Abstract:Island birds that were victims of anthropic extinctions were often more specialist species, having evolved their most distinctive features in isolation, making the study of fossil insular birds most interesting. Here we studied a fossil cranium of the ‘giant’ extinct scops owl
Otus murivorus
from Rodrigues Island (Mascarene Islands, southwestern Indian Ocean), to determine any potential unique characters. The fossil and extant strigids were imaged through X-ray microtomography, providing… Show more
“… Figure 9 Comparison of orbit posterior angle which is used to measure the orbital margin convergence (measured as in Menegaz & Kirk [ 14 ] and Duhamel et al . [ 48 ]). …”
Section: Resultsmentioning
confidence: 99%
“…We combined methods from Duhamel et al . [ 48 ] and Borges et al . [ 49 ] and used Materialise Mimics angle, distance and plane tools.…”
Nocturnal birds display diverse adaptations of the visual system to low-light conditions. The skulls of birds reflect many of these and are used increasingly to infer nocturnality in extinct species. However, it is unclear how reliable such assessments are, particularly in cases of recent evolutionary transitions to nocturnality. Here, we investigate a case of recently evolved nocturnality in the world's only nocturnal hawk, the letter-winged kite
Elanus scriptus
. We employed phylogenetically informed analyses of orbit, optic foramen and endocast measurements from three-dimensional reconstructions of micro-computed tomography scanned skulls of the letter-winged kite, two congeners, and 13 other accipitrid and falconid raptors. Contrary to earlier suggestions, the letter-winged kite was not unique in any of our metrics. However, all species of
Elanus
have significantly higher ratios of orbit versus optic foramen diameter, suggesting high visual sensitivity at the expense of acuity. In addition, visual system morphology varies greatly across accipitrid species, likely reflecting hunting styles. Overall, our results suggest that the transition to nocturnality can occur rapidly and without changes to key hard-tissue indicators of vision, but also that hard-tissue anatomy of the visual system may provide a means of inferring a range of raptor behaviours, well beyond nocturnality.
“… Figure 9 Comparison of orbit posterior angle which is used to measure the orbital margin convergence (measured as in Menegaz & Kirk [ 14 ] and Duhamel et al . [ 48 ]). …”
Section: Resultsmentioning
confidence: 99%
“…We combined methods from Duhamel et al . [ 48 ] and Borges et al . [ 49 ] and used Materialise Mimics angle, distance and plane tools.…”
Nocturnal birds display diverse adaptations of the visual system to low-light conditions. The skulls of birds reflect many of these and are used increasingly to infer nocturnality in extinct species. However, it is unclear how reliable such assessments are, particularly in cases of recent evolutionary transitions to nocturnality. Here, we investigate a case of recently evolved nocturnality in the world's only nocturnal hawk, the letter-winged kite
Elanus scriptus
. We employed phylogenetically informed analyses of orbit, optic foramen and endocast measurements from three-dimensional reconstructions of micro-computed tomography scanned skulls of the letter-winged kite, two congeners, and 13 other accipitrid and falconid raptors. Contrary to earlier suggestions, the letter-winged kite was not unique in any of our metrics. However, all species of
Elanus
have significantly higher ratios of orbit versus optic foramen diameter, suggesting high visual sensitivity at the expense of acuity. In addition, visual system morphology varies greatly across accipitrid species, likely reflecting hunting styles. Overall, our results suggest that the transition to nocturnality can occur rapidly and without changes to key hard-tissue indicators of vision, but also that hard-tissue anatomy of the visual system may provide a means of inferring a range of raptor behaviours, well beyond nocturnality.
“…Capuchin waiting times were shorter in the tool‐use area, which is consistent with capuchins chasing other animals away. In island systems, populations have been suggested to be less exposed to interspecific competition than mainland populations (Diamond, 1978; Duhamel et al., 2020). The observed pattern of short capuchin waiting times could thus be explained by the frequency of visits and the interval between them.…”
Interspecific interactions play an important role in structuring wildlife communities. On islands, which often have reduced species assemblages, species may expand their niches resulting in unusual patterns of interactions with other members of the ecological community. In this study, we compared spatio‐temporal interactions of two food competitors between a site with predators and two predator‐free islands in the Coiba archipelago, Panama. Here, capuchin monkeys (Cebus capucinus imitator) exhibit high levels of terrestriality, and some groups engage in stone tool use. This potentially leads to competition with sympatric agoutis (Dasyprocta coibae), which have overlapping diets. We used camera‐trap surveys to estimate temporal overlap between both species, distinguishing between arboreal and terrestrial activity of capuchins. We also compared detection rates and intervals between consecutive detections of both species at sites in which the monkeys use stone tools (tool‐use area) and sites in which they do not (non‐tool‐use area). We found high spatio‐temporal overlap between agouti and capuchin on the forest floor of both islands. While capuchins visited the tool‐use area four times as often as the non‐tool‐use area, agoutis avoided the tool‐use area, capture rates being 25 times as low. Waiting times were shorter for both species at the tool‐use area. These results suggest temporal overlap and spatial segregation. Niche expansions on islands thus cause unique interactions that do not occur on the mainland.Abstract in Spanish is available with online material.
“…of pigeons (Columbiformes)endocranial volume not smaller than expected from pigeon allometryMauritiusallometric analysis[99] Rodrigues Island giant owl (Otus murivorus ), compared to 10 extant spp. of owls (Strigidae)reduction of brain volume in extinct island endemicRodrigues, Mauritiusdiverseabsence of predators, reduction of interspecific competitionbrain expansion cannot follow pace of body size increase (evolutionary pace dissociation)comparative analysis of brain size[100] Haast's eagle ( Harpagornis moorei ), compared to 35 spp. of eagles (Accipitridae)island endemic had low endocranial volume for its body massNew Zealanddiverseabsence of predators, competitors on islandmismatch between neural and somatic growthcomparative analysis of brain size[101] 40 crow and raven species ( Corvus )brain size does not predict ability to colonize islandsislands worldwidemainland sites throughout the worldislands are challenging environments, promoting enhanced cognitioncomparative analysis of brain size[102] 1900+ species of birdsinsular species have larger brainsdiversediversehigh environmental unpredictability across yearsnatural selection; high phenotypic plasticity may inhibit evolutionary change in some cladescomparative analysis of brain size[103] Deer mouse ( Peromyscus maniculatus )insular mice displayed shorter latencies to solve a Morris water-maze taskMoresby Island, CanadaBritish Columbia, Canadadifferences in swimming abilities (rather than cognitive skills) between populationsunknownlaboratory observations[104]…”
Section: The Current Evidence For a Behavioural Component To The Isla...mentioning
Animals on islands typically depart from their mainland relatives in assorted aspects of their biology. Because they seem to occur in concert, and to some extent evolve convergently in disparate taxa, these changes are referred to as the ‘island syndrome’. While morphological, physiological and life-history components of the island syndrome have received considerable attention, much less is known about how insularity affects behaviour. In this paper, we argue why changes in personality traits and cognitive abilities can be expected to form part of the island syndrome. We provide an overview of studies that have compared personality traits and cognitive abilities between island and mainland populations, or among islands. Overall, the pickings are remarkably slim. There is evidence that animals on islands tend to be bolder than on the mainland, but effects on other personality traits go either way. The evidence for effects of insularity on cognitive abilities or style is highly circumstantial and very mixed. Finally, we consider the ecological drivers that may induce such changes, and the mechanisms through which they might occur. We conclude that our knowledge of the behavioural and cognitive responses to island environments remains limited, and we encourage behavioural biologists to make more use of these ‘natural laboratories for evolution’.
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