Jordi Pascual

Mating patterns in late-maturing female Mediterranean tarantulas may reflect the costs and benefits of sexual cannibalism

Abstract During courtship and mating, males of some invertebrate predators risk being killed and consumed by females, who in turn can obtain a foraging benefit from feeding on males. In these invertebrates, the sex ratio at the end of the mating season is usually female biased, probably due to sexual cannibalism and other sources of male mortality. Thus, at the end of the mating season males can be a limited resource to females as both mates and prey. Because of the high risk incurred when approaching females, males should show mate choice. To date there are little data on the costs and benefits of sexual cannibalism in natural populations. For one month we followed the mating patterns of 60 late-maturing Mediterranean tarantula, Lycosa tarentula L., females in a desert grassland population. The later a female matured, the shorter was her cohabitation time with males and the lower her probability of cohabiting with a male at all, suggesting that late-maturing females may be limited in their access to males as mates. At the end of the mating season, nonsexually cannibalistic late-maturing females also had poorer body conditions than did both sexually cannibalistic late-maturing females and early-maturing females, suggesting that late-maturing females may be also limited in their access to males as food. Females had higher mating success if they were smaller or in better condition (better fed). This pattern may reflect either male choice, or the possibility that small, well-fed females have higher mating success because they are less aggressive towards males. Copyright 2003 Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour.

Antipredator behavioural compensation of proactive personality trait in male Eurasian siskins

Many animals show behavioural syndromes (i.e. suites of correlated behaviours across multiple situations). These behavioural correlations, however, imply limitations in the behavioural plasticity of individuals when facing the trade-off between predation risk and starvation risk. Some models suggest that proactive animals prioritize the reduction of starvation risk, while reactive animals do the opposite. Therefore, fast explorers that are also bold (i.e. proactive) are assumed to pay a predation cost associated with their behavioural trait. However, it has recently been suggested that proactive individuals may be able to compensate for their higher risk of predation by adopting some antipredator behaviours. In this study we tested these two alternative hypotheses with wild wintering Eurasian siskins, Carduelis spinus, foraging at artificial feeders. Male siskins have a melanin-based black bib that has been found to be correlated with exploratory behaviour, aggressiveness and dominance, and therefore is a signal of proactivity. We found that male siskins with large black bibs uttered more distress calls upon capture and displayed a vigilance strategy that improved predator detection. Moreover, this vigilance strategy did not reduce food intake rate. These results show that proactive individuals are not reckless, but instead compensate for their personality trait with stronger antipredator behaviours, and thus, do not necessarily have to pay a predation cost. Our results support the view of a positive relationship between eumelanism, proactive personality and the display of antipredator behaviours.

Differential effects of predation risk and competition over vigilance variables and feeding success in Eurasian siskins (Carduelis spinus)

Many investigations have studied the effects of predation risk and competition over vigilance and feeding success, but they have proven to be difficult to discriminate. Moreover, none of the studies that have avoided the confusion has considered all the vigilance variables, food intake rate and time spent in the foraging patch. In this study, we designed an experiment with Eurasian siskins Carduelis spinus foraging on three bird table feeders: one with low predation risk and competition, one with low predation risk and high competition and one with high predation risk and intermediate competition. Birds responded to increasing interference competition by increasing mean scan durations (probably due to the birds having to be vigilant for both other flock members and predators) and maintaining the length of mean inter-scan durations, while they responded to increasing predation risk by reducing mean inter-scan durations (probably in order to detect the predator sooner) while maintaining similar length of mean scan durations. Birds were often ejected from the feeder or departed because of disturbances, so time spent on feeders was reduced both because of competition and predation risk. Pecking rates were affected by competition but not by predation risk. Our results clearly show that birds vigilance strategy while foraging might be very different when they are mainly concerned with scanning for predators or when they primarily monitor competing flock companions. In addition, they stress the importance of recording all the vigilance and feeding variables when studying the effect of ecological factors over the foraging behaviour of birds.

Reducing the availability of food to control feral pigeons: changes in population size and composition.

BACKGROUND As feeding by humans is one of the main food resources to pigeons (Columba livia), there is general agreement that public education that aims to reduce the food base may be the most feasible way to reduce pigeon abundance. However, except for the classic example of Basel, the method has rarely been tested or implemented. We provide results from a 1 year study in the city of Barcelona where we tested the effect of public education on pigeon population abundance and composition. RESULTS The quantity of food provided by people to pigeons was significantly reduced during the study. Feral pigeon density was reduced by 40% in the two experimental districts, but no variation was detected in the control district. Detailed analyses in one of the districts showed that the reduction was mainly related to the reduction in food availability but not to culling. Pigeons captured at the end of the experiment were larger than at the start of the study, but body condition was reduced. CONCLUSION Results show the effectiveness of public information to manage feral pigeon populations in a large city, and that control operations can exert important selection pressure on the population, leading to changes in population composition.

Plumage brightness, vigilance, escape potential, and predation risk in male and female Eurasian Siskins (Spinus spinus)

ABSTRACT According to the “sexual selection hypothesis” (SSH), plumage conspicuousness has evolved through mate choice because it signals the quality of the bearer, and this is an honest signal because it involves a predation cost in terms of increased detectability to predators. Alternatively, according to the “unprofitable prey hypothesis” (UPH), conspicuousness is an aposematic signal indicating higher escape potential. We should expect the animals with higher predation risk (either conspicuous or dull, depending on the hypothesis) to have evolved antipredator behaviors to compensate for their higher predation risk (i.e. the “compensation hypothesis”). We tested these hypotheses by studying the vigilance behavior of wintering Eurasian Siskins (Spinus spinus) foraging on three feeders with different predation-risk and competition levels. Males were, on average, 50% more brightly colored than females. Males and females had similar wing loading, which allows us to reject male unprofitability related to higher takeoff speed. Males had shorter mean interscan durations (which improves predator detection) than females, especially at the high-predation-risk feeder (which males avoided), but the sexes did not differ in foraging-bout length, percentage of time spent scanning, and mean scan duration. In males, length of yellow tail stripe and brightness were positively correlated with percentage of time spent scanning. Therefore, our results on vigilance behavior and wing loading support the compensation hypothesis and the SSH assumption of a predation cost of conspicuousness, whereas they reject the predictions of the UPH. Compensation vigilance and other antipredator behaviors are expected to have also evolved in the conspicuous sex in other dichromatic species, and we predict that a correlation between plumage conspicuousness and vigilance should be found in future comparative studies.

Resident but not transient Eurasian Siskins reduce body mass in response to increasing predation risk: a natural experiment

The body mass of birds is the result of a trade-off between predation and starvation risks. According to the mass-dependent predation hypothesis, birds reduce their body mass when predation risk increases. Many studies have supported this hypothesis, but it has rarely been possible to investigate the mass-dependent predation risk response by comparing individuals of the same species foraging simultaneously at the same location, in the field and facing a real (not simulated) risk of predation. Wintering Siskins (Carduelis spinus) are divided in two subpopulations: residents, which stay in a foraging area for several weeks or months, and transients, which only remain a few hours or days. In this paper, we present a natural experiment by comparing the body mass variation of resident and transient Siskins between a period of the wintering season without avian predators and another period with a Sparrowhawk (Accipiter nisus) that was hunting regularly. We found that resident Siskins reduced their body mass with the presence of the hawk, while transients did not. Since in a previous study with no avian predators at the study area it was found that the difference in body condition between residents and transients did not vary throughout the wintering season, we can confidently say that the reduction in body mass observed in this study was directly linked to the presence of the hawk. We additionally found that this reduction was not associated with the dominance of residents over transients. We discuss the advantages of residence related to the knowledge of actual predation risk. Our results strongly support the mass-dependent predation hypothesis.ZusammenfassungOrtsansässige, aber nicht durchziehende Erlenzeisige verringern ihre Körpermasse bei erhöhtem Prädationsrisiko: ein natürliches Experiment Die Körpermasse von Vögeln beruht auf einer Wechselbeziehung von Prädationsrisiko und der Gefahr des Hungertodes. Laut der Hypothese der masseabhängigen Prädation verringern Vögel ihre Körpermasse mit steigendem Prädationsrisiko. Diese Hypothese wird von vielen Studien gestützt, aber wurde noch nie an einem System im Feld getestet, in dem Individuen einer Art verglichen wurden, die zur gleichen Zeit am gleichen Ort nach Nahrung suchen und dabei einem echten (nicht simulierten) Prädationsrisiko ausgesetzt sind. Überwinternde Erlenzeisige (C. spinus) werden in zwei Untergruppen geteilt: ortsansässige, die mehrere Wochen oder Monate am selben Ort bleiben, und Durchzügler, die sich nur einige Stunden oder Tage am selben Ort aufhalten. In diesem Bericht präsentieren wir ein natürliches Experiment: wir verglichen die Variation in der Körpermasse ortsansässiger und durchziehender Erlenzeisige zwischen einer Periode ohne Anwesenheit von Beutegreifern und einer Periode, in der ein Sperber (A. nisus) regelmäßig dort jagte. Es zeigte sich, dass ortsansässige Erlenzeisige ihre Körpermasse verringerten als der Sperber anwesend war, die Durchzügler hingegen nicht. Da eine frühere Studie im selben Gebiet ohne Anwesenheit von Beutegreifern ergab, dass die Körpermassen der ortsansässigen und durchziehenden Erlenzeisige innerhalb der Wintersaison nicht schwankten, sind wir überzeugt, dass die hier beobachtete Verringerung der Körpermasse direkt auf die Anwesenheit des Sperbers zurückzuführen ist. Des Weiteren fanden wir keinen Zusammenhang zwischen der verringerten Körpermasse und der Dominanz der ortsansässigen gegenüber den durchziehenden Erlenzeisigen. Wir diskutieren die Ergebnisse mit Blick auf die Vorteile der Ortsansässigkeit in Bezug auf das Wissen um das bestehende Prädationsrisiko. Unsere Ergebnisse stützen die Hypothese der masseabhängigen Prädation.

Prior residence effect in wintering male Eurasian siskins is not related to resource holding power

Animals competing for resources follow a general rule for which prior residents usually win contests over intruders. This prior residence effect might arise because animals possess a genetically fixed convention so that ‘residents always win’ (i.e. an uncorrelated asymmetry), because residents have a higher resource holding power (RHP) than intruders or because residents have a higher motivation to defend territories (i.e. pay-off asymmetry). The discrimination between these different hypotheses, though, has proven to be difficult. Eurasian siskins (Spinus spinus) provide us with an adequate opportunity to test for the effect of RHP on the prior residence effect. Siskins show two different strategies while in the wintering grounds: residents remain for several weeks on a given location while transients continuously move and residents are dominant over transients. The black bib area of male siskins signals their RHP. In this study, we compared the black bib area of a large sample of male resident and transient siskins and we found no differences between the two subpopulations. Hence, residence status in this species is not related to black bib size, which is a good proxy for RHP. Our results support the view that asymmetries in RHP are not required to explain the prior residence effect. We discuss the important implications that it has on the evolution of partial migration.

First survey on zoonotic helminthosis in urban brown rats (Rattus norvegicus) in Spain and associated public health considerations

The brown rat, Rattus norvegicus, with a worldwide distribution, is the most commensal species among synanthropic rodents, since its main habitat, in urban as well as in rural areas, is always linked to humans. Therefore, people living in close proximity to rodent populations can be exposed to infection. Whereas bacteria and viruses are the best known rat-associated zoonoses in urban environments, the role of brown rats as reservoirs for helminth parasites and the associated risk for humans are less well known. Specifically, this role has not been analyzed in Spain to date. A total of 100 R. norvegicus trapped in the sewage system (n = 85), and parks (n = 15) of Barcelona was examined. The overall prevalence of helminth infection was 85%. The helminths found were Hymenolepis nana (17%), H. diminuta (33%) (Cestoda), Calodium hepaticum (17%), Eucoleus gastricus (28%), Aonchotheca annulosa (12%), Trichosomoides crassicauda (7%), Nippostrongylus brasiliensis (46%), Heterakis spumosa (62%), Gongylonema neoplasticum (20%) (Nematoda) and Moniliformis moniliformis (6%) (Acanthocephala). Five of the ten helminth species are considered zoonotic parasites, with rats acting as reservoirs for human infection, i.e. H. nana, H. diminuta, C. hepaticum, G. neoplasticum and M. moniliformis. G. neoplasticum and M. moniliformis are reported for the first time in urban rats in Europe. H. nana, H. diminuta and C. hepaticum are the most widespread species in European cities. For H. nana and C. hepaticum, rats act as effective spreaders of the human infective stage (eggs). For H. diminuta, G. neoplasticum and M. moniliformis, rats act as indirect reservoirs of the zoonoses since the eggs shed by the rats are infective for their insect intermediate hosts only. Medical practitioners need to be made aware of the range of parasites carried by rats, as there is a realistic likelihood that ill health currently caused by rat infestations may be misdiagnosed.