Joan Bertran

Estación Biológica de Doñana, Hispalis, Andalusia, Spain

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Publications (25)32.86 Total impact

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    ABSTRACT: We compared methods of assessing the diet of the bearded vulture (Gypaetus barbatus) during the nestling period in the Pyrenees, northeast Spain. We determined diet from direct observations of food items delivered to the nest, recent prey remains present in the nest, remains collected in the nests after fledging, and remains collected in the ossuaries (bone-breaking sites). Data suggest that direct observation (food items delivered and recent prey remains present in the nest) is the only valid method of assessing the bearded vulture's diet accurately. Remains overestimated the presence of large mammals, such as cows (Bos taurus) and horses (Equus caballus), Suidae, and birds; delivered samples contained a higher proportion of small mammals, medium-sized mammals, micromammals, and reptiles. Ossuaries also differed from delivered samples because remains collected there overestimated large and medium-sized mammals. Concerning the skeletal parts, ossuaries, compared to all other methods, underestimated extremities and overestimated long bones, such as femur, humeri and tibiae, scapulae, vertebrae, and skulls. Remains samples, which overestimated scapulae, also differed from delivered and present samples. Our results suggest that bearded vultures favor extremities of prey (78% of the mammal remains, which make up 95% of the diet). The prevalence of small carcasses (almost 17%) suggests that vultures select small animals for food for the young. Because food quality may influence breeding success, future conservation projects based on the selective provision of food to breeding pairs should add to food stations meat remains and small carcasses consistent with our assessment of the birds’ dietary needs.
    Journal of Wildlife Management 12/2010; 71(5):1621 - 1625. · 1.64 Impact Factor
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    ABSTRACT: From 2000–2008 we used transmitting video cameras to document the breeding biology of the endangered Bearded Vulture in the Pyrenees (NE Spain), focusing the study on sibling aggression. Our goals were to study the feasibility of rescuing second-hatched chicks for conservation purposes in this species that shows obligate brood reduction. The age at which the second chick died varied between 4 and 9 days (n 5 5). Prey items delivered per hour were not related to the survival time of the second chick or the aggressiveness of the first-hatched chick towards their sibling. Although sibling aggression generally began on day 1 after hatching, in two nests supplemented with food, aggression was delayed until the second and third day after hatching and the second chick survived for nine days. Our results on the death of the second chick and the test involving the rescuing of a second-hatched chick aged five days, suggest that the recommended age for intervention should be between 3 and 6 days, with 4–5 days probably being the optimal age for the rescue.
    Bird Conservation International 01/2010; 20:55-61. · 1.07 Impact Factor
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    Antoni Margalida, Joan Bertran
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    ABSTRACT: We examined copulation patterns and associated sexual behaviour in the colonial Eurasian Griffon vulture Gyps fulvus during the pre-laying period. Eurasian Griffon vulture pairs conducted an average of 71.7 copulation attempts per clutch, with an average copulation frequency of 1.2 copulation attempts per day. Low copulation frequencies compared to other raptors and absence of mate-guarding suggest that this species does not possess adaptive behaviour aimed at increasing paternity assurance. However, the gradual increase in copulations during the fertile period is consistent with the sperm competition hypothesis.
    Journal of Ethology 01/2010; 28(1):179-182. · 1.00 Impact Factor
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    ABSTRACT: Social behaviour in species forced to form atypical breeding coalitions is poorly documented. The saturation of optimum territories in the Bearded vulture Gypaetus barbatus population in the Pyrenees has led floating males to settle in already occupied territories, thereby forming polyandrous trios. We examined the patterns of intrasexual aggression in five trios (nine reproductive events in total) during courtship. Alpha males initiated 82% of agonistic encounters that were mainly aimed at preventing or disrupting copulations. During the fertile period in recently formed groups, intrasexual aggression had a negative influence on the frequency of heterosexual copulations, which may be a contributing factor to the lower productivity of polyandrous trios. Females rejected a higher proportion of beta male- than alpha male-initiated copulations, and rejected copulations with both alpha and beta males more often when the other male was present close by. These results indicate that alpha males cannot effectively prevent all copulation attempts by beta males and that females avoid harassment by minimizing sexual activity when both males are present. Aggression between males decreased with time, occurring less often in established than in recent trios, despite the fact that the frequency of heterosexual copulations – the cause of conflicts – was similar. The frequency of homosexual interactions tended to increase in established trios, suggesting that this behaviour may help to regulate aggression within these groups, although no significant relationship between homosexual interactions and aggression was found. In summary, reproductive conflicts in trios seem to be unavoidable, although they tend to decrease if the group is maintained. This suggests that, for birds in these groups, the maintenance of a quality territory is more important than solving sexual conflicts.
    Ethology 04/2009; 115(5):429 - 438. · 1.95 Impact Factor
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    ABSTRACT: The Bearded Vulture Gypaetus barbatus population in the Pyrenees is managed using feeding stations to increase breeding success and reduce mortality in the pre-adult population. Nevertheless, very little quantitative and qualitative information has been published on such basic aspects of the species’ ecology as feeding habits and dietary preferences. This study investigated both aspects through direct and unbiased observation of breeding Bearded Vultures during the chick-rearing period. Bearded Vulture diet comprises mammals (93%), birds (6%) and reptiles (1%), with medium-sized ungulates (mainly sheep/goats) the most important species in the diet (61%, n = 677). Prey items were not selected in proportion to their availability, with the remains of larger species (cows and horses) being avoided, probably due to the variable cost/benefit ratios in handling efficiency, ingestion process and transport. There is no relationship between the proportion of sheep limbs in the diet and the proximity of feeding stations, suggesting that these sites are probably less important for breeding adults than for the pre-adult population. On the other hand, diet specificity seems related to productivity, with territories with greater trophic breadth being those with higher fecundity. Bearded Vultures prefer to eat limbs, although meat remains (provided principally by small mammals) can play an important role in guaranteeing breeding success during the first few weeks after hatching. The management of carrion provided by animals that die naturally in extensive livestock practices and the remains of wild ungulates which have died naturally or by human hunting, are important conservation tools for the Bearded Vulture and other carrion-eating species.
    Ibis 03/2009; 151(2):235 - 243. · 2.36 Impact Factor
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    ABSTRACT: The social organization of a population is the consequence of the decisions made by individuals to maximize their fitness, so differences in social systems may arise from differences in ecological conditions. Here, we show how a long-lived species that used to breed monogamously, and at low densities, can change its mating system in response to habitat saturation. We found that a significant proportion of unpaired birds become potential breeders by entering high-quality territories, or by forming polyandrous trios as a strategy to increase their individual performance. However, productivity of territories was reduced when those occupied by breeding pairs changed to trios, suggesting that the third individual was costly. The decision of some individuals to enter into breeding trios as subordinates also had clear negative consequences to population demography. This unusual mating behaviour is thus compromising the conservation effort directed to this endangered species; management to encourage floaters to settle in other suitable but unoccupied areas may be beneficial.
    Biology letters 01/2007; 2(4):624-7. · 3.35 Impact Factor
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    ABSTRACT: ABSTRACT We designed a system of solar-powered video cameras that transmitted images via telemetry to a monitor. This system allowed us to study the breeding behavior of the Bearded Vulture (Gypaetus barbatus) in the Pyrenees (northeastern Spain). From 2000 to 2004, 12 nests in seven territories were equipped with video cameras. To avoid disturbing the birds, equipment was installed 3–8 weeks before egg-laying. The acceptance rate was 75%. No decline in productivity was observed for nests monitored with video cameras compared to control nests. The cameras enabled us to document egg-laying, hatching asynchrony, the nestlings' diet, and the parents' breeding behavior from distances of 2–3 km, although technical problems temporarily interrupted the transmission of images. Video cameras can be used successfully to study the Bearded Vultures, and probably other cliff-nesting raptors, without reducing productivity.SINOPSISDiseñamos un sistema de cámaras de vídeo alimentado por energía solar que transmite imágenes por telemetría a un monitor. Este sistema permitió estudiar el comportamiento reproductor del Quebrantahuesos (Gypaetus barbatus) en los Pirineos (NE España). Durante el periodo de 2000–2004 se equiparon con cámaras de video 12 nidos en siete territorios. Los equipos se instalaron entre 3 y 8 semanas antes de la puesta, para reducir las molestias a las aves. El éxito de aceptación fue del 75%. No se observó un descenso en la productividad de los nidos estudiados con las cámaras con respecto a los no equipados con dicho sistema. El sistema permitió documentar a una distancia de 2–3 kms, la asincronía de puesta y eclosión, la dieta del pollo y el comportamiento de los adultos en el nido, aunque se detectaron algunos problemas técnicos que temporalmente interrumpieron la emisión de las imágenes. Las cámaras de vídeo pueden ser utilizadas para estudiar a otras aves rupícolas sin afectar la productividad.
    Journal of Field Ornithology 02/2006; 77(1):7 - 12. · 1.10 Impact Factor
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    Journal of Raptor Research 01/2006; 40:159-163. · 0.73 Impact Factor
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    Joan Bertran, Antoni Margalida
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    ABSTRACT: We present the first report of reverse mounting in the Bearded Vulture (Gypaetus barbatus). The reverse mounting, which occurred in the Pyrenees of northeastern Spain, took place between the female and the alpha male in a polyandrous trio. The function of reverse mountings is discussed in relation to the previously reported high frequency of male-male mountings in this raptor species.
    The Wilson Journal of Ornithology 01/2006; · 0.52 Impact Factor
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    Antoni Margalida, Joan Bertran
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    ABSTRACT: We present the frequency and duration of prolonged incubation in the Bearded Vulture and test different hypotheses on the possible adaptive significance of this behaviour. The mean and median prolonged incubation lasted 29 and 25 days respectively (n = 10), i.e., 54% and 46% respectively longer than the average incubation period. There was a negative correlation between the duration of prolonged incubation and the egg-laying date: prolonged incubation lasted longer in earlier clutches than in later ones, and territories with many breeding attempts showed short incubation prolongations. On the other hand, no correlation was found between the duration of prolonged incubation and productivity or breeding success. The results suggest that more experienced birds, which occupy higher quality territories and lay their eggs earlier, prolonged their incubation to a greater extent. Although prolonged incubation may constitute an example of adaptive behaviour, the extensive periods documented in some cases do not appear to support this assumption.
    Acta Ornithologica 01/2006; · 1.68 Impact Factor
  • Antoni Margalida, Joan Bertran
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    ABSTRACT: Territoriality and agonistic behaviour against conspecifics and heterospecifics was recorded for nine breeding pairs of bearded vulture Gypaetus barbatus between 1992 and 1996 in the Pyrenees (NE Spain). For both sexes, the defence intensity increased from the pre-laying to the chick-rearing period. The intensity of nest defence was significantly higher in males during the pre-laying period but no sex differences were found during the incubation and chick-rearing periods. Competition for nest sites, food and the potential risk of predation may affect the bearded vulture's nest defence behaviour towards other species. Most agonistic interactions took place against Eurasian griffon vultures (the most abundant species and the most important competing for nest sites) and common ravens (the most likely potential predator and a kleptoparasitic species). Nest defence against conspecifics mainly took place during the pre-laying period and may be linked to sperm competition and food resource competition.
    Ethology Ecology and Evolution 01/2005; · 1.12 Impact Factor
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    ABSTRACT: We report data on laying and hatching asynchrony in the Bearded Vulture Gypaetus barbatus, and provide the first detailed description of the provisioning of nestlings, sibling aggression and cannibalism. The results suggest that brood reduction was mediated through the age and size differences between siblings, which resulted in the superior competitive ability of the older chick. Thus, brood reduction occurred through starvation facilitated directly by the older chick's aggression. The results support the hypothesis that the second egg probably functions as insurance in case the first egg does not hatch. The insurance-egg hypothesis is supported by the following facts: 1) in three of six breeding attempts, the second egg produced a chick when the first egg failed to hatch or the first chick died young. At least two of these B chicks fledged; 2) in the Bearded Vulture most breeding failures occur during the hatching period and thus the insurance value of last-hatched eggs would be especially important in this species; 3) clutch replacement, an alternative to laying an insurance egg, is relatively uncommon in this species and 4) the laying interval (5–7 days) and the hatching asynchrony (5–8 days) of this species are the longest recorded in any raptor, suggesting that they might represent an adaptive mechanism facilitating the rapid loss of the second chick if the first one hatches.
    Ibis 06/2004; 146(3):386 - 393. · 2.36 Impact Factor
  • Joan Bertran, Antoni Margalida
    Ethology Ecology and Evolution 01/2004; · 1.12 Impact Factor
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    Joan Bertran, Antoni Margalida
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    ABSTRACT: Male-male mountings appear to be very common in polyandrous bearded vulture Gypaetus barbatus trios. We observed sexual activity in two trios that occupied the same territory in different years. We recorded a total of 167 copulation attempts. The percentage of male-male mountings recorded was 26.1 and 11.4%, in the period of 1991–1992 and 2000–2001, respectively, with respect to total, homo- and heterosexual matings. We conclude that homosexual interactions do not appear to be directly associated with intrasexual competition (i.e. hierarchical dominance, sperm competition). Rather, our results are more consistent with the idea that this behaviour can regulate the aggression of the males in these groups.
    Journal of Avian Biology 11/2003; 34(4):334 - 338. · 2.02 Impact Factor
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    ABSTRACT: We present data from an extensive study of Bearded Vulture Gypaetus barbatus breeding biology in the Pyrenees from 1992 to 1999. Average laying date was 6 January (range 11 December to 12 February, n = 69) with no significant differences between years. Eighty per cent of clutches were of two eggs (n = 20) and average incubation was 54 days (range 52–56, n = 14). Hatching occurred on average between 21 February and 3 March (range 5 February–7 April) and the first and last chicks fledged in 21–27 May and 20 July, respectively. The average chick age at fledging was 123 days (range 103–133, n = 20). Bearded Vulture density increased significantly during the study period. Breeding success and productivity declined apparently as a consequence of the increase in the percentage of breeding failures during incubation and chick rearing, most during the hatching period. The factors that may determine breeding failure and the decline in breeding performance are analysed and management recommendations for more effective conservation measures are discussed.
    Ibis 03/2003; 145(2):244 - 252. · 2.36 Impact Factor
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    Antoni Margalida, Joan Bertran
    Journal of Raptor Research 01/2003; · 0.73 Impact Factor
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    J. Bertran, A. Margalida
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    ABSTRACT: Griffon Vultures (Gyps fulvus) are responsible for most cases of usurpation of nests of Bearded Vultures (Gypaetus barbatus). However, little is known about how both species interact during reproduction. We studied territorial behaviour during the breeding season in four Bearded Vulture pairs in the eastern Pyrenees of northeastern Spain. Frequency of agonistic behavior was positively correlated with Griffon Vulture colony size. However, no significantly higher frequency of aggressive interactions was found that suggested actual competition for nest sites between these species. Nonetheless, Bearded Vulture pairs maintained a continuous defence of the area immediately surrounding their nests throughout the breeding season. Our data suggest that the Bearded Vulture’s territorial behavior was more closely associated with defence of breeding space than with specific defence of actual nest sites. SINOPSIS.
    01/2002;
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    Antoni Margalida, Joan Bertran
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    ABSTRACT: We analyze the use and functionality of ossuaries by the Bearded Vulture (Gypaetus bar- batus) in the Pyrenees during the nestling period. In 71% of cases, the ossuary was used to prepare food for chicks, in 11% for storing food, and only in 18% for preparing the adults' own food. Pairs used an av- erage of two ossuaries at a mean distance from the nest of 789 m (SE 6 377). The average time dedicate to breaking bone was 5.3 min (SE 6 4.2) and 4.5
    The Auk 01/2001; · 2.40 Impact Factor
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    ANTONI MARGALIDA, JOAN BERTRAN
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    ABSTRACT: Monogamous biparental care is expected to occur when opportunities for extra-pair copulations are rare, and both parents are required to raise the chick. Bearded Vultures Gypaetus barbatus fulfill these conditions. Contributions by male and female Bearded Vulture to nest building, nest defence, incubation, nest attendance and chick feeding were studied over five years in eight pairs from the Pyrenees [Catalonia, northeast Spain). Overall, the sexes show equal investment, although the degree of parental effort developed differs depending on the specific activities. During pre-laying, males were significantly more active than females in supplying material to the nest and in territorial defence behaviour, which increased (in both sexes) as the season advanced. Incubation was shared equally both by day and by night. During chick-rearing, the nest was attended by both sexes and the presence of both parents at the nest decreased in parallel with the growth of the chick. Activities related to chick feeding were also equally divided. These results are discussed in the context of female selection of mates and the particular ecology of this species.
    Ibis 03/2000; 142(2):225 - 234. · 2.36 Impact Factor
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    Antoni Margalida, Joan Bertran
    Ardea -Wageningen- 01/2000; · 0.89 Impact Factor