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Article
Amaia A. Urquia Samele, Auteur ; Steven J. Portugal, AuteurDominance hierarchies are a social dynamic common in many species, which help balance the costs and benefits of social living. Which individuals in a group occupy high-ranking positions is influenced by a multitude of different intrinsic and/or [...]
Article
Jennifer C. Cantlay, Auteur ; Steven J. Portugal, Auteur ; Graham R. Martin, AuteurWide variation in visual field configuration has been recorded among avian species and it is hypothesized that this variation is driven primarily by foraging ecology and predator detection. It has also been shown that visual field configurations[...]
Article
Eleanor Lucas, Auteur ; Steven J. Portugal, AuteurAvian visual fields have been predicted to be highly conserved at the intraspecific level and be repeatable within an individual, yet this has never been previously determined empirically. Typically, only 2–3 individuals of a species are measure[...]
Article
Rhianna L. Ricketts, Auteur ; Daniel W. E. Sankey, Auteur ; Bryce P. Tidswell, Auteur ; Joshua Brown, Auteur ; Joseph F. Deegan, Auteur ; Steven J. Portugal, AuteurDans Ibis (164(2) 2022)The benefits of dominance are well known and numerous, including first access to resources such as food, mates and nesting sites. Less well studied are the potential costs associated with being dominant. Here, the movement of two flocks of domes[...]
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Jennifer C. Cantlay, Auteur ; Steven J. Portugal, Auteur ; Graham R. Martin, AuteurDans Ibis (161(4) 2019)The visual fields of Blacksmith Lapwings Vanellus armatus show the characteristics of visual guided foragers that use precision pecking for prey capture – a binocular field of narrow width and limited vertical extent, with the projection of the [...]
Article
Steven J. Portugal, Auteur ; James Bowen, Auteur ; Christina Riehl, AuteurDans Ibis (160(1) 2018)Birds’ eggshells are primarily composed of calcite, an abundant polymorph of calcium carbonate (CaCO3). However, the eggshells of some species are coated with spherules of vaterite, a rare and thermodynamically unstable polymorph of CaCO3, the f[...]
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Steven J. Portugal, Auteur ; Laura Sivess, Auteur ; Graham R. Martin, Auteur ; Patrick J. Butler, Auteur ; Craig R. White, AuteurDominant individuals within animal groups will frequently place themselves in the most beneficial position for maximal protection against predation. Higher perches are generally associated with reduced predation risk in birds, so we predicted th[...]
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Steven J. Portugal, Auteur ; Campbell P. Murn, Auteur ; Graham R. Martin, AuteurThe visual fields of the Aegypiinae vultures have been shown to be adapted primarily to meet two key perceptual challenges of their obligate carrion-feeding behaviour: scanning the ground and preventing the sun's image falling upon the retina. H[...]
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Phillip Cassey, Auteur ; Ivan Mikšík, Auteur ; Steven J. Portugal, Auteur ; Golo Maurer, Auteur ; John G. Ewen, Auteur ; Erica Zarate, Auteur ; Mary A. Sewell, Auteur ; Filiz Karadas, Auteur ; Tomáš Grim, Auteur ; Mark E. Hauber, AuteurThe colourful appearance of avian eggshells is a prominent aspect of maternal reproductive effort in birds. Some differences in eggshell coloration have been reported to co-vary with various measures of maternal condition and these patterns supp[...]
Article
Golo Maurer, Auteur ; Steven J. Portugal, Auteur ; Phillip Cassey, AuteurThe thickness of avian eggshells is used to assess shell quality in wild and domestic species, as an indicator of environmental pollution and as an adaptive explanation for shell maculation. Both direct measurements and calculated eggshell thick[...]
Article
Graham R. Martin, Auteur ; Steven J. Portugal, AuteurVariations in visual field topography among birds have been interpreted as adaptations to the specific perceptual challenges posed by the species' foraging ecology. To test this hypothesis we determined visual field topography in four bird speci[...]
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Steven J. Portugal, Auteur ; Rhian Isaac, Auteur ; Kate L. Quinton, Auteur ; S. James Reynolds, AuteurMany different behavioural changes have been observed in wild waterfowl during the flightless stage of wing moult with birds frequently becoming inactive and reducing time spent foraging. Increased predation risk, elevated energetic demands of f[...]
Article
Steven J. Portugal, Auteur ; Jonathan A. Green, Auteur ; Theunis Piersma, Auteur ; Goetz Eichhorn, Auteur ; Patrick J. Butler, AuteurMany species of waterfowl undergo a post-breeding simultaneous flight feather moult (wing moult) which renders them flightless and vulnerable to predation for up to 4 weeks. Here we present an analysis of the correlations between individual time[...]
Article
Steven J. Portugal, Auteur ; Patrick J. Butler, Auteur ; Jonathan A. Green, Auteur ; Phillip Cassey, AuteurBone is continually undergoing cycles of apposition and resorption referred to as adaptive remodelling. We tested the hypothesis that captive moulting Barnacle Geese (Branta leucopsis) would show adaptive bone mineralisation during the flightles[...]
Article
Lewis G. Halsey, Auteur ; Steven J. Portugal, Auteur ; Jennifer A. Smith, Auteur ; Campbell P. Murn, Auteur ; Rory P. Wilson, AuteurMeasuring body movements using accelerometry data loggers is a relatively new technique, the full applicability of which has yet to be tested on volant birds. Our study illustrates the potential of accelerometry for research on large birds by us[...]
Article
Golo Maurer, Auteur ; Steven J. Portugal, Auteur ; Phillip Cassey, AuteurCurrent research into the evolution and adaptive function of avian eggshell pigmentation, including maculation, has focused mostly on signalling-based and structural function hypotheses but ignored the potential consequences of shell pigmentatio[...]
Article
Steven J. Portugal, Auteur ; Matthieu Guillemain, AuteurIncreased vigilance in male animals has been attributed to mate guarding (male investment hypothesis), to secondary sexual characteristics increasing predation risk (male constraint hypothesis) or for the benefit to the female (female benefits h[...]
Article
Graham R. Martin, Auteur ; Steven J. Portugal, Auteur ; Campbell P. Murn, AuteurThe visual fields of vultures contain a small binocular region and large blind areas above, below and behind the head. Head positions typically adopted by foraging vultures suggest that these visual fields provide comprehensive visual coverage o[...]
Article
Kaat Brulez, Auteur ; Pankaj K. Choudhary, Auteur ; Golo Maurer, Auteur ; Steven J. Portugal, Auteur ; Rebecca L. Boulton, Auteur ; Simone L. Webber, Auteur ; Phillip Cassey, AuteurEggshell pattern scoring, a method to quantify the degree of surface maculation, can potentially be a quick, inexpensive and reliable method to obtain information on eggshell appearance and spot patterns. The key pigment responsible for red-brow[...]
