The ability to locate high-quality stopover habitat has fitness implications for migrating landbi... more The ability to locate high-quality stopover habitat has fitness implications for migrating landbirds, and alteration of stopover habitats due to human land-use change, including the introduction of nonnative plants, has been identified as a conservation concern. We tested whether the use and selection of shrublands dominated by exotic plants differed from that of native-dominated shrublands. Specifically, we compared capture rates, transfer rates between habitats, within-foraging-range habitat selection, and food items of Swainson's Thrushes (Catharus ustulatus) and Gray Catbirds (Dumetella carolinensis) between exotic-and native-dominated shrublands in Michigan, USA, during fall migration of 2012 and 2013. Capture rates were .20% higher for thrushes and .250% higher for catbirds in native shrubland. Capture-recapture data showed that birds moved from exotic to native shrubland at higher rates than vice versa. For radio-tagged thrushes and catbirds, native shrubland was~30% more likely to be used than expected by land cover at the within-foraging-range scale. Thrushes, but not catbirds, avoided exotic shrubs within their foraging ranges. Native Lindera benzoin fruit was .50% more likely to be found in fecal samples from both bird species in native-dominated shrubland than in exotic-dominated shrubland, and was the predominant food item in the former habitat type. Collectively, our results suggest that fall migrating Swainson's Thrushes and Gray Catbirds select, and hence occur at higher densities in, predominantly native shrublands rather than exotic-dominated shrublands. One mechanism for this pattern may be their preference for certain native fruits, such as L. benzoin. Our results suggest that native shrubland may be an especially important stopover habitat for frugivorous birds during fall migration.
Innate immune functions are proposed to develop rapidly post-hatch in altricial nestlings, compar... more Innate immune functions are proposed to develop rapidly post-hatch in altricial nestlings, compared with adaptive immune defenses that require development of receptor specifi city and memory. Studies of ontogenetic changes in altricial birds have been few until relatively recently and often do not encompass the entire developmental period. We examined the patterns of development in constitutive innate and adaptive immune indices in house sparrow nestlings (3, 6, 9 and 12 days (d) post-hatch), hatch-year birds and adults. Lysozyme activity signifi cantly decreased with age, likely representing catabolism of maternal investment of lysozyme in the egg albumen. Levels of total IgY (indexing adaptive immune function), as well as agglutination and lysis (indexing innate immune function), increased throughout the nestling period, but were signifi cantly below levels found in fully-grown birds at the time of fl edging. Th ere were no signifi cant diff erences between hatch-year birds and adults in these measures, indicating that rapid, full maturation occurs early in the postfl edging period. In combination with previous studies, these data highlight the importance of sampling fl edglings to assess full immune ontogeny and suggest that fl edgling birds may be more vulnerable to infection than adults.
BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access t... more BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses.
The ability to locate high-quality stopover habitat has fitness implications for migrating landbi... more The ability to locate high-quality stopover habitat has fitness implications for migrating landbirds, and alteration of stopover habitats due to human land-use change, including the introduction of nonnative plants, has been identified as a conservation concern. We tested whether the use and selection of shrublands dominated by exotic plants differed from that of native-dominated shrublands. Specifically, we compared capture rates, transfer rates between habitats, within-foraging-range habitat selection, and food items of Swainson's Thrushes (Catharus ustulatus) and Gray Catbirds (Dumetella carolinensis) between exotic-and native-dominated shrublands in Michigan, USA, during fall migration of 2012 and 2013. Capture rates were .20% higher for thrushes and .250% higher for catbirds in native shrubland. Capture-recapture data showed that birds moved from exotic to native shrubland at higher rates than vice versa. For radio-tagged thrushes and catbirds, native shrubland was ~30% more likely to be used than expected by land cover at the within-foraging-range scale. Thrushes, but not catbirds, avoided exotic shrubs within their foraging ranges. Native Lindera benzoin fruit was .50% more likely to be found in fecal samples from both bird species in native-dominated shrubland than in exotic-dominated shrubland, and was the predominant food item in the former habitat type. Collectively, our results suggest that fall migrating Swainson's Thrushes and Gray Catbirds select, and hence occur at higher densities in, predominantly native shrublands rather than exotic-dominated shrublands. One mechanism for this pattern may be their preference for certain native fruits, such as L. benzoin. Our results suggest that native shrubland may be an especially important stopover habitat for frugivorous birds during fall migration. Uso de há bitat de matorral dominado por exóticasex´exóticas y nativas por migrantes de otõ no de Catharus ustulatus y Dumetella carolinensis en Michigan, EEUU RESUMEN La habilidad de localizar hábitat de parada de alta calidad tiene implicancias para la adecuací on bioí ogica de las aves terrestres migratorias, y la alterací on de los hábitats de parada debido al cambio antrópicoantr´antrópico de uso del suelo, incluyendo la introduccí on de plantas no nativas, ha sido identificada como una preocupací on de conservací on. Evaluamos si el uso y la seleccí on de matorrales dominados por plantas exóticasex´exóticas y por plantas nativas difirieron entre sí. Específicamente, comparamos tasa de captura, tasa de transferencia entre hábitats, seleccí on de hábitat dentro del rango de forrajeo e ´ ıtems de forrajeo de Catharus ustulatus y Dumetella carolinensis entre matorrales dominados por exóticasex´exóticas y nativas en Michigan, EEUU, durante la migrací on de otõ no de 2012 y 2013. Las tasas de captura fueron .20% más altas para C. ustulatus y .250% más altas para D. carolinensis en el matorral nativo. Los datos de captura-recaptura mostraron que las aves se movieron desde el matorral exóticoex´exótico al nativo a tasas más altas que a la inversa. Para los individuos de C. ustulatus y D. carolinensis marcados con radios, el matorral nativo tuvo ~30% más probabilidad de ser usado que lo esperado en base a la cobertura del suelo a la escala dentro del rango de forrajeo. C. ustulatus, pero no D. carolinensis, evitóevit´evitó los arbustos exóticosex´exóticos adentro de su rango de forrajeo. El fruto nativo de Lindera benzoin presentópresent´presentó .50% más probabilidad de ser hallado en muestras de ambas especies de aves en el matorral dominado por nativas y fue eí ıtem alimenticio predominante en este tipo de hábitat. En conjunto, nuestros resultados sugieren que los migrantes de otõ no de C. ustulatus y D. carolinensis seleccionan y por ende aparecen a mayores densidades en los matorrales predominantemente nativos que en los matorrales dominados por exóticasex´exóticas. Un mecanismo para explicar este patrónpatr´patrón pueden ser sus preferencias por ciertos frutos nativos, como los de L. benzoin. Nuestros resultados sugieren que el matorral nativo puede ser un hábitat de parada especialmente importante para las aves frugívoras durante la migrací on de otõ no.
Migration is a physiologically demanding activity. Recent studies suggest that migrating birds ca... more Migration is a physiologically demanding activity. Recent studies suggest that migrating birds can improve their immune and antioxidant status during stopover, implying that variation in stopover habitat can affect migrants' health. We studied 2 species that are strongly frugivorous during fall migration, Swainson's Thrushes (Catharus ustulatus) and Gray Catbirds (Dumetella carolinensis). We asked whether birds that used shrubland dominated by exotic plants experienced differences in mass change, immune function, and antioxidant status relative to conspecifics in native-dominated shrubland during fall stopover in Michigan, USA, in 2012–2013. We found no habitat-related differences in any of the measured health parameters for Swainson's Thrushes. However, Gray Catbirds using native-dominated shrubland retained mass while those in exotic-dominated shrubland lost mass in 2013. Gray Catbirds in exotic-dominated habitat that year also had poorer immune status (elevated granulocyte:lymphocyte ratio and reduced hemagglutination and haptoglobin) and had lower plasma total carotenoids (immunostimulatory antioxidants) relative to conspecifics in native-dominated shrubland. While these findings were not replicated in 2012, circulating antioxidant capacity was lower in both years in Gray Catbirds captured in exotic habitat. Habitat-specific estimates of dietary energy, carotenoid, and antioxidant content per unit mass of fruit were similar between habitat types for Swainson's Thrushes. For Gray Catbirds, however, the fruit diet was lower in carotenoids and antioxidant capacity, but not in energy, in exotic habitat. Our results provide evidence that differential use of stopover habitats may affect the immune and antioxidant status of migrating landbirds. Furthermore, our results suggest that habitat may affect health status based on the complex relationships among quality and abundance of food, food preferences, and refueling performance, which vary among species. We suggest that future studies measure immune and antioxidant metrics in addition to refueling performance to better understand the effects of stopover habitat use on landbird migrant health. This information may improve assessment of habitat quality for migrants.
The ability to locate high-quality stopover habitat has fitness implications for migrating landbi... more The ability to locate high-quality stopover habitat has fitness implications for migrating landbirds, and alteration of stopover habitats due to human land-use change, including the introduction of nonnative plants, has been identified as a conservation concern. We tested whether the use and selection of shrublands dominated by exotic plants differed from that of native-dominated shrublands. Specifically, we compared capture rates, transfer rates between habitats, within-foraging-range habitat selection, and food items of Swainson's Thrushes (Catharus ustulatus) and Gray Catbirds (Dumetella carolinensis) between exotic-and native-dominated shrublands in Michigan, USA, during fall migration of 2012 and 2013. Capture rates were .20% higher for thrushes and .250% higher for catbirds in native shrubland. Capture-recapture data showed that birds moved from exotic to native shrubland at higher rates than vice versa. For radio-tagged thrushes and catbirds, native shrubland was~30% more likely to be used than expected by land cover at the within-foraging-range scale. Thrushes, but not catbirds, avoided exotic shrubs within their foraging ranges. Native Lindera benzoin fruit was .50% more likely to be found in fecal samples from both bird species in native-dominated shrubland than in exotic-dominated shrubland, and was the predominant food item in the former habitat type. Collectively, our results suggest that fall migrating Swainson's Thrushes and Gray Catbirds select, and hence occur at higher densities in, predominantly native shrublands rather than exotic-dominated shrublands. One mechanism for this pattern may be their preference for certain native fruits, such as L. benzoin. Our results suggest that native shrubland may be an especially important stopover habitat for frugivorous birds during fall migration.
Innate immune functions are proposed to develop rapidly post-hatch in altricial nestlings, compar... more Innate immune functions are proposed to develop rapidly post-hatch in altricial nestlings, compared with adaptive immune defenses that require development of receptor specifi city and memory. Studies of ontogenetic changes in altricial birds have been few until relatively recently and often do not encompass the entire developmental period. We examined the patterns of development in constitutive innate and adaptive immune indices in house sparrow nestlings (3, 6, 9 and 12 days (d) post-hatch), hatch-year birds and adults. Lysozyme activity signifi cantly decreased with age, likely representing catabolism of maternal investment of lysozyme in the egg albumen. Levels of total IgY (indexing adaptive immune function), as well as agglutination and lysis (indexing innate immune function), increased throughout the nestling period, but were signifi cantly below levels found in fully-grown birds at the time of fl edging. Th ere were no signifi cant diff erences between hatch-year birds and adults in these measures, indicating that rapid, full maturation occurs early in the postfl edging period. In combination with previous studies, these data highlight the importance of sampling fl edglings to assess full immune ontogeny and suggest that fl edgling birds may be more vulnerable to infection than adults.
BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access t... more BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses.
The ability to locate high-quality stopover habitat has fitness implications for migrating landbi... more The ability to locate high-quality stopover habitat has fitness implications for migrating landbirds, and alteration of stopover habitats due to human land-use change, including the introduction of nonnative plants, has been identified as a conservation concern. We tested whether the use and selection of shrublands dominated by exotic plants differed from that of native-dominated shrublands. Specifically, we compared capture rates, transfer rates between habitats, within-foraging-range habitat selection, and food items of Swainson's Thrushes (Catharus ustulatus) and Gray Catbirds (Dumetella carolinensis) between exotic-and native-dominated shrublands in Michigan, USA, during fall migration of 2012 and 2013. Capture rates were .20% higher for thrushes and .250% higher for catbirds in native shrubland. Capture-recapture data showed that birds moved from exotic to native shrubland at higher rates than vice versa. For radio-tagged thrushes and catbirds, native shrubland was ~30% more likely to be used than expected by land cover at the within-foraging-range scale. Thrushes, but not catbirds, avoided exotic shrubs within their foraging ranges. Native Lindera benzoin fruit was .50% more likely to be found in fecal samples from both bird species in native-dominated shrubland than in exotic-dominated shrubland, and was the predominant food item in the former habitat type. Collectively, our results suggest that fall migrating Swainson's Thrushes and Gray Catbirds select, and hence occur at higher densities in, predominantly native shrublands rather than exotic-dominated shrublands. One mechanism for this pattern may be their preference for certain native fruits, such as L. benzoin. Our results suggest that native shrubland may be an especially important stopover habitat for frugivorous birds during fall migration. Uso de há bitat de matorral dominado por exóticasex´exóticas y nativas por migrantes de otõ no de Catharus ustulatus y Dumetella carolinensis en Michigan, EEUU RESUMEN La habilidad de localizar hábitat de parada de alta calidad tiene implicancias para la adecuací on bioí ogica de las aves terrestres migratorias, y la alterací on de los hábitats de parada debido al cambio antrópicoantr´antrópico de uso del suelo, incluyendo la introduccí on de plantas no nativas, ha sido identificada como una preocupací on de conservací on. Evaluamos si el uso y la seleccí on de matorrales dominados por plantas exóticasex´exóticas y por plantas nativas difirieron entre sí. Específicamente, comparamos tasa de captura, tasa de transferencia entre hábitats, seleccí on de hábitat dentro del rango de forrajeo e ´ ıtems de forrajeo de Catharus ustulatus y Dumetella carolinensis entre matorrales dominados por exóticasex´exóticas y nativas en Michigan, EEUU, durante la migrací on de otõ no de 2012 y 2013. Las tasas de captura fueron .20% más altas para C. ustulatus y .250% más altas para D. carolinensis en el matorral nativo. Los datos de captura-recaptura mostraron que las aves se movieron desde el matorral exóticoex´exótico al nativo a tasas más altas que a la inversa. Para los individuos de C. ustulatus y D. carolinensis marcados con radios, el matorral nativo tuvo ~30% más probabilidad de ser usado que lo esperado en base a la cobertura del suelo a la escala dentro del rango de forrajeo. C. ustulatus, pero no D. carolinensis, evitóevit´evitó los arbustos exóticosex´exóticos adentro de su rango de forrajeo. El fruto nativo de Lindera benzoin presentópresent´presentó .50% más probabilidad de ser hallado en muestras de ambas especies de aves en el matorral dominado por nativas y fue eí ıtem alimenticio predominante en este tipo de hábitat. En conjunto, nuestros resultados sugieren que los migrantes de otõ no de C. ustulatus y D. carolinensis seleccionan y por ende aparecen a mayores densidades en los matorrales predominantemente nativos que en los matorrales dominados por exóticasex´exóticas. Un mecanismo para explicar este patrónpatr´patrón pueden ser sus preferencias por ciertos frutos nativos, como los de L. benzoin. Nuestros resultados sugieren que el matorral nativo puede ser un hábitat de parada especialmente importante para las aves frugívoras durante la migrací on de otõ no.
Migration is a physiologically demanding activity. Recent studies suggest that migrating birds ca... more Migration is a physiologically demanding activity. Recent studies suggest that migrating birds can improve their immune and antioxidant status during stopover, implying that variation in stopover habitat can affect migrants' health. We studied 2 species that are strongly frugivorous during fall migration, Swainson's Thrushes (Catharus ustulatus) and Gray Catbirds (Dumetella carolinensis). We asked whether birds that used shrubland dominated by exotic plants experienced differences in mass change, immune function, and antioxidant status relative to conspecifics in native-dominated shrubland during fall stopover in Michigan, USA, in 2012–2013. We found no habitat-related differences in any of the measured health parameters for Swainson's Thrushes. However, Gray Catbirds using native-dominated shrubland retained mass while those in exotic-dominated shrubland lost mass in 2013. Gray Catbirds in exotic-dominated habitat that year also had poorer immune status (elevated granulocyte:lymphocyte ratio and reduced hemagglutination and haptoglobin) and had lower plasma total carotenoids (immunostimulatory antioxidants) relative to conspecifics in native-dominated shrubland. While these findings were not replicated in 2012, circulating antioxidant capacity was lower in both years in Gray Catbirds captured in exotic habitat. Habitat-specific estimates of dietary energy, carotenoid, and antioxidant content per unit mass of fruit were similar between habitat types for Swainson's Thrushes. For Gray Catbirds, however, the fruit diet was lower in carotenoids and antioxidant capacity, but not in energy, in exotic habitat. Our results provide evidence that differential use of stopover habitats may affect the immune and antioxidant status of migrating landbirds. Furthermore, our results suggest that habitat may affect health status based on the complex relationships among quality and abundance of food, food preferences, and refueling performance, which vary among species. We suggest that future studies measure immune and antioxidant metrics in addition to refueling performance to better understand the effects of stopover habitat use on landbird migrant health. This information may improve assessment of habitat quality for migrants.
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