, scoters used each of the broad coastal stopover areas

that we delineated, with the exception that SQ birds did not

stop in two areas. On the lower coast below Puget Sound,

the San Francisco Bay, the Central California coast, and Oregon coast were used as staging areas. Little is known about

habitat use and foraging ecology of scoters during spring

migration at sites along this stretch of the lower Pacific

coast. Scoters are likely not foraging on herring roe in California, as spawns in this region occur prior to the initiation

of migration. For example, the peak of herring spawn in San

Francisco Bay is in January, and most spawn events are

completed by March (California Department of Fish and

Game 2005). However, on the Oregon coast, herring spawning can last through April (Haegele and Schweigert 1985)

and may be available to migrating scoters.

Once migrants reach PS and latitudes north of this migration area, LOS at stopover sites increases dramatically and it

is unclear what factors drive this change. Lok (2008) provide evidence that migrating scoters make prolonged visits

to herring spawn sites at these latitudes, but they also found

scoter use of spawn varied and birds did not respond to all

spawn sites. The two coastal areas that had the greatest

number of staging individuals and the longest LOS were the

Puget Sound and Haines Southeast Alaska migration areas.

Both are the final stopover areas before inland migration for

the majority of Pacific coast surf scoters that use the Southern Inland and Northern Coastal routes. These areas historically have supported very large herring spawns (Stick 2005;

Lok 2008), the timing of which corresponds with the migration of scoters. However, in both areas, herring populations

have declined dramatically in the past several years (Stick

2005; Willson and Womble 2006).

Regardless of the source of food in these areas, studies of

arctic-nesting birds have established the critical importance

of the final staging area before take-off to breeding areas

for building capital income (Drent et al. 2003; Prop et al.

2003). An extended stay in the Lynn Canal region within

the Haines Southeast Alaska migration area to accumulate

energy stores may be valuable for scoters using the Northern

Coastal route, as the largely mountainous path they take to

the breeding area seems to present limited opportunities to

stop at thawed lakes for foraging. Instead, these birds migrate inland rapidly, making few stops and arriving shortly

before initiating nesting. The strategy of scoters using the

Southern Inland route allows them time to forage at more

southern interior sites. Several inland stopover areas were

used by a large number of individuals, but staging was most

prevalent in the Fraser River Plateau (encompassed by the

Southern Inland British Columbia and Central Inland British

Columbia migration areas) and in the Lesser Slave Lake

area. These areas are characterized by lower elevation river

lata) migrating along the Pacific coast in two consecutive years.

Inland

Departure Stopover Settling

Ordinal date (days) Latitude (8N) No. LOS (days)

Arrival

(ordinal date; days) Ordinal date (days) Latitude (8N)

151.0 49.8 2 3.5 155.5 158.0 60.5

132.0 49.4 2 4.3 136.0 140.5 60.5

141.0 59.3 1 2.0 143.0 143.0 67.6

146.5 57.6 1 5.0 151.5 151.5 67.6

145.0 50.0 4 3.0 150.0 157.0 60.9

125.5 49.3 2 9.5 137.5 144.5 60.9

136.0 57.6 1 6.0 142.0 142.0 62.4

142.0 57.9 0 0.0 142.0 142.0 62.4

127.0 48.3 3 7.0 141.0 148.0 60.0

126.5 49.0 2 11.0 130.5 148.5 60.0

126.0 48.7 3 5.7 141.0 143.0 60.8

125.0 47.7 2 7.5 140.0 140.0 60.8

De La Cruz et al. 1081

Published by NRC Research Press
Fig. 7. Repeated migratory routes for six individual female surf scoters (Melanitta perspicillata) from two wintering sites (Puget Sound

(PS), San Francisco Bay (SF)) followed by satellite transmitter during the springs of 2005 and 2006. Solid lines represent first journeys

(2005) and broken lines indicate second journeys (2006). Circles represent stopover sites in 2005, whereas squares represent stopovers in

2006.

1082 Can. J. Zool. Vol. 87, 2009

Published by NRC Research Press
drainages and lakes, as opposed to other more mountainous

stopover areas. Scoters have been observed using freshwater

lakes during migration (Savard et al. 1998), and several individuals in this study staged at the same large lakes on the

Fraser River Plateau.

Conservation implications and future research

Conservation of migratory birds requires a complete

understanding of year-round geographical ranges and habitat

requirements (Webster et al. 2002). Until recently, very little

was known about the life history of the surf scoter, including connectivity between wintering sites and breeding areas

(Sea Duck Joint Venture (SDJV) Management Board

2001)3. Results from our effort to delineate spring migration

of surf scoters indicate that individual scoters do not follow

specific routes to the breeding area based on their wintering

site. However, our study does show that different migratory

routes confer unique migratory strategies and have strong

latitudinal relationships to nest sites. Given these relationships, it seems possible to examine whether or not one migratory route is more advantageous than another by looking

at reproductive success of individuals at different latitudes.

It should also be possible to use stable isotope ratios in

somatic tissues and eggs to determine if marine or freshwater reserves accumulated during spring migration play a

bigger role in the body condition and reproduction of individuals taking one route over another (Gauthier et al. 2003;

Schmutz et al. 2006; Yerkes et al. 2008). These methods

would be useful in discerning the effects of climate change

and habitat loss on scoters following coastal or inland strategies. As a result of climate change, migratory birds have

been shown to alter their migration phenology in an attempt

to match changing temperatures or prey phenology (Cotton

2003; Drever and Clark 2007). Temperature change could

alter spawning timing of Pacific herring or the emergence

of invertebrates in freshwater lakes, and thus could affect

birds disproportionately depending on their migration strategy.

Our study underscores the importance of the Puget Sound,

Strait of Georgia, and Lynn Canal as final coastal staging

areas for the majority of Pacific coast surf scoters. In addition to these and other specific southeast Alaska coastal

staging sites already deemed significant to migrating surf

scoters (see Lok 2008), our broader view of scoter migration

routes highlights the need to better understand the role and

importance of stopover areas in California and on the Oregon coast. Similarly, inland lakes and drainages on the

Fraser River Plateau, British Columbia, and in northern Alberta were identified as key staging areas for migrating

scoters, but little is known about their resource value for

this species. Use of these stopover areas should be further

evaluated to identify specific areas that may be important to

conserve.

Acknowledgements

This study was funded by the USGS Alaska Science Center (SQ), the Sea Duck Joint Venture (SQ, SG, PS), USGS

Western Ecological Research Center under the Coastal Ecosystems and Land-Sea Interface Program (SF), the CALFED

Ecosystem Restoration Program Mercury Project (SF), the

Dennis Raveling Chair at the University of California (SF),

and Signals of Spring (SF). Many individuals working from

all four wintering sites contributed to make this project successful. We thank E. Bohman, T. Bowman, K. Brodhead, S.

Duarte, S. Duarte-Etchart, C. Eldermire, P. Fontaine, A.

Keech, S. Iverson, E. Lok, D. Mulcahy, D. Rizzolo, K.

Sage, and M. Shepherd (SQ); E. Palm, D. Gaube, L. Terrazas, J. Anhalt, C. Kereki, J. Chastant, H. Goyert, J. Wasley,

J. Seyfried, P. Gibbons, M. Nagendran, C. Scott, P. Tucker,

C. Salido (SF); B. Hall, J. Gaydos, D. Lambourn, T. Cyra,

B. Murphie, G. Schirato (PS); and D. Mulcahy, S. Iverson

(SG) for their helpful field assistance. We thank E. Palm

and K. Spragens for their help with data compilation and

figures for the manuscript. We also thank T. Bowman

(SDJV) who encouraged the integration of our data, as well

as J. Eadie, K. Miles, M. Johnson, S. Iverson, and K. Spragens for helpful discussions and comments on earlier drafts.

Use of trade names does not imply government endorsement.

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