The quality of a breeding site may have major fitness consequences.A fundamental step to understanding the process of nest-site selection is the identification of the information individuals use to choose high-quality...The quality of a breeding site may have major fitness consequences.A fundamental step to understanding the process of nest-site selection is the identification of the information individuals use to choose high-quality nest sites.For secondary cavity-nesting bird species that do not add nest lining material,organic remains (faeces,pellets)accumulated inside nest cavities during previous breeding events may be a cue for high-quality nest-sites,as they contain information about past successful breeding and may improve thermal insulation of eggs during incubation.However,cavities in which breeding was successful might also contain more nest-dwelling ectoparasites than unoccupied cavities, offering an incentive for prospective parents to avoid them.We exposed breeding cavity-nesting lesser kestrels (Falco naumanni)to nestbox dyads consisting of a dirty (with a thick layer of organic substrate) and a clean nestbox (without organic material).Dirty nestboxes were strongly preferred,being occupied earlier and more frequently than clean ones.Hatching success in dirty nestboxes was significantly higher than in clean ones,suggesting a positive effect of organic nest material on incubation efficiency, while nestbox dirtiness did not significantly affect clutch and brood size.Nestlings from dirty nestboxes had significantly higher ectoparasite load than those from clean nestboxes soon after egg hatching,but this difference was not evident a few days later.Nest substrate did not significantly affect nestling growth.We concluded that nest substrate is a key driver of nest-site choice in lesser kestrels,although the adaptive value of such a strong preference appears elusive and may be context-dependent.展开更多
Context dependence arises when ecological relationships vary with the conditions under which they are observed. Context dependence of interactions involving parasites is poorly known, even if it is key to understandin...Context dependence arises when ecological relationships vary with the conditions under which they are observed. Context dependence of interactions involving parasites is poorly known, even if it is key to understanding host–parasite relationships and food web dynamics. This paper investigates to which extent predation pressure on an avian ectoparasite (Carnus hemapterus) is context-dependent. Based on a predator-exclusion experiment, predation pressure on C. hemapterus pupae in the host's nest for 3 years, and its variation between habitat types are quantified. Variation in precipitation and normalized difference vegetation index (NDVI) is also explored as a likely cause of context dependency. We hypothesize that predation pressure should fluctuate with such surrogates of food availability, so that inter-annual and intra-annual differences may emerge. The number of nests with significant reduction of pupae varied widely among years ranging from 24% to 75%. However, average pupae reduction in nests where a significant reduction occurred did not vary between years. No differences in predation rates between habitat types were detected. Precipitation and NDVI varied widely between years and NDVI was consistently lower around nests on cliffs than around nests on trees and farmhouses. Parallels were found between variation in predation pressure and precipitation/NDVI at a wide scale (highest predation the driest year, and much lower the 2 rainier ones), but not at the nest scale. This paper shows clear context-dependent insect predation pressure on an ectoparasite under natural conditions, and that such interaction changes in signs rather than magnitude between years. The causes for these variations require longer-term studies and/or well-designed, large-scale experiments.展开更多
文摘The quality of a breeding site may have major fitness consequences.A fundamental step to understanding the process of nest-site selection is the identification of the information individuals use to choose high-quality nest sites.For secondary cavity-nesting bird species that do not add nest lining material,organic remains (faeces,pellets)accumulated inside nest cavities during previous breeding events may be a cue for high-quality nest-sites,as they contain information about past successful breeding and may improve thermal insulation of eggs during incubation.However,cavities in which breeding was successful might also contain more nest-dwelling ectoparasites than unoccupied cavities, offering an incentive for prospective parents to avoid them.We exposed breeding cavity-nesting lesser kestrels (Falco naumanni)to nestbox dyads consisting of a dirty (with a thick layer of organic substrate) and a clean nestbox (without organic material).Dirty nestboxes were strongly preferred,being occupied earlier and more frequently than clean ones.Hatching success in dirty nestboxes was significantly higher than in clean ones,suggesting a positive effect of organic nest material on incubation efficiency, while nestbox dirtiness did not significantly affect clutch and brood size.Nestlings from dirty nestboxes had significantly higher ectoparasite load than those from clean nestboxes soon after egg hatching,but this difference was not evident a few days later.Nest substrate did not significantly affect nestling growth.We concluded that nest substrate is a key driver of nest-site choice in lesser kestrels,although the adaptive value of such a strong preference appears elusive and may be context-dependent.
文摘Context dependence arises when ecological relationships vary with the conditions under which they are observed. Context dependence of interactions involving parasites is poorly known, even if it is key to understanding host–parasite relationships and food web dynamics. This paper investigates to which extent predation pressure on an avian ectoparasite (Carnus hemapterus) is context-dependent. Based on a predator-exclusion experiment, predation pressure on C. hemapterus pupae in the host's nest for 3 years, and its variation between habitat types are quantified. Variation in precipitation and normalized difference vegetation index (NDVI) is also explored as a likely cause of context dependency. We hypothesize that predation pressure should fluctuate with such surrogates of food availability, so that inter-annual and intra-annual differences may emerge. The number of nests with significant reduction of pupae varied widely among years ranging from 24% to 75%. However, average pupae reduction in nests where a significant reduction occurred did not vary between years. No differences in predation rates between habitat types were detected. Precipitation and NDVI varied widely between years and NDVI was consistently lower around nests on cliffs than around nests on trees and farmhouses. Parallels were found between variation in predation pressure and precipitation/NDVI at a wide scale (highest predation the driest year, and much lower the 2 rainier ones), but not at the nest scale. This paper shows clear context-dependent insect predation pressure on an ectoparasite under natural conditions, and that such interaction changes in signs rather than magnitude between years. The causes for these variations require longer-term studies and/or well-designed, large-scale experiments.
