ldentification of American Sandwich Tern

ldentificationof American
Tern
Sandwich
Martin Carner,Ian Lewington& JasonCrook
acuflaf, mericanSandwichTernSternasandvicensis
tlvida (hereafteracuflavida)is the North American
counterpartof EuropeanSandwichTern5 s sandvicensis
(hereaftersandvicensis)
and alsoknown asCabot'sTern.
It has occurredas a vagrantin the WesternPalearctic
twice but hasonly beendetectedthroughringingrecoveries. However,acuflavidahas a sufficientlydistinct
'potentially'
in a numberof plumagesto be
appearance
is
as a vagrantin the field.lts identification
identifiable
exploredin this paper.The abilityto agean individual
of the effectsof
biid aswell as havingan understanding
skillsneededin the finer
moult and wear are essential
thistaxon.
pointsof identifying
Distribution
coastlineof
Acuflavidabreedsalong the south-eastern
North America on the Atlantic and Culf coastsfrom
as
to Belizein the Neotropics
Virginia,USA,southward
More than 90% of
well as on islandsin the Caribbean.
the breedingpopulationis confinedto the Culf Coast,
particularly
Louisiana
and Texas,USA.It wintersreguand Peru,with
larlyfurthersouthto Colombia,Ecuador
someindividuals
asfar southasChileand north-eastern
Brazil.Thereis someoverlapandapparentintrogression
betweenacuflavidaand CayenneTern5 s eurygnathain
the southernCaribbean,wherethe rangeof the latteris
(Shealer
1999).
northwards
apparently
expanding
on the separation
Althoughthereis liftleinformation
ol acuflavida and sandvicensrs,researchhas suggested
side.The effectsof moult and wear could createprob-
acuflavida,adult-wintersand first392 AmericanSandwichTerns/ AmerikaanseCrote SternsSternasandvicensis
without
are not discernable
winters/Dominical,CostaRica,12 January2001 (RendPop).While finercharacters
closerviews, overall ratherdistinct appearanceof smaller,stout-billedacuflavidawith white crown and greasy
vagrantin the Western
may invitecloserscrutinyof a suspected
black nape(comparedwith nominatesandvicensis)
Palearctic.
lDutch Birding29: 273-287,2OOz
z/ J
tdentification of American Sandwich Tern
SandwichTern
AmericanSandwichTern
plain scapulars
and wlng coverts
juvenile
olaln blackish based t€rtials
with broad whit€ fring€s
yellowish bill
typical juvenile
lst winter
som€ birds 5how dark
spad€ shrp€d markings on scapulars
(r€tained
Juv prlmarl€E
tertla13 and tail)
r-.-.+r{xn
-
whlt€ for€h€ad
gp€akl€d r€ar crown
%-*
retarded
lst winter
JanlFeb
blacklsh cGntr€d t€rtials
wlth broad whlto frlng€s
(r6talned
iuv primariet
tartlals .nd out.r t.ll)
.-.
lst wint€r JanlFeb
(r6taln6d Juv p.lmarl€s
tsrtlals and tail)
-.
lst winter
Jan/Fab
lrosh 6dult Drimari€6
with narrow whltc fringes
to Inn€r w€b9 and tlps
tuv
f
I
3hortcr and
de€Der ba9€d
outer
(i€tained
primarl6s
.nd out€r tall - adult
t€rtlals and Inn6r prlmarl€3)
LF
adult JanlFeb
long sl€nd€r
American Sandwich Terns have a
latermoult than SandwichTems,
hence 1st winters often have full sels
of tertials. primaries and tail-feathers
into March
f.€sh adult primari6s
with broad whit€ fring€9
to inn€r w€b3 and tlpt
adult JanlFeb
acuflavidaand
CroteSternSternasandvicensis
of AmericanSandwichTern/ Amerikaanse
1 Comparison
FICURE
in juvenile,first-winter
and adult-winterplumages(lan Lewington)
SandwichTern/ CroteStern5 s sandvicensis
274
Identification
l e m s w h e n a t t e m p t i n gt o i d e n t i f y a p a r t i c u l a ri n d i v i d u a l ,
a l t h o u g h i t w o u l d s e e mt h a t w i t h g o o d v i e w s t h e i d e n t i f i c a t i o n o f m a n y i n d i v i d u a l sc a n b e r e s o l v e d .W h i l e t h e
f e a t u r e sa r e s u b t l e ,t h e e x a m i n a t i o no f p h o t o g r a p h sa n d
o u r o w n o b s e r v a t i o n so f S a n d w i c hT e r n s i n B r i t a i n a n d
lreland during the lastthree winters revealed at they
c o u l d a l l b e c o n f i d e n t l y a s s i g n e dl o s a n d v ' i c e n
Vagrancy
There have been two European records of acuilavtda,
both recoveries of birds ringed as chicks in North
C a r o l i n a ,U S A , a n d f o u n d d e a d l a t e r i n t h e s a m e y e a r a s
f i r s G w i n t e r s O n e w a s r i n g e c la t C a p e L o o k o u t o n 2 3
June 1978 June and found at Veerse Meer, NoordB e v e l a n d , Z e e l a n d , t h e N e t h e r l a n d s ,o n 2 3 D e c e m b e r
l 84
1 9 7 8 . A n o t h e rw a s r i n g e da s a c h i c k o n 2 5 . J u n e . 9
n e a r B e a u f o r ta n d i n i t i a l l y r e p o r t e db y t e l e p h o n e t o t h e
B r i t i s hT r u s t f o r O r n i t h o l o g y ( B T O ) a s f o u n d d e a d n e a r
H a y - o n - W y e ,P o w y s ,W a l e s ,s o m et i m e b e f o r eC h r i s t m a s
1 9 8 4 . L a t e r i n v e s t i g a t i o nr e v e a l e d t h a t t h i s b i r d w a s
a c t u a l l y f o u n d d e a d b y a F o r e s t r yC o m m i s s i o nr a n g e ra t
Newhouse Wood, Herefordshire,on 28 November
1984. This seemsan unlikely location for a Sandwich
T e r n b u t t h e f i n d e r i d e n t i f i e dt h e b i r d a s a t e r n a t t h e
t i m e . A m a z i n g l y ,t h i s w a s o n l y t h e t h i r d c o u n t y r e c o r d
f o r S a n d w i c hT e r n o f a n y s u b s p e c i e s( S c h a r r i n g a19 7 9 ,
M e a d & H u d s o n 19 8 6 , O u w e n e e l 19 8 9 , v a n d e n B e r g &
B o s m a n2 0 0 . 1 ;M a r k C r a n t h a m p e r s c o m m ) .
C i v e n t h e o c c u r r e n c eo f t w o r i n g e d i n d i v i d u a l sa n d
the paucity of identificationcriteria, it seems highly
l i k e l y t h a t t h e r e h a v e b e e n o t h e r a c u f l a v i d ao c c u r r i n g i n
E u r o p ew h i c h h a v es i m p l y g o n e u n n o t i c e d( c f O u w e n e e l
1 9 8 9 ) . W i t h b o t h r i n g e d i n d i v i d u a l so c c u r r i n g i n l a t e
November and December,the winter may be an apposite time to look for vagrant acuflavida, when sandvic e n s i s i s p a r t i c u l a r l ys c a r c e i n E u r o p e ,w i t h , e g , o n l y a
h a n d f u l w i n t e r i n g r e g u l a r l y i n t h e s o u t h - w e s t e r np a r t o f
t h e N e t h e r l a n d sa f t e r a n u p s u r g eo f 10 + r v i n t e r i n g i n d i viduals here in the 1980s (cf Ouweneel 1989); after
d e c l i n i n gn u m b e r si n t h e 1 9 9 0 s a n d e a r l y 2 0 0 0 s , a n other upiurge was noted in the winter ol 2006/07, witl't
a m a x i m u m o f 1 3 i n J a n u a r y2 0 0 7 . H o w e v e r ,t h e y c o u l d
e a s i l yo c c u r a t a n y t i m e o f t h e y e a r S i v e nt h e o c c u r r e n c e
'p a t t e r n so f o t h e r t e r n s f r o m t h e A m e r i c a s .
I n t h e A z o r e s , S a n d w i c hT e r n i s a r a r e v i s i t o r w i t h 4 4
individuals recorded up to 2005 (apart from 12 in
S e p t e m b e r1 9 6 4 a n c l1 0 i n O c t o b e r l 9 9 8 , o n l y s i n g l e
b i i d s o r s m a l l g r o u p so f u p t o t h r e e h a v e b e e n r e c o r d e d ) .
E i g h t o f t h e 4 4 w e r e s e e n i n N o v e m b e r J a n u a r y( h t t p : / /
a z " o r e s . s e a w a t cnhgi.n e V li s t s ) .B e in g a p r i m e l o c a t i o n f o r
Nearctic vagrants and given the scarcity of sandvicensis,
any Sandwich Tern in the Azores should be carefully
c h e c k e dt o c o n s i d e rt h e p o s s i b i l i t yo l a c u f l a v i d a
ldentification
of American Sandwich Tern
m o u l t a n d w e a r o n t h e v a r i o u sp l u m a g e si s c r u c i a l ,a n d
t h e a s s e s s m e nat n d i n t e r p r e t a t i o no f i n d i v i d u a l f e a t u r e s
n r u s t b e a r t h e s e e f f e c t si n m i n d . S e c o n d , i d e n t i f i c a t i o n
sandylcensls
F e a t u r e sc o m m o n t o a l l a g , ec l a s s e s
A c u f l a v i c l aa v e r a g e s m a l l e r t h a n s a n d v i c e n s i sT. h e b i l l
o t t e n a p p e a r ss u b t l b u t d i s t i n c t l v d i f t e r e n tf r o m t h a t o f
s a n d v i c e n s i sB. i o m r i c s i n d i c a t et h a t i t a v e r a g e ss h o r t e r
a n d p r o p o r t i o n a t e l ys l i g h t l yt h i c k e r .T h e e f f e c t i s o f t e n o f
gn d o b v i o u s l yt h i c k - b a s e d
a d i s t i n c t l ys t r a i g h t e r - l o o k i n a
s p i k y b i l l o n a c i f l a v i d a . O n a v e r a g e t, h e g o n y d e a la n g l e
a p p e a r st o b e s l i g h t l y m o r e p r o n o u n c e d .I n c o n t r a s t ,t h e
b i l l o f s a n d v l c e n s r it e n d s t o a p p e a r l o n g e r a n d s l i g h t l y
more slender overall, with a fine and slightly droopt i p p e d e f f e c to r a l e a s tw i t h a n o v e r a l l s l i g h t d e c u r v a t u r e
t o t h e b i l l ( p a r t i c u l a r ltyo t h e u p p e r m a n d i b l e )J. u v e n i l e s
a n d f i r s G w i n t e r sh a v e s h o r t e rb i l l s t h a n a d u l t s ; h o w e v e r ,
by early to mid-wintet the differencesin bill shape
between adults and first-winters does seem to become
l e s sa p p a r e n t .
In winter plumage, the black rear crown and napef e a t h e r so n a c u f l a v l d aa r e n o r m a l l y l o n g e r ,b l a c k e r a n d
m o r e g r e a s y - l o o k i n gt h a n t h o s eo n s a n d v l c e n s l sa, n d t h e
f o r e h e a d a n d c r o w n ( i n s t r o n g c o n t r a s t )a r e c o m p a r a t i v e l y u n m a r k e dw h i t e
Ju ven i le (Ju ly-Octobe r )
T h i s s t a g eo f p l u m a g e i s u s u a l l y o b v i o u s a s t h e y o u n B
b i r d s a r e i n f r e s hp l u m a g ew i t h d i s t i n c tb l a c k m a r k i n g s
on the mantle, scapularsand to some extent in the
c o v e r t s .B l a c k m a r k i n g sa r e a l s o c l e a r l y p r e s e n ti n t h e
p r i m a r y c o v e r t s ,s e c o n d a r i e t e r t i a l sa n d r e c t r i c e s .
A c u i l a v ' i d aa n d s a n d v l c e i s i n f r e s h l u v e n i l e p l u m a g e , a r o u n d t h e t i m e o f f l e d g i n g , a r e a s d i f f e r e n tf r o m
o n e a n o t h e r a s c h a l k a n d c h e e s e .T h e m o s t i m m e d i a t e l y
striking difference is in the bill and head. Many very
f r e s h j u v e n i l e a c u f l a v i d ah a v e w h o l l y g r e y i s h ,y e l l o w o r
even orange bills and a bright white foreheadto midcrown with a black wedge through the eye to the rear
crown and nape forming a crest even before fledging
S a n d v i c e n s i sh a s a n a l l - d a r k g r e y - b r o w n c a p ( a s i n
young Roseatefern S dougallil) with a mostly black bill
(which can have paler, yellowish cutting edges),alt h o u g h i t h a s r a r e l yb e e n r e c o r d e da s a l l - y e l l o w ( M i t c h e l l
19 8 9 ) .
J u v e n i l ea c u f l a v i d ah a s e s s e n t i a l l yp l a i n g r e y c o v e r t s
w i t h o n l y l e s s e ra n d m a r g i n a l c o v e r t s a n d s o m e i n n e r
g r e a t e rc o v e r t sm a r k e d w i t h p l a i n g r e y i s h - b l a c kt,h e l a t ter particularly on birds with dark patterning on the
m a n t l e a n d s c a p u l a r sT
. h e s c a p u l a rp a t t e r nv a r i e ss o m e w h a t b e t w e e n i n d i v i d u a l s .M a n y h a v e a p a l e p a t t e r n o f
b r o a d e n e d d a r k s h a f t - s t r e a k sp, r o d u c i n g a l i g h t l y s p o t ted or streaked effect on the upperparts. More strongly
marked individualshave a bold solid-blackpattern of
m a r k ss u b t e r mi n a lI y o n t h e s c a p u r o u g hI y s p a d e - s h a p e d
tars
M o r e o c c a s i o n a l l y ,b i r d s h a v e p l a i n g r e y s c a p u l a r s
w i t h n o r e a l p a t t e r n T h e t e r t i a l so n f r e s hj u v e n i l e a c u f l a -
aatr
Identification of American Sandwich Tern
juvenile,BolivarFlats,Texas,
acuflavida,
393 AmericanSandwichTern/AmenkaanseCroteSternSternasandvicensis
USA, 17 luly 2O07 (JosephKennedy).Exampleof coarselymarkedjuvenile acuflavidawith black spade-shaped
greatercovert,with similarmarks,mostwing-coverts
are plain pale
but apartfrom innermost
markson scapulars
g r e yE v e n t h o u g h t h i s b i r d h a s n o t f u l l y f l e d g e d ( p r i m agr ireoswsi tni lgl ) , c r o w n i s e x t e n s i v e l y w h i t e , u n l i k e n o m i n a t e
Tern/ Amerikaanse
which at this stagewould haveextensively
darkcrown. 394 AmericanSandwich
sandvicensis
juvenile,TexasCity Dike,Texas,USA,24 August2O07(JosephKennedy).
acuflavida,
CroteSternSternasandvicensis
wing-coverts
interrupted
on back,lesser
and
by darkplainfeathercentremarkings
Noteoverallplaingreyupperparts
juvenile
characterising
with bolderplainblackcentreto tertialsThereareno coarsemarkings
innergreatercoverts,
acuflavida,
nominatesandvicensis 395 AmericanSandwichTern/ AmerikaanseCrote SternSternasandvicensis
juvenile
juvenile,FortDe SotoPark,St Petersburg,
Florida,USA,15 August2006 (ArthurMorris/BirdasArt).'Classic'
sandvicensis.
Plaingreyplumtowardsmoreyellowor orangeoverbill thannominate
whichhastendency
acuflavida
mostevidenton tertials,and Iackingcoarselymarkedappearance
which
with plainblackishcentres,
agepatterned
is standardfeatureof juvenilenominatesandvicensis.
276
ldentification of American Sandwich Tern
juvenile, Portrush,Antrim, Northernlreland,
sandvicensis,
396 SandwichTern/ Crote SternSternasandvicensis
'V'shaped
juvenilenominatesandvicensis
with coarse'U'and
Classicwell-marked
29 lulv 2007(DerekCharles).
tertials
dark
and
mottled
wing-coverts.
Crown
and
especially
scapulars
over mantle,
internalmarksextensively
black'andwhite.Barepartsof freshjuvenilescan showyellow,quitestrikinglyso on this indistronglyvariegated
sandvicenTern/ CroteSternSternasandvicensis
397 Sandwich
is straightforward.
identification
viduaj,'butov'erall
well-marked
Exampleof .paler,.less
Antrim,Northeri lreland,.29
)uly 2OO7(DerekCharles).
srs,juvenile,Portrush,
are at
but.wing-coverts
obviouson mantleand scapulars
Coarsepatterningis sufficiently
nominatesandvicensis.
of which patternis closerto
hideplainerouter.tertials,
tertialspartially
innerm-ost
Variegated
palerend of spectrum.
that of AmericanSandwichTern5 s acuflavida
277
ldentification of American Sandwich Tern
3 g B A m e r i c a n S a n d w i c h T e r n / A m e r i k a a n s e C r o t e S t e r n S t esrannad v r c e n s i s a c u f l a v t fdi ar s, t - w i n t e r , T e x a s C i t y D i k e ,
) .u i c k l y a g e d b y l a c k o f y e l l o w i n b i l l - t i p a n d e x t e n s i v e d a r k a r e a
T e x a s , U S A , Z S e p r e m b e r 2 O O( JTo s e p h K e n n e d yQ
i n t e r t i a l s ,t h i s i n d i v i d u a l h a s p e r f o r m e d p a r t i a l m o u l t M a n t l e a n d s c a p u l a rf e a t h e r sa r e r e p l a c e db u t m o s t o f . w i n g c o v e r t sa ; e r e t a i n e dj u v e n i l e f e a t h e r sw i t h s o m e p a t c h i n e s sp, r e s u m a b l yi n d i c a t i n gs o m e f e a t h e rr e p l a c e m e n tb e g i n ' r e a d ' m o u l t c o n t r a s ti n w i n g - c o v e r t so f f i r s t - w i n t e rS a n d w i c hT e r n si s c r i t i c a l t o i d e n t i f i c a t i o n
n i n q h e r e . B e i n ga b l e t o
o f a ' c u f l a v i d aR. " e t a i n e jdu v e n i l e w i n g - c o v e r t so f n o m i n a t e s a n d v i c e n s issh o u l d b e m o r e o b v i o u s l y p a t t e r n e da n d a n y
r e t a i n e do u t e r t e r t i a l s m o r e v a r i e g a t e di n p a t t e r n 3 9 9 A m e r i c a n S a n d w i c hT e r n / A m e r i k a a n s eC r o t e S t e r n S t e r n a
s a n d v i c e n s ias c u f l a v i d a ,f i r s t - w i n i e r ,F l o r i d a , U S A , 2 N o v e m b e r 2 0 0 5 ( T h o m a sJ D u n k e r t o n ) T h i s i s t h e p l u m a g e
w h i c h t h e t w o W e s t e r nP a l e a r c t i cr e c o r d sh a v eo c c u r r e d t r
' g r e a s y 'b l a c k a n d t e r t i a l sw i t h
w o r n . R e a rc r o w n - f e a t h e r s
t i o n I n n o m i n a t e s a n d v i c e n s i s ,a l l t h e s e f e a t u r e s d i f f e r
Ameril<aanseCrote Sterns Sternasandvicertsisacuflavida,
USA, 8 February 2005 (Arnoud B vart den Bery) Wingr e t a i n e dj u v e n il e f e a t h e r i n gi n c l u d i n g( i m p o r t a n t l yp) l a i n ,
p r i m a r v t o u e r t r . N o t e , h o w e v e r , c l e a r c o n t r a s t b e t r v e e n t h e s e a n d f r e s h g r e y f e a t h e r so n i n n e r p r i m a r i e s , i n n e r
. o m e t a i l f e a t h e r sh a v e a l s o b e e n r e p l a c e d b u t o b v i o u s l y b l a c k - t i p p e do u t e r r e c g r e a t e rc o v e r t sa n d s e c o n d a r i e s S
c h a r a c t e ro l a c u f l a v i d ai n b o t h a g e c l a s s e s .
tricesremain. Note very white-crowned/black-naped
278
Identification of American Sandwich Tern
401 AmericanSandwich
Tern/Amerikaanse
CroteStern
Sterna sandvicensis acuflavida. first-winter, Veracruz,
Mexico, T October 2O06 rChristianArtusot. Aged by
combination
of extensive
dark in tail-feathers,
seiondaries, lesserwing-covertsand primary coverts.Crown
appears
extensively
whitewith blackrearcrownlacking
obviouswhite tipping.This,togetherwith plain grey
(outergreatercovertsappearto be moultwrng-coverts
ing), stronglysuggests
acuflavida.Furtherviews on the
groundwould helpconfirmimpression
of headpattern
andapparent
ageof wing-coverts,
whichareIikelyto be
slightlywornjuvenilefeaLhers.
vida arc normallystrikinglyplain blackishwith rather outertertialswith wide whitefringe(notvariegated
dark
wide whitishfringes.
and pale);and 4 relativelvunmarkedwhite iorecrown
ln contrast,juvenilesandvicensis
hasan overallvery
and plainblackgreasy-looking
longnape-feathers,
with
coarsepatternof black U- or V-shapedsubterminal whitefringes/tips
eitherverysmallor lacking.
marks(with buff earlyon) to mostof the coverts,mantle
and scapularsThefreshtertialsaretypicallyblackano
First-wi nter (O ctober-M arch)
whitewith a coarsepatterncomposedof a blackfeather- Juveniles
undergoa progressive
moult into first-winter
centre punctuatedby a variegatedpattern of white
plumage.
Theextentto whichdarkjuvenilefeathering
is
notches
andblackwavylines/bars.
Thisis mostapparent retained
variesbetweenindividuals.
All Sandwich
Teins
on the innermost(uppermost)
tertials,with the underlying outertertialshavingplainerdark centreswith a
palefringemorelikeacuflavida.The
overallappearance,
includingthe completegrey-brown
crown,is similarto
a typical.juvenile
Roseate
Ternandclearlydifferent
from
acuflavida.Some paler, lesswell-markedindividuals
might suggestacuflavidabut careful inspectionof the
outertertialpatternand presenceof at leastsomedark
U-shapedmarkson the mantleand covertswill resolve
moredifficultindividuals
Thepost-juvenile
moultcoincides
with blackening
of
A comparisonbetweenthe moult strategies
ol acuflathe bill in acuflavida
and whitenineof the foreheadin
vida and sandvicensishas revealedsome differences
sandvicensis
so that the initiallvaistinct differences. that can aid the identification.First-winteracuflavida
suchas bill colourand headpattern.becomelessrel- appearsto havea moreprotractedmoult so that, in mid.
evantto identification.However,some key aspectsoi
winter,some individualsstill show all-worn juvenile
juvenileplumagearemaintained
rightthroughthe wincovertsand tertials.Somesandvicensis
retainiusta few
ter So, understanding
the distinctiveappearance
juvenilecovertsand tertials.Additionally.first-winter
of
juvenileplumagecan providethe cluesto helpidentify acuflavidaappearsto mostly retainan unmoultedand
individuals
seenlaterduringtheirfirstwinter
distinctlypatterned
juvenilehead.Theverywhite forejuvenileacuflavida
ln summary,
in July-October
can
headand crown (sometimes
with blackfleckinson the
be identifiedby four characters:
I blackishmarkson
midcrown)contrasts
with the blackwedgethro."ugh
the
freshjuvenilemantlefeathers
andscapulars
restricted
to
eyeandthe greasy-looking
longblacknape-feathers.
shaft-streaks
or spade-shaped
subterminalmarks (not
Most first-wintersandvicensis
appearto undergoa
and coarse-looking).
U- or V-shaped
Notethatthis may
more extensivemoult in late autumnto early winter.
only be usefulfor a short period before post-juvenile FromDecember
onwards,it can be difficultto agesandmoultcommences
and thesefeathers
are reolaced
with
vicensis.They more rarely retainworn juvenile tertials
plain grey first-winterones;2 plain grey coverts,apart and secondaries
throughthe winter,the formerat least
from blackishmarginaland lessercovertsforminga
appearingto be somehowlessdurablethan those on
contrastingly
darkerleadingedgeto the otherwise
plain acuflavida.Both first-winterand adult sandvicensis
can
upperwing(but also with a dark trailingedge).First- show ratherdark plain grey oval-shaped
markingson
winter sandvicensrs
can retain some dark U-shaoed thefreshtertialsfollowinsmoult.Theforehead
and midmarksin all coverts
to November
andoccasionally
even crowncan be white,usuillywith greyfleckingoverthe
(pers obs); J solidly black-centred midcrown, and the black nape-feathers
to February-March
appearto be
279
ldentification of American Sandwich Tern
402 Sandwich Tern / Crote Stern Sternasandvicensissandvicensis,first-winter,Tarifa, Spain, 19 October 2005 (Sampo
L a u k k a n e n )A. l t h o u g h s i m i l a r i n o v e r a l la p p e a r a n c et o f i r s t - w i n t e rA m e r i c a n S a n d w i c hT e r n 5 s a c u f l a v i d aa l s o p h o t o g r a p h e d i n O c t o b e i ( p l a t e 4 0 1 ) , t h e r e a r e s u b t l e d i f f e r e n c e sM o s t i m p o r t a n t l y ,i t i s p o s s i b l et o s e e r e t a i n e dj u v e n i l e
i o v e r t s w i t h c r i s p b l a c k m a r k i n g si n m i d u p p e n v i n ga n d r a t h e rm e s s yp a t t e r no f b l a c k i n l e s s e rc o v e r t s T h e s ef e a t u r e s
w o u l d b e e v e n m o r e o b v i o u s o n t h e g r o u n d 4 0 3 A m e r i c a n S a n d w i c hT e r n / A m e r i k a a n s eC r o t e S t e r nS t e r n as a n d , e x i c o , 7 O c t o b e r 2 0 0 6 ( C h n s t i a nA r t u s o ) A l l - w h i t e t a i l t o g e t h e rw i t h
v i c e n s i sa c u f l a v l d a ,a d u l t - w i n t e r , V e r a c r u zM
m o s t l y g r e y u p p e r w i n g a n d e x t e n s i v ey e l l o w o n b i l l - t i p a g e t h i s a s a n a d u l t a t t h i s t i m e o f y e a r .S u b t l y i m p o r t a n tc h a r a c t e ri s p r e s e n c eo f d a r k b a r a l o n g n e w l y g r o w i n g s e c o n d a r i e so, f t e n f o u n d i n a c u f l a v i d ai n a d u l t p l u m a g e ( a n d _s i m i l a r l y f o u n d i n E l e g a n t T e r nS e l e g a n sb) u t n o t n o r m a l l y i n n o m i n a t es a n d v i c e n s i sF. u r t h e rv i e w s o n t h e g r o u n d o f h e a d
p a t i e r n ,b i l l s h a p ea n d e x t e n to f w h i t e o n n e w p r i m a r i e sw o u l d h e l p s e p a r a t ew i n t e r - p l u m a g e da c u f l a v i d af r o m n o m i nate sandvlcensrs404 Sandwich Tern / Crote SternSternasandvicensissandvicensis,first-winter,Rhoscolyn,Anglesey,
W a l e s , 1 O c t o b e r 2 0 0 5 ( M i k e A t k i n s o n )T h i s b i r d h a s m o u l t e d m a n t l ea n d s c a p u l a r sb u t r e t a i n e dj u v e n i l ew i n g - c o v e r t s
' V ' s h a p e sa n d v a r i e g a t e dt e r t i a lp a t t e r ne n a b l e c o n f i d e n t i d e n t i f i c a t i o n F
. u r t h e r m o r eb, l a c k
w i t h c o a r s eb l a c k ' U ' a n d
rear crown-feathersare more extensivelyfringed wh ite than in American Sandwich TernS s acuflavida. Note little yellow
on bill+ip, typical of both taxa in their first winter. 405 Sandwich Tern / Crote Stern Sterna sandvicensissandvicensis,
first-winter, dhoscolyn, Anglesey,Wales, 1 October 2006 (Mike Atkinson). Freckled pattern of dark marks on wingc o v e r t sa n d b l a c k r e a r c r o w n h e a v i l yp e p p e r e dw i t h w h i t e w o u l d p o i n t t o i d e n t i f i c a t i o na s n o m i n a t es a n d v i c e n s i s .
2BO
ll
ldentification of American Sandwich Tern
acuflavida,adultwinter,Florida,USA,
Crote SternSternasandvicensis
406 AmericanSandwichTern/ Amerikaanse
2 November2OO5(ThomasJ Dunkerton).One aspectof acuflavidaplumageis that they havemore dark areasin
tail-feathers,
includingvariableamountsof dark in secondaries,
freshwinterplumagethan nominatesandvicensis,
andtail,and foreheadand crownarevery
Somedarkcan be seenhereon secondaries
orimarvcovertsand'tertials.
appear
rearcrown.Longest
new Srownouterprimaries
sharplywith jet-black(notwhitepeppered)
whitecontrasting
to haveverylittleblackat tipsand alongfringe,which is usuallymuchmoreobviousin nominatesandvicensis.
shorterthan thoseon similar-agedacuflavidawith ob-
primarycovefts,outer
outer primariesand sometimes
all of whichwill havedark
andsecondaries,
tail-feathers
markings,the lattershowingas a dark bar along the trailwill appearmuch
ine edge.Any newlymoultedfeathers
with themuchdarker,
prler undfreiherandwill conlrast
Newly moultedprimaolderretainedjuvenilefeathers.
rieswill be palerand fresherthanon adultsat thistime
of year.
at
from sandvicensis
Acuflavidacan be distinguished
patternon the new outerprithis ageby the adult-type
maries(thewidth of whiteon the innerwebsand at the
blackmarks
tips).Theymayalsohavemoreconspicuous
and a darkerbaracross
on some(moulting)
secondaries
such
differences,
coverts.
Thesubtlestructural
the Iesser
shouldlook smallerin direct
as overallsize(acuflavida
and bill shape,remain
comparisonwith sandvicensis)
of
and shouldalsoorovidea clue to the identification
Tern.
Sandwich
anyfirst-summer
Ad ult-wi nter (NovemberMarch)
Adults, in comparisonto juvenilesand first-winters,
have all tail-feathers
and primarycovertsplain grey
(althoughsomeapparentadulracuflavidahavedark in
earlierin theseaprimarycoverts),
moulttheirprimaries
sonand havemoreyellowin the billtip.
A major differencebetween acuflavidaand sandvicensis
isthe width of the whitefringeto the innerweb
of the outerprimaries.On acuflavida,the white fringeis
the
very narrow (1-1.5 mm) whereas,on sandvlcensts,
fringe is wider (2-4 mm), each primary also having 3 5
mm of white at the feather-tip(lackingin acuflavida)
-l
(Olsen& Larsson
hasbeen
995).Thisexactdifference
examinedin the NaturalHistory
notedon all specimens
Museum(NHM),Tring,and hasbeenput to the teston
pubIishedimagesol acufIavida andsandvi censis and ap-
281
-
Identificationof American SandwichTern
282
tdentification of American Sandwich Tern
4 0 8 A m e r i c a n S a n d w i c h T e r n / A m e r i k a a n s e C r o t e S t e r n S t e r n a s a n d v i c e n s i sa c u f l a v i d a , a d u l t - w i n t e r , S a n i b e l ,
F l o r i d a ,U S A , 3 1 J a n u a r y2 O O 7( J u l i a nH o u g h ) . H e a d p a t t e r na l o n e m a y b e f i r s t i n d i c a t o r o f v a g n t a c u f / a v i d a W h i t e
, i t h m o s t l y b l a c k r e a r c r o w n h a v i n g o n l y v e r y l i i t e d w h i t e t i p s .T h i s ,
f o r e h e a dt o m i d c r o w n m u c h m o r e c o n t r a s t i n gw
c o m b i n e d w i t h s h o r t e r a n d t h i c l < e r - b a s ebdi i l , w i t h q u i t e e x t e n s i v ey e l l o w i l l - t i p , c a u s e s o m e a c u f l a v i d at o l o o l <
e r o t e S t e r nS t e l s a n d v i c e n s i sa c u f l a v i d a ,a d u l t - w i n t e t
o u i t e s t r i k i n e . .4 0 9 A m e r i c a n S a n d w i c hT e r n / A m e r i l < a a n s C
H o u g h ) . S a m e i n d i v i d u a l a s i n p l a t e 4 O B .T w o i n t e r e s t i n ga s p e c t s( ) 1
S a n i b e l , f l o i i d a , U S R , F e b r u a r y2 O O 7 ( J u l i a n
p l u m a g e n b e s e e n h e r e . N o t e q u i t e o b v i o u s d a r l <i r r e g u l a rs p o t s o n t e r t i a l sw h i c h c a n b e f o u n d o n s o m e a d u l t
n d v i c e n s i sa, l t h o u g h u s u a l l yn o t w i t h d a r l (o n s e c o n d a r i e sa s w e l l . A l s o , n e w l y g r o w n l < - r n g eps rt i m a r y p 8
nominite
haswhite fringeand tip, which is just about too limited for any nominate sandvlcensls
:
11'
"'r,
-\:l!\:!+
'
283
ldentification of American Sandwich Tern
Zeeland/Zuidsandvicensis,
adult-winter,Brouwersdam,
41O-411SandwichTern/ Crote SternSternasandvicensis
H o l l a n d , N e t h e r l a n d1sF, e
. l b r u a r y 1 9 B 9 ( A r i e d e K nTi i hf fi)s i n d i v i d utaels t s t h e i d e a t h a t a d u l t n o m i n a t e s a n d v i c e n '
At firstglance,whitefringesand
in adultplumages.
can be separated
TernS s acuflavida
slsandAmericanSandwich
thisbird hasin the pastbeensuspected
and,therefore,
appeartoo limitedfor nominatesandvicensis
tipsto primaries
However,with headpatternof 'peppered'blackand white rearcrown and ratherweakoi being vagranta,cuflavida.
Plate411 offersa morehelpfulview
is morelikenominatesandvicensis.
lookingdecurvedbill, overallappearance
showingbroaderwhitefringeandtip, which is not as strikingas in manynominatesandvicensis
primaries,
of oute-r
is resolved.
Combinedwith headpatternand bill shape,identification
but ii too markedfor mostacuflavida.
284
ldentification of American Sandwich Tern
worn and blackishoutermostprimariesevenwhen on
groundsin June-July.
When it can be estabthe breeding
lishedthat pale grey,apparentlyfreshouter primaries
are new ones,then the much narrowerwhite fringeto
the innerwebsand reducedwhitetipsof adultacuflaviAs in someother
da primariesshouldbe discernible.
largeterns,suchas ElegantTernS elegans,someacuflabar in otherwisefull adult
vlda havea dark secondary
plumageduringthe breeding
seasonAdultsandvicensis
bar
normallylackssucha secondary
feaIn summary,and combinedwith the structural
tures,the key featuresof acuflavidain adult-summer
wrth replumageare: / latermoult of outerprimaries,
2 narrower
old outerprimaries;
tentionof conspicuously
whitefringeto innerweb and reducedwhitetipsof new
primaries;
3 presence
of dark secondary
bar
outermost
4 smallersize;and
in some(alsovisibleon underwing);
bill.
thickerand spikier-looking
5 shorter,
Conclusions
The plumageand structureof acuflavidaandsandvicenslsare sufficientlydifferentto suggestthat at leastsome
acuflavidashould be identifiablein the field in the
WesternPalearcticThe ootentialfor acuflavidato occul
hasalreadybeen
as a vagrantin the WesternPalearctic
lt mustonly be a matterof time beforeone
established.
lt is hopedthatthesenoteswill
morewill be identified.
providea startingpoint,in termsof identification
criteWe look forwardto these
ria, for this to be realised.
in the near
ideasbeingtestedin thefieldand developed
IUtUTC.
Acknowledgments
Particular
thankssoesto Mark Adamsat the NHM in
Tringand to Marli Cranthamat the BTO for clarifying
the detailsof the Britishrecord.Also thankseo to
Ar[uso,Mike Atkinson,Arnoudvan denBerg.
Christian
ThomasDunkerton,PaulHackett,Clive
DerekCharles,
Harris,JulianHough,AlvaroJaramillo,
JoesphKennedy,
ArthurMorris,Ren6Popandalsothe
SampoLaukkanen,
and Peterde
lateArie de Knijfffor their photographs,
Knijffand CeraldOreelfor theirassistance
Samenvatting
vAN AMERKAANsE
GRorE STERNDit artikel behandelt
HERKENNTNC
de herkenninp van Amerikaanse Crote Stern Sternasandvicensis
acuflavida (hierna acuflavida) in vergelijking met nominaat Grote
Stern 5 s sandylce nsis (6ierna sandvicensis) Acuflavida komt voor
i n z u i d e l i j k N o o r d - A m e r i k ae n M i d d e n - A m e r i k ae n o v e r w i n t e r t
tot in noordelijk Zuid-Amerika; 90% van de wereldpopulatie
broedt rondom de Colf van Mexico Er zijn twee gevallen in
Europa, beide vondsten van eerstejaarsdie in North Carolina, VS,
w a r e n g e r i n g d D e e e r s t e w a sg e r i n g do p 2 3 j u n i 1 9 7 8 e n d o o d
gevonden bij het Veerse Meer, Zeeland, Nederland, op 23 december 1978, en de tweede was geringd op 25 juni 1984 en
dood gevonden in Herefordshire, Engeland, op 28 november
'1984
(opmerkelijk is dat beide vondsten uit de (vroege) winter
stammen, wanneer sandvlcensiszeldzaam is 1nWest-Europa) In
de meeste kleden is acuflavida te onderscheiden van sandvicensls maar in adult zomerkleed is het onderscheid lastig Een goede
bepaling van de leeftijd als eerstestap bij de determinatie en kennis van (de effecten van) rui en sleet op het verenkleed ziin voor
een zekere determinatie van groot belang
Enkele verschillen zi.ln in alle kleden aanwezig: 1 acuflavida
is gemiddeld iets kleiner dan sandvicensis;2 de snavel is gemiddeld iets korter en dikker en daardoor meer dolkvormig; en 3 in
a l l e w i n t e r k l e d e nz i j n d e z w a r t e v e r e n o p h e t a c h t e r s t ed e e l v a n
de bovenkop en in de hals langer, zwarter en meer glanzend b _
acuflavida (witte randen/totrpen zeer klein of ontbrekend) en
voorhoofd en kruin vrijwel ongetekend wit, zodat een sterk contrast aanwezie is
I n i u v e n i e f k l e e d ( i u I i - o k t o b e r )v e r s c h i l t a c u f l a v i d ai n d e v o l g e n d e k l e e d k e n m e r k e nv a n s a n d v i c e n s i s7: d o n k e r e m a r k e r i n gen op verse juveniele mantel- en schouderveren beperkt tot de
schachtstreepof spatelvormige subtermi nale teken i ng (n iet U- of
V-vormig als bij sandvicensis);2 egaal gri.jze dekveren, met uilz o n d e r i n g v a n z w a r t a c h t i g ek l e i n s t ee n k l e i n e d e k v e r e n ,w a a r door een contrasterende donkere vleugelboeg aan de verder
egaal bovenvleugel ontstaaq 3 buitenste tertials met volledrg
donker centrum en brede witte rand (niet donkerlicht gevlekt);
e n 4 e e r d e r g e n o e m d e v e r s c h i l l e ni n k o p t e k e n i n g Z e e r j o n g e
vogels (rond het verlaten van het nest) verschillen nog sterker
van sandvicensisdoor de lichte (grijze, gele of soms zelfs oranje)
s n a v e l e n d o n k e r e ' w i g ' v a n a f h e t o o g t o t o p d e a c h t e r k o pe n
daar een korte kuif vormend (bij sandvicensisin dit stadium is de
snavel meestal bijna geheel zwart en de gehele bovenkop grijsb r ui n )
In eerste winterkleed verschilt acuflavlda in de voleende
k l e e d k e n m e r k e n :I e v e n t u e l e n i e t - g e r u i d ej u v e n i e l e d e k v e r e n
of tertials vertonen het hierboven beschreven kenmerkende patroon en op de armpennen (boven- en ondervleugel) kan een
donkere achterrand zichtbaar zijn; 2 op reeds doorgeruide
buitenste handpennen is het kenmerkende'adulte' patroon
z i c h t b a a r( z i e o n d e r ) j e n J e e r d e rg e n o e m d ev e r s c h i l l e ni n k o p reKenIng
In eerste zomerkleed verschill acuflavida in de volsende
k l e e d k e n m e r k e n I: o p r e e d sd o o r g e r u i d eI l u i t e n s t eh a n d p e n n e n
i s h e t k e n m e r k e n d e' a d u l t e ' p a t r o o n z i c h t b a a r( z i e o n d e r ) ;2 d e
tekeningop de donkere armpennen kan meer opvallend zijn,
e v e n a l sd e d o n k e r e b a a n o v e r d e k l e i n e d e k v e r e n ;e n 3 e e r d e r
g e n o e m d e v e r s c h i l l e ni n k o p t e k e n i n g
ln adult winterkleed verschilt acuflavida in de volsende
kleedkenmerken: I nieuue handpennen ,vanaf december
j a n u a r i )v e r t o n e ne e n z e e r s m a l l e l i c h t e r a n d a a n d e b i n n e n v l a g
en bijna geen wit aan de top (doordat acuflavida later ruit dan
sandvicensis hebben veel exemplaren nog oude donkere handp e n n e n t o t i n j a n u a r i e n s o m s t o t i n m a a r t ) ;d e b r e e d t e v a n d e
rvitte rand is 1-1 5 mm bij acuflavida en 2-4 mm 6ij sandvicen.
sis; daarnaast heett sandvlcensis3-5 mm wit aan de handpentop
( o n t b r e k e n d6 i j a c u i l a v i d a ) ; 2 a a n w e z i g h e i dv a n d o n k e r e m a r keringen op de armpennen waardoor een donkere achterrand
van de vleugel ontstaat; en J eerder genoemde verschillen in
koptekening, waarbij witte randen of toppen aan de verlengde
zwarte kopveren zeer smal of geheel alweztgzijn
ln adult zomerkleed verschilt acuflavida in de voleende
k l e e d k e n m e r k e n :I l a t e r e r u i v a n d e b u i t e n s t eh a n d p e n n i n e n
daardoor aanwezigheid van opvallend donkere en gesleten
buitenste handpennen; 2 nieuwe handpennen met een zeer
s m a l l e l i c h t e r a n d a a n d e b i n n e n v l a ge n b i j n a g e e n w i t a a n d e
top; en 3 aanwezigheid bij sommige vogels van een donkere
( o o k z i c h t b a a ro p d e o n d e r v l e u g e l ) .
vleugelachterrand
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285
ldentification of American Sandwich Tern
412 SandwichTern/ Crote SternSternasandvicensis
sandvicensis,
adult-summer,
Cemlyn Bay,Anglesey,Wales,
30 May 2006 (Mike Atkinson).There is little obvious differencebetweennominatesandvicensis
and American
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Tern/ Amerikaanse
CroteStern
Sternasandvicensisacuflavida,adult-summer,BolivarPeninsula,Texas,USA,il
April20OT(JosephKennedy).Ihere
is not much to separateadult-summer
acuflavidaand nominatesandvicensis.
However,in acuflavidain Marchano
April at least,bill shapeis straighter,
and relatively
freshouterprimaries,
as well as havingnarrowwhitefringesto
outerweb, alsolackobvious'hooks'of whitearoundtip. Nominatesandvicensis
normallyhasmuchmoreobvious
broadwhitefringeandtip to thesefeathers
in earlyspring.
286
ldentification of American Sandwich Tern
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l a n d sD u t c hB i d i n g l l : 1 7 2 - 1 7 4
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S c h a r r i n gJa1, 9 7 9 .A m e r i c aS
D u t c hB i r d i n g
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D 1999. SandwichTern(Sterna
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Martin Carner, l6 Daniel Hill Terrace,Upperthorpe,Sheffield56 3lE, UK ([email protected])
Road,Didcot, OxfordshireOXl l 7Be UK ([email protected]
co.uk)
lan Lewington,1l9 Brasenose
co uk)
JasonCrook, 14 Stroudwood Road,Havant, HampshirePOg 2HX, UK (jasoncrook@tiscali
287