Faire face à l'hiver. Quelles réponses à l'hétérogénéité de la ressource en agroécosystème ? L'exemple de l'alouette des champs (Alauda arvensis)

La quantité et la qualité de la ressource alimentaire varient dans le temps et dans l'espace sous l'influence des conditions environnementales. Il est à présent reconnu qu'une diminution de cette ressource est à l'origine d'un déclin pour bon nombre d'espèces granivores inféodées aux milieux cultivés. Face à cette hétérogénéité, les individus mettent en place différentes stratégies individuelles ou collectives pour garantir leurs besoins énergétiques. Dans ce contexte, ce travail s'est attaché à comprendre les stratégies mise en place chez une espèce aviaire caractéristique des agrosystèmes. L'étude expérimentale du compromis alimentation/prédation révèle l'importance de variables environnementales, liées à la ressource, à la taille du groupe ou encore au risque de prédation sur leurs gains énergétiques des individus. Plus étonnamment, nos résultats ont mis en évidence des différences sexuelles dans les stratégies d'acquisitions d'énergie. Les choix effectués par les individus dans la réalisons de ce compromis ont des conséquences sur la sélection de l'habitat. L'étude de la réponse agrégative a ainsi souligné l'impact du type de culture ou de variables paysagères dans l'utilisation de l'habitat. Enfin, une étude sur le sex-ratio en fonction de la latitude en France a pu mettre en évidence une ségrégation spatiale entre les sexes, avec une forte proportion de mâles au nord, et un rééquilibrage vers le sud. Cette ségrégation sexuelle a pu être mise en relation avec des capacités physiologiques différentes (dépenses énergétiques et hypothermie), soulignant une plus forte tolérance des mâles aux faibles températures hivernales rencontrées dans les latitudes plus élevées.Both quantity and quality of food vary in time and space under the influence of environmental conditions. It is now recognized that a decrease of food is involving in a decline for many species of seed-eating farmland birds. According to this heterogeneity, individuals promote strategies to ensure individual and collective energy needs. In this context, this work has focused on understanding the strategies developed in an avian species characteristic of farmland. The experimental study of the trade-off between foraging and predation reveals the importance of environmental variables related to the resource, the group-size and group density, or the predation risk on the intake rate of individuals. More surprisingly, our results have shown sexual differences in energy acquisition strategies. The choices made by individuals under this trade-off have strong consequences on habitat selection. The study of the aggregative response has highlighted the impact crop type and different landscape variables in habitat use, more specially for foraging habitat. Finally, a study on the sex ratio in relationships with latitude in France has been able to demonstrate a spatial segregation between the sexes, with a high proportion of males in the north. This sexual segregation could be related with different physiological capabilities (energy expenditure and hypothermia), emphasizing a greater tolerance of males at low winter temperatures encountered in the higher latitudes during wintering period.POITIERS-SCD-Bib. électronique (861949901) / SudocSudocFranceF

Wintering strategies of granivorous birds in farmland, the study case of the Eurasian Skylark (Alauda arvensis)

La quantité et la qualité de la ressource alimentaire varient dans le temps et dans l'espace sous l'influence des conditions environnementales. Il est à présent reconnu qu'une diminution de cette ressource est à l'origine d'un déclin pour bon nombre d'espèces granivores inféodées aux milieux cultivés. Face à cette hétérogénéité, les individus mettent en place différentes stratégies individuelles ou collectives pour garantir leurs besoins énergétiques. Dans ce contexte, ce travail s'est attaché à comprendre les stratégies mise en place chez une espèce aviaire caractéristique des agrosystèmes. L'étude expérimentale du compromis alimentation/prédation révèle l'importance de variables environnementales, liées à la ressource, à la taille du groupe ou encore au risque de prédation sur leurs gains énergétiques des individus. Plus étonnamment, nos résultats ont mis en évidence des différences sexuelles dans les stratégies d'acquisitions d'énergie. Les choix effectués par les individus dans la réalisons de ce compromis ont des conséquences sur la sélection de l'habitat. L'étude de la réponse agrégative a ainsi souligné l'impact du type de culture ou de variables paysagères dans l'utilisation de l'habitat. Enfin, une étude sur le sex-ratio en fonction de la latitude en France a pu mettre en évidence une ségrégation spatiale entre les sexes, avec une forte proportion de mâles au nord, et un rééquilibrage vers le sud. Cette ségrégation sexuelle a pu être mise en relation avec des capacités physiologiques différentes (dépenses énergétiques et hypothermie), soulignant une plus forte tolérance des mâles aux faibles températures hivernales rencontrées dans les latitudes plus élevées.Both quantity and quality of food vary in time and space under the influence of environmental conditions. It is now recognized that a decrease of food is involving in a decline for many species of seed-eating farmland birds. According to this heterogeneity, individuals promote strategies to ensure individual and collective energy needs. In this context, this work has focused on understanding the strategies developed in an avian species characteristic of farmland. The experimental study of the trade-off between foraging and predation reveals the importance of environmental variables related to the resource, the group-size and group density, or the predation risk on the intake rate of individuals. More surprisingly, our results have shown sexual differences in energy acquisition strategies. The choices made by individuals under this trade-off have strong consequences on habitat selection. The study of the aggregative response has highlighted the impact crop type and different landscape variables in habitat use, more specially for foraging habitat. Finally, a study on the sex ratio in relationships with latitude in France has been able to demonstrate a spatial segregation between the sexes, with a high proportion of males in the north. This sexual segregation could be related with different physiological capabilities (energy expenditure and hypothermia), emphasizing a greater tolerance of males at low winter temperatures encountered in the higher latitudes during wintering period

Faire face à l'hiver - Quelles réponses à l'hétérogénéité de la ressource en agroécosystème ? L'exemple de l'alouette des champs (Alauda arvensis)

Both quantity and quality of food vary in time and space under the influence of environmental conditions. It is now recognized that a decrease of food is involving in a decline for many species of seed-eating farmland birds. According to this heterogeneity, individuals promote strategies to ensure individual and collective energy needs. In this context, this work has focused on understanding the strategies developed in an avian species characteristic of farmland. The experimental study of the trade-off between foraging and predation reveals the importance of environmental variables related to the resource, the group-size and group density, or the predation risk on the intake rate of individuals. More surprisingly, our results have shown sexual differences in energy acquisition strategies. The choices made by individuals under this trade-off have strong consequences on habitat selection. The study of the aggregative response has highlighted the impact crop type and different landscape variables in habitat use, more specially for foraging habitat. Finally, a study on the sex ratio in relationships with latitude in France has been able to demonstrate a spatial segregation between the sexes, with a high proportion of males in the north. This sexual segregation could be related with different physiological capabilities (energy expenditure and hypothermia), emphasizing a greater tolerance of males at low winter temperatures encountered in the higher latitudes during wintering period.La quantité et la qualité de la ressource alimentaire varient dans le temps et dans l'espace sous l'influence des conditions environnementales. Il est à présent reconnu qu'une diminution de cette ressource est à l'origine d'un déclin pour bon nombre d'espèces granivores inféodées aux milieux cultivés. Face à cette hétérogénéité, les individus mettent en place différentes stratégies individuelles ou collectives pour garantir leurs besoins énergétiques Dans ce contexte, ce travail s'est attaché à comprendre les stratégies mise en place chez une espèce aviaire caractéristique des agrosystèmes. L'étude expérimentale du compromis alimentation/prédation révèle l'importance de variables environnementales, liées à la ressource, à la taille du groupe ou encore au risque de prédation sur leurs gains énergétiques des individus. Plus étonnamment, nos résultats ont mis en évidence des différences sexuelles dans les stratégies d'acquisitions d'énergie. Les choix effectués par les individus dans la réalisons de ce compromis ont des conséquences sur la sélection de l'habitat. L'étude de la réponse agrégative a ainsi souligné l'impact du type de culture ou de variables paysagères dans l'utilisation de l'habitat. Enfin, une étude sur le sex-ratio en fonction de la latitude en France a pu mettre en évidence une ségrégation spatiale entre les sexes, avec une forte proportion de mâles au nord, et un rééquilibrage vers le sud. Cette ségrégation sexuelle a pu être mise en relation avec des capacités physiologiques différentes (dépenses énergétiques et hypothermie), soulignant une plus forte tolérance des mâles aux faibles températures hivernales rencontrées dans les latitudes plus élevées

Sex-Related Differences in the Trade-Off between Foraging and Vigilance in a Granivorous Forager

The relationship between intake rate and food density can provide the foundation for models that predict the spatiotemporal distribution of organisms across a range of resource densities. The functional response, describing the relationship between resource density and intake rate is often interpreted mechanistically as the relationships between times spend searching and handling. While several functional response models incorporate anti-predator vigilance (defined here as an interruption of feeding or some other activity to visually scan the environment, directed mainly towards detecting potential predators), the impacts of environmental factors influencing directly anti-predator vigilance remains unclear. We examined the combined effects of different scenarios of predation risk and food density on time allocation between foraging and anti-predator vigilance in a granivorous species. We experimentally exposed Skylarks to various cover heights and seed densities, and measured individual time budget and pecking and intake rates. Our results indicated that time devoted to different activities varied as a function of both seed density and cover height. Foraging time increased with seed density for all cover heights. Conversely, an increased cover height resulted in a decreased foraging time. Contrary to males, the decreased proportion of time spent foraging did not translate into a foraging disadvantage for females. When vegetation height was higher, females maintained similar pecking and intake rates compared to intermediate levels, while males consistently decreased their energy gain. This difference in anti-predator responses suggests a sexually mediate

Group size modulates time budget and foraging efficiency in captive Skylarks, Alauda arvensis

Abstract Skylarks (Alauda arvensis) are known to adopt a typical aggregative behaviour during the wintering period. A further benefit is that individuals in larger groups can decrease the amount of time they spent being vigilant, while maintaining a high probability of predator detection. Using wild birds temporarily housed in outdoor aviaries, we investigated the influence of group size (1, 2 and 4 individuals) on individual time budget (vigilance vs. foraging), and the pecking (number of pecks) and intake rates (number of seeds consumed). Results showed that individuals reduced their vigilance and increased their pecking rate when group size increased. However, the intake rate was not maximised in the largest group suggesting that large flocks would negatively affect individual foraging efficiency. A consideration of the whole set of costs and benefits will be necessary before the adaptive value of group living in any species can be fully assessed

Sex-related differences in the trade-off between foraging and vigilance in a granivorous forager.

The relationship between intake rate and food density can provide the foundation for models that predict the spatiotemporal distribution of organisms across a range of resource densities. The functional response, describing the relationship between resource density and intake rate is often interpreted mechanistically as the relationships between times spend searching and handling. While several functional response models incorporate anti-predator vigilance (defined here as an interruption of feeding or some other activity to visually scan the environment, directed mainly towards detecting potential predators), the impacts of environmental factors influencing directly anti-predator vigilance remains unclear. We examined the combined effects of different scenarios of predation risk and food density on time allocation between foraging and anti-predator vigilance in a granivorous species. We experimentally exposed Skylarks to various cover heights and seed densities, and measured individual time budget and pecking and intake rates. Our results indicated that time devoted to different activities varied as a function of both seed density and cover height. Foraging time increased with seed density for all cover heights. Conversely, an increased cover height resulted in a decreased foraging time. Contrary to males, the decreased proportion of time spent foraging did not translate into a foraging disadvantage for females. When vegetation height was higher, females maintained similar pecking and intake rates compared to intermediate levels, while males consistently decreased their energy gain. This difference in anti-predator responses suggests a sexually mediated strategy in the food-safety trade-off: when resource density is high a females would adopt a camouflage strategy while an escape strategy would be adopted by males. In other words, males would leave risky-areas, whereas females would stay when resource density is high. Our results suggest that increased predation risk might generate sexually mediated behavioural responses that functional response models should perhaps better consider in the future

Seed depletion and landscape structure affect aggregative response in two wintering passerine birds

International audienceCapsule: Seed abundance but also seed depletion during winter modifies habitat use and aggregation behaviour of Eurasian Sky Lark Alauda arvensis and Meadow Pipit Anthus pratensis.Aims: To investigate the effect of seed abundance on the density of two passerine birds, the Eurasian Sky Larks and the Meadow Pipit, at an agricultural landscape scale during winter.Methods: Bird counts as well as seed density measurements were carried out in winter to quantify the aggregative response of farmland birds to seed abundance from November to March.Results: Seed resources varied by a factor of ten between crop types, but declined so sharply over the winter that seed abundance was low and similar among crop types by late winter. Sky Larks selected for higher seed density plots, but only at the end of winter when the resources were the lowest. Conversely, Meadow Pipits did not show any aggregative response to seed abundance.Conclusion: These results show that an uptake of seed-rich habitats in agricultural landscape would be very beneficial for wintering granivorous birds, by fulfilling the late winter ‘hungry gap’. The inclusion of seed mixtures in habitats that attract high densities of birds and retain seeds until late winter is of primary interest

Is blood a reliable indicator of trace metal concentrations in organs of small mammals?

International audienceIn wildlife ecotoxicology, the rationale for using blood rather than other body fluids or tissues is that sampling blood is a minimally invasive technique without animal mortality, providing both ethical and scientific benefits. To date, few studies are available on the relationships between blood and organ metal concentrations of small mammals living in contaminated sites. The present work aimed to study the relationships between the concentrations of 18 essential and nonessential metals in blood and their concentrations in the liver and kidneys, two accumulation and target organs, in wood mice from a former lead and zinc smelter, Metaleurop Nord, in northern France. The results from Se, Pb and Tl indicate that blood levels may be used to predict concentrations in organs of small mammals. Conversely, for Cd, Cu, Fe, Mo, Ti and Zn, blood concentrations were poorly or not related to liver and kidney concentrations. In addition to accurately predicting the concentrations of some metals in target organs, blood can provide important information about the physiological and biochemical status of organisms, but further toxicokinetic research is required to develop the use of blood sampling as a minimally invasive biomonitoring and ecotoxicological method in wildlife

Vegetation structure and inter-individual distance affect intake rate and foraging efficiency in a granivorous forager, the Eurasian Skylark Alauda arvensis

International audienceEin Leben in größeren Gruppen ist für Tiere vorteilhaft, weil dadurch Feinde eher entdeckt werden, das Risiko für jedes einzelne Tier geringer ist und Räuber bei einem Angriff verwirrt werden. Ein weiterer Vorteil liegt darin, dass einerseits jedes Einzeltier weniger Zeit in Wachsamkeit und Aufpassen investieren muss, während andererseits die Wahrscheinlichkeit, Feinde zu entdecken, durch die Gruppe weiterhin hoch bleibt. Dadurch gewinnt jedes einzelne Tier zusätzliche Zeit, die für die Nahrungsaufnahme genutzt werden kann. Das Leben in Gruppen, oder Schwärmen, hat jedoch auch seine Kosten: eine erhöhte Konkurrenz zwischen den einzelnen Tieren innerhalb der Gruppe mit entsprechend negativen Auswirkungen auf die Nahrungsaufnahme. Ziel unserer Studie war, in unterschiedlichen Lebensräumen die Vorteile des Gruppenlebens gegen die Nachteile der intensiveren Konkurrenzsituation abzuwägen. Bei Tieren von Beutearten, die davon abhängen, Räuber so rasch wie möglich zu entdecken, beeinflusst die Struktur der Vegetation vermutlich das empfundene Risiko, erbeutet zu werden. Deshalb überprüften wir für eine körnerfressende Art, die Eurasische Feldlerche (Alauda arvensis), experimentell den kombinierten Effekt von Vegetationshöhe und Abständen zwischen den Einzeltieren auf die Dauer, Häufigkeit und Effizienz der Nahrungsaufnahme. Die Ergebnisse unserer Experimente mit zeitweise gekäfigten Vögeln zeigen, dass die für die Nahrungsaufnahme verwendete Zeit mit wachsenden Abständen zwischen den Einzeltieren abnahm, es aber keinen Zusammenhang mit der Vegetationshöhe gab. Wurde jedoch beides, die Vegetationshöhe und die Abstände zu anderen Gruppenmitgliedern, erhöht, ergab sich daraus ein Nachteil für die Ernährung: eine Verminderung sowohl der Häufigkeit als auch der Effizienz der Nahrungsaufnahme. Unsere Ergebnisse zeigen, dass beides, die Vegetationsstruktur und die Abstände zwischen Einzeltieren, Auswirkungen auf den Nahrungs-Ertrag haben können und liefern so ein weiteres Beispiel dafür, wie die Schwarmdynamik den trade-off, das Ausbalancieren der Vor- und Nachteile, von Nahrungsaufnahme und Wachsamkeit beeinflussen kann.Animals gain benefits from group living through increased probability of predator detection, dilution of individual risk and confusion of predators during attack. A further benefit involves larger groups in which individuals may further decrease the amount of time spent being vigilant, while maintaining the probability of predator detection by allocation of this extra time to foraging activities. Living in groups or flocks, however, also incurs costs, e.g., by increasing inter-group competition, with negative impacts on intake rates. Our aim was to investigate the trade-offs between the costs of competition and the benefits of group living in contrasted habitats. For prey species that rely on sight for detecting predators, vegetation structure may influence the perceived predation risk. Hence, we experimentally examined the combined effects of vegetation height and inter-individual distance on foraging time, intake rate and foraging efficiency in a granivorous species, the Eurasian Skylark (Alauda arvensis). Our experimental results based on temporally captive birds indicate that time devoted to foraging decreased with increasing inter-individual distance, but was unrelated to cover height. Conversely, increasing both vegetation height and distance with other group members did translate into a foraging disadvantage, i.e. reduced intake rate as well as foraging efficiency. Overall, our results show that both vegetation structure and inter-individual distances modify patch profitability, and therefore provide another example of how flock dynamics can influence the trade-off between vigilance and foraging

Effects of chronic exposure to toxic metals on haematological parameters in free-ranging small mammals

Blood circulates through the vascular system to carry oxygen, nutrients and metabolites to and away from tissues, and as such is a key-component of animal physiology. The impacts of metal pollution on blood, however, are poorly documented in free-ranging vertebrates. While the counteracting effect of selenium on mercury toxicity is well known in marine mammals, its potential role against the toxicity of other metals is less studied, especially on terrestrial wildlife. We explored the consequences of chronic exposure to two non-essential metals (cadmium and lead) along a pollution gradient in Northern France, on eleven haematological parameters in two free ranging small mammals, the wood mouse Apodemus sylvaticus and the bank vole Myodes glareolus. We hypothesized that haematology was related to metal concentrations in tissues, and that selenium might exert modulating effects. Concentrations of cadmium and lead in the tissues indicated an increased chronic exposure to and accumulation of metals along the gradient. Some haematological parameters were not explained by any measured variables while some others varied only with gender or age. Red blood cells, red blood cells distribution width, and blood iron concentration, however, decreased with increasing cadmium in the tissues in wood mice. Red blood cells and haemoglobin decreased with increasing renal lead and hepatic cadmium, respectively, in bank voles. Red blood cells distribution width in wood mice increased with cadmium concentrations in the liver but this was counteracted by high selenium levels in the same organ. An interaction of selenium and lead on red blood cells was also observed in bank voles. Further, selenium concentrations were associated with an increase of monocytes in wood mice. The present results show that toxic metals were related to haematology changes, particularly erythrocyte indicators, and that some essential elements like selenium should be measured as well since they may counteract toxic effects