PHILOPATRY AND NATAL DISPERSAL OF THE WESTERN SNOWY PLOVER

2007·5.4 MB·English

by  Mark A Colwell

The Wilson Journal ofOrnithology 119(3):378-385, 2007
PHILOPATRY AND NATAL DISPERSAL OF THE WESTERN
SNOWY PLOVER
MARK A. COLWELL, SEAN E. McALLISTER,^ CHERYL B. MILLETT,i>3
AMBER N. TRANSOU,2^ STEPHEN M. MULLIN,‘ ZACH J. NELSON,'
CAROL A. WILSON,' AND RON R. LeVALLEY^
—
ABSTRACT. Conservation of threatened species requires knowledge of individual movements within and
among spatially distinct subpopulations. We quantified philopatry, local dispersal, and number ofbreeding sites
used by 62 Western Snowy Plovers (Charadrius alexandrinus nivosus) that were marked as chicks and returned
to a breeding area in coastal northern California. Slightly more males (17%) than females (12%) returnedtothe
study area. Natal dispersal (distance between natal nest and first nest as a yearling) was similar for males and
females, and greater than reported for other shorebirds. Philopatric plovers dispersed shorter distances between
successive nests within a breeding season compared to the distance between successive nests from one year to
the next. Most males and females thatbred locally wintered in the study area. Those that wintered locallytended
to be from later clutches compared to the few migrants that hatched earlier in the season. The population of
Snowy Plovers in coastal northern California is linked by dispersal with otherbreeding plovers alongthe Pacific
coast. Dispersal estimates indicate that wide-ranging movements are typical ofSnowy Plovers throughout their
range, which should facilitate recolonization ofhabitats. Received 17March 2006. Accepted4 September2006.
Conservation efforts for rare and patchily opatric individual from its natal site to where
distributed species require knowledge of pat- it first breeds.
terns and causes of dispersal of individuals The Snowy Plover (Charadfins alexandri-
among and within subpopulations. These data nus) in North America is divided into two
help biologists understand the genetic struc- subspecies (Page et al. 1995, Funk et al.
ture ofpopulations (Avise and Hamrick 1996) 2007). One (C. a. tenuirostris) breeds in the
and may enhance efforts to manage reproduc- Caribbean and a second (C. a. nivosus) is dis-
tive success. Dispersal estimates, as well as tributed in the western Great Plains, Great Ba-
demographic data on survival and reproduc- sin, and along the Pacific coast. The U.S. Fish
tion, are key elements of models predicting and Wildlife Service listed the Pacific coastal
population persistence and recovery (Morris population segment in 1993 as threatened un-
and Doak 2002). Dispersal is quantified in one der the Endangered Species Act (U.S. De-
of two ways (Oring and Lank 1984). First, partment of Interior 1993). The listed popu-
philopatry is often gauged by the proportion lation segment has been well studied for over
of birds of either gender returning to breed at a quarter century (e.g., Warriner et al. 1986,
a location, although “return” at times is de- Page et al. 1991). Stenzel et al. (1994, 2007)
fined as an individual being observed (Col- documented dispersal of a population in cen-
well et al. 1988, Reynolds and Cooke 1988). tral California. Males and females occasion-
This definition fails to distinguish between in- ally dispersed long distances (50-1,140 km)
dividuals seen once versus multiple times within and between breeding seasons, and fe-
(resident) in an area. In contrast, natal dis- males were more likely than males to be ab-
persal quantifies the distance moved by a phil- sent from their primary site during a portion
of the breeding season. Stenzel et al. (1994)
inteipreted these patterns as a consequence of
sity‘,DeArpeaarttam,eCntAo9f55W2i1l,dliUfSe,A.Humboldt State Univer- the species’ long breeding season (—120 days
2Mad River Biologists, 920 Samoa Blvd., Ste 210, of egg laying), uniparental (male) care of
Areata, CA 95521, USA. chicks, and dynamic breeding habitats. These
The Nature Conservancy, Lake Wales Ridge Pro- features allow females to nest successfully up
gramC,alPi.foOr.niBaoSxta6t3e0P,arBkasb,sPo.nO.PaBrok,xF20L063,38E2u7r,ekUaS,AC.A to three times, often at widely disjunct loca-
95502, USA. tions.
Corresponding author; e-mail; The recovery plan for the listed population
[email protected] segment of the Western Snowy Plover (U.S.
378
Colwell et al. • SNOWY PLOVER DISPERSAL 379
METHODS
Department of Interior 2001) designated six
recovery units extending from the northern We began marking adult plovers and newly
ilinmgittonofsotuhethsptehcrioeusg’hbCraeleidfionrgnira.anMgeositn bWraesehd-- hataitncgheadncihnitceknssiivne 2m0o0n0i,to1riynegarprporgiorramt.o Einaictih-
ing plovers in coastal northern California (Re- year, we captured breeding adults at nests us-
covery Unit 2) are concentrated at a few lo- ing noose mats and circular walk-in nest traps.
cations around Humboldt Bay (Colwell et al. We marked adults with a unique combination
2005b), which are several hundred km from of a federal aluminum band (wrapped in col-
other large concentrations ofbreeding plovers ored tape) and three colored leg bands. We
north and south. Recovery Unit 2 is targeted marked all siblings of a brood at hatch with
for a population of 150 breeding plovers (U.S. an aluminum band wrapped with brood-spe-
Department of Interior 2001), but the popu- cific colored tape, which allowed us to distin-
lation has not reached this level, varying be- guish between similar-age chicks from differ-
tween 54 and 74 adults over a 6-year period ent broods in an area. We are confident that
(2001-2006; Mullin 2006). we captured and banded >95% of all newly
We initiated a study in 2000 to individually hatched chicks and breeding adults in the
mark breeding plovers in Recovery Unit 2. study area each year. We recaptured adults that
Our objectives were to examine gender dif- we first marked as chicks and marked them
ferences in (1) return of plovers marked as with unique adult band combinations. Observ-
chicks to the local breeding population, and ers surveyed breeding plovers almost daily in
(2) dispersal from natal nest to first and sub- each habitat from mid March to early Septem-
sequent nests. ber. We recorded the identity of banded plo-
vers, found nests, and monitored broods dur-
STUDY AREA ing surveys. Upon finding a nest, we recorded
the number of eggs and estimated hatch date
We studied plovers from 2000 to 2006 in (for complete clutches) using egg flotation
Del Norte, Humboldt, and Mendocino coun- methods (Alberico 1995). We estimated hatch
ties in northern California (Fig. 1). We con- date for incomplete clutches by adding 27
ducted most fieldwork in Humboldt County days (average incubation period; Page et al.
where the majority of plovers bred, but ob- 1995) to the date the last egg was laid. We
servers from state and federal agencies con- erected predator exclosures at most (61%)
ducted bimonthly surveys ofsuitable breeding nests on beaches but did not construct exclo-
habitat throughout Recovery Unit 2. Plovers sures around nests along rivers. We monitored
bred in two distinct habitats in the study area fledging success ofplovers beginning in 2001
(Colwell et al. 2005b). Many plovers nested through 2006 (Colwell et al. 2005a, 2007) by
in fine, sandy substrates of ocean-fronting visiting sites with broods at 1-4 day intervals
beaches amidst sparse debris fields of dried and recording the presence of adults and
brown algae, shells, dead vegetation, drift- young until chicks fledged at 28 days (Page
wood, and occasional garbage. These beaches et al. 1995).
were often vegetated sparsely with native We defined philopatry as the breeding of a
plants (e.g., Abronia, Leymus), dense stands locally-hatched chick in the study area (coast-
of introduced European dune grass {Ammo- al northern California; Recovery Unit 2
phila arenaria), and patches of sea rocket [RU2]) or repeated sightings during the nest-
{Cakile). Plovers also nested on gravel bars of ing season suggesting breeding or attempted
the lower Eel River near its confluence with breeding. We quantified natal dispersal as the
the Pacific Ocean upriver approximately 16 straight-line distance (m) between an individ-
km (Colwell et al. 2005b). Plovers breeding ual’s natal nest and its first nest as a yearling
along the river nested in coarse, heteroge- using a geographic information system. We
neous substrates varying in size from sand to categorized breeding dispersal, the distance
pea-sized gravel and large stones, which were between successive nests of an individual in
vegetated sparsely by willow {Salix spp.) and two ways. Within-season dispersal was the
white sweet clover {Melilotus alba). distance between successive nests in a given
380 THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 119, No. 3, September2007
FIG. 1. Study areas (A) in the three counties ofcoastal northern California that comprise Recovery Unit 2;
(B) where Snowy Plovers were color-marked and monitored from 2000 to 2006. Individual gravel bars along
the lower Eel River are shown in (C).
Colwell et al. • SNOWY PLOVER DISPERSAL 381
TABLE 1. Philopatry of Snowy Plovers breeding
in coastal northern California, 2001-2006.
Total#banded %Return %Return
Year previousyear Females(n)^ Males(n)^
2006 71 11 (4) 17 (6)
2005 76 11 (4) 16 (6)
2004 61 13 (4) 13 (6)
2003 69 14 (5) 12 (4)
2002 93 13 (6) 17 (8)
2001 58 7 (2) 24 (7) 0-1 10-100 10-100 >100
Totals 428 11.7 (25) 17.3 (37) Distance (Km)
^Assumes anequal sex ratioamong newly hatchedchicks (Szekelyet FIG. 2. Dispersal distances ofSnowy Plovers (fe-
al.2004). males [, n = 20] and males [, n = 26]) in coastal
northern California.
breeding season; between-year dispersal was
the distance between an individual’s first nest RESULTS
of the year and the location of its last nest of Philopatry and Natal Dispersal.—Sixty-
the previous year. We summarized data for two (14.4%) of432 marked chicks returned to
males and females separately, and distin- the study area; most (94%) bred locally as
hgauticshheadndbetthwoeseeninnewshtsicihn awthilecahsteognges efagiglesduct-o pyleaorvleirnsgs(6(.T5a%b)lewe1r).eFoobusreorfvetdhere6p2eaptheidllopyatdruirc-
cessfully hatched. We tallied the number of ing a breeding season suggesting they nested
breeding locations occupied by individuals locally; however, we did not find nests for
based on observations of color-marked birds. these individuals. Philopatry (ofmales and fe-
We defined a location (e.g., gravel bar or lin- males combined) annually ranged from 13.0
ear stretch of beach) as a breeding site occu- to 16.4%. Males (17.3%) tended to be more
pied by one or more plovers, often separated philopatric than females (11.7%) (JC = 2.72,
by unsuitable (e.g., river channel, rocky inter- df = 1, P = 0.10). There was no gender dif-
btiedaacl)h)orhabuintoactcfurpoiemdot(he.egr.,lolcoantgionsstrbetychaesdios-f 0f.e8r2e)nc(eFiign. n2a)t.alFedmiaslpeersaanld(mCa6,l2oe^yea0r.l2i3n,gsPes=-
tance greater than the extent of any particular tablished first nests within northern California
site (Fig. 1). We collated data over weekly in- (RU2) at distances of 16.0 ± 29.2 km (median
tervals spanning 15 March to 15 July, the pe- = 4.8, range = 0.4-125.7) and 18.2 ± 33.6
riod in which plovers initiated nests (Colwell km (median = 5.0, range = 0.06-163.8), re-
et al. 2005b) and prior to the formation of spectively, from their natal nests. Considering
post-breeding flocks. only the years 2001 through 2005 when we
We analyzed return rates using Chi-square intensively monitored fledging success, 53
tests, assuming an equal sex ratio at hatch (31.5%) of 168 fledged chicks returned to the
(Szekely et al. 2004). Each individual plover northern California study area.
was considered once in this analysis (i.e., re- Philopatric plovers comprised 10-22% of
turned either as a yearling or 2 years of age). the local breeding population each year. Plo-
We summarized dispersal as jc ± SD, and vers bearing bands from Recovery Unit 2
compared samples for males and females us- have been recaptured or observed during the
ing a r-test of untransformed linear distances breeding season elsewhere along the Pacific
between an individual’s natal nest and first coast (Table 2). A yearling female dispersed
known nest as an adult. We used logistic re- 474 km from the local population in 2005 to
gression to examine relationships between breed at Moss Landing, California after high
date ofhatching for an individual and whether water on the Eel River destroyed her initial
or not it was observed as a winter resident or nest. Another female, hatched in 2000, dis-
migrant. We used SAS (SAS Institute 1991) persed 354 km to breed in Oregon; she sub-
to analyze data. sequently returned to breed in Humboldt
382 THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 119, No. 3, September2007
TABLE 2. Snowy Plover dispersal to breed outside ofcoastal northern California.
Hatchyear Gender Breedinglocation Yearbred
1999 F Siltcoos, OR
2000 M New River, OR 2003
2000 F Tahkenitch, OR 2001
2000 F Bandon, OR 2001
2001 M Sutton Beach and Coos Bay, OR 2002-04
2001 F New River and Bandon, OR 2003, 2005
Unknown M Sutton Beach, OR 2001
Unknown M Leadbetter Pt. and Willapa Bay, WA 2002
Unknown M Midway Beach, WA 2002
Unknown F Bandon, OR 2002
Unknown Unk Pt. Reyes, CA 2002
Unknown M Pt. Reyes, CA 2003
Unknown Unk Vandenberg, CA 2003
2004 F Moss Landing, CA 2005
WA
2004 F Leadbetter Pt., 2005
M WA
2004 Leadbetter Pt., 2005
M WA
2004 Leadbetter Pt., 2005
County (2003) and Mendocino County km) males or between five successful (0.4 ±
(2004). 0.4 km) and four unsuccessful (118.7 ± 236.8
A greater percentage of river-hatched plo- km) females (Mann-Whitney f/-test, z = 0.37,
vers returned to the study area (16.3% of 203 P = 0.71).
chicks) compared to beaches (7.9% of 229 Within a year, individuals commonly bred
hatched chicks). However, this analysis was at a single site (yearlings and older adults
based on chicks marked at hatch. Return rates combined; males: 86—100% and females: 76—
based on fledged chicks were similar (31.0% 90%) within the study area, rather than mov-
of 58 chicks fledged from beaches; 30.0% of ing among sites (Fig. 1). This pattern was
1 10 river-fledged chicks). Most (69.4% of49) higher (4-14% annually) for males than fe-
philopatric plovers first bred in their natal hab- males in each year. As yearlings, males (1.9
itats (i.e., beach vs. river); 30.6% (15 of 49 ± 1.0) and females (1.6 ± 0.9) bred at similar
yearlings) switched habitats. Similar numbers numbers of sites, and the number of breeding
of yearling males and females (n = 16 total sites was similar as individuals bred in their
birds) moved from their natal beach habitat to second (males: 1.9 ± 1.1; females: 1.9 ± 1.2),
breed on the river (four males and three fe- third (males: 1.6 ± 1.2; females: 1.7 ± 1.0)
males), and from natal river habitat to breed or fourth year (males: 1.0 ± 0.0; females: 1.5
on the beach (three males and five females). ± 0.7).
Two plovers (one male and one female) were Migratory Movements and Winter Residen-
—
absent as yearlings but returned to breed when cy. Most philopatric plovers were resident
they were 2 years of age in their natal river year-round, as evidenced by repeated obser-
habitat; one male plover first bred on his natal vations in post-breeding and winter flocks.
beach as a 2-year-old. Fourteen of 17 philopatric males observed
Between-year and Within-season Dispers- during winter occurred at one of several sites
—
al Individuals typically moved greater dis- where flocks form near breeding areas (Clam
tances between than within years (Table 3). Beach, South Spit, and at the mouth ofthe Eel
There was no clear difference in the average River). Three other philopatric males wintered
distance moved by either males or females in southern California. Nine of 11 philopatric
that were successful or failed to hatch their females (with known wintering sites) wintered
first clutch. There was no difference (Mann- locally; two wintered south of the study area.
Whitney U-iest, z = 0.83, P = 0.43) in dis- There was a tendency for individuals (males
persal distance between two successful (10.7 and females combined, n = 27) that hatched
± 14.3 km) and six unsuccessful (2.3 ± 2.8 from early clutches to become migrants
Colwell et al. • SNOWY PLOVER DISPERSAL 383
TABLE 3. Distance (km) (jc ± SD) between successive nests of male and female Snowy Plovers.
Females Males
Fateofpreviousnest Fateofpreviousnest
Nesting
Age attempt Hatched(n) Failed(«) Hatched(n) Failed(n)
Yearling 2nd 0.4 ± 0.4 (5) 118.7 -P 236.8 (4) 10.7 ± 14.3 (2) 2.3 ± 2.8 (6)
0.9 ± 1.1 (4)
4th 0.7 ± 0.8 (2)
Second Yr 1st 10.4 ± 20.4 (5) 15.4 -h 24.3 (3) 11.7 -P 20.2 (12) 1.9 -t- 2.4 (5)
2nd 2.2 ± 2.5 (2) 1.2 -P 1.5 (3) 1.0 -P 0.8 (3) 1.5 ± 1.2 (8)
2.7 -P 2.3 (5) 0.7 -P 0.4 (4) 1.7 ± 1.9 (2)
4th 0.9 -P 0.2 (2) 0.9 ± 0.6 (4)
S'*’ 23.5 -P 31.8 (2) 47.5 ± 0.0 (1)
Third Yr 1st 9.0 ± 15.8 (6) 0.2 -P 0.0 (1) 2.9 ± 4.3 (8) 2.0 + 2.3 (2)
2nd 2.1 -P 2.0 (5) 0.5 -P 0.6 (3) 0.8 -1- 1.1 (4)
3rd 2.8 ± 0.0 (1) 0.1 -P 0.0 (1) 1.3 -+- 1.0 (3)
4th 0.7 + 0.6 (2)
0.6 -1- 0.6 (2)
6th 0.1 -t- 0.0 (1)
Fourth Yr 1st 6.1 -P 0.0 (1) 21.2 -P 36.4 (3) 4.9 + 0.0 (1)
2nd 0.9 ± 0.4 (2)
3^‘i 1.1 + 0.0 (1)
4th 2.7 + 0.0 (1)
5'h 1.3 -1- 0.0 (1)
Fifth Yr 1st 3.2 -P 0.0 (1)
whereas individuals from later clutches were male settlement nearer natal sites for the
more likely to become local winter residents Banded Dotterel {Charadrius bicinctus) in
O = 0.05 ± 0.03, Wald = 3 25 P = 0.07). New Zealand. Gratto (1988) reported no gen-
. ,
der bias in philopatry for the Semipalmated
DISCUSSION
Sandpiper {Calidris pusilla).
Male and female Snowy Plovers in coastal The Snowy Plover has a serially polyga-
northern California had similar patterns ofna- mous, territorial mating system; males and fe-
tal dispersal and use of breeding sites; males males share incubation, but males typically
tended to be more philopatric than females. care for chicks alone while females pursue ad-
These findings are similar to patterns from a ditional mates (Page et al. 1995). As a con-
long-term study (with a much larger sample) sequence, during the long (—120 day) breed-
in central California (Stenzel et al. 2007). In ing season typical ofthe species along the Pa-
the Monterey Bay area, philopatry was male cific coast, females may breed successfully up
biased, a pattern reported for most other to three times whereas males may breed twice.
shorebirds where gender differences exist. Or- The Snowy Plover occupies dynamic habitats
ing and Lank (1984) concluded there was a that vary greatly in quality owing to frequent
tendency for male-biased philopatry among natural disturbance (e.g., tidal over-wash, river
the 12 species of shorebirds they reviewed. flooding, drifting sand). Coupled with high
Recent studies strengthen the case for male- nest failure rates from predation (Page et al.
biased philopatry. Jackson (1994) reported 1995; Colwell et al. 2005a, 2005b), these fac-
that males and females of three territorial ets place a premium on dispersal rather than
shorebirds (Redshank [Tringa totanus]. Dun- being faithful to a particular nest site (Stenzel
lin [Calidris alpina schinzii], and Ringed Plo- et al. 1994). We found no relationship be-
ver [Charadrius hiaticula]) breeding in the tween nesting success and breeding dispersal;
Western Isles, United Kingdom returned at a finding also reported by Stenzel et al.
similar rates and that males settled signifi- (1994), but in contrast to other shorebirds (Or-
cantly nearer their natal sites than females. ing and Lank 1984).
Pierce (1989) reported a similar finding of Comparatively large dispersal distances of
384 THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 119, No. 3, September2007
Snowy Plovers in this study were similar to cally, chicks from early hatching clutches may
those reported by Stenzel et al. (1994, 2007) become migrants because they develop a ten-
for Snowy Plovers of varying age. For both dency to wander in search of other plovers
populations, the comparatively large dispersal when most adults are still breeding. In con-
distances may stem from two facets related to trast, late-hatching chicks often fledge in the
the spatial scale of study, the first methodo- vicinity of post-breeding flocks, which begin
logical and the second biogeographical. First, to form in mid-July in our study area and else-
we intensively monitored dispersal over a where (Stenzel et al. 1994). Thus, we specu-
large area. Jackson (1994) quantified dispersal late that late season young are incorporated
by intensively monitoring shorebirds on four into what will become the wintering flock and
study plots of 40-120 ha separated by a few establish their winter residency patterns. If
km of suitable habitat, which he surveyed oc- this scenario is accurate, it may explain the
casionally for dispersing birds. Jackson’s increasing evidence that habitat protection for
(1994) study areas roughly correspond in size non-breeding flocks can lead to establishment
to each of our locations. Dispersal estimates ofbreeding plovers at wintering sites (Lafferty
for Snowy Plovers would have been compa- 2001).
rable to those for Ringed Plover (1.5 and 2.4 CONSERVATION IMPLICATIONS
km for males and females, respectively) had
we limited the spatial scale of our study area Breeding Snowy Plovers in coastal northern
California are linked through dispersal with
to similar sized plots. Second, the disjunct dis-
tribution of breeding sites may have also con- subpopulations elsewhere in the range of the
listed population segment. Large dispersal dis-
tributed to large average dispersal distances.
tances of yearlings may be a consequence of
Average dispersal distance for both males and
females approached 20 km (median distances this isolation and disjunct breeding locations.
were ~5 km and comparable to those reported Individuals occasionally move long distances
by Stenzel et al. 2007). The average dispersal (to breed) both north and south on the Pacific
distance is intermediate between movements coast (Stenzel et al. 1994, 2007). These large
within and between locations (e.g.. Clam movements indicate that plovers are capable
of colonizing suitable habitat throughout the
Beach, South Spit, and gravel bars of the Eel
River). Our dispersal estimates combine two species’ range. The establishment of local
breeders, however, may be enhanced by the
groups of plovers: those that would be
( 1 ) presence of flocks of post-breeding plovers
considered truly philopatric as they returned
to within a few km of their natal site, and (2) when fledglings search for a wintering site.
The absence of a relationship between nesting
those that remained in the local area but
mloocvateidoninotehxecrestshanofth1e0irknmatatlo sbirtee.ed first at a sStuecnczeesls eatnadl.d(i1s9p9er4s)alwhsotrseunggtgheesntsedfithnadtinwgisdeo-f
The breeding population of Snowy Plover ranging movements ofindividuals were acon-
sequence ofthe species’ long breeding season,
in coastal northern California consists of a
sequentially polygamous mating system, use
mix ofyear-round residents and migrants sim-
of dynamic breeding habitats, and frequent
ilar to that reported for central California
(Stenzel et al. 1994). The tendency to become mneuslttifpalielusriet.esInwdiitvhiidnuaalnsdmaomvoengwibrdeeeldyinagmosenag-
migratory versus resident correlated with tim-
sons to capitalize on breeding habitat ofvary-
ing of an individual’s Hedging in the popula-
ing quality, including the availability ofmates
tion; chicks from late hatching clutches were
more likely to become residents. Pierce (1989) (Stenzel et al. 1994). Wide-ranging move-
ments suggest that plovers are capable ofcol-
reported similar findings for the Banded Dot-
terel. We offer the following scenario for the onizing formerly unoccupied sites such as
newly restored habitats and those areas af-
development of resident versus migrant be-
forded enhanced protection under the Endan-
haviors in Snowy Plovers. The tendency for
gered Species Act.
plovers from early and late hatching clutches
ACKNOWLEDGMENTS
to become migratory and resident, respective-
ly, may stem from the proximity of a post- B. R Atkinson, H. E. Beeler, N. S. Burrell, A. M.
breeding flock for a Juvenile to Join. Specifi- Clarke, T. J. L. Colwell, W. P. Goldenberg, M. A. Har-
Colwell et al. • SNOWY PLOVER DISPERSAL 385
dy, S. J. Hurley, T. L. Klemetson, A. J. Leist, D. M. delity in three monogamous wader species in the
LeValley, J. J. Meyer, G. B. Reid, K. G. Ross, and R. Western Isles, U.K. Ibis 136:463-473.
R. Smith assisted in the field on many occasions; nu- Lafferty, K. D. 2001. Human disturbance to winter-
merous volunteers and individuals from state and fed- ing Snowy Plovers at a southern Californiabeach.
eral agencies conducted surveys in Del Norte, Hum- Biological Conservation 10:1-14.
boldt, and Mendocino counties. We are grateful toJim Morris, W. F. and D. F. Doak. 2002. Quantitativecon-
Watkins for supporting our efforts. Comments ofsev- servation biology. Sinauer Associates, Sunder-
eral anonymous reviewers and G. W. Page improved land, Massachusetts, USA.
themanuscript. OurworkwasfundedbytheCalifornia Mullin, S. M. 2006. Apparentsurvivalandpopulation
Department ofEish and Game, California Department growthofWestern SnowyPlovers(Charadriusal-
of Parks and Recreation, Humboldt County Fish and exandrinus nivosus) in Humboldt County, Cali-
Game Advisory Commission, Humboldt County Plan- fornia. Thesis. Humboldt State University, Areata,
ning Department, Humboldt State University, Mad California, USA.
River Biologists, Marin Rod and Gun Club, MRB Re- Oring, L. W. and D. B. Lank. 1984. Breeding area
search, Inc., Redwood Region Audubon Society, fidelity, natal philopatry, andthe social systemsof
Stockton Sportsmen’s Club, Western Section of The sandpipers. Pages 125-147 in Shorebirds: breed-
Wildlife Society, U.S. Bureau of Land Management, Oilnlga,beEhdaivtiorosr).anPdleponpuumlaPtrieosnss, (NJ.eBwurYgoerrk,anUdSAB.. L.
U.S. Fish and Wildlife Service, and the CaliforniaDe- Page, G. W, L. E. Stenzel, D. W. Shuford, and C.
partment ofFish and Game’s Oil Spill Response Trust
R. Bruce. 1991. Distribution and abundance of
Fund through the Oiled Wildlife Care Network at the the Snowy Plover on its western North American
WildlifeHealthCenter, SchoolofVeterinaryMedicine,
breeding grounds. Journal of Field Ornithology
University ofCalifornia, Davis. 62:245-255.
Page, G. W, J. S. Warriner, J. C. Warriner, and P.
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