MOLT AND BODY MASS OF RED KNOTS IN THEEASTERN UNITED STATES

2007·5.1 MB·English

by  Brian A Harrington

The Wilson Journal ofOrnithology 19(1):35^2, 2007
1
MOLT AND BODY MASS OF RED KNOTS IN THE
EASTERN UNITED STATES
BRIAN A. HARRINGTON,'-^ BRADFORD WINN,^ AND STEPHEN C. BROWN'
—
ABSTRACT. Red Knots (Calidris canutiis) that spend winter in the southeastern United States are known
to have been genetically separated from their congeners that migrate to Patagonian wintering grounds forabout
12,000 years. We examined and documented differences between the two groups in their use of southward
migration stopoverlocations, flightfeathermolt, fidelityto winteringzones, anddifferencesin massatsouthward
migration stopover locations. Red Knots wintering in the southeastern United States do so consistently, and
knots wintering in Patagonia have not changed to wintering in the southeastern United States. The twowintering
groups have distinct differences in their nonbreeding season biology (e.g., migration strategies, chronology of
pre-basic molt), and these differences have been maintained for decades if not millennia. Received 24 August
2004. Accepted22 July 2006.
Red Knots {Calidris canutiis), a Holarctic developed distinctly different migrations as
breeding shorebird, have a relatively large, al- reflected in differences of their flight-feather
beit poorly-known breeding range in the Ne- molt, migration-related mass gain, principal
arctic (Harrington 2001). There are at least migration stopover locations, as well as win-
two regions in the Western Hemisphere where tering locations.
relatively large numbers of Red Knots are
METHODS
known to spend their winter, one on the Pa-
—
tagonian coasts of Argentina and Chile (Pa- Study Areas We studied two regions used
.
tagonian-wintering knots), and the other by knots during southward migration; Cape
(northern-wintering knots) —9,500 km to the Cod and western Cape Cod Bay in Massachu-
north, including areas in the southeastern setts, and the Altamaha River Estuary on the
United States (Morrison and Harrington Georgia Atlantic coast. Sites in Massachusetts
1992). Based on evidence of differing migra- included Third Cliff Beach (42° 10' N, 70°
tion strategies and differential survival esti- 43' W), and Monomoy Island and South
mates for these two wintering groups, Har- Beach in Chatham (41° 38' N, 69° 58' W). In
rington et al. (1988) questioned whether knots Georgia we worked mostly on Wolf Island
from the Patagonian and U.S. wintering re- (31° 19' N, 81° 17' W), Little Egg Island Bar
gions were from different breeding groups (31° 18' N, 81° 16' W), and Little St. Simons
with little genetic exchange. Buehler and Bak- Island (31° 17' N, 81° 16' W). Additional ob-
er (2005) confirmed that Patagonian-wintering servations were on the Florida west coast,
and northern-wintering knots have been ge- principally between Bonita Springs (26° 24'
netically isolated for about 12,000 years. Lit- N, 81° 54' W) and Honeymoon Island in Dun-
tle additional information is known about how edin (28° 04' N, 82° 50' W).
—
these two groups differ in their biology. Capture and Banding We captured knots
.
The objectives ofour study were to explore using rocket and cannon nets placed at loca-
the possibility that Red Knots wintering in the tions where flocks of knots gathered at high-
U.S. differed from those wintering in Pata- tide roosts during the day. We used trained,
gonia in flight-feather molt, movement ofcol- volunteer crews to remove captured birds
or-banded birds, plumages, and migration from nets to well-ventilated holding contain-
chronology. We tested the hypotheses that Pa- ers prior to processing. Standard, uniquely-
tagonian and northern-wintering knots have numbered U.S. Federal bands and color bands
were applied to tarsi and meta-tarsi in com-
Bo'xMa17n7o0m,eMtanCoemnteetr,fMorACo0n2s3e4r5v,atUiSoAn.Sciences, P. O. binations to allow visual identifications of
capture location and date. Birds were released
^Georgia Department of Natural Resources, One
Conservation Way, Brunswick, GA 31523, USA. at capture locations.
^Corresponding author; We used a rocket net in Massachusetts for
e-mail: [email protected] capturing 1,363 adult Red Knots at Third Cliff
35
36 THE WILSON JOURNAL OL ORNITHOLOGY • Vol. 119, No. I, March 2007
Beach and Plymouth Beach (42° 59' N, 70°. schedules at other times of year, but collected
39' during July and August, 1980-1983. counts as opportunity allowed.
—
Birds were evaluated for flight feather molt, Primary Feather Molt. Knots have a se-
and body mass to the nearest gram. Birds were quential primary flight-feather molt starting
processed and released on site. We assigned with the innermost feather and moving cen-
age (adult orjuvenile) based on plumage char- trifugally (Ginn and Melville 1983). This en-
acters (Hayman et al. 1986). During August ables scoring molt stages using the Ashmole
2004 and 2005 we also collected information (1962) system where each of the 10 primary
on flight feather molt by watching flocks feathers on the right wing can score between
through telescopes when wing-stretching is 0 and 5 points, depending on age and growth
commonly seen, i.e., shortly before flocks de- stage. A knot with 10 new primary feathers
part high-tide roosts for foraging areas (BAH, would score 50, one where the molt had pro-
pers. obs.), and by careful scrutiny of close- gressed about half way from inner to outer
by knots in flight. primary feathers would score —25, and one
We used a rocket net to capture, color-mark, with 10 old primary feathers would score 0.
and release knots during January (n = 212 Old primary feathers are distinguishable from
adults) and October {n = 99 adults) 1981 at new feathers by fading and extensive wear
Longboat Key (27° 20' N, 82° 36' W) on the whereas new feathers are darker (less faded)
west coast of Florida. Birds from all catches with little wear. We scored the molt on sam-
were evaluated for flight feather molt, and ples ofknots captured in Massachusetts, Geor-
were weighed to the nearest 0.1 g using a tri- gia, and Florida. We used one-way ANOVAs
ple-beam balance. Birds were processed and to compare score means between years within
released on site. We did not use data from study sites, and among—study sites.
individuals less than 12 months of age, based Color-hand Searches. We searched through
on plumage characters (Hayman et al. 1986). flocks ofknots in Massachusetts, Georgia, and
We captured 226 adult knots in Georgia us- Florida to And color-marked individuals, re-
ing a cannon net set at three high-tide roosting cording whether they were those we marked
locations in the Altamaha River Estuary (31° in Georgia, or ones marked by other research-
18' N, 81° 17' W). We processed most catches ers in Delaware Bay or South America. We
at the capture location, taking measurements used Chi-square analysis to compare the rel-
of mass to the nearest 1.0 g using a Pesola® ative frequencies with which we found knots
spring scale, and scoring the primary feather from these three banding origi—ns.
molt condition. Body Plumage Evaluation. We recorded
Migration Count.s.—We used International body plumage appearance of adult knots in
Shorebird Survey (ISS) data collected be- Georgia, assigning scores ranging between 1
tween 1975 and 2004 to evaluate numbers of (complete basic plumage) and 5 (complete al-
knots counted in the eastern Lfnited States be- ternate plumage). The.se data were from knots
tween June and December. ISS project guide- randomly selected (/? = 143) from flocks dur-
lines ask cooperators to count shorebirds at ing studies of foraging birds on tidal flats
sites they choo.se three times a month during clo.se to our capture locations. Our samples in
spring and autumn migration periods. Data Massachusetts (/? = 346) and Florida {n =
225) were from photographs of flocks taken
evaluated for this study were those collected
btheetweMeanssa1cJhuulsyetatnds 3c1oaDstece(6m7besritaets;sit4e,s0o6n6 astcooruerd caasptbuerteweleoncat1ioanns.d T3hoerpbleutmwaegeens4wearnde
5 because only partial views were possible
counts), the Georgia and South Carolina coast
(16 sites; 415 counts), and the Florida coast fuartoimonpshowteorgerapchosn.siRdeesrueldtssiogfnisftiactainstticaatl ePval<-
(61 sites; ,614 counts).
We bega1n held study of knots in the Alta- 0.05.
maha Estuary in Georgia in September 1998,
RESULTS
and estimated numbers each year during Sep-
—
tember through 2003. We made no effort to Autumn Migration Counts. Peak counts of
estimate numbers systematically on regular southward passage Red Knots in Massachu-
Harrington el al. • RED KNOT MOLT AND MKJRA1ION 37
Massachusetts
1238
FIG. 1. Mean numbers (±1 SE) of Red Knots counted between July and December by the International
Shorebird Surveys (ISS).
setts were during the first third ofAugust, well considerably between years with maxima
before peak numbers were counted on the ranging from 5,000 (1999) to 1(),()0() (2001)
South Carolina-Georgia and Florida coasts birds.
—
(Fig. 1). We did not document the full sea- Sightings of Color-banded Birds. The in-
sonal chronology ofthe knot passage in Geor- formation on the numbers of knots on the
gia because we were present only during Sep- Massachusetts and Georgia coasts does not
tember. However, by canvassing a number of identify whether the knots visiting the Mas-
BW
visitors and occasional visits by and sachusetts coast were also visiting the Georgia
BAH, we believe the general pattern was that coast. We believe that most knots transiting
numbers increased during August, reached through Massachusetts during southward mi-
peak abundance during late September, and gration have South American destinations,
declined during October (Fig. 1). Our separate and that most of those transiting through the
counts at the Altamaha Estuary during Sep- Georgia stopover are enroute to U.S. or other
tember indicated that numbers of knots varied northern wintering areas. We used resightings
)
38 THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 119, No. I, March 2007
TABLE NumbersofMassachusettsandGeorgia wintering group. These results (Table 1) show
sightings du1r.ing southward migrations (2003-2004) of that many of the knots transiting the Georgia
Red Knots color-banded in either Georgia or South migration stopover area during September
America. have winter-ground destinations on the Flori-
Bandedin da west coast. The results also indicate that
some unknown, but small, fraction of knots
Resightedin Georgia SouthAmerica
transiting the Georgia stopover have South
Georgia 82 9 American winter-ground destinations. This
Massachusetts 5 77 was confirmed by sighting a small number of
Florida 60 0
the thousands that had been color-banded in
Patagonia.
—
of color-banded knots at both locations in Plumage. During July and early August in
2003 and 2004 to examine use of the Mas- Massachusetts, virtually all of the 346 adult
knots whose plumage molt we scored from
sachusetts and Georgia stopover locations in
ctiweos woafyksn:ot(s1 )mtahrekreedlatiinveGeroersgigihatianngdfrseeqeuneni-n pagheot(osgcroarpehssbheatdwemeonst4lyanadlte5r,nante—bo33d2y).plFuemw-
Massachusetts, and (2) the relative resighting had actively molting body plumage feathers,
frequencies of Red Knots marked in South and it appeared the pre-basic molt had begun
America and seen in Massachusetts as com- but became an*ested north of (or possibly in)
pared to Georgia. This comparison (Table Massachusetts. The few (i.e., low hundreds)
1
shows that substantially higher proportions of of adult Red Knots remaining in Massachu-
the knots transiting through Massachusetts setts between late August and October had
versus Georgia have South American desti- progressively greater amounts of basic plum-
nations. age, and were in virtually complete basic
We also compared the relative frequencies plumage by October.
with which knots marked in either Georgia or Most ofthe adult knots at the Altamaha Es-
South America were seen during winter tuary, Georgia were in predominately basic
(Nov-Feb 20()3-2()04) on the west coast of plumage by early September (Fig. 2), and
Florida, i.e., within the range of the northern more than halfhad attained virtually complete
FIG. 2. Plumages (mostly alternate or mostly basic) of adult Red Knots in Massachusetts (Jul-early Aug),
Georgia (Sep), and Florida (Oct).
Harrington et al. • RED KNOT MOLT AND MIGRA'TION 39
basic plumage (i.e., the pre-basic molt was TABLE 2. Body mass of adult Red Knots at dif-
substantially more advanced than in Massa- ferent stagesofprimary feathermolt during September
chusetts). In Florida, during both October and 2()()()-2()()3 on the Georgia coast.
January, virtually all adult knots were in basic
plumage. Groups - Mean weight(g) SD
—
Primary Feather Molt. We checked the Primary score 0 7 141.0“ 12.0
primary flight feather molt in 1,363 adult Scores 7-49 169 132.1 10.4
knots captured on western Cape Cod Bay, Scores 50 19 149.6 22.6
Massachusetts during July and August, 1980- ‘‘LowerthantheMassachusettsmeanof161.7ginJuly/August.
1983; all but two were prior to 13 August,
after which date numbers of knots declined
rapidly. We found no flight-feather molt molt). The Elorida mean molt score from Oc-
amIonngcotnhtersaestkntootst.he above, BAH and Jake t<ob0e.r01w)asthhainghtehre (mAeNanOVsAc,oreE,f,r(,oom=m2i2d.-S2e,pP-
Walker found primary feather molt in 99 of tember in Georgia.
—
610 adult knots they checked on eastern Cape Body Mass. The average mass ofcaptured
Cod during 2004 and 2005. Many of these knots \x = 161.06 ± 0.64 SE, n = 1,341) in
birds appeared to be in a first basic plumage Massachusetts during July-August (1980-
(dorsal body feathers substantially faded, with 1983) was greater (ANOVA, P < 0.01) than
primary feather tips faded and heavily worn). for knots captured after August in Georgia (x
In contrast, only one of 80 knots = 10.95, = 134.4 ± 0.9, n — 199) or Florida during
P < 0.001) checked on western Cape Cod Bay October (T = 124.9 ± 0.7, n = 99) and Jan-
(where banding occurred 1980-1983) showed uary 1981 (x = 137.1 ± 0.7, n = 145). Mean
primary feather molt. body mass of birds caught in Massachusetts
We had sufficient captures in Georgia dur- on different dates generally increased until
ing September 2000-2002 to evaluate stages principal migration departures on —10 Au-
of primary feather molt in adult knots. We gust. For example, mean values were 132.3 g
found no differences (ANOVA, F = 0.72, ± 1.2 SE (n = 161) on 26 July 1983, 153.0
P — 0.49) of mean scores bet2w1e94en years ± 1.2 on 1 August 1984 in = 146), and 185.1
among knots actively or recently having com- ± 1.3 (n = 132) on 7 August 1980.
pleted (score 50) molt, and combined years Body mass of Red Knots in Georgia was
for analysis. The average primary molt score lower (ANOVA, = 5.59, P = 0.004) in
of knots with actively growing feathers was 2001 versus 2000 or 2002. The knots during
34.8 {n — 171, including 7 that were not 2001 were foraging principally on sodbanks
weighed), indicating the typical molt had pro- after their favored local prey (bivalves in the
gressed from primary number 1 to primaries genera Mulinea and Donax) had largely dis-
6-8. There were some individuals (/? = 5) appeared. Weights of knots from Georgia
with scores below 20 (involving primaries 1- were slightly more variable than at the Mas-
4). In addition, others had recently completed sachusetts and Elorida sites. The annual vari-
the primary feather molt (score = 50, n = 19), ation of mass in Georgia was apparently re-
and a few had 10 old primary feathers (score lated to annual differences in food resources.
= 0, = 7). We combined data from all years to com-
All but one of the 272 knots we captured pare the mean body mass of knots that were
in January 1981 in Florida had all new and not molting primary flight feathers to those
fully grown primary flight feathers. Most that that were molting. Those molting were
knots (90 of 99 adults) on 10 October 1981 lighter (ANOVA, ^ = 34.8, P < 0.001)
2,194
had growing primaries: the average score than knots that were not molting (Table 2).
among 90 adults that were molting was 40.2
± 0.53. We compared this October value to DISCUSSION
the mean value of a single group of 72 (score We conclude from our data (Table 3) that
mean = 34.7 ± 0.8 SE) captured at Altamaha Red Knots in Massachusetts and Georgia rep-
Estuary, Georgia on 11 September 2001 (re- resent groups with distinctly different winter-
stricted to adults having active primary feather ing destinations. Most that passage south
40 THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 119, No. J, March 2007
TABLE 3. Chronology and molt of Red Knots migrating south through Massachusetts and Georgia.
Massachusetts Georgia/Florida
Chronology Depart mid-Aug Depart in Oct
Principal months for primary Nov-Jan in Patagonia Aug-Nov in Georgia and Florida
feather molt
Weight change Rapid body mass gain in Jul/Aug Little or slow mass gain in Sep
Body plumage molt Alternate plumage in Aug, with ar- Little alternate plumage remaining
rested pre-basic molt in Aug, ongoing pre-basic molt
Color-banded birds from South Many with bands from South Amer- Few with bands from South Ameri-
America ican wintering areas can wintering areas
Color-banded birds from Geor- Few with bands applied during Sep Many in Florida banded during Sep
gia in Georgia in Georgia
through Massachusetts migrate to Patagonia, Knots passing through Massachusetts during
whereas most of those in Georgia winter in July and August have a predominately alter-
the Northern Hemisphere including the south- nate plumage. Active pre-basic molt of body
eastern U.S. These results support earlier plumage in Massachusetts becomes arrested,
speculation (Harrington et al. 1988) and recent and molt does not resume prior to the prin-
genetic studies (Buehler and Baker 2005) cipal migration departure during mid-August
which show the two wintering areas are pop- (Morrison and Harrington 1992). The small
ulated by separate groups of knots. numbers of adults that remain in Massachu-
—
Counts During Autumn and Winter. Num- setts after mid-August possibly represents
bers of southward migrating Red Knots in- birds that are enroute to southeastern U.S.
crease on the Massachusetts coast during the states.
second half of July and decline after reaching Most Red Knots in Georgia during August/
peak levels in the first or second third of Au- September have ongoing pre-basic molt as ev-
gust. The decline in Massachusetts (mid-Aug) idenced by plumages changing from largely
occurs at about the same time that knots begin alternate to largely basic (Fig. 2). Most adult
to appear in northern South America (Spaans knots in Georgia also have active primary
1978). feather molt (Table 2), with the majority hav-
Our information from color banding as well ing molted slightly more than half of the pri-
as previous information (Harrington et al. mary feathers —by mid-September.
1988) shows that most knots on the Massa- Body Mass. The average body mass for
chusetts coast during early August travel by Red Knots in Georgia was greater in birds that
direct, over-ocean flights to South America were not molting flight feathers than in birds
(Harrington 2001). It is possible that some that were molting flight feathers. We interpret
knots departing Massachusetts follow the U.S. these data as evidence they were preparing for
Atlantic coast southwards, comprising a small a long-distance, non-stop migration flight
fraction of the knots that visit southeastern (Gudrnundsson et al. 1991). An alternative
states. idea is that non-molting knots were heavier
The increase in numbers of knots in the simply because they were not molting, i.e., as
southeastern U.S. begins in late July/early Au- a consequence of a presumed close relation-
gust as in Massachusetts. However, numbers ship between active primary feather molt and
in Georgia do not decline in August, but re- low body mass (Lindstrom et al. 1994). How-
main stable or perhaps continue to increase ever, Holmgren et al. (1993) found no rela-
slowly between August and October, after the tionship between body mass and presence or
early October arrival dates of knots in Argen- absence of flight feather molt in Dunlin {Cal-
tina (Harrington 2()01). Knots marked in idris alpina).
Georgia are commonly found on the Florida It is generally believed that shorebirds do
west coast, a contrast to their numbers found not gain mass unless preparing for migration
in Massachusetts (Table 1 ). — (Burns and Ydenberg 2002) or for cold winter
Plumage and Primary Feather Molt. Red weather (Dugan et al. 1981). The mean mass
Harriiif’ton et al. • RBD KNOT MOLT AND MICJRATION 41
of597 Red Knots wintering in Tierra del Fue- thank Patrick and Doris Leary for their extraordinary
go, Argentina during February, when primary contributions of information. (Jur work has benefited
feather molt was presumably eompleted, was substantially from the banding and color-marking pro-
grams of other researchers, especially A. K. Baker
126.8 g (Baker et al. 1996). This average is (Royal Ontario Museum), R M. Gonzalez (Fundacon
—14 g less than the average mass in the small Inalafquen), L. J. Niles (New Jersey Division of Fish
sample of knots having molt scores of 0 in and Wildlife), and K. Kalasz (Delaware Division of
Georgia, and —22 g less than the average for Fish and Wildlife). We are grateful to the Georgia De-
the Georgia knots that had all new primary partment ofNatural Resources and the Manomet Cen-
feathers. Thus, there is insufficient evidence ter for Con.servation Sciences for support, and to nat-
to show that knots without active primary uSriamliosntss aInsldanodthfeorrsftiaeflfdoafssTihsteanLceodagnedapterLmititslseioSnaintto
feather molt would necessarily weigh more work on the Island. We thank U.S. Fish and Wildlife
than knots that do have active primary feather Service staffwho arranged forSpecial Use Permits for
molt. refuge lands in the Altamaha River Estuary. For help-
CONSERVATION IMPLICATIONS ful suggestions for improvement of earlier drafts of
this paper we thank R. I. G. Morrison, T. Piersma, an
Our results confirm there are at least two anonymousreviewer,J. A. Sedgwick, andC. E. Braun.
distinct wintering groups of Red Knots in the LITERATURE CITED
Western Hemisphere. However, we do not
know the relative proportions that historically Ashmole, N. P. 1962. The Black Noddy Anous tenui-
used Delaware Bay during spring. The Pata- rostris on Ascension Island. Part 1. General biol-
gonian wintering group, once estimated to be ogy. Ibis 103(B):235-273.
100,000-150,000 knots (Morrison and Har- Atkinson, P. W., A. J. Baker, R. M. Bevan, N. A.
Clark, K. B. Cole, P. M. Gonzalez, J. Newton,
rington 1992), is undergoing an alarming pop- L. J. Niles, and R. A. Robinson. 2005. Unravel-
ulation decline, and now number fewer than ling the migration and moult strategies ofa long-
20,000 birds (Morrison et al. 2004). The pop- distance migrant using stable isotopes; Red Knot
ulation status of the northern-wintering group Calidriscanutus movements in the Americas. Ibis
147:738-749.
of knots is being assessed, but early evidence
(Harrington et al. in prep) does not suggest it BakeBrl,aAn.coJ,.,OR.. EB.orMoawnirki,quEe.z,EeLr.raGn.dBoe,neP.gadse,GDo.eijE.,
is declining. If the population decline of the P. M. Gonzalez, J. Gonzalez, C. D. T. Minton,
knots that winter in Patagonia is linked to Del- M. Peck, T. Piersma, and M. S. Ramirez. 1996.
aware Bay food resources, and if the same Red Knots Calidris canutus rufa at their farthest
was true for northern-wintering knots, then we south; an international expedition to Tierra del
would expect to see commeasurable declines Euego, Argentina, in Eebruary 1995. WaderStudy
in numbers of the northern-wintering knots. Group Bulletin 79:103-108.
Ongoing studies suggest an explanation for Buehdlievre,rgDe.ncMe.tiamneds aa.ndj.hBiastkoerric.al20d0e5m.ogPorpauplhaytioinn
this ‘disconnect’ is forthcoming. Red Knots and Dunlins. Condor 107:497-513.
Earlier work (Harrington et al. 1988) sug- Burns, J. G. and R. C. Ydenberg. 2002. The effects
gests the northern-wintering group of Red of wing-loading and gender on the escape flights
Knots were proportionately less common on ofLeastSandpipers {CalidrisminutiUa)andWest-
Delaware Bay than the Patagonian-wintering ern Sandpipers {Calidris mauri). Behavioural
Ecology and Sociobiology 52:128-136.
group. Recent (2003-2004) feather isotope Dugan, P. J., P. R. Evans, L. R. Goodyear, and N. C.
analyses (Atkinson et al. 2005) suggest that a Davidson. 1981. Winter fat reserves in shore-
third of the knots using Delaware Bay during birds: disturbance of regulated levels by severe
northward migration are from the “northern” winter conditions. Ibis 123:359-363.
wintering area. This suggests that a significant Ginn, H. B. and D. S. Melville. 1983. Moult in birds.
proportion of the northern-wintering knot British Trust for Ornithology Guide 19. British
Trust for Ornithology, Tring, United Kingdom.
population migrates through Delaware Bay in Gudmundsson, G. a., a. Lindstrom, and T. Aler-
spring, and/or that the “northern” group has STAM. 1991. Optimal fat loads and long-distance
a substantially larger population size than we flights by migrating knots Calidriscanutus, Sand-
have estimated. erlings Calidris alba and turnstones Arenaria in-
ACKNOWLEDGMENTS terpres. Ibis 133:140—152.
Harrington, B. A. 2001. Red Knot{Calidriscanutus).
We have been helped by many volunteerfield assis- The birds of North America. Number 563.
tants, too many to name individually. We especially Harrington, B. A., J. M. Hagan, and L. E. Leddy.
42 THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 119, No. 1, March 2007
1988. Site fidelity and survival differences be- conflict between moult and migratory fat deposi-
tween two groups ofNew World Red Knots (Cal- tion: aphotoperiodic experimentwith Bluethroats.
idris canutiis). Auk 105:439-445. Animal Behaviour 48:1173-1181.
Hayman, R, J. Marchant, and T. Prater. 1986. Morrison, R. I. G. and B. A. Harrington. 1992. The
Shorebirds: an identification guide to the waders migration system of the Red Knot Calidris can-
of the world. Houghton Mifflin, Boston, Massa- utiis riifa in the New World. Wader Study Group
chusetts, USA. Bulletin 64 (Supplement):?1-84.
Holmgren, N., H. Ellegren, and J. Pettersson. Morrison, R. I. G., R. K. Ross, andL. J. Niles. 2004.
1993. Stopover length, body mass and fuel de- Declines in wintering populations of Red Knots
position rate in—autumn migrating adult Dunlins in southern South America. Condor 106:60-70.
Calidris alpinci evaluating the effects of moult- Spaans, a. L. 1978. Status and numerical fluctuations
ing status and age. Ardea 81:9-20. of some North American waders along the Suri-
Lindstrom, a., S. Daan, andG. H. Visser. 1994. The nam coast. Wilson Bulletin 90:60-83.