![]() For instance, birds can modulate their incubation behaviour in order to reduce humidity and thus conferring protection from precipitation or water that favour bacterial penetration. Although costly immunological barriers of eggs are quite effective fighting off potential pathogens, parents have also evolved additional defensive mechanisms to maintain their eggs free of parasites and pathogenic bacteria. However, eggs have numerous defensive traits against pathogens like the eggshell and antimicrobial contents. ![]() They can cross the eggshell, cause diseases in embryos and, thus, reduce egg viability. Microorganisms are also common in nests, some of them being highly pathogenic for developing embryo. The best known are nest-dwelling ectoparasites, like mites and fleas. Because of costs associated to nest building, birds should adjust nest building effort to expected bacterial environments during incubation, a prediction that should be further explored.īird nests are infected by numerous parasites that affect dramatically their reproductive output. ![]() All these results considered together confirm the antimicrobial functionality mainly of feathers but also of plants used as nest materials, and highlight the importance of temporally and geographically environmental variation associated with risk of bacterial proliferation determining the strength of such effects. Results from artificial nests allowed us to discuss and discard alternative scenarios explaining the detected association, particularly those related to the possible sexual role of feathers and aromatic plants in starling nests. Pigmented and unpigmented feathers reduced eggshell bacterial load in starling nests and artificial nest boxes. The beneficial effects of feathers and plants were more easily detected in artificial nests with no incubation activity, suggesting an active role of incubation against bacterial colonization of eggshells. Support for the hypothetical antimicrobial function of nest materials was mainly detected for the year and location with larger average values of eggshell bacterial density. We also experimentally increased bacterial density of eggs in natural and artificial nests and explored the effects of nest lining treatments on eggshell bacterial load. This was also explored in artificial nests without incubation activity. During two consecutive years, we explored experimentally the effects of these nest materials on loads of different groups of bacteria (mesophilic bacteria, Enterobacteriaceae, Staphylococcus and Enterococcus) of eggshells in nests of spotless starlings ( Sturnus unicolor) at the beginning and at the end of the incubation period. However, experimental evidence suggesting such effects is scarce in the literature. Due to the antimicrobial properties of volatile compounds of green plants and of chemicals of feather degrading bacteria, the use of aromatic plants and feathers for nest building has been suggested as one of these barriers. Selective pressures imposed by pathogenic microorganisms to embryos have selected in hosts for a battery of antimicrobial lines of defenses that includes physical and chemical barriers. In 2013, we included an additional within nest experimental treatment consisting on contaminating some eggshells in the nests and, thus, contamination and the interaction with sampling event were included as additional within nest effects (repeated measures). Thus, the models included study area and experimental treatments as between factors and sampling events and its interaction with study area and experimental treatments as within factors. Samples were collected 5, 9 and 17 (only in 2013) days after the onset of the experiment. The experiments were performed in two different areas and two different years. The artificial nests were subjected to two different experiments: plants (aromatic plants, non-aromatics plants or no plants) and feathers (pigmented, unpigmented or no feathers) as nest lining materials in a full factorial design. ![]() The specimens shown on this page were photographed in Cabanas de Tavira.S4 Appendix: Results from Repeated Measures ANOVAs explaining mesophilic bacterial loads of quail eggs in experimental nest-boxes without incubation activity. It is found throughout the Algarve in farmland, coastal areas, old olive and almond groves and in and around buildings. Females in winter and immatures are lightly spotted but never show the intensity of spots so typical of Common Starling. The Spotless Starling is very similar to the Common Starling, but adults in summer and males in winter display no hint of spots. Spotless Starling - Sturnus unicolor Pictures - John Foss
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