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Kleptoparasitism and Temporal Segregation of Sympatric Corvids Foraging in a Refuse Dump


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El cleptoparasitismo, definido como la acción de robar comida a otros individuos de la misma o de diferentes especies, es frecuente en las aves y representa una forma de competencia directa que podría influir sobre la estructura de las comunidades. Evaluamos esta idea analizando el comportamiento de forrajeo y los patrones espacio-temporales de uso de un vertedero en cuatro especies de có;rvidos (Corvus frugilegus, Corvus corone, Corvus monedula y Pica pica). Corvus corone mostró; un peculiar grado de especializació;n en el cleptoparasitismo, dedicando el mayor tiempo a vigilar desde la periferia del vertedero y atacando a otros individuos en lugar de buscar directamente el alimento entre las basuras. En invierno, cuando la abundancia de corvidos fue más elevada, las especies se segregaron mediante diferentes horarios de visita al vertedero, siendo C. frugilegus y C. monedula las más abundantes durante las primeras horas del día, C. corone durante la mitad de la manana y Pica pica durante las primeras horas de la tarde. Sugerimos que el cleptoparasitismo jugó; un papel en determinar la agregatión temporal de las especies en el vertedero. Por una parte, C. corone coincidió; en el patrón diario de abundancia de sus principales hospedadores (Sturnus spp.), aumentando sus oportunidades de cleptoparasitarlos. Por otra parte, la llegada tardía de Pica pica les previno de superponerse con C. corone, reduciendo el riesgo de ser robados y por lo tanto aumentando la eficiencia de forrajeo. La segregatión temporal de especies ha sido descrita raramente entre los vertebrados, pero nuestros resultados sugieren que puede ser un mecanismo importante de coexistencia de especies cuando los recursos se encuentran concentrados espacialmente.
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—El cleptoparasitismo, definido como la acción de robar comida a otros individuos de la misma o de diferentes especies,
es frecuente en las aves y representa una forma de competencia directa que podría influir sobre la estructura de las comunidades.
Evaluamos esta idea analizando el comportamiento de forrajeo y los patrones espacio-temporales de uso de un vertedero en cuatro
especies de córvidos (Corvus frugilegus, Corvus corone, Corvus monedula y Pica pica). Corvus corone mostró un peculiar grado de
especialización en el cleptoparasitismo, dedicando el mayor tiempo a vigilar desde la periferia del vertedero y atacando a otros individuos
en lugar de buscar directamente el alimento entre las basuras. En invierno, cuando la abundancia de córvidos fue más elevada, las especies
se segregaron mediante diferentes horarios de visita al vertedero, siendo C. frugilegus y C. monedula las más abundantes durante las
primeras horas del día, C. corone durante la mitad de la mañana y Pica pica durante las primeras horas de la tarde. Sugerimos que el
cleptoparasitismo jugó un papel en determinar la agregación temporal de las especies en el vertedero. Por una parte, C. corone coincidió
en el patrón diario de abundancia de sus principales hospedadores (Sturnus spp.), aumentando sus oportunidades de cleptoparasitarlos.
Por otra parte, la llegada tardía de Pica pica les previno de superponerse con C. corone, reduciendo el riesgo de ser robados y por lo
tanto aumentando la eficiencia de forrajeo. La segregación temporal de especies ha sido descrita raramente entre los vertebrados, pero
nuestros resultados sugieren que puede ser un mecanismo importante de coexistencia de especies cuando los recursos se encuentran
concentrados espacialmente.
e Auk 126(3):566578, 2009
e American Ornithologists’ Union, 2009.
Printed in USA.
e Auk, Vol.  , Number , pages . IS SN -, electron ic ISSN -.  by e A merican Or nithologi sts’ Union. A ll rights r eserved. Ple ase direc t
all requests for permission to photocopy or reproduce article content th rough the University of Cali fornia Press’s Rights and Permi ssions website, http://www.ucpressjournals.
com/reprintInfo.asp. DOI : . /auk . .
Cleptoparasitismo y Segregación Temporal de Especies Simpátricas de Córvidos durante
el Forrajeo en un Vertedero
Vi t t o r i o Ba g l i o n e 1, 3 a n d da n i e l a Ca n e s t r a r i 2
1Department of Agroforestry, University of Valladolid, Avda. de Madrid 44, 340 04 Palencia, Spain; and
2Department of Animal Biology, Faculty of Science, University of Granada , University Campus Fuente Nueva, 18071 Granada, Spain
A.—Kleptoparasitism, in which an individual steals food from other individuals of the same or a different species, is frequent
in birds and represents a form of direct competition that can potentially influence the structure of communities. We addressed this idea
by analyzing the foraging behavior and the spatiotemporal patterns of use of a refuse dump by four species of corvids: the Rook (Corvus
frugilegus), Ca rri on Crow (C. corone), E ur asi an Jac kda w (C. monedula), an d Eu rop ea n M agp ie ( Pica pica). Carrion Crows showed a unique
degree of specialization in kleptoparasitism, allocating most of their time to scanning from the periphery of the dump and attacking
other individuals rather than searching directly for food on the refuse. During winter, when the presence of corvids was highest, the
species segregated through different timing of visits to the dump: Rooks and Eurasian Jackdaws were most abundant in the early hours,
Carrion Crows in the middle of the morning, and European Magpies in the early afternoon. We suggest that kleptoparasitism played a
role in shaping the temporal assemblage of species in the dump. On one hand, Carrion Crows matched the daily pattern of abundance
of their main hosts, the starlings (Sturnus spp.), thus increasing their opportunities for kleptoparasitism. On the other hand, European
Magpies’ delayed arrival prevented overlapping with Carrion Crows, which reduced their risk of being robbed and, therefore, enhanced
the efficiency of foraging. Temporal segregation of species has rarely been reported among vertebrates, but our results suggest that it may
be an important mechanism of coexistence on spatially clumped food resources. Receive d  July , accepted  Feb ruar y .
Key words:
corvids, Corvus spp., European Magpie, kleptoparasitism, Pica pica, segregation of species, temporal niche partitioning.
K  
theft of food or other valuable re-
sources from hosts of the same or different species (Buckley ).
It occurs in a large variety of animals, including mollusks (Zamora
and Gómez , Iyengar ), insects (Filippi et al. ),
arachnids (Koh and Li ), fishes (Hamilton and Dill ), rep-
tiles (Cooper and Pérez-Mellado ), mammals (Gorman et al.
, Di Bitetti and Janson ), and birds (Brockmann and Bar-
nard ). In birds, kleptoparasitsm is nonrandomly distributed
among taxa (Morand-Ferron et al. ), being most frequent in
the order Pelicaniformes (where it has been described in .% of
 species), in Falconiformes (.% of  species), and in Char-
adriformes (.% of  species). Kleptoparasitism is rare among
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Kl e p t o p a r a s i t i s m in sy m p a t r i C Co r V i d s
Passeriformes other than corvids, in which it has been described
in .% of  species (Morand-Ferron et al. ). Unlike the
five species of frigatebirds (Fregata spp.), which are specialized
kleptoparasites (Brockmann and Barnard ), most avian spe-
cies use robbing tactics facultatively, typically when there is a high
concentration of potential hosts on a predictable source of food
or when food is in short supply (Brockmann and Barnard ).
Under these circumstances, kleptoparasitism can become the
prevalent foraging technique and can seriously threaten hosts.
Well-known cases include larids (Larus spp.) stealing food from
puffins (Fratercula spp.) when the latter return to breeding col-
onies to feed their young, which substantially reduces the hosts’
reproductive success (St. Clair et al. , Finney et al. ), and
Spotted Hyenas (Crocuta crocuta) driving African Wild Dogs
(Lycaon pictus) to local extinction by stealing their kills (Gorman
et al. ).
ese examples show that kleptoparasitism can potentially
influence the structure of species communities, playing a role
similar to that of predation or other kinds of competition for re-
sources. However, studies on kleptoparasitism have focused
mainly on its costs and benefits in comparison with other feeding
techniques (Ha and Ha ), and little is known on how this be-
havior influences species coexistence and niche partitioning. As
a result, although kleptoparasitism is reasonably well understood
both theoretically and empirically in the context of optimal-for-
aging theory, its function in shaping communities is still largely
Refuse dumps meet most conditions that favor the occur-
rence of kleptoparasitism in birds, namely predictable availabil-
ity of food, large and visible food items, and high concentration of
potential hosts (Brockmann and Barnard ). Indeed, some in-
stances of food stealing have been reported in this kind of anthro-
pogenic environment (Steele and Hockey , Galván ). A
refuse dump in northern Spain, near the city of León, is regularly
used by birds, in particular by four species of corvids: the Carrion
Crow (Corvus corone), Rook (C. frugilegus), Eurasian Jackdaw (C.
monedula), and European Magpie (Pica pica). ese species have
similar ecology in terms of diet, habitat selection, and feeding be-
havior (Waite b), and several studies have addressed some
mechanisms of niche partitioning that allow them to coexist in
natural environments (Waite a, b; Rolando ).
Our aim was to investigate the occurrence of kleptoparasit-
ism in the corvid guild and to determine whether robbing behavior
plays a role in shaping the patterns of spatial and temporal use of
the dump at the interspecific level. We compared the feeding strat-
egies of the four species, their use of different parts of the dump,
their daily and annual cycle of abundance, the frequency and suc-
cess rate of their kleptoparasitism, and their choice of hosts.
Me t h o d s
Refuse dump, avian community, and bird counting.—e dump
tha t we stu di ed ( °N,°W) wa s op ene d in th e la te  s a nd
served the city of León in northwest Spain. e dump was perma-
nently exposed, and the birds had access to the whole refuse area
(~. ha). Every day, new refuse was dumped on top of previous
layers and flattened mechanically. An area of ~. ha adjacent to
the dump (hereafter “periphery”) that was used for storing empty
containers and maneuvering trucks also was used by birds, mostly
for escaping machines working on the refuse or for resting. Other
than the four species of corvids, Spotless Starlings (Sturnus uni-
color) and European Starlings (S. vulgaris) were the most abun-
dant avian species.
From  January  until  December , we visited the
dump approximately every other week (n =  visits) to census
corvids with binoculars and a spotting scope from a single van-
tage point. Beginning in September , we counted starlings as
well. Counts started  h after sunrise and were repeated every  h
until dusk. e location of birds (refuse surface vs. periphery) was
recorded. e use of a voice recorder allowed a quick and uninter-
rupted scan of the dump, which was divided in six sectors. Dur-
ing the counts, which lasted ~ min, we recorded birds moving
across sectors and to and from the dump, to avoid double count-
ing. When we failed to keep track of moving birds, we aborted the
count and immediately began again (sometimes up to three or
four times). When starlings were present in the thousands, we had
to estimate their numbers separately, after counting corvids. e
two species of starlings are too similar to be differentiated during
a quick count, so we pooled their numbers. Correlations between
the daily maximum numbers of individuals of the different species
counted in the dump throughout the year were tested with Spear-
man rank correlation, and within-species differences in the num-
ber of individuals counted at different times of day were analyzed
with Kruskal-Wallis analysis of variance (ANOVA).
Foraging behavior.—Between November and February, we
conducted two kinds of behavioral observations of corvids for-
aging in the dump: focal sampling and ad-libitum recording of
kleptoparasitic interactions. Observations took place both in the
morning and in the afternoon, typically between bird counts,
avoiding the late hours when birds mainly engaged in pre-roost
social activities rather than foraging.
We used focal sampling to describe the foraging behavior
of the four corvid species. Focal individuals were followed for
min, and their behavior was videotaped. Observations that
lasted min, because of the bird’s departure or for any other
reason, were discarded. We calculated the proportions of time
spent in five categories of behavior: moving, handling refuse
(picking items on a spot), scanning (vigilant posture with head
raised), flying, and resting (perching without scanning). Because
the food handled was rarely recognizable, food intake was as-
sessed as the frequency of swallows. To avoid biasing the sam-
ple toward individuals that displayed a particular behavior, we
chose individuals of each species according to the activity they
displayed when we first looked at them, following a sequence
that made the five behavioral categories equally represented. At-
tempted kleptoparasitism was recorded as well, taking note of
the species of the host, the direction of the attempt (focal indi-
vidual stealing food or being stolen from), and its outcome. We
defined an “attempt” at kleptoparasitism as a quick approach of
an individual to its target, either by flying, jumping, or walking,
overtly aimed at stealing the food that the latter was consum-
ing. is often involved pecking or other kinds of physical con-
tact. e attempt was considered successful if the initiator stole
the food or displaced the host from the feeding spot and took
over in handling the food. We sampled  individuals of the
four species feeding on the refuse area and  on the periphery
11_Baglione_08-146.indd 567 7/20/09 6:06:21 PM
Ba g l i o n e a n d Ca n e s t r a r i
au K , Vo l .
(see details below). Although birds in the dump were unbanded,
th e hig h nu mbe rs m ade it u nlik ely th at i ndiv idu als wer e sa mpl ed
more than once. We therefore considered the focal samples sta-
tistically independent.
Besides focal sampling, we also scanned the refuse surface
and the periphery with binoculars to record attempted kleptopar-
asitism. For every instance observed (n = ), the identity of the
host was recorded, as well as the outcome of the attempt when
possible. To avoid biasing the sample, we distributed our scans
homogeneously over the whole dump. Because all corvids were
equally visible on the dump, these ad-libitum observations were
a suitable complement to the focal sampling.
To analyze feeding behavior, we used Kruskal-Wallis ANOVA
and Mann-Whitney U tests for comparisons involving only two
samples. We used chi-square tests for among-species differences
in host choice and kleptoparasitic success rate. To avoid predicted
frequencies <, it was sometimes necessary to delete data on Euro-
pean Magpies, as described below. Fisher’s exact test was used for
×tables of contingency.
Re s u l t s
Annual Cycle
e annual cycles of abundance in the dump varied among species
(Fig. A, B). Rooks and Eurasian Jackdaws showed annual max-
ima during the postbreeding periods (July–September). Carrion
Crows’ abundance peaked in winter and European Magpies were
most common in late summer and winter. All species showed a
sharp decrease during the breeding months (April–June). Most
birds at the dump in late autumn and winter (November–February)
were European and Spotted starlings, which together reached
peaks of ~, individuals simultaneously foraging on rubbish
(Fig. A). roughout the year, the numbers of Carrion Crows and
starlings were highly correlated (Spearman rank correlation, r =
., P <.; Fig. A), as were the numbers of Rooks and Eurasian
Jackdaws (r = ., P = .; Fig. B). Both correlations remained
significant when applying Bonferroni sequential correction for
multiple testing (Holm ).
Fig . 1. Maximum numbers of (A) starlings and Carrion Crows and (B) Eurasian Jackdaws, Rooks, and European Magpies recorded in the refuse dump
from 15 September 1992 until 1 December 1993. Every datum represents a day of censusing at the dump.
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Kl e p t o p a r a s i t i s m in sy m p a t r i C Co r V i d s
Daily Cycle
e daily cycle of visits to the dump varied among corvid species
(Fig. B–E). In the cold months (November–February), Rooks
arrived en masse in the early morning, and most left within the
next  h (Kruskal-Wallis ANOVA, difference among -h peri-
ods: H = ., df = , P < .). Eurasian Jackdaws also peaked
in the early morning (H = ., df = , P < .), but their pres-
ence was more constant throughout the day. Among the four spe-
cies, only European Magpies used the dump more intensively in
the afternoon (H = ., df = , P < .). Carrion Crows arrived
at the dump later in the morning than the other corvids (Fig. B),
typically when starlings also began to be abundant (Fig. A), and
their presence decreased sharply after midday (H = ., df = ,
P < .). During the rest of the year (March–October), Rooks and
Eurasian Jackdaws showed a peak of abundance at dusk (Kruskal-
Wallis nonparametric ANOVA, difference among -h periods
for the two species, respectively: H = ., df = , P < . and
H = ., df = , P < .; Fig. ), when they used the dump for
pre-roost gathering, with little foraging activity. Conversely, Eu-
ropean Magpie abundance did not show any significant variation
throughout the day (H = ., df = , P = .). e few Carrion
Crows that visited the dump during this period showed a peak in
the late morning (H = ., df = , P < .), as in winter.
Habitat Use and Winter Feeding Behavior
Rooks, Eurasian Jackdaws, and European Magpies were more
commonly seen in the refuse area, whereas Carrion Crows used
the per iph er y mo re i nt ens ivel y, a s sh own by t he ave rag e (± S E) p ro-
portion of individuals in this part of the dump at any bird count:
Carrion Crows, .± .; Rooks, . ± .; Eurasian Jackdaws,
. ± . ; Eu ro pe a n M ag pi es ,  .  ±. (Kruskal-Wallis ANOVA,
H = ., df = , P = ., n = ).
Feeding behavior on the refuse area.—e proportion of time
spent handling rubbish, moving, scanning, and flying significantly
differed among the four species (Kruskal-Wallis nonparametric
ANOVA, handling: H = ., P = .; moving: H = ., P <.;
scanning: H =   .  , P < .; flying: H = . , P = .; df =  for all
analyses; Carrion Crow, n = ; Rook, n = ; Eu rasian Ja ckdaw, n =
; European Magpie, n = ; Fig. A). Carrion Crows spent most of
their time scanning and spent less time handling rubbish than the
other species. Rooks showed the highest overall frequency of swal-
low s (H = ., d f = , P < .; Fig. B) and the highest rate of food
intake when handling a rubbish item (average [± SE] frequency of
swallows per minute of handling rubbish: Rook, . ± .; Car-
rion Crow, . ±.; Eurasian Jackdaw, . ± .; European
Magpie, . ± .; Kruskal-Wallis ANOVA, H =  .  , P < .,
n = ). Carrion Crows showed the highest frequency of attempted
kleptoparasitism (H = ., df = , P < .; Fig. B), whereas Eur-
asian Jackdaws were more likely to be kleptoparasitized (H =
., df = , P < .; Fig. B). Neither Rooks nor Eurasian Jack-
daws showed differences in their foraging behavior on the dump
between morning and afternoon (none of the six variables mea-
sured was significant in a Mann-Whitney U-test; Carrion Crows
could not be tested because of the limited number of birds sam-
pled in the afternoon). Conversely, European Magpies proved to be
far more efficient during their afternoon peak (Fig. A, B), allocat-
ing more time to handling food (Mann-Whitney U-test, U = ,
Fig . 2. Average (± SE) number of (A) starlings, (B) Carrion Crows,
(C) Rooks, (D) Eurasian Jackdaws, and (E) European Magpies at the refuse
dump throughout a day. The timing of each count is indicated on the x
axis as number of hours after sunrise. For every corvid species, the dif-
ferences within each period of the year (autumn–winter and spring–sum-
mer) were significant (P < 0.05), with the exception of European Magpies
in spring–summer.
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Ba g l i o n e a n d Ca n e s t r a r i
au K , Vo l .
P =.) and less to moving (U =    , P =  .  ) a n d s c a n n i n g ( m a r g i n -
ally nonsignificant; U =  , P = .), a nd ob tai ning a s ignifica ntly
higher intake of food (frequency of swallows, U = ., P = .).
Also, the European Magpies were less likely to be kleptoparasitized
in the afternoon than in the morning hours (U =., P = .).
Feeding behavior on the periphery.—European Magpies were
rarely seen on the periphery of the dump and were, therefore, ex-
cluded from the analyses. Rooks and Eurasian Jackdaws used the
periphery mostly for resting (Kruskal-Wallis ANOVA, differ-
ence among species in the proportion of resting: H = ., df = ,
P < .; Carrion Crow, n = ; Rook, n = ; Eurasian Jackdaw,
n = ; Fig. A), although sometimes they used this area for han-
dling food items brought from the refuse area when disturbed by
machines at work on the dump. Unlike the other species, Carrion
Crows scanned most of the time (among species, H = ., df = ,
P = .; Fig. A) and showed the highest frequency of attempted
kleptoparasitism (H =  . , df =  , P < .; Fig . B ).  ere wer e no
differences among species in the number of swallows obtained (H =
., df = , P = .; Fig. B).
Number of Aggressions and Host Choice
During both focal sampling and random sampling of birds forag-
i ng o n t he d um p, w e o bse r ved  ag gr es sio ns in wh ich an in di vi d-
ual attempted to steal food handled by another bird of the same or
a different species. Of those,  were initiated by Carrion Crows,
 by Rooks,  by Eurasian Jackdaws, and  by European Mag-
pies. e two kinds of sampling returned very similar frequency
of attacks (see frequency of attacks per species in Fig. B and num-
ber of total attacks per species in Fig.  for a qualitative compari-
son) and host choice (comparison of frequencies of attack per host
species between the two sampling methods: Carrion Crow, χ =
., df = , P =.; Rook, χ = ., df = , P = .; Eurasian Jack-
daw, χ = ., df = , P = .; European Magpie, χ = ., df = ,
P =.) and were therefore pooled. Carrion Crows and European
Magpies preferentially attacked starlings, whereas Rooks and Eur-
asian Jackdaws were more aggressive toward conspecifics (Fig. ).
Such differences among species in host choice were highly signifi-
ca nt (χ = ., df = , P < .; European Magpies were excluded
from the calculation to avoid expected frequencies <).
Unlike the other corvid species, Carrion Crows attacked more
often on the periphery of the dump (χ = . , df = , P < .) . e y
Fig . 3. Feeding behavior of focal individuals (sample sizes in parenthe-
ses) of the four corvid species in the refuse area. (A) Proportion of time
spent handling rubbish, moving, scanning, and flying. (B) Frequency of
swallows and of attacks made against and received from other birds for-
aging on the dump. Asterisks indicate significant differences between
species (P < 0.05).
Fig . 4. Foraging behavior of European Magpies (number of individuals
in parentheses) on the refuse area in the morning and in the afternoon.
(A ) Pr opor tion of t ime spe nt h and ling rubb ish, m oving , sc ann ing , an d fly -
ing. (B) Frequency of swallows and of attacks made against and received
from other birds foraging on the dump. Asterisks indicate significant
differences between morning and afternoon (P < 0.05).
11_Baglione_08-146.indd 570 7/20/09 6:06:28 PM
Ju l y 2009
Kl e p t o p a r a s i t i s m in sy m p a t r i C Co r V i d s
typically perched on a metallic fence (~ m high) on the periphery
and, from that vantage point, spotted potential victims handling
food brought from the refuse area. e attacks consisted of a fast
flight that usually ended on the ground but that also was sometimes
followed by an aerial pursuit. On the refuse area, Rooks and Eurasian
Jackdaws usually attacked birds foraging nearby on the ground, but
Carrion Crows often performed aerial attacks to reach more dis-
ta nt vic tims. Notably, C arrion Crows typica lly attacke d after a pro -
longed period of scanning from vantage points, whereas Rooks and
Eu ras ian Jac kdaw s see med to b e mor e opp ort uni sti c, t aki ng advan -
tage of occasional encounters, within the flock, with neighbors that
were handling food. In addition, Carrion Crows showed intimidat-
ing postures and physically aggressive contacts with the hosts more
often than the other species, whereas Eurasian Jackdaws often were
more st ealt hy when confro nted w ith l arger hosts.
No difference was found among species in the overall propor-
tion of successful attacks (χ = ., df = , P =.; result obtained
pooling data of all hosts species). e high number of aggressive ac-
tions by Carrion Crows allowed some further analysis for this spe-
cies. e proportion of successful attacks did not vary according to
Fig . 5. Feeding behavior of focal Carrion Crows, Rooks, and Eurasian
Jackdaws (sample sizes in parentheses) on the periphery of the dump.
European Magpies were rarely seen in this part of the dump and, there-
fore, were excluded from the analyses. (A) Proportion of time spent han-
dling rubbish, moving, scanning, flying, and resting. (B) Frequency of
swallows and of attacks made against and received from other birds for-
aging on the dump. Asterisks indicate significant differences between
species (P < 0.05).
Fig . 6. Host choice of four corvid species kleptoparasitizing in the dump
(number of attacks recorded in parentheses).
ho st sp eci es (χ =  ., df = , P = . ; Eu ro pe an Mag pi e w as exc lu ded
from the analysis because of low sample size) and was not signifi-
cantly affected by the location in the dump (refuse area vs. periphery;
Fisher’s exact test, P =.; obt aine d by pooli ng dat a for all host spe -
cies). No difference between refuse area and periphery was found,
even when we restricted the analysis to Carrion Crows’ preferred
hosts, starlings (Fisher’s exact test, P =.) and Ro oks (P = . ).
di s c u s s i o n
Urban refuse is an abundant, high-energy, predictable food re-
source that is commonly used by wild populations of animals,
especially birds (Donázar , Pons and Migot , Olea and
Baglione ). When resources are clumped, individuals have
few options for reducing overlap in spatial distribution or food
choice, which are the niche dimensions along which species com-
monly segregate. Direct competition, of which kleptoparasitism is
an example, is likely to arise (Goldberg et al. ). In León’s dump,
all corvids kleptoparasitized other individuals, but there were im-
portant differences among species. We also observed that, even
in such conditions of food concentration, corvid species could re-
duce their overlap in dump use by temporal segregation, on both a
daily and a seasonal scale. Below, we first address patterns of klep-
toparasitism in the corvid guild, discussing the unique degree of
specialization exhibited by Carrion Crows. We then analyze the
role of kleptoparasitism in shaping the temporal segregation of
corvids at the dump.
Kleptoparasitism at the Dump
Among the four corvid species that used the refuse dump, Car-
rion Crows had the most peculiar feeding behavior, spatial distri-
bution in the dump (refuse area vs. periphery), and daily cycle of
abundance, which together indicate a degree of specialization in
kleptoparasitism. During winter, when their numbers were high-
est, Carrion Crows preferentially used the periphery of the dump
rather than foraging directly on the refuse. On the periphery, Car-
rion Crows mainly scanned and showed the highest frequency
of attempts at kleptoparasitism, in contrast to the other spe-
cies, which used this area mainly for resting. Carrion Crows also
11_Baglione_08-146.indd 571 7/20/09 6:06:30 PM
Ba g l i o n e a n d Ca n e s t r a r i
au K , Vo l .
frequently attacked other birds on the refuse area and allocated
most of their time there to scanning rather than directly search-
ing for food. With regard to temporal distribution on the dump,
Carrion Crows’ daily cycle of abundance matched, to a remarkable
degree, that of their main hosts, the starlings, whose late arrival in
the morning was likely attributable to the large distance between
the dump and the riparian plantations of poplar (Populus spp.) in
southern León province where they roosted. We suggest that Car-
rion Crows synchronized their timing of visits to the dump with
that of the starlings. Alternative explanations seem unlikely. Be-
cause refuse is abundant and predictable (Pons and Migot )
and, hence, represents an ideal solution to the high energetic de-
mand after a cold night, we would have expected the abundance
of Carrion Crows to peak at dawn, like that of Rooks and Eurasian
Jackdaws, rather than later in the morning. e distance from
roost to dump could not account for the morning delay of Carrion
Crows, because they typically roosted communally with Rooks
and Eurasian Jackdaws near the dump (V. Baglione unpubl. data,
P. Olea and F. J. Purroy pers. comm.). Avoidance of competition
with other species also seems unlikely, because Carrion Crows are
dominant within this corvid guild (Bossema et al. ).
e correlation between the annual cycles of Carrion Crows
and starlings, characterized by highest abundance in winter,
could also reflect active kleptoparasite–host synchronization, but
alternative explanations are plausible. In particular, the absence of
Carrion Crows in the dump during the postbreeding period, when
other corvids are usually abundant, may be attributable to the fact
that they live in cohesive kin groups in this part of Spain (Bagli-
one et al. b) and leave the breeding territories only in winter
(Baglione et al. ), when food is in short supply.
Overall, our data indicate that, although kleptoparasitism
is part of the behavioral repertoire of all corvids, Carrion Crows
have reached the highest degree of specialization. Below, we ad-
dress some possible explanations for this pattern.
Why Carrion Crows?
It has been suggested that nutrition is not the sole factor driving
kleptoparasitism and that food theft can be involved in establish-
ing intraspecific social dominance (LeBaron and Heppner ).
In the present study, this hypothesis may apply to Rooks and Eur-
asian Jackdaws, which attacked mostly conspecifics, but it is un-
likely to explain the behavior of Carrion Crows, which usually
parasitized other species at the expense of direct search for food.
Interspecific dominance is also unlikely, because it cannot account
for Carrion Crows’ preference for starlings, which are not direct
competitors, nor for their synchronization with the daily cycle of
the starlings. erefore, we believe that kleptoparasitism in Car-
rion Crows must be interpreted as a true foraging technique.
e observed prevalence of kleptoparasitism in Carrion
Crows is surprising, considering that Carrion Crows, Rooks, Eur-
asian Jackdaws, and European Magpies share many ecological and
morphological features, in that all are generalist omnivorous birds
with strong beaks that have a tearing-edge typical of scavengers
and that all have rather similar foraging repertoires (Waite a).
e similarity is especially striking between Carrion Crows and
Rooks, which also are the same size and shape and have similar
flying abilities—and might be expected, therefore, to be equally
likely to be kleptoparasitic. Indeed, we found that Carrion Crows
and Rooks had the same success when stealing food; however,
Rooks seemed to be better foragers in the refuse area. Assuming
that the two species ingested food items of similar size and qual-
ity, Rooks’ higher frequency of swallows (Fig. B) and higher num-
ber of swallows obtained per piece of rubbish handled indicate a
more efficient use of refuse. Such efficiency, which could be re-
lated to natural digging habits of Rooks that may be helpful when
searching among refuse, may explain why Rooks are not special-
ized kleptoparasites.
An alternative explanation is that Carrion Crows possess
a larger behavioral flexibility than Rooks, which allows them to
increase the benefits of theft. Carrion Crows can adjust their so-
cial organization from social monogamy to kin-group living and
cooperative breeding (Baglione et al. b) in response to the
environment (Baglione et al. a, ). e Carrion Crows ad-
justed their daily cycle of use of the dump to that of starlings and
used the fence on the periphery of the dump in a unique way, start-
ing their attacks from above and probably improving the energetic
balance of theft. It is intriguing that in , in the same dump,
only % of the total number of Carrion Crows counted in 
censuses were observed on the periphery (A. Reija pers. comm.),
whereas .% were thus observed in the present study. Although
a statistical comparison with our data is not possible because of
differences in methodology, this datum suggests, at least qualita-
tively, a modification of Carrion Crows’ foraging tactics over time
and a progressive specialization in kleptoparasitism. If Rooks lack
the behavioral plasticity of Carrion Crows, they may have been
incapable of increasing the profitability of food theft as compared
with direct search on the refuse area.
Temporal Segregation of Species: The Role of Kleptoparasitism
How species coexist in sympatry has been the focus of inten-
sive research for decades (for a pioneering, influential paper, see
Hutchinson ), and habitat and diet appeared from the begin-
ning to be the most important niche dimensions along which spe-
cies segregate (Lack , Schoener ). A sampling of recent
literature (–; see Appendix) confirmed this view. Of 
studies on both vertebrate and invertebrate communities,  re-
port on spatial segregation of species, and  account for differ-
ences in diet or foraging behavior as mechanisms of coexistence.
Conversely, reports on temporal distributions of species, both
daily and seasonal, are uncommon ( studies of ) and seem even
rarer among terrestrial vertebrates ( studies of ). Nevertheless,
our data showed differences in the assemblage of corvids in the re-
fuse dump throughout the year and, remarkably, throughout the
day in winter, when all four species were abundant. In particular,
the daily activity patterns of Carrion Crows, which peaked late in
the morning, and European Magpies, which peaked in the early
afternoon, reduced the temporal overlapping of species on the
Previous studies have shown that kleptoparasitism can play
a role in shaping important behavioral patterns in birds—for
example, territorial behavior in Northern Harriers (Circus cya-
neus; Temeles ). An interesting question here is the extent
to which Carrion Crows’ kleptoparasitism, a form of direct com-
petition for resources, drove the observed winter daily patterns
of the corvid guild. Although both Rooks and Eurasian Jackdaws
11_Baglione_08-146.indd 572 7/20/09 6:06:30 PM
Ju l y 2009
Kl e p t o p a r a s i t i s m in sy m p a t r i C Co r V i d s
left the dump in the morning when Carrion Crows arrived, the
most parsimonious explanation of their daily cycle is that they
had satisfied the morning energetic demand and left to seek al-
ternative sources of food. Neither Rooks nor Eurasian Jackdaws
returned en masse to forage in the dump when Carrion Crows
had left. Furthermore, both species attended the dump in high
numbers and, therefore, diluted the risk of being robbed. Con-
versely, we suggest that European Magpies actively avoided klep-
toparasitism, especially by Carrion Crows, by shifting their peak
of activity toward the early afternoon. It may be argued that Eu-
ropean Magpies are the least likely to be attacked by Carrion
Crows (Fig. ) and that this weakens the avoidance hypothesis.
However, as in many species in which low rates of predation do
not necessarily imply that the actual risk of predation is low (Du-
rant ), the low frequency of Carrion Crows’ kleptoparasitic
attacks on European Magpies may indicate that the European
Magpies’ mechanism of avoidance is highly efficient, and not
that the level of competition is low. In this regard, it is interest-
ing to note the following. () In the afternoon peak, European
Magpies increased their foraging efficiency, engaging more in
handling potential food items and obtaining significantly more
food than in the morning. () Fewer European Magpies ()
were at the dump than other potential hosts of kleptoparasitism
and, therefore, they were less likely to dilute their risk of being
robbed; moreover, they are highly visible birds, they are subor-
dinate to Carrion Crows (Bossema et al. ), and they handled
rather large and visible food items while foraging at the dump,
which made them ideal hosts for kleptoparasites (Brockmann
and Barnard ). () As for Carrion Crows, the delay in arriv-
ing at the dump cannot be attributable to large roost-dump dis-
tan ces, beca use E uro pe an M ag pie usua ll y ro os ted nea r t he d um p
in winter (V. Baglione unpubl. data, P. Olea pers. comm.). And
most notably (), during spring and summer, when few Carrion
Crows were at the dump, the afternoon peak of abundance of Eu-
ropean Magpies disappeared and individuals attended the dump
more constantly throughout the day.
Our data suggest that kleptoparasitism has a role in shaping
the temporal distribution of corvids at the dump in winter, deter-
mining, on one hand, the delayed arrival of Carrion Crows in the
morning, to synchronize with their main hosts, and, on the other,
the peculiar afternoon peak of European Magpies that allowed
them to avoid aggression by kleptoparasites. Alternatively, Euro-
pean Magpies may have delayed their arrival to avoid competition
for hosts, given that they shared with Carrion Crows a preference
for starlings (Fig. ). However, the fact that European Magpies
decreased (though not significantly) the frequency of their klep-
to pa rasi tic atta ck s in the a ft erno on ( Fig . B ) se ems t o we ake n sup -
port for this hypothesis.
Although flexible adjustments of daily activity are common
among vertebrates (Beltrán and Delibes , Zalewski ) and
offer a potential immediate response to situations of direct com-
petition for resources, temporal segregation of species seems rare
among terrestrial vertebrates. e present study, however, sug-
gests that the temporal dimension of the niche can be important
in reducing species overlap and, to some extent, in preventing di-
rect competition. is mechanism may be more common than
previously thought, especially when species congregate on spa-
tially clumped food resources.
Ac k n o w l e d g M e n t s
We are grateful to D. C. Dearborn, J. J. Luque, J. Morand-Ferron,
and an anonymous reviewer for useful comments on the manu-
script and to Ayuntamiento of León for permission to work in the
refuse dump. e work was supported by the Spanish Ministry of
Education and Science (ref. CGL-/BOS), the “Ramón
y Cajal Program” (FEDER-FSE), and the Diputación de León (to
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. . Does
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S, W. K.,  P. A. R. H
. . Factors influencing rate
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ap p e n d i x . Review of 208 papers published between 1992 and 2007, returned by searching for “niche partitioning” or “species segregation” within the
kingdom Animalia in the Web of Knowledge (Thompson Reuters). Of those papers, 56 provided relevant information on the dimension of the niche
along which partitioning occurred. This appendix is not meant to be a comprehensive review of all works published on this topic, but rather a sample
to assess the relative importance of the different mechanisms of coexistence of species.
Orders and
families Species
Type of niche
(intraspecific vs.
Dimension of niche partitioning
ReferenceSpatial Temporal Diet
Rhabditida Scottnema lindsayae and
Plectus antarcticus
Interspecific ×Nkem et al. 2006
Araneae Six species of Araneidae
and Tetragnathidae
Interspecific ×Ward and Lubin 1992
Plecoptera Nine species Interspecific × × Smith et al. 2000
Five dominant species Interspecific ×Lockwood et al. 1996
Cicindela circumpicta
and C. togata
Interspecific ×Hoback et al. 2000
24 specie s Interspecific ×Verdú et al. 2006
38 species Interspecific ×Jordal 2006
24 specie s Interspecific ×Biesmeijer and Slaa 2006
Hymenoptera Nectar-feeding ant communities
(43 species)
Interspecific ×Blüthgen and Fiedler 2004
Hymenoptera Seven species Interspecific × × Albrecht and Gotelli 2001
Heteropsis ssp. Interspecific ×Monte-Alegre et al. 2005
Leptidea sinapis and L. reali Interspecific ×Amiet 2004
Izeniola obesula and
Stefaniola defoliata
Interspecific ×Dorchin 2006
Ceratitis catoirii, C. rosa,
C. Capitata, and
Bactrocera zonata
Interspecific ×Duyck et al. 2006
Diptera Seventeen families from
freshwater wetlands
Interspecific × × × × Keiper et al. 2002
Copepoda Large assemblage
of Scolecitrichidae
Interspecific ×Kuriyama and Nishida 2006
Copepoda Acartia clausi, Oithona
nana, Temora longicornis
and Euterpina acutifrons
Interspecific ×Guisande et al. 2002
Amphipoda Jassa falcata and J. marmorata Interspecific ×Karez and Ludynia 2003
(Continued )
Z, A.
. Seasonal and sexual variation in diel activ-
ity rhythms of Pine Marten Martes martes in the Białowieża
Nat ional Pa rk (Poland). Acta eriologica :–.
Z, R.,  J. M. G
. . Carnivorous plant–slug inter-
action: A trip from herbivory to kleptoparasitism. Journal of Ani-
ma l Ecol ogy :– .
11_Baglione_08-146.indd 576 7/20/09 6:06:34 PM
Ju l y 2009
Kl e p t o p a r a s i t i s m in sy m p a t r i C Co r V i d s
Orders and
families Species
Type of niche
(intraspecific vs.
Dimension of niche partitioning
ReferenceSpatial Temporal Diet
Perciformes Pomacentridae and Labridae Interspecific ×Floeter et al. 2007
Perciformes Siganus rivulatus and S. luridus Interspecific ×Lundberg et al. 2004
Perciformes Eight species of chiclids Interspecific × × Genner and Turner 2005
Salmoniformes Salvelinus namaycush Intraspecific × × Morbey et al. 2006
Salmoniformes Salvelinus malma and
S. leucomaenis
Interspecific ×Nakano et al. 1999
Large assemblage of species Interspecific × × Herder and Freyhof 2006
Squamata Bothrops jararaca Intraspecific ×Furtado et al. 2006
Squamata Laticauda colubrina Intraspecific ×Shine et al. 2002
Squamata Morelia spilota imbricata Intraspecific ×Pearson et al. 2002
Caudata Ambystoma ssp. Interspecific ×Brodman and Jaskula 2002
Caudata Triturus alpestris Intraspecific × × Denoël and Joly 2001
Anura Rana esculenta complex Mother species
vs hybrids
×Pagano et al. 2001
Procellariiformes Thalassarche chrysostoma
and T. melanophrys
Interspecific ×Arata et al. 2003
Anseriformes Clangula hyemalis, Melanitta
nigra, and Aythya marila
Interspecific × × Kondratyev 1992
and Gruiforme s
Anas strepera and Fulica
Interspecific ×McKnight and Hepp 1998
Four species Interspecific ×Abbasi and Yahya
unpublished data
Falconiformes Circus cyaneus and C. pygargus Interspecific × × Garcia and Arroyo 2005
Falconiformes Accipiter novaehollandiae and
A. fasciatus
Interspecific ×Burton and Olsen 2000
and Gaviformes
Uria aalge and Cerorhinca
Interspecific ×Lance and Thompson 2005
Coraciiformes Phoeniculus purpureus Intraspecific ×Radford and Du Plessis
Piciformes Dendrocopos major
and D. medius
Interspecific ×Kosi´nski and Winiecki 2004
Piciformes Dendrocopos medius Intraspecific ×Pasinelli 2000
Passeriformes Meliphaga ssp. Interspecific ×Norman et al. 2007
Passeriformes Zonotrichia albicollis Intraspecific ×Formica et al. 2004
Passeriformes Certhia familiaris Intraspecific ×Aho et al. 1997
Carnivora Lynx rufus Intraspecific ×McLean et al. 2005
Chiroptera Thre e species Interspecific × × Delaval et al. 2005
Primates Pygathrix nemaeus Intraspecific ×Workman and Covert 2005
Primates Callimico goeldii, Saguinus
labiatus, and S. fuscicollis
Interspecific ×Garber and Leigh 2001
Rodentia Apodemus argenteus
and A. speciosus
Interspecific ×Renaud and Millien 2001
Artiodactyla Odocoileus hemionus,
Cervus elaphus, and Bos taurus
Interspecific × × Stewart et al. 2003
Artiodactyla Cervus elaphus and
Odocoileus hemionus
Interspecific × × × Stewart et al. 2002, 2003
Artiodactyla Ourebia ourebi
and other ungulates
Interspecific ×Mduma and Sinclair 1994
Artiodactyla Fossil records of extinct
herbivore community
Interspecific ×MacFadden and
Higgins 2004
(Continued )
ap p e n d i x . Continued.
11_Baglione_08-146.indd 577 7/20/09 6:06:36 PM
Ba g l i o n e a n d Ca n e s t r a r i
au K , Vo l .
Orders and
families Species
Type of niche
(intraspecific vs.
Dimension of niche partitioning
ReferenceSpatial Temporal Diet
Diprotodontia Macropus eugenii and
M. parma
Interspecific ×Lentle et al. 2003
Mixed assemblage
and Coleoptera
Several species of Lycosidae,
Salticidae, and Carabidae
Interspecific ×Baldridge and Moran 2001
Fishes and
Sixteen fish species and four
invertebrate species
Interspecific × × Attrill and Power 2004
ap p e n d i x . Continued.
11_Baglione_08-146.indd 578 7/20/09 6:06:36 PM
... Corvids have a long history of being hunted by people (F. Coombs, 1978), and are often persecuted as farm pests (e.g. in the UK; Henderson, 2002) and for frequenting refuse dumps (Baglione & Canestrari, 2009;Baxter & Robinson, 2007). Seven of the eight species of UK corvid-the exception being the red-billed chough (Pyrrhocorax pyrrhocorax)-are widespread across Britain despite the large anthropogenic changes that characterize the UK landscape. ...
... Whether or not this designation actually helps farmland is debatable because evidence from Cyprus suggests that the presence of corvids could benefit agriculture when they eat crop damaging insects (Hadjisterkotis, 2003). Jackdaws are often found foraging with rooks out in open fields (Lockie, 1956), and even in heavily degraded habitats such as landfills (Baglione & Canestrari, 2009). Foraging flocks in suburban areas tend to be smaller than those on rural farmland (Jadczyk, 2009). ...
Full-text available
Neophobia, or the fear of novelty, is thought to restrict animals’ ecological niches and hinder their propensity for innovation; two processes that should limit behavioural adjustment to human-induced changes in the environment. However, birds within the corvid family ($\textit{Corvidae}$) defy this trend by being highly neophobic, yet highly successful alongside humans across diverse habitats. This thesis examines the causes and ecological consequences of neophobia to unravel corvids’ puzzling neophobic tendencies. Throughout the thesis I find evidence that corvids are very neophobic, but that individuals differ in their level of novelty avoidance. Neophobia is not a fixed trait across time and towards all types of novelty. Neophobia levels differ depending on the type of novel stimuli being presented, and individuals can be inconsistent when environments change seasonally (Chapter Three). Although individual differences in neophobia are expected to be associated with fitness outcomes, I found no direct connections between neophobia, reproductive success or offspring stress hormone expression (Chapter Four). Moreover, if neophobia levels were defined by human presence, populations should differ in their novelty avoidance according to their proximity to humans. However, corvids show similar patterns of object neophobia between urban and rural areas (Chapter Five). The lack of connection between neophobia, fitness, and urbanization indicates that corvids might be able to circumvent individual differences in neophobia that might otherwise restrict behavioural adjustment. Accordingly, experience observing conspecifics consume novel foods and approach threatening objects encourages individual risk-taking, such that highly neophobic individuals could benefit from social information (Chapter Six). I therefore propose that corvids’ flexibility and their success alongside humans may be due to their ability to overcome their fear through learning. How animals make decisions in the face of ecological novelty may predict whether they behaviourally adjust to human-altered habitats and is relevant in the wider context of species conservation.
... As such, although fruits and seeds are available at all hours, Passerines begin activity at dawn when there is sufficient light to detect their food resources (Roth and Lima 2007). Temporal segregation of foraging can also be driven by pressures to avoid predators or kleptoparasites (Baglione and Canestrari 2009), such as frigatebirds. Such adaptive behavior is thought to have contributed to the evolution of nocturnal foraging behavior by some pelagic species (Hailman 1964). ...
Timing of activity can reveal an organism's efforts to optimize foraging either by minimizing energy loss through passive movement or by maximizing energetic gain through foraging. Here, we assess whether signals of either of these strategies are detectable in the timing of activity of daily, local movements by birds. We compare the similarities of timing of movement activity among species using six temporal variables: start of activity relative to sunrise, end of activity relative to sunset, relative speed at midday, number of movement bouts, bout duration, and proportion of active daytime hours. We test for the influence of flight mode and foraging habitat on the timing of movement activity across avian guilds. We used 64570 days of GPS movement data collected between 2002 and 2019 for local (non‐migratory) movements of 991 birds from 49 species, representing 14 orders. Dissimilarity among daily activity patterns was best explained by flight mode. Terrestrial soaring birds began activity later and stopped activity earlier than pelagic soaring or flapping birds. Broad‐scale foraging habitat explained less of the clustering patterns because of divergent timing of active periods of pelagic surface and diving foragers. Among pelagic birds, surface foragers were active throughout the day while diving foragers matched their active hours more closely to daylight hours. Pelagic surface foragers also had the greatest daily foraging distances, which was consistent with their daytime activity patterns. This study demonstrates that flight mode and foraging habitat influence temporal patterns of daily movement activity of birds.
... Depending on the species' foraging ecology, scrounging can take different forms (Giraldeau & Caraco, 2000), from exploiting a food patch found by others to directly stealing food from others. Hereby, kleptoparasitism commonly refers to those cases where individuals use force, or threat of force, to obtain the food from others (Baglione & Canestrari, 2009), whereas pilfering refers to those cases where food is stolen out of another individual's cache and physical interactions between cache owner and thief are avoided (Emery & Clayton, 2001; but see Giraldeau & Caraco, 2000 for a slightly different terminology). Game theoretical models have been successfully used to understand the conditions under which individuals adopt producer or scrounger roles (Afshar & Giraldeau, 2014;Giraldeau & Caraco, 2000). ...
Full-text available
Social foraging provides several benefits for individuals but also bears the potential costs of higher competition. In some species, such competition arises through kleptoparasitism, that is when an animal takes food which was caught or collected by a member of its social group. Except in the context of caching, few studies have investigated how individuals avoid kleptoparasitism, which could be based on physical strength/dominance but also cognitive skills. Here, we investigated the foraging success of wild common ravens, Corvus corax, experiencing high levels of kleptoparasitism from conspecifics when snatching food from the daily feedings of captive wild boars in a game park in the Austrian Alps. Success in keeping the food depended mainly on the individuals’ age class and was positively correlated with the time to make a decision in whether to fly off with food or consume it on site. While the effect of age class suggests that dominant and/or experienced individuals are better in avoiding kleptoparasitism, the effect of decision time indicates that individuals benefit from applying cognition to such decision‐making, independently of age class. We discuss our findings in the context of the ecological and social intelligence hypotheses referring to the development of cognitive abilities. We conclude that investigating which factors underline kleptoparasitism avoidance is a promising scenario to test specific predictions derived from these hypotheses.
... Opvallend is het frequente bezoek aan de nabijgelegen vuilnisbelt tijdens de derde tijdsperiode. Foerageren op vuilnisbelten twee weken na het broedseizoen werd ook vastgesteld door Baglione & Canestrari (2009) ongeschikter raken van de andere foerageerplekken, daar Roeken in het algemeen korte vegetaties als gras prefereren (Whittingham & Devereux 2008). In het laatste tijdvak werden meer bezoeken gebracht aan een kersenboomgaard die eerder alleen sporadisch werd aangedaan. ...
Full-text available
To study space and habitat use of urban Rooks, we tracked an adult breeding bird using a GPS-logger. The bird was caught at a colony in the city of Utrecht, the Netherlands, just before its young fledged. With chicks still in the nest, the bird had a relatively small home range, moving only up to 500 m from the colony. It mainly foraged on a grass field next to the colony and some undeveloped fallow land within the city. In June, after the young had fledged, the home range gradually became bigger, and the bird started to forage on more distant sites such as a cherry orchard at about 1 km from the nest and a rubbish dump at 2.5 km from the nest. In the meantime, the breeding colony was visited less and less often, and the bird started to roost outside the colony. Around the 10th of June it abandoned the (vicinity of the) colony and moved to an agricultural grassland area south of the colony. Thus, despite the fact that the bird bred in the city, it ultimately switched to agricultural habitats, showing that these urban Rooks do not complete their annual cycle within the city itself. During the fledging period the bird visited three existing Rook colonies near its colony of origin, likely together with its young. This suggests that the different rookeries in the area act as one metapopulation.
... The difference in the preferential colour suggests that an animal judge the edibility and novelty of the food by observing the feeding behaviour of conspecifics. Social learning in animals is supposed to either avoid risky substances or newer food resources, but results suggest that avian social learning is fundamentally different from other corvids as wells as other taxa (Baglione and Canestrari, 2009). ...
Full-text available
We observed the feeding and behavioural ecology of birds and small mammals in their natural habitat. Experiments were carried out to check the preference of foods items by the animals based on the nutritional quality of the given food that are rich in carbohydrate and/or protein. The passerine birds such as babblers and myna showed greater affinity towards the carbohydrate rich food rewards; whereas, corvids and mongooses showed greater affinity towards the protein rich rewards. Moreover, the experiment was tested to know whether olfaction plays any role in the food localization among birds and mammals. In order to test this objective, proteinaceous food with odour and without odour were provided in the experimental feeding site. Interestingly, mongooses responded to the proteinaceous food availed with odour whereas corvids responded to both. There was significant variation in response among birds and animals between the protein and carbohydrate rich rewards (t = 2.73, df = 18, p = 0.014), and also between protein rewards with and without odour (t = 2.67, df = 21, p = 0.014). Hence, it is most likely to conclude that olfaction plays a vital role among the mongooses in food localization; whereas, corvids depend on visual cues rather than the olfactory cues for the food localization.
... In a study in Italy, inter-specific interactions between corvid species were a potential factor in ecological segregation of both foraging and resting behavior (Rolando and Giachello, 1992). Further, Baglione and Canestrari (2009) Further, corvids are often also involved in nesting associations Ueta, 2000), and the influence of these behavioral characteristics on foraging when nests are associated has not been measured. ...
Full-text available
One goal of community ecology is to examine proximate and ultimate factors driving interactions between species. Part of this work addresses breeding bird aggregations, termed nesting associations. I evaluated costs and benefits of nesting along an association gradient in smaller black-billed magpies (Pica hudsonia) and larger American crows (Corvus brachyrhynchos) over two nesting seasons in Jackson, Wyoming. Specifically, I explored mechanisms of proximate protective benefits gained by magpies nesting nearer crows, along with foraging costs of associating with crow competitors. I also evaluated ultimate influences of association on nesting success for crows and magpies. Protection can operate under two non-exclusive proximate mechanisms, termed predator exclusion and information transfer. I found both mechanisms influenced nest protection for magpies. Crows performed more defensive behaviors at magpie nests nearer their own nests, and magpies responded to crow defensive signals. However, I did not find fitness benefits for magpies related to nesting nearer or farther from crows. I also explored the competitive foraging costs of heterospecific nesting associations by quantifying resource discovery behaviors and providing novel resource extraction problems to crows and magpies. Crows and magpies behaviors differed related to resource 196 extraction problems such that magpies were less neophobic than crows. However, magpies paid a cost, measured as higher food losses to kleptoparasitism, for nesting nearer to crows. Further, crows came to dominate shared resources initially discovered by magpies. These results highlight potential foraging benefits to crows for associating with magpies. Despite these proximate benefits, crows also did not have greater nesting success when nesting nearer to magpies. Crows also experienced proximate costs to associating, measured as increased defensive behaviors and longer latencies to complete more complex resource extraction problems when nearer to magpies. I found that crow nesting success was related to success of associated conspecifics, but was not related to the number of defenders participating in nest defense. In my study system of crows and magpies, both species experienced benefits and costs to nesting nearer a heterospecific associate. However, costs and benefits may balance each other out such that there is no observable difference in fitness for either species based on association.
... Firstly, the relative kleptoparasite pressure on host individuals, which as stated above was expected to be synonymous with the number of kleptoparasite individuals per host. Secondly, the timing of when, both within a day and a season, the host foraging attempt occurs, may aff ect the relative value of the food item for both the forager and kleptoparasite (Baglione and Canestrari 2009). Animal foraging decisions are known to be sensitive to seasonal changes in food quantity, quality and exploitation costs (Wood et al. 2013). ...
Kleptoparasitism involves the theft of resources such as food items from one individual by another. Such food-stealing behaviour can have important consequences for birds, in terms of individual fitness and population sizes. In order to understand avian host–kleptoparasite interactions, studies are needed which identify the factors which modulate the risk of kleptoparasitism. In temperate European intertidal areas, Eurasian oystercatchers Haematopus ostralegus feed primarily on bivalve molluscs, which may be stolen by kleptoparasitic species such as carrion crows Corvus corone and herring gulls Larus argentatus. In this study we combined overwinter foraging observations of oystercatchers and their kleptoparasites on the Exe Estuary, UK, with statistical modelling to identify the factors that influence the likelihood of successful food stealing behaviour occurring. Across the winter, 16.4% of oystercatcher foraging attempts ended in successful kleptoparasitism; the risk of theft was lowest in February (10.8%) and highest in December (36.3%). Using an information theoretic approach to compare multiple logistic regression models we present evidence that the outcome of host foraging attempts varied with the number of kleptoparasites per host within the foraging patch for two out of five individual months, and for all months grouped. Successful, kleptoparasitism was more likely to occur when the total number of all kleptoparasites per host was greater. Across the entire winter study period, oystercatcher foraging attempts that resulted in kleptoparasitism were associated with a mean number of kleptoparasites per host that was more than double that for foraging attempts that ended in the oystercatcher successfully consuming the mussel. Conversely, the stage of the tidal cycle within the estuary did not affect the outcome of oystercatcher foraging attempts. Our study provides evidence that bird numbers influence the risk of kleptoparasitism within avian assemblages.
Timing of activity can reveal an organism's efforts to optimize foraging either by minimizing energy loss through passive movement or by maximizing energetic gain through foraging. Here, we assess whether signals of either of these strategies are detectable in the timing of activity of daily, local movements by birds. We compare the similarities of timing of movement activity among species using six temporal variables: start of activity relative to sunrise, end of activity relative to sunset, relative speed at midday, number of movement bouts, bout duration, and proportion of active daytime hours. We test for the influence of flight mode and foraging habitat on the timing of movement activity across avian guilds. We used 64570 days of GPS movement data collected between 2002 and 2019 for local (non‐migratory) movements of 991 birds from 49 species, representing 14 orders. Dissimilarity among daily activity patterns was best explained by flight mode. Terrestrial soaring birds began activity later and stopped activity earlier than pelagic soaring or flapping birds. Broad‐scale foraging habitat explained less of the clustering patterns because of divergent timing of active periods of pelagic surface and diving foragers. Among pelagic birds, surface foragers were active throughout the day while diving foragers matched their active hours more closely to daylight hours. Pelagic surface foragers also had the greatest daily foraging distances, which was consistent with their daytime activity patterns. This study demonstrates that flight mode and foraging habitat influence temporal patterns of daily movement activity of birds. This article is protected by copyright. All rights reserved.
Full-text available
Behavioural plasticity is believed to reduce species vulnerability to extinction, yet global evidence supporting this hypothesis is lacking. We address this gap by quantifying the extent to which birds are observed behaving in novel ways to obtain food in the wild; based on a unique dataset of >3,800 novel behaviours, we show that species with a higher propensity to innovate are at a lower risk of global extinction and are more likely to have increasing or stable populations than less innovative birds. These results mainly reflect a higher tolerance of innovative species to habitat destruction, the main threat for birds. Bird species with a higher propensity towards innovative behaviours are at a lower risk of global extinction and are more likely to have increasing or stable populations than less innovative birds
Conference Paper
Exact absorbing and periodic boundary conditions allow to truncate grating problems' infinite physical domains without introducing any errors. This work presents exact absorbing boundary conditions for 3D diffraction gratings and describes their discretization within a high-order time-domain discontinuous Galerkin finite element method (TD-DG-FEM). The error introduced by the boundary condition discretization matches that of the TD-DG-FEM; this results in an optimal solver in terms of accuracy and computation time. Numerical results demonstrate the superiority of this solver over TD-DG-FEM with perfectly matched layers (PML)-based domain truncation.
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Two medium-sized woodland hawks, the Grey Goshawk Accipiter novaehollandiae and the Brown Goshawk Accipiter fasciatus, are sympatric in the Australian wet tropics. Because females are considerably larger than males, the two species and sexes form a four-member guild. Typically, when similar raptor species occur together they partition resources. Radio-tracking was used to study habitat use and composition, and interactions between the Australian goshawks. Sample sizes were small and there was considerable individual variation. Nevertheless, there was evidence of niche partitioning according to home range size and overlap, habitat composition and habitat use. In general, both species frequented forests or woodlands and adjacent open country. Consistent with morphological, dietary and hunting differences, Grey Goshawks, especially the males, frequented closed forest types and Brown Goshawks more open habitats of woodlands, crops and edges. In the non-breeding season, females ranged widely and their ranges overlapped both inter- and intra-specifically, whereas those of males of each species tended not to overlap with males and females of either species. In the breeding season, home range overlap declined markedly between neighbouring pairs of the two species, and there was no overlap between the females. The two species have relatively small home ranges, attributable to their rich habitat. In turn, this may facilitate co-existence of two such similar-sized accipiters. Nevertheless, there was evidence of competition between the two most similar-sized members of the guild, the male Grey Goshawk and the female Brown Goshawk.
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Hen Harriers Circus cyaneus and Montagu's Harriers Circus pygargus are medium-sized raptors that differ in size (Hen Harrier being slightly bigger than Montagu's Harrier) and breeding system (Montagu's Harriers are semi-colonial and Hen Harriers defend nesting-hunting territories). In contrast, the diets of the two species when in sympatry are very similar. We evaluated food-niche differentiation among these coexisting raptor species and how between-species differences in body size and social system influence interspecific relationships. We present data from a study conducted in 1997 and 1998 in northeastern Madrid province (central Spain). Diet of the two species largely overlapped (55-95%) during the breeding season, but Hen Harriers preyed more often on larger species. This segregation was observed both in the average size of the primary prey (lagomorphs) and in the alternative prey (birds for Hen Harriers vs. insects for Montagu's Harriers), and was particularly apparent late in the season. Accordingly, feeding frequency of Montagu's Harriers, but not of Hen Harriers, increased later in the season. Size differences between species in prey brought to the nest were apparent for both males and females. Foraging behaviour also differed, as Hen Harriers spent more time hunting close to the nest than did Montagu's Harriers. This implies that segregation in foraging areas may also exist. Observed niche partitioning may relax the potential for competition between these species.
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Behavior is an important factor affecting competitive and predatory interactions among species. We investigated how the behavior of common arthropod predators in old-fields may affect coexistence of this diverse group of organisms. Through pitfall trapping, we found that different taxonomic groups varied their peak activities, possibly to avoid activities of other species. However, the major determinant of activity level appeared to be size, not taxonomic affiliation. Small predators, which are more vulnerable to intraguild predation, were most active when larger predators were not. Field experiments on some of the more common species (the lycosid spiders Rabidosa rabida, R. punctulata, Salticid spiders, and the omnivorous beetle Harpalus sp.) indicated that arthropod emigration rates were affected by the presence of other species. Potentially competing species had higher emigration rates when placed in plots together. When smaller predators, that could also be potential prey, were placed with larger predators, the larger predators reduced their emigration rates, because the increase in availability of food (i.e., the smaller predators) apparently outweighed any competitive effect between species. These experiments indicate that behavior can be an important component of predatory interactions. We suggest that behavioral adjustments can facilitate coexistence of predatory species, and are especially important in arthropod communities in which numerous species have overlapping resource use.
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We studied nest-site selection of the Great- and Middle Spotted Woodpecker inhabiting the riverine forest remnants of Central Poland. In addition to nest tree characteristics and location in relation to edge proximity, a comparison between nesting and random sites within the woodpeckers' territories allowed a study of the importance of stand structure on nest tree selection. Unlike the Great Spotted Woodpecker, we found that the Middle Spotted Woodpecker showed an affinity to nest near forest edges. Both species excavated nest holes within trees with a diameter at breast height larger than the diameter of available trees suitable for hole-excavation. Trees with the presence of former woodpecker holes, polyporous fungi and limb holes were highly selected, with nest chambers commonly built in dead parts of the trees (74% and 90% of nests of Great- and Middle Spotted Woodpeckers, respectively). Both the Great- and Middle Spotted Woodpeckers nested more often in trunks than in limbs, with the former species favouring live oaks and alders and the latter snags. Vegetation immediately surrounding nest trees had probably a low influence on species nest-site selection. The nest tree was, in the majority of cases, the only tree suitable for hole-excavation in the nest site. Our results suggest that gap-phase dynamics and the presence of old and dead deciduous standing trees are key components of habitat quality for breeding woodpeckers, particularly for the declining Middle Spotted Woodpecker.
Irish streams have fewer macroinvertebrate species than those of continental Europe, and thus offer useful natural models for the study of community patterns and processes. Plecoptera distribution and spatial overlap amongst species were examined across 15 sites in the River Araglin Catchment Study Area in south west Ireland over a three-year period; the larval life histories and temporal overlap of nine species were examined in detail at two of the sites over twelve months. Chloroperla tripunctata took two years to complete larval growth, whilst all of the other species - Siphonoperla torrentium, Isoperla grammatica, Leuctra fusca, L. inermis, L. hippopus, Protonemura meyeri, Amphinemura sulcicollis and Brachyptera risi - were univoltine. Three additional species occur in the Araglin catchment but not at either of the two intensively-studied sites - Nemurella pictetii, Nemoura cambrica (in smallest streams) and Perla bipunctata (in the main river). Apparent temporal segregation between closely related Plecoptera has been reported by others, and two cases were examined in detail in this study. The overlap of observed seasonal growth patterns in three Leuctra species was lower than most simulated overlaps based on alternative model permutations of their respective seasonal distributions; under the rather conservative model used, provenance of the low overlap by chance (p <0.05) could not be rejected. Temporal segregation of larval growth amongst two Chloroperlidae species was also compelling visually but this arose from their differing voltinism, rather than the absolute timing of their specific larval growth periods. An inverse correlation between temporal and spatial overlap of the detritivorous species might be expected if species with contemporaneous growth patterns were competing for similar resources. At the spatial scale of typical benthic samples and at the catchment scale examined here, however, no such relationship was found.
Females of the subsocial shield bug Parastrachia japonensis Scott progressively provision nymph-containing nests with drupes of the single host tree Schoepfia jasminodora Sieb. et Zull. The resource is unreliable and typically poor, and females invest considerable time in searching for suitable drupes. Earlier observations have indicated that although some females nest under the host tree, most prefer to nest far from the food source, despite the difficulty involved in transporting drupes to a distant nest. Because we have observed females stealing drupes from other females' nests, we considered that kleptoparasitism might be a factor in determining nest site preference. A manipulated field study was carried out to clarify the prevalence of kleptoparasitism in nests close to and far from the host tree and to determine how these factors affect nest success. Surprisingly, in the year of this study, when drupes were particularly scarce, more drupes were stolen, but females still collected significantly more drupes and had greater nest success, in nests located under the host tree than in those that were 5 m away. The ecological factors relevant to kleptoparasitism and nest site choice are discussed.
Common Murres (Uria aalge; hereafter “murres“) and Rhinoceros Auklets (Cerorhinca monocerata; hereafter “auklets“) breed and forage sympatrically over much of their range. They have similar diets during the breeding season, which suggests that they partition prey during the breeding season by foraging (1) at different locations, (2) at different times of day, (3) at different water depths, (4) on different proportions of the same prey species, or (5) some combination of the four. We examined possible mechanisms of niche partitioning during late summer and fall in Puget Sound, Washington, in 1993-1996. Murres and auklets fed mainly on Pacific herring (Clupea pallasii, occurring in 74.2% and 48.1%, respectively, of gastrointestinal tracts with contents), Pacific sand lance (Ammodytes hexapterus; 45.8% and 62.3%), and salmonid (Oncorhynchus spp.) species (21.9% and 9.7%). Auklets also consumed considerable amounts of threespine stickleback (Gasterosteus aculeatus; 26.6%). Murres and auklets did not differ significantly (1) in their diet (between age classes or sexes of either species, or among years); (2) in mean lengths of Pacific herring (101 and 109 mm, respectively) and Pacific sand lance (82 and 86 mm) they consumed; or (3) in the mean depth (7–8 m) at which they were entangled in gill nets. Dietary diversity was low, with most gastrointestinal tracts containing only one or two prey species in both murres and auklets. Murres were caught and therefore presumably feed more frequently in the afternoon and evening; whereas auklets were entangled more often in early morning. We found differences between murres and auklets in the diel chronology of prey taken, which may partly explain how murres and auklets coexist during the breeding season and months thereafter, prior to auklet emigration from Puget Sound. Chevauchement du Régime Alimentaire et de la Quête Alimentaire chez Uria aalge et Cerorhinca monocerata après la Saison de Reproduction
The ecology of two sibling-species of Pieridae, Leptidea sinapis and L. reali, has been studied from 1997 to 2002 in a 70 x 60 km area the centre of which is Nyons (department of Drôme). L. sinapis and/or L. reali have been found in 347 localities. L. sinapis was alone in 55% of these localities, and L. reali in 22%, whereas both species were found together in 23% of them. This relatively low degree of syntopy is mainly the result of different vertical distributions. L. sinapis is spread from the lowest to the highest elevations of the studied area, whereas L. reali is lacking in the Mediterranean zone and, more generally, in driest habitats. Ovipositions of 34 sinapis females and 33 reali females have been observed. The plant-host choice is clearly different: females of L. sinapis may oviposite on several species of Fabaceae, mainly Dorycnium spp. at low altitude and Lotus spp. and Lathyrus pratensis above 800-1,000 m. On the contrary, females of L. reali lay their eggs only on Lathyrus pratensis. Ecology of these host-plants is briefly described. Syntopy/allotopy and vertical distribution of both L. sinapis and L. reali appear to be closely related to the availability of their host-plants. In the studied area, observations "in natura" show that L. sinapis and L. reali are ecologically well differentiated. This result does not agree with experimental evidence obtained in Germany with captive individuals. This discrepancy is discussed. It may be due to methodological differences or, more probably, to geographic variation in the female host-plant specialisation.