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Sex-Rela ed Seasonal Di e ences in he Fo aging S a egy o he Ken ish Plo e
Au ho (s): MacA ena Cas o, Jose A. Mase o, Alejand o Pé ez-Hu ado, Juan A. Ama , and Cesa Megina
Sou ce: The Condo , 111(4):624-632. 2009.
Published By: Coope O ni hological Socie y
URL: h p://www.bioone.o g/doi/ ull/10.1525/cond.2009.080062
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624
The Condo 111(4):624 – 632
¡The Coope O ni hological Socie y 2009
The Condo , Vol. 111, Numbe 4, pages 624–632. ISSN 0010-5422, elec onic ISSN 1938-5422. 2009 by The Coope O ni hological Socie y. All igh s ese ed. Please di ec
all eques s o pe mission o pho ocopy o ep oduce a icle con en h ough he Uni e si y o Cali o nia P ess’s Righ s and Pe missions websi e, h p://www.ucp essjou nals.com/
ep in In o.asp. DOI: 10.1525/cond.2009.080062
Resumen. En especies de a es con cuidado bipa en al, cada sexo puede ene sus p opios eque imien os de
ene gía y/o esquema de iempo pa a la alimen ación, lo cual pod ía conduci a di e encias en las es a egias de
alimen ación en e ambos sexos. En los es ua ios, las especies de playe os como Cha ad ius alexand inus pueden
o ajea en angos in e ma eales y en hábi a s sup ama eales adyacen es an o du an e el in ie no así como du-
an e la época ep oduc i a. Aquí, analizamos la die a, el uso de hábi a de o ajeo, la asa de inges ión (biomasa
inge ida po unidad de iempo) y el iempo dedicado al o ajeo po el macho y la hemb a de C. alexand inus du-
an e ambas empo adas en una zona es ua ina donde los angos in e ma eales y las salinas adyacen es son las
p incipales á eas de alimen ación. La p incipal p esa pa a C. alexand inus ue un polique o (Ne eis di e sicolo ),
una p esa in e ma eal que suplió más del 80% de la biomasa consumida en cada es ación. Ambos sexos inc emen-
a on sus asas de alimen ación du an e la época ep oduc i a, y disminuye on sus iempos diu nos de o ajeo. Po
el inc emen o de la asa de inges ión du an e la época ep oduc i a, las a es minimiza on el iempo que pasa on
en los angos in e ma eales, lo que les pe mi ió maximiza el iempo dedicado a las ac i idades de ep oducción
en las salinas adyacen es. Po lo an o, el conflic o en e alimen a se en los angos e sus el desa ollo de las ac-
i idades de ep oducción (en las salinas), ue esuel o aco ando el iempo en los angos, minimizando el iempo
ue a de las zonas de nidada. Hubo di e encias elacionadas con el sexo en el iempo diu no dedicado al o ajeo:
las hemb as dedica on dos ho as menos a la alimen ación y concen a on su ac i idad de alimen ación en las ho as
cen ales de la ma ea baja.
SEX-RELATED SEASONAL DIFFERENCES
IN THE FORAGING STRATEGY OF THE KENTISH PLOVER
Di e encias Es acionales Relacionadas con el Sexo en la Es a egia de Alimen ación
de Cha ad ius alexand inus
Abs ac . In species o bi ds wi h bipa en al ca e, each sex may ha e i s own ene gy equi emen s and/o
schedule o eeding, possibly leading he sexes o di e in o aging s a egy. In es ua ies, sho ebi ds such as he
Ken ish Plo e (Cha ad ius alexand inus alexand inus) may o age on in e idal mudfla s and in adjacen su-
p a idal habi a s du ing win e as well as du ing he b eeding season. In his s udy, we analyzed he die , use o
o aging habi a , ood-in ake a e (biomass inges ed pe uni ime), and ime alloca ed o o aging by male and
emale Ken ish Plo e s a bo h seasons in an es ua y nea Cádiz, Spain, whe e in e idal mudfla s and adjacen
sal wo ks a e he main habi a s o o aging. The plo e s’ main p ey was he agwo m (Ne eis di e sicolo ), an
in e idal polychae e ha supplied mo e han 80% o he biomass consumed a each season. Du ing he b eeding
season, bo h sexes inc eased hei in ake a e and dec eased hei dayligh o aging ime. By inc easing he diu nal
in ake a e du ing he b eeding season, he bi ds minimized hei ime spen o aging on he in e idal mudfla s,
allowing hem o maximize he ime o ac i i ies associa ed wi h b eeding in he adjacen sal wo ks. The e o e,
he plo e s sol ed he conflic be ween o aging on he mudfla s and b eeding in he sal wo ks by sho ening he
o aging ime on he mudfla s, minimizing ime away om he nes ing a eas. The sexes di e ed in he dayligh
ime alloca ed o o aging, wi h emales spending 2 h less on o aging and concen a ing hei eeding ac i i y
in o he cen al hou s o low ide.
4Cu en add ess: Cen o de In es igación en Ecosis emas de la Pa agonia, Bilbao 449, Coyhaique, Chile. E-mail: maca ena.cas [email protected]
MACARENA CASTRO
1,4,
JOSE A. MASERO
2,
ALEJANDRO PÉREZ-HURTADO
1,
JUAN A. AMAT
3,
AND
CESAR MEGINA
1
1Depa amen o de Biología Animal, Facul ad de Ciencias del Ma y Ambien ales, Uni e sidad de Cádiz,
E-11510 Pue o Real, Spain
2G upo de In es igación en Conse ación, Á ea de Zoología, Facul ad de Ciencias, Uni e sidad de Ex emadu a,
A enida de El as s/n, E-06071 Badajoz, Spain
3Es ación Biológica de Doñana, Consejo Supe io de In es igaciones Cien íficas,
Apdo 1056, E-41080 Se illa, Spain
Manusc ip ecei ed 23 Oc obe 2008; accep ed 4 Augus 2009.
Key wo ds:
Cha ad ius alexand inus, o aging, habi a use, in ake a e, sal wo ks, sex di e ence, Ken ish
Plo e , sho ebi ds.
SEASONAL VARIATION IN THE KENTISH PLOVER’S FORAGING STRATEGY 625
INTRODUCTION
Di e en beha io s equi e ime and/o ene gy and canno be
ca ied ou simul aneously. This conflic may lead o ade-
o s among di e en ac i i ies. Fo ins ance, eeding is no
compa ible wi h any o he ene gy-demanding ac i i y (Cu hill
and Hous on 1997). Such ade-o s a e likely o be mo e ap-
pa en du ing he b eeding season, when esou ce alloca ion
can a ec ecundi y, su i al, and ime de o ed o ep oduc-
ion s ongly (Sibly and Calow 1986, Williams 1996). In many
species o bi ds, success ul b eeding equi es bipa en al ca e.
In hese species, bo h pa en s spend a subs an ial ac ion o
each day on he nes , educing he ime a ailable o o ag-
ing. Du ing incuba ion, ex ended absences om he nes may
esul in changes in egg empe a u es ha can a ec emb yo
de elopmen nega i ely (Webb 1987, Ama and Mase o 2007)
as well as inc ease he ime o exposu e o p eda o s (Tulp and
Schekke man 2006). The e o e, he wo sexes should no o -
age a he same ime so ha he nes can be almos con inu-
ously a ended by an adul .
Many mig a o y sho ebi ds (Cha ad ii) ely on in e idal
habi a s o o aging du ing bo h he win e and he b eeding
season. Owing o hei small size and hei high mass-specific
me abolic a es, sho ebi ds ha e a limi ed capaci y o s o e en-
e gy be o e he onse o b eeding and a e he e o e obliged o
eed du ing incuba ion (Tulp and Schekke man 2006). The
in e idal habi a is a ailable o only pa o each day, and
du ing he b eeding season males and emales mus al e na e
lea ing he nes o he in e idal a eas o sa is y hei equi e-
men s o bo h ood and nes a endance. None heless, sea-
sonal di e ences in sho ebi ds’ o aging beha io ha e been
s udied only in equen ly (Du ell 2001).
The Ken ish/Snowy Plo e (Cha ad ius alexand inus) is a
mig a o y sho ebi d wi h bipa en al incuba ion, emales incu-
ba ing by day, males by nigh (Wa ine e al. 1986, F aga and
Ama 1996). In es ua ies, i can eed in in e idal mudfla s as
well as in adjacen sup a idal habi a s (Pie sma 1996, Mase o
e al. 2000). In his s udy we compa ed he o aging s a egies
o male and emale Ken ish Plo e s in he win e and b eeding
season in an es ua y in which in e idal mudfla s and adjacen
sal wo ks (salinas o sal pans) a e he main o aging g ounds
(Mase o e al. 2000, Cas o 2001). Because he Ken ish Plo-
e can nes only in he sup a idal habi a , we expec ed an in-
c ease du ing he b eeding season in he use o sal wo ks o
o aging as a esul o , o example, e i o ial beha io . The
o aging beha io o ypical plo e s is highly s e eo yped, and
sho -billed species such as he Ken ish Plo e all o age isu-
ally in a un–s op–sea ch manne (Mase o e al. 2007). The en-
e ge ic demands o b eeding Ken ish Plo e s may di e by sex,
explaining di e ences in o aging pa e ns. Howe e , Ama e
al. (2000) ound no changes in body mass du ing incuba ion
and ea ly chick ea ing o ei he males o emales, and nei he
did hey find sex- ela ed di e ences in he ene ge ic cos s o in-
cuba ion. Ne e heless, di e en oles du ing ep oduc ion may
s ill lead o di e ences be ween he sexes in pa e ns o o ag-
ing. Because emales incuba e by day and males by nigh , we
expec ed sexual di e ences in pa e ns o habi a use, die , in-
ake a e (biomass inges ed pe uni ime), and ime alloca ed o
eeding du ing he b eeding season.
In bo h Eu ope and he Ame icas Cha ad ius alexand i-
nus is su e ing sha p popula ion declines (B own e al. 2000,
Delany and Sco 2006), and many ini ia i es o hal his de-
cline ha e in ol ed habi a - es o a ion plans (La e y e al.
2006). Because popula ions o mig a o y bi ds can be influ-
enced by e en s du ing win e , mig a ion, o b eeding (Sil-
le e al. 2000), e ec i e sho ebi d conse a ion equi es an
unde s anding o when and how popula ions a e limi ed and
egula ed (Skagen 2006). In his con ex , in ake a e is used
by modele s o es ima e ene gy budge s, p eda o –p ey in e -
ac ions, he quali y o eeding g ounds, and o he ac o s ha
may a ec fi ness, such as he isk o being aken by a p eda-
o , and ood- ela ed ep oduc i e success (Goss-Cus a d e
al. 2006). Acco dingly, ou esul s o seasonal a ia ion in in-
ake a e may bea significan ly on he success o conse a ion
plans o C. alexand inus.
METHODS
STUDY SITE
We chose an indus ial sal wo ks o 400 ha in he no h o
Cádiz Bay Na u al Pa k (36n 23` N, 6n 8` W), sou hwes e n
Spain, as he s udy a ea, oge he wi h 20–30 ha o adjacen
in e idal mudfla s a a dis ance o 50–800 m (Fig. 1). Abou
400 Ken ish Plo e s egula ly win e in his sal wo ks, while
du ing b eeding he e a e abou 120 indi iduals (Mase o e
al. 2000, his s udy). The in e idal mudfla s a e exposed (i.e.,
a ailable o sho ebi ds) o 7–9 h daily (semidiu nal ides).
The s udy a ea (sal wo ks and adjacen in e idal mud-
fla s) is su ounded by an h opogenic habi a s unsui able o
sho ebi ds, hus cons i u ing an isola ed we land in he no h
o Cádiz Bay (Fig. 1). O e all, he s udy a ea unc ions as a
closed sys em o o e win e ing sho ebi ds. Small sho ebi ds
such as he Ken ish Plo e es a high ide in he sal wo ks
and o age in he adjacen in e idal mudfla s a low ide, wi h
no appa en mo emen s be ween his isola ed we land and he
es o he bay h oughou he win e (Ho as 1997, Mase o
e .al. 2000, Mase o e al. 2001). A Cádiz Bay, Ken ish Plo e s
ha e been banded since 1994 wi h bo h me al and colo bands
(e.g., Pé ez-Hu ado e al. 1994, To ija 2005). Du ing ou
s udy, 36% o he Ken ish Plo e s b eeding in he s udy a ea
we e colo -banded (pe s. obs.), and we no ed ha a leas 44%
o hese colo -banded Ken ish Plo e s b eeding in he sal -
wo ks had win e ed in he same a ea p e iously (pe s. obs.).
Sex ecogni ion was possible in mos cases by plumage
dimo phism (males ha e a black ba on he on o hei o e-
heads, emales do no ; see Hayman e al. 1995 o plumage de-
sc ip ions). We could dis inguish he sexes ~86% o he ime
e en in win e when he plumage is mo e c yp ic (Table 1).
626 MACARENA CASTRO ET AL.
USE OF FORAGING HABITAT
Ou field obse a ions ex ended om Decembe 1996 o June
1997. The numbe o male and emale Ken ish Plo e s o -
aging and es ing (including p eening) in he sal wo ks was
eco ded once pe week (excep one week in win e in which
wea he condi ions made i impossible), a bo h high and low
ides, in Decembe and Janua y (win e ) and in May and June
(b eeding season). The maximum numbe s o ac i e nes s
and adul bi ds eco ded in he sal wo ks du ing his b eed-
ing season we e 57 and 113, espec i ely. Du ing he obse a-
ions o o aging in he sal wo ks a high ide, we no ed ha
all hese Ken ish Plo e s we e engaged in ypical b eeding
beha io s such as nes a endance, dis ac ion displays, o
e i o ial figh s (on a e age, 80% o he pai s we e in ol ed
in nes a endance and less han 10% we e ca ing o chicks;
pe s. obs.). Acco dingly, we assumed ha all adul Ken ish
Plo e s eco ded du ing he o aging s udies in he s udy a ea
in May and June we e b eeding bi ds (ju eniles can be dis in-
guished by he na ow bu inges on hei co e s and scapu-
la s; Hayman e al. 1995).
Diu nal ac i i y. We assumed he coun in he sal wo ks
a high ide o be he o al numbe o Ken ish Plo e s in he
s udy a ea and he di e ence be ween he o al coun ed in he
sal wo ks a high and low ides o be he pa o he popula ion
isi ing he mudfla s. We eco ded ac i i y o plo e s on he
in e idal mudfla s a low ide on he day a e he census in he
FIGURE 1. S udy a ea, showing in e idal mudfla s (in e idal channel) and adjacen sal wo ks (sup a idal a ea). The s udy a ea cons i-
u es an isola ed we land in he no h o Cádiz Bay, sou hwes e n Spain.
TABLE 1. Numbe s o male and emale Ken ish Plo e s eco ded in he sal wo ks (high
and low ide) and on he in e idal mudfla s du ing win e and he b eeding season. Mean
o aging ac i i y (pe cen age o bi ds o aging o 1 SD) is gi en in pa en heses.
Sal wo ks
High ide Low ide In e idal mudfla s
Win e ing
Females 139 (26.43 o 10.41) 12 (100) 152 (95.61 o5.66)
Males 150 (10.35 o5.29) 21 (100) 135 (96.82 o8.63)
Sex unknown 45 (32.51 o 10.22) 4 (100) 10 (95.41 o7.45)
B eeding
Females 48 (19.38 o1.03) 28 (3.6 o 2.42) 15 (52.3 o 36.19)
Males 65 (25.22 o6.04) 38 (7.89 o 3.64) 20 (74.76 o 34.62)
Sex unknown 4 (40.03 o5.82) 4 (15.22 o 4.04) 1 (100)
SEASONAL VARIATION IN THE KENTISH PLOVER’S FORAGING STRATEGY 627
sal wo ks and unde simila condi ions. Ken ish Plo e s eed-
ing and es ing on he in e idal mudfla s we e coun ed e e y
hou du ing low ide (7–9 h ). Fo aging ac i i y on he mud-
fla s, exp essed as he pe cen age o Ken ish Plo e s o aging,
was calcula ed o each coun , and he pe cen ages we e la e
a e aged o he en i e low- ide pe iod (Zwa s e al. 1990).
Noc u nal ac i i y. Du ing he b eeding season, we used
a ligh in ensifie (Canon; 6.5 magnifica ion, ligh -in ensi-
ying ac o 70 000 ) o eco d he bi ds’ numbe and ac i -
i y a nigh , always a a dis ance o 10 o 50 m om he ocal
indi iduals. E e y 14 days we ca ied ou noc u nal coun s in
he same a ea as ou diu nal coun s bu du ing he pe iod be-
ween 2 h be o e and 2 h a e low ide. Noc u nal o aging
ac i i y on in e idal mudfla s was calcula ed by compa ing
he numbe s o indi iduals eeding by nigh and by day a he
same si e (Zwa s e al. 1990). Nigh censuses in he sal wo ks
we e ca ied ou in he same way as he dayligh censuses.
Ligh om a nea by illage acili a ed iden ifica ion o bi ds
and hei o aging ac i i y, al hough sexing indi iduals was
no possible. Fo win e , da a on noc u nal ac i i y we e de-
i ed om a s udy ca ied ou a he same si e he same yea
(Mase o e al. 2000).
Fo aging- ime alloca ion. The daily ime spen o aging
was de i ed om he p opo ions o males and emales o ag-
ing in each habi a (in e idal mudfla s o sal wo ks) ela i e o
hei o al numbe s, numbe o minu es ha habi a was a ail-
able, and p opo ion ime he plo e s spen o aging. Fo his
calcula ion, we conside ed he du a ion o he low- ide pe iod
in he sal wo ks he same as he pe iod du ing which he in-
e idal mudfla s we e exposed; he es , up o he comple ion
o he idal cycle, was conside ed o be high ide (Mase o and
Pé ez-Hu ado 2001). We could no dis inguish he plo e s’
sex a nigh , so we assumed he sex a io o bi ds o aging a
nigh was simila .
DIET AND INTAKE RATE
P ey iden ifica ion and size. We andomly selec ed ac i ely
o aging indi iduals, 30m om he obse e , and obse ed
hem o 1 min wi h a 20–60 zoom elescope. A e 1 min,
a new ocal indi idual a leas 10 m om he p e ious indi-
idual was chosen o a oid pseudo eplica ion (Hu lbe 1984).
In e e y sequence, we eco ded he ollowing da a: bi d’s sex,
eeding a e (success ul pecks min−1), ype and size o p ey
i ems cap u ed, and ime since low ide. In he sal wo ks, plo-
e s o aged on small p ey i ems a ailable a high densi ies
along he sho e o he pans, and we assumed ha a p ey i em
was inges ed e e y ime he bi d pecked (pe s. obs.; see simi-
la p ocedu e in Mase o and Pe ez-Hu ado 2001).
P ey size was es ima ed in ela ion o a e age bill leng h.
A Cádiz Bay he e we e no significan di e ences be ween
males and emales in bill leng h ( 43  0.37, P 0.72; unpub-
lished da a), so we used an a e age leng h o 16 mm (15.56 o
0.82 mm; n 45 indi iduals, bo h sexes combined). Visual
obse a ions we e con as ed wi h analyses o ecal samples
(32 eces in win e and 30 in he b eeding pe iod, collec ed in
oos ing a eas o when eeding bi ds we e obse ed exc e -
ing). Mase o e al. (1999) and Cas o (2001) p o ided in o -
ma ion abou he species composi ion, size dis ibu ion, and
biomass o he p ey a ailable o sho ebi ds in he s udy a ea.
Acco ding o hose s udies, on he mudfla s he plo e ’s po-
en ial p ey we e he polychae e agwo m Ne eis di e sicolo ,
he bi al es Ce s ode ma edule and Sc obicula ia plana, he
gas opod Hyd obia ul ae, and he isopod Cya hu a ca i-
na a, while in he sal wo ks hey we e he b ine sh imp (A -
emia spp.), adul s and la ae o he coleop e an Och hebius
spp., and la ae o he dip e ans Chi onomus salina ius and
Ephyd a spp. All hese po en ial p ey lea e ecognizable ha d
pa s a e passing h ough a plo e ’s diges i e ac (Cas o
2001).
Following he me hod o Zwa s and Blome (1992), we
used he cumula i e equency dis ibu ion o p ey sizes ound
in eces o co ec isual es ima es o p ey sizes.
Biomass inges ed. We con e ed he leng h o each p ey
i em in o biomass by he equa ions in Mase o e al. (1999) and
Mase o and Pe ez-Hu ado (2001). We we e no able o es i-
ma e accu a ely in he field he species and he leng h o poly-
chae e wo ms sho e han hal a plo e ’s bill leng h (which
co esponded o 12 mm a e co ec ion o he isual es-
ima es; see abo e). Fo his size class o p ey, we assumed
as a e age biomass he a e age biomass o he polychae es
smalle han 12 mm a ailable in he in e idal mud (da a om
Mase o e al. 1999 and Cas o 2001; see p e ious sec ion).
Finally, we es ima ed in ake a e (mg o ash- ee d y mass
sec−1) by mul iplying he numbe o each size class aken pe
minu e by he ash- ee d y mass o ha size class.
The e a e no published da a on seasonal a ia ion in he
condi ion o in e eb a es in Cádiz Bay. The e o e, ou es i-
ma es o in ake a es du ing he b eeding season may be con-
side ed conse a i e gi en ha wa me empe a u es may
a ec he a ailabili y and condi ion o in e eb a es (Zwa s
and Wanink 1993). Likely, i he e a e seasonal o sex- ela ed
di e ences in in ake a e, hey may be sligh ly highe han
hose we epo .
STATISTICAL ANALYSES
We used a co a iance analysis (ANCOVA) o explo e sex-
ela ed di e ences in he pe cen age o indi iduals using he
mudfla s and sal wo ks a each season. In his analysis, sex
(male/ emale), season (win e /b eeding), and si e (mudfla s/
sal wo ks) we e fixed ac o s. Since he numbe o o aging
indi iduals could be influenced by he o al numbe o bi ds in
he a ea, we included he o al numbe o indi iduals o each
sex as co a ia e. Seasonal changes in o aging ac i i y (pe -
cen age o eeding bi ds), o aging ime, and sex- ela ed di -
e ences in eeding a e and in ake a e we e e alua ed also
by ANCOVA wi h sex, season, and si e as fixed ac o s and

628 MACARENA CASTRO ET AL.
densi y o bi ds as a co a ia e. Densi y o bi ds (ha−1) was in-
cluded as co a ia e because a s udy in he same in e idal zone
sugges ed ha a high densi y o sho ebi ds influences he be-
ha io o he in e eb a e p ey, possibly a ec ing he bi ds’
in ake a e nega i ely (Mase o and Pé ez-Hu ado 2001).
We assessed di e ences in mean diu nal and noc u nal ac-
i i y wi h S uden ’s - es . The da a we e inspec ed o no -
mali y and homoskedas ici y and we e no malized by a csine
ans o ma ion i needed. When analyses showed significan
di e ences, a pos -hoc Tukey es was used. Unless s a ed
o he wise, mean alues a e p esen ed wi h o SD, and he sig-
nificance le el o all es s was se a A 0.05. All s a is i-
cal analyses we e pe o med wi h S a is ica 7.0 (S a So , Inc.,
2004).
RESULTS
FORAGING
The pe cen age o indi iduals mo ing o he in e idal zone a
low ide dec eased om 88% in win e o 30% in he b eed-
ing season (F1, 25  74.93, P 0.05). Mean o aging ac i i y
on in e idal mudfla s dec eased om win e o he b eeding
season o bo h sexes (F1,24  65.44, P 0.05), pa icula ly o
emales (F1,24  25.20, P 0.05; Table 1). This change was
because emales sho ened hei ime o aging on he mud-
fla s, du ing he b eeding season concen a ing hei o aging
mainly be ween 2 h be o e and 1 h a e he maximum low
ide (Fig. 2).
The a io o indi iduals o aging a nigh inc eased om
0.37 in win e o 0.51 in he b eeding season ( 6 −7.02 P
0.05). Th oughou he s udy pe iod he e was no noc u nal
o aging in he sal wo ks a nigh .
Du ing he b eeding season emales alloca ed less ime
o o aging han did males (614.75 o 27.65 and 282.28 o 37.11
min day−1 o emales; 627.86 o 19.26 and 405 o 40.54 minu es
pe day o males, du ing he win e and b eeding season, e-
spec i ely; F1,12  11.64, P 0.05).
DIET
Combining da a om isual obse a ions, eces collec ed in
each habi a , and he knowledge o a ailable p ey yielded a
eliable es ima e o he plo e ’s p ey and hei sizes. On he
mudfla s he main p ey was he polychae e wo m Ne eis di e -
sicolo , which appea ed in 100% o eces analyzed and 100%
o isual obse a ions, supplying mo e han he 80% o he
biomass he plo e s consumed a bo h seasons (Fig. 3). The
aqua ic bee le Och hebius sp. appea ed in mos eces (70%)
a bo h seasons, bu i supplied less han 10% o he biomass
he plo e s inges ed (Fig. 3). The emaining p ey i ems ap-
pea ed in 30% o eces and supplied less han 10% and 20%
o he inges ed biomass in win e and he b eeding season, e-
spec i ely (Fig. 3).
A bo h seasons Ken ish Plo e s inges ed p edominan ly
polychae es ~10 cm long (Fig. 4). We could no assess he
leng h o he Och hebius bee les inges ed, bu he leng h o
hose a ailable in he sal wo ks anged om 1 o 3 mm a bo h
seasons (Cas o 2001). To calcula e in ake a e, we collec ed a
andom sample o 60 indi iduals o his bee le om he pans
o calcula e he a e age biomass pe indi idual (mean biomass
pe indi idual: 6.67 10−5 g ash- ee d y mass).
INTAKE RATE
Al hough eeding a es we e significan ly highe in he sal wo ks
han on he mudfla s (F1,164  42.99, P 0.05, Table 2), in ake
a es we e significan ly highe (a ound 10 highe ) on he mud-
fla s han in he sal wo ks (F1,164  70.95, P 0.05; Table 2). The
plo e s inc eased hei in ake a e om win e o he b eeding
season significan ly on he mudfla s (F1,164  4.45, P 0.05; Ta-
ble 2) bu no in he sal wo ks (F1,164  0.07, P 0.79; Table 2),
al hough he e we e no significan di e ences be ween he
sexes a ei he season o in ei he habi a (F1,164  0.07, P 0.79;
Table 2). The densi y o eeding bi ds on he mudfla s had no
significan e ec on in ake a e (F1,164  0.78, P 0.38).
FIGURE 2. Mean hou ly o aging ac i i y o male and emale
Ken ish Plo e s du ing dayligh on in e idal mudfla s in ela ion o
ides du ing he win e (a) and b eeding season (b).
SEASONAL VARIATION IN THE KENTISH PLOVER’S FORAGING STRATEGY 629
DISCUSSION
The o aging s a egy o Ken ish Plo e s, as measu ed by
habi a use, in ake a e, and ime alloca ed o eeding, shi ed
seasonally. Bo h sexes inc eased hei in ake a e du ing he
b eeding season and dec eased hei dayligh eeding ime, so
ha he conflic o o aging on he mudfla s (whe e he main
p ofi able p ey we e a ailable) wi h nes ing (which necessa -
ily akes place on he adjacen sup a idal habi a ) was esol ed
by sho ening he o aging ime on he mudfla s and he e o e
minimizing ime away om he nes ing a eas.
Acco ding o ene gy-maximiza ion p inciples (S ephens
and K ebs 1986), he sal wo ks we e a subop imal o aging
habi a o he plo e s, which ob ained en imes less biomass
(ene gy) pe uni ime in his habi a han on he in e idal
mudfla s. Indeed, acco ding o Zwa s and Wannik’s (1993)
equa ion o assessing minimum p ofi able in ake a e as a
unc ion o a sho ebi d’s body mass, he plo e s’ in ake a e
FIGURE 3. Occu ence (a) and biomass (b) o he p ey eco ded in he eces o Ken ish Plo e s du ing he win e (n = 32) and b eeding
season (n = 30).
630 MACARENA CASTRO ET AL.
in he sal wo ks was only 27% o he minimum in ake a e ex-
pec ed o i . Use o he sal wo ks a low ide du ing he b eed-
ing season inc eased. Because no densi y-dependen ac o s
we e appa en ly ope a ing in he in e idal mudfla s, he
FIGURE 4. Compa ison o he leng h classes o he agwo m
Ne eis di e sicolo a ailable on he in e idal mudfla s (solid line)
and in he eces o Ken ish Plo e s (b oken line) du ing he win e (a)
and b eeding season (b). Da a on leng h classes a ailable on mud-
fla s a e om Cas o (2001).
TABLE 2. Mean (o 1 SD) eeding a e and in ake a e o male and emale Ken ish Plo e s
o aging on he in e idal mudfla s and in he adjacen sal wo ks du ing he win e and b eed-
ing season.
In e idal mudfla s Sal wo ks
Feeding a e In ake a e nFeeding a e In ake a e n
Win e
Males 13.77 o 6.58 0.20 o 0.10 20 19.89 o 4.49 0.03 o 0.01 12
Females 13.59 o 5.57 0.22 o 0.11 23 23.72 o 5.49 0.03 o 0.02 17
B eeding
Males 13.39 o 8.10 0.33 o 0.20 43 26.54 o 17.28 0.04 o 0.03 18
Females 12.35 o 7.11 0.34 o 0.31 27 19.09 o 6.91 0.03 o 0.01 13
longe ime ha he bi ds spen in he sal wo ks du ing he
b eeding season was likely no due o hei being displaced
om he mudfla s by o he indi iduals. The esul s sugges
ha he bi ds emain in he sal wo ks du ing low ide because
o hei b eeding.
By inc easing hei in ake a es du ing he b eeding sea-
son, he plo e s ob ained mo e ene gy in a sho e ime han
in win e , hus minimizing o aging ime and inc easing
ime a ailable o o he ac i i ies. Females alloca ed almos
2 h less o o aging du ing dayligh in he b eeding sea-
son, mo ing on o he mudfla s o eeding jus du ing maxi-
mum mud exposu e, when, a p io i, mo e p ey a e a ailable
(Esselink and Zwa s 1989). Males also dec eased hei eed-
ing on he mudfla s, al hough he dec ease was no as sha p as
o emales.
Depending on he phase o b eeding, each sex’s ime con-
s ain o eeding is g ea e o lesse . Females incuba e mainly
du ing dayligh , males mos ly a nigh (Wa ine e al. 1986,
F aga and Ama 1996, Kosz olányi and Székely 2002). The e-
males usually dese he b ood when chicks a e 7–20 days old
(Wa ine e al. 1986, Székely and Lessells 1993, Ama e al.
1999). The e o e, du ing incuba ion emales a e mo e ime-
cons ained o eeding han a e males, al hough he opposi e
is he case a e ha ching. We did no ollow indi idual bi ds,
and ou es ima es a e popula ion-based, so ha emales and
males we s udied may ha e been in di e en s ages o b eed-
ing. Howe e , we measu ed all a iables when we ound he
g ea es numbe o ac i e nes s, implying ha mos indi idu-
als eco ded du ing ou obse a ions we e a a simila s age.
Mul iplying he daily ime alloca ed o eeding by he in-
ake a e, and assuming an assimila ion e ficiency o 80% o
Ne eis di e sicolo (Cas o e al. 2008) and 70% o Och he-
bius (Bell 1990), one can es ima e he plo e s’ daily ene gy
consump ion. Using he equa ion o Nagy e al. (1999) o es i-
ma e he daily heo e ical ene gy consump ion o wild bi ds,
one can compa e he ene gy consump ion we es ima e wi h he
heo e ical alue. Acco ding o ou es ima es, males consumed
131.42 kJ day−1 and 121.58 kJ day−1, emales 141.02 kJ day−1
and 97.98 kJ day−1 du ing he win e and b eeding season, e-
spec i ely. Acco ding o he heo e ical es ima es, he ene gy
SEASONAL VARIATION IN THE KENTISH PLOVER’S FORAGING STRATEGY 631
sho ebi d conse a ion assessmen : sho ebi d conse a ion s a-
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inges ed should be 138.03 kJ day−1 and 147.53 kJ day−1 du ing
hese wo pe iods, espec i ely (we used a mean body mass
o 39.55 o 3.95 o win e and 43.13 o 3.78 o he b eeding
season—da a om bi ds cap u ed in he sal wo ks. In ou
s udy a ea he masses o males and emales we e simila : 13 
−0.83, P 0.43, and 21  1.59, P 0.13, o win e ing and
b eeding bi ds, espec i ely). Females’ appa en ly low en-
e gy consump ion could be a consequence o he assump ions
we made abou noc u nal o aging. Following Zwa s e al.
(1990), we measu ed noc u nal ac i i y wi hin 2 h o low ide
and assumed ha he e we e nei he sex- ela ed di e ences in
in ake a e no di e ences in o aging bi ds’ sex a io. None-
heless, a nigh , emales’ in ake a e should be highe (Kuwae
2007) o hei ac i i y should be highe han we ound in his
s udy, wi h emales o aging h oughou he low- ide pe iod.
Die did no change by season, wi h he polychae e wo m
Ne eis di e sicolo being he plo e ’s p ima y p ey. B eeding is
conside ed o be an ac i i y wi h a g ea equi emen o p o ein
(Mu phy 1994). Ne eis di e sicolo is a p o ein- ich in e eb a e
wi h a p o ein con en 50% (Cas o e al. 2008), sugges s ha i
p o ides he plo e he p o ein i equi es o b eeding, so ha i
does no need o shi i s die du ing he b eeding season.
The Ken ish and Snowy Plo e s a e unde going a sha p
nume ical decline in Eu ope and he Ame icas (B own e al.
2000, Delany and Sco 2006). To he bes o ou knowledge,
no p e ious s udies ha e es ima ed he seasonal a ia ion in
his species’ in ake a es. Ou esul s indica e ha , o ealis-
ic assessmen s o p ey acquisi ion, ene gy budge s, o habi a
quali y, he species’ conse a ion plans should ake in o ac-
coun hese a ia ions in in ake a es.
ACKNOWLEDGMENTS
We a e g a e ul o Gonzalo Muñoz and S. Ma in o hei field assis-
ance and o Isabel To ija and Angeles Muñoz o hei help wi h
iden i ying in e eb a es. We also hank he s a o he en i onmen-
al o fice o Cádiz Bay Na u al Pa k o acili a ing all he pe mis-
sions and he company Unión Saline a o allowing us o s udy a he
Salinas La Tapa.
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