17 resultados para Vertical pull-out failure


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Context Egg depredation is a major cause of reproductive failure among birds and can drive population declines. In this study we investigate predatory behaviour of a corvid (little raven; Corvus mellori) that has only recently emerged, leading to widespread and intense depredation of eggs of a burrow-nesting seabird (little penguin; Eudyptula minor). Aims The main objective of this study was to measure the rate of penguin egg depredation by ravens to determine potential threat severity. We also examined whether penguin burrow characteristics were associated with the risk of egg depredation. Ravens generally employ two modes of predatory behaviour when attacking penguin nests; thus we examined whether burrow characteristics were associated with these modes of attack. Methods Remote-sensing cameras were deployed on penguin burrows to determine egg predation rates. Burrow measurements, including burrow entrance and tunnel characteristics, were measured at the time of camera deployment. Key results Overall, clutches in 61% of monitored burrows (n≤203) were depredated by ravens, the only predator detected by camera traps. Analysis of burrow characteristics revealed two distinct types of burrows, only one of which was associated with egg depredation by ravens. Clutches depredated by ravens had burrows with wider and higher entrances, thinner soil or vegetation layer above the egg chamber, shorter and curved tunnels and greater areas of bare ground and whitewash near entrances. In addition, 86% were covered by bower spinach (Tetragonia implexicoma), through which ravens could excavate. Ravens used two modes to access the eggs: they attacked through the entrance (25% of burrow attacks, n≤124); or dug a hole through the burrow roof (75% of attacks, n≤124). Burrows that were subject to attack through the entrance had significantly shorter tunnels than burrows accessed through the roof. Conclusions The high rates of clutch loss recorded here highlight the need for population viability analysis of penguins to assess the effect of egg predation on population growth rates. Implications The subterranean foraging niche of a corvid described here may have implications for burrow-nesting species worldwide because many corvid populations are increasing, and they exhibit great capacity to adopt new foraging strategies to exploit novel prey. Journal compilation

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The discourse around students from low socio-economic backgrounds often adopts a deficit conception in which these students are seen as a problem in higher education. In light of recent figures pointing to an increase in the number and proportion of these students participating in higher education [Pitman, T. 2014. "More Students in Higher ed, But it's no more Representative." The Conversation 28: 1-4] and an absence of evidence to support deficit thinking, this deficit discourse requires re-examination. Qualitative data from 115 interviews carried out across 6 Australian universities as part of a national study reveal that, contrary to the conception of these students as a problem, students from low SES backgrounds demonstrate high levels of determination and academic skills and that they actively seek high standards in their studies. This paper critically examines deficit conceptions of these students, drawing on findings from qualitative interviews with 89 successful students from low SES backgrounds and 26 staff members recognised as exemplary in their provision of teaching and support of students from low SES backgrounds. Drawing on these findings, this paper challenges the deficit discourse and argues for a more affirmative and nuanced conception of students from low SES backgrounds.