JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. University of California Press and CooperOrnithological Society are collaborating with JSTOR to digitize, preserve and extend access to The Condor.Abstract. The fates of 121 nests of Northern Cardinals (Cardinalis cardinalis) in southwestern Ohio were determined in 1991 and 1992. Success rate was only 15%, estimated by the Mayfield method. All failed nests were known or suspected to have been preyed upon. Several hypotheses to explain differences between the location of successful and failed nests were tested. None of those considered explained why the contents of particular nests were taken. We propose that a high incidence of predation by a rich guild of nest predators precludes the existence of predictably safe nest sites for cardinals. Instead, cardinals appear simply to be well-adapted to renest rapidly in response to the near randomness of nest predation. A similar adaptation may characterize many passerines.
Scaling of avian brain:body mass throughout the diversi®cation of the class was investigated by analysis of a large collection of adult brain and body masses. Linear regression model analysis of whole-class brain:body scaling resulted in scaling exponents ranging from 0.574 to 0.609, values which exclude several prior empirical and theoretical estimates. Taxonomic level-speci®c analysis of brain:body scaling was performed by major-axis regression of trait variances partitioned among levels of taxonomic distinction. Brain:body scaling exponents varied markedly among avian orders, but were not easily related to ecological differences among taxa. Avian brain:body scaling exhibited a partial taxon-level effect, in that scaling exponents vary with the taxonomic level of investigation. However, scaling exponents were greatest at the family level, a pattern not consistent with prior ontogenetic or genetic covariance models of trait diversi®cation. Instead, it is suggested that initial diversi®cation among birds was largely through body size diversi®cation, while later diversi®cation of families within orders contained a relatively greater degree of brain size diversi®cation. Avian developmental mode, known to in¯uence avian brain size at hatching, was associated with relatively little variance in adult brain mass. Avian brain:body diversi®cation has occurred relatively uniformly in precocial taxa, while diversi®cation within altricial taxa is marked by a relatively high degree of brain mass diversi®cation among families within orders.
Summary 1.A method based on the calculation of major and minor axes of bivariate ellipses to estimate relative rates of evolutionary diversification of two traits is presented. The advantage of ellipse analysis over the more common allometric or regression approaches to variation in comparative data is that diversification of each trait is estimated relative to that of the other. This can reveal differences in the relative rates of diversification of two traits among sister groups or, through hierarchical analysis, over the history of a lineage. 2. Equations are provided for calculating the size, shape and orientation of bivariate ellipses based on the variance-covariance matrix of the original data. Standard errors and biases of these parameters are also quantified. 3. Applications of ellipse analysis to the relationship between egg size and incubation period in birds illustrate differences in the diversification of two traits between independent lineages. Nested analysis of covariance based on taxonomic levels further illustrates how relative rates of evolutionary diversification may vary through the history of a monophyletic group. 4. A simple model incorporating both independent (special) and correlated (general) change in two traits shows how different shapes and orientations of bivariate ellipses can be produced by different rates of evolutionary diversification in special and general genetic factors. 5. Ellipse analysis is a descriptive tool that can clarify patterns of diversification. It cannot distinguish differences in evolutionary responsiveness (phylogenetic constraint) from differences in the selective environment affecting the shape and orientation of the bivariate ellipse. It can, however, provide a more detailed characterization of trait evolution than other comparative methods, taking advantage of the additional information provided by the shape and, in some cases, the dimensions of the bivariate ellipse.
For many songbirds, the vocal repertoire constitutes acoustically distinct songs that are flexibly used in various behavioral contexts. To investigate how these different vocalizations are represented in the song neural system, we presented multiple song stimuli while performing extracellular recording in nucleus HVC in adult male song sparrows Melospiza melodia, a species known for its complex vocal repertoire and territorial use of song. We observed robust auditory responses to natural song stimuli in both awake and anesthetized animals. Auditory responses were selective for multiple songs of the bird's own repertoire (BOR) over acoustically modified versions of these stimuli. Selectivity was evident in both awake and anesthetized HVC, in contrast to auditory selectivity in zebra finch HVC, which is apparent only under anesthesia. Presentation of multiple song stimuli at different recording locations demonstrated that stimulus acoustic features and local neuronal tuning both contribute to auditory responsiveness. HVC auditory responsiveness was broadly distributed and nontopographic. Variance in auditory responsiveness was greater among than within HVC recording locations in both anesthetized and awake birds, in contrast to the global nature of auditory representation within zebra finch HVC. To assess the spatial consistency of auditory representation within HVC, we measured the repeatability with which ensembles of BOR songs were represented across the nucleus. Auditory response ranks to different songs were more consistent across recording locations in awake than in anesthetized animals. This spatial reliability of auditory responsiveness suggests that sound stimulus acoustic features contribute relatively more to auditory responsiveness in awake than in anesthetized animals.
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