Jay D. Carlisle

An experimental investigation into the effects of traffic noise on distributions of birds: avoiding the phantom road

Many authors have suggested that the negative effects of roads on animals are largely owing to traffic noise. Although suggestive, most past studies of the effects of road noise on wildlife were conducted in the presence of the other confounding effects of roads, such as visual disturbance, collisions and chemical pollution among others. We present, to our knowledge, the first study to experimentally apply traffic noise to a roadless area at a landscape scale—thus avoiding the other confounding aspects of roads present in past studies. We replicated the sound of a roadway at intervals—alternating 4 days of noise on with 4 days off—during the autumn migratory period using a 0.5 km array of speakers within an established stopover site in southern Idaho. We conducted daily bird surveys along our ‘Phantom Road’ and in a nearby control site. We document over a one-quarter decline in bird abundance and almost complete avoidance by some species between noise-on and noise-off periods along the phantom road and no such effects at control sites—suggesting that traffic noise is a major driver of effects of roads on populations of animals.

A phantom road experiment reveals traffic noise is an invisible source of habitat degradation

Significance Using landscape-scale traffic noise playbacks to create a “phantom road,” we find that noise, apart from other factors present near roads, degrades the value of habitat for migrating songbirds. We found that nearly one third of the bird community avoided the phantom road. For some bird species that remained despite noise exposure, body condition and stopover efficiency (ability to gain body condition over time) decreased compared with control conditions. These findings have broad implications for the conservation of migratory birds and perhaps for other wildlife, because factors driving foraging behavior are similar across animals. For wildlife that remains in loud areas, noise pollution represents an invisible source of habitat degradation. Decades of research demonstrate that roads impact wildlife and suggest traffic noise as a primary cause of population declines near roads. We created a “phantom road” using an array of speakers to apply traffic noise to a roadless landscape, directly testing the effect of noise alone on an entire songbird community during autumn migration. Thirty-one percent of the bird community avoided the phantom road. For individuals that stayed despite the noise, overall body condition decreased by a full SD and some species showed a change in ability to gain body condition when exposed to traffic noise during migratory stopover. We conducted complementary laboratory experiments that implicate foraging-vigilance behavior as one mechanism driving this pattern. Our results suggest that noise degrades habitat that is otherwise suitable, and that the presence of a species does not indicate the absence of an impact.

LANDBIRD MIGRATION IN THE AMERICAN WEST: RECENT PROGRESS AND FUTURE RESEARCH DIRECTIONS

Abstract. Our knowledge of avian behaviors during the nonbreeding period still lags behind that of the breeding season, but the last decade has witnessed a proliferation in research that has yielded significant progress in understanding migration patterns of North American birds. And, although historically the great majority of migration research has been conducted in the eastern half of the continent, there has been much recent progress on aspects of avian migration in the West. In particular, expanded use of techniques such as radar, plasma metabolites, mist-netting, count surveys, stable isotopes, genetic data, and animal tracking, coupled with an increase in multi-investigator collaborations, have all contributed to this growth of knowledge. There is increasing recognition that migration is likely the most limiting time of year for migratory birds, increasing the importance of continuing to decipher patterns of stopover ecology, identifying critical stopover habitats, and documenting migration routes in the diverse and changing landscapes of the American West. Here, we review and briefly synthesize the latest findings and advances in avian migration and consider research needs to guide future research on migration in the West.

STOPOVER ECOLOGY OF AUTUMN LANDBIRD MIGRANTS IN THE BOISE FOOTHILLS OF SOUTHWESTERN IDAHO

Abstract The topography of western North America provides a complex landscape for landbird migrants, and stopover patterns in this region are poorly understood. We examined seven years of stopover data (1997–2003) from a montane area in southwestern Idaho to determine whether this area provides suitable stopover habitat. We compared the proportion of birds recaptured, stopover duration, and changes in energetic condition within and among species and between two mist-netting sites located in different habitats. The proportion of birds recaptured ranged from zero to over 20%, and fewer than 5% of individuals were recaptured in most species. Mean minimum stopover durations from recapture data ranged from 1 to 10 days; most species averaged less than 6 days. Stopover duration estimates from open-population models were comparable but generally greater than estimates from recapture data. As found in stopover studies from other regions, stopover metrics varied within and among species in Idaho. However, most migrants in this study exhibited an ability to gain mass, evidenced both by recapture data and by regression of energetic condition against time since sunrise. These data imply that montane habitats in Idaho are suitable stopover sites. It follows that these habitats might serve an important role for many landbird migrants during the period of late summer molt and autumn migration, a time when many lowland areas of the West, including some riparian systems, are especially arid. We suggest that including montane nonriparian habitats in future stopover ecology studies will allow for a more complete understanding of migrant habitat needs in the West. Ecología de Aves Migrantes de Otoño Durante Períodos de Escala en el Piedemonte de Boise, Suroeste de Idaho Resumen. La topografía del oeste de Norte América representa un paisaje complejo para las aves terrestres migratorias, y los patrones de escala migratoria en esta región son poco conocidos. En este estudio examinamos datos de escalas migratorias colectados a través de siete años (1997–2003) en un área montana del suroeste de Idaho para determinar si esta área provee hábitats de escala adecuados. Comparamos la proporción de aves recapturadas, la duración del período de escala y los cambios en la condición energética por especie y entre especies y entre dos sitios de captura con redes de niebla ubicados en hábitats diferentes. La proporción de aves recapturadas varió entre cero y más del 20%, y en la mayoría de las especies menos del 5% de los individuos fueron recapturados. La duración mínima promedio de los períodos de escala estimada a partir de datos de recapturas estuvo entre uno y 10 días, y la estancia promedio de la mayoría de las especies fue menor de seis días. Los estimados de la duración de los períodos de escala calculados con modelos de población abierta fueron comparables (pero generalmente mayores) a los estimados basados en datos de recaptura. Tal como se ha encontrado en estudios sobre escalas migratorias realizados en otras regiones, en Idaho las mediciones tomadas durante el período de escala variaron dentro de cada especie y entre especies. Sin embargo, la mayoría de las especies migrantes que estudiamos tuvieron la habilidad de incrementar su peso, lo que se evidenció por medio de los datos de recaptura y de análisis de regresión entre la condición energética y el tiempo transcurrido desde la salida del sol. Estos datos implican que los ambientes montanos de Idaho son lugares de escala migratoria adecuados. Por lo tanto, estos hábitats pueden ser importantes para muchas aves terrestres durante el período de la muda del final del verano y la migración de otoño, un momento durante el cual muchas áreas de tierras bajas del oeste, incluyendo sistemas riparios, son especialmente secas. Sugerimos que incluir ambientes montanos no riparios en estudios futuros de la ecología de los períodos de escala migratoria permitirá tener un entendimiento más completo de los requerimientos de hábitat de las aves migratorias en el oeste.

Habitat Associations, Relative Abundance, and Species Richness of Autumn Landbird Migrants in Southwestern Idaho

Abstract We used count surveys and mist-net captures to compare habitat associations, relative abundance, species richness, and community similarity of migrant landbirds among four major habitats in the Boise Foothills of southwestern Idaho. Count surveys were conducted from August through October 1997–2000 in conifer forest, mountain shrubland, shrubsteppe, and riparian shrubland. We compared bird detections among habitats for all birds pooled, individual species, and three migration strategies: Neotropical, temperate, and resident (including irruptive migrants). Mountain shrubland supported the highest numbers of temperate migrants; both mountain shrubland and riparian shrubland had the highest numbers of Neotropical migrants; and conifer forest had the highest numbers of residents. Species richness was highest in riparian shrubland and lowest in shrubsteppe, whereas diversity and evenness were highest in conifer forest and mountain shrubland. Mist netting was conducted from mid-July to mid-October in two habitats: mountain shrubland (1997– 2002) and riparian shrubland (1998–1999). Captures (adjusted for effort) were compared among habitats in 1998–1999 and were similar for temperate migrants, whereas mountain shrubland had higher abundance of Neotropical migrants and riparian shrubland had higher abundance of irruptive migrants. Richness, diversity, and evenness were similar and there was high community similarity between mountain shrub and riparian shrubland habitats. These results emphasize the importance of montane habitats, especially deciduous shrub communities, to migrants in the Intermountain West. Asociaciones de Hábitat, Abundancia Relativa y Riqueza de Especies de Aves Migratorias Terrestres de Otoño en el Sudoeste de Idaho Resumen. Empleamos muestreos por conteos y capturas con redes de niebla para comparar asociaciones de hábitat, abundancia relativa, riqueza de especies, y similitud entre comunidades de aves migratorias terrestres, presentes en los cuatro hábitats principales de piedemonte de Boise en el sudoeste de Idaho. Los conteos fueron realizados entre agosto hasta octubre de los años 1997–2000 en bosque de coníferas, hábitat de matorral de montaña, matorral de estepa, y en matorral ripario. Comparamos la detección de aves entre hábitats para todas las especies juntas, para cada especie por separado y para tres categorías de estrategia de migración: especies migratorias neotropicales, especies migratorias de la zona templada y especies residentes (incluyendo migrantes irruptivas). El hábitat de matorral de montaña tuvo los números más altos de especies migratorias templadas. Los hábitats de matorral de montaña y matorral ripario tuvieron los números más altos de especies migratorias neotropicales y el bosque de coníferas tuvo los números más altos de especies residentes. La riqueza de especies fue mayor en el matorral ripario y menor en el matorral de estepa, mientras que la diversidad y la equidad fueron mayores en bosque de coníferas y matorral de montaña. El muestreo con redes de niebla se llevó a cabo desde mediados de julio hasta mediados de octubre en dos hábitats: matorral de montaña (1997–2002) y matorral ripario (1998–1999). Las capturas (ajustadas por esfuerzo de muestreo) fueron comparadas entre hábitats en 1998–1999. La abundancia de las especies migratorias de la zona templada fue similar entre hábitats, mientras que el hábitat de matorral de montaña tuvo la mayor abundancia de especies migratorias neotropicales y el matorral ripario tuvo la mayor abundancia de especies migratorias irruptivas. La riqueza, la diversidad y la equidad fueron similares entre hábitats y las comunidades de los hábitats de matorral de montaña y matorral ripario presentaron alta similitud. Estos resultados enfatizan la importancia de los hábitats de montaña, especialmente la de los hábitats de comunidades arbustivas deciduas, para las especies migratorias en el oeste intermontano.

MOLT STRATEGIES AND AGE DIFFERENCES IN MIGRATION TIMING AMONG AUTUMN LANDBIRD MIGRANTS IN SOUTHWESTERN IDAHO

Abstract Intraspecific patterns of autumn migration timing are not well known, particularly in the western United States. Here, we (1) describe autumn migration timing and age ratios of landbird migrants in southwestern Idaho, (2) examine differences in timing among age and sex classes, and (3) demonstrate how prebasic molt strategies affect migration timing differences between age classes. As a group, Neotropical migrants were most common from late July through early September, whereas temperate migrants were most common from mid-September into early October. Proportion of hatch-year birds was 74.5% for all migrants combined and ranged from 33.3% to 100% for individual species. Timing differences between sex classes were detected in only a few species and no general patterns emerged. In 22 of 31 Neotropical and temperate migrants examined, there were significant differences in timing between adults and hatch-year birds. In species in which adults begin fall migration before replacing flight feathers, adults migrated earlier than hatch-year birds. Conversely, in species in which adults molt flight feathers on or near the breeding grounds before departing on fall migration, hatch-year birds migrated earlier than adults in all but one case. Therefore, it appears that molt strategy is a powerful determinant of intraspecific migration timing differences and, to our knowledge, this is the first study to document this pattern among migrant passerines of North America. Estrategias de Muda y Diferencias en el Momento de Migración Otoñal en Migrantes Terrestres en el Suroeste de Idaho

Species Richness and Nesting Success of Migrant Forest Birds in Natural River Corridors and Anthropogenic Woodlands in Southeastern South Dakota

Abstract Forest fragmentation is thought to be partially responsible for declines in many Neotropical migrant birds due to the combined effects of higher rates of brood parasitism and increased predation near forest edges. A majority of the forested habitat in the northern prairie region is found in riparian corridors, but this native habitat has been much reduced from its historical extent. However, additional woodland nesting habitat has been established within the last century in the form of isolated woodlots on farms. We compared abundance, species richness, and nesting success of migrant forest birds breeding in native riparian corridors and anthropogenic woodlots. The two habitats had similar bird abundances but native riparian woodlands were more species-rich than woodlots. We located a total of 650 nests, with 320 nests of 15 species in woodlots and 331 nests of 25 species in riparian corridors. Nesting success was not significantly different between the two habitats for all species combined or for individual species with ≥15 nests in each habitat. Nests above 5 m were more successful than lower nests, but distance to woodland edge did not influence nesting success. Nests initiated in the middle and late portions of the nesting season were more successful than early season nests, significantly so in woodlots. Thus, anthropogenic woodlots were as suitable as natural habitats for successful nesting. However, many of the Neotropical migrants occurring in riparian habitats were absent from woodlots, which suggests that riparian corridors are especially important habitats for breeding birds in the northern prairie region.

Effects of Prey Abundance on Breeding Season Diet of Northern Goshawks (Accipiter gentilis) Within an Unusual Prey Landscape

Abstract A critical element of diet analysis is species adaptability to alternative prey sources. The breeding-season diet of Northern Goshawks (Accipiter gentilis) includes both mammalian and avian species, varies geographically, and is often dependent upon tree squirrels of the genera Sciurus and Tamiasciurus. We studied alternative prey sources of Northern Goshawks in the South Hills of south-central Idaho, an area where tree squirrels are naturally absent and other prey frequently important in the diet of goshawks, such as smaller corvids, are uncommon. We quantified the diet of goshawks using nest cameras and surveyed abundance of prey using line transects. We found that goshawks consumed roughly 18.5% birds and 78.7% mammals by biomass, with diet dominated by the Beldings ground squirrel (Urocitellus beldingi, also known as Spermophilus beldingi; 74.8% of total biomass consumed); however, the percentages of mammals and birds in the diet varied between years. The diet was low in diversity, with high overlap among nests, indicating a strong local dependence on the dominant food item. Lastly, the proportion of mammalian prey in the diet was greater in larger broods than in smaller broods. This study provides new insight into the adaptability of the goshawk, particularly in areas with unique prey assemblages. EFECTOS DE LA ABUNDANCIA DE PRESAS EN LA DIETA DURANTE LA ÉPOCA REPRODUCTIVA DE ACCIPITER GENTILIS DENTRO DE UN PAISAJE INUSUAL DE PRESAS Un elemento crítico del análisis de la dieta es la adaptabilidad de las especies a fuentes de presa alternativas. La dieta de la estación reproductiva de Accipiter gentilis varía geográficamente e incluye especies de mamíferos y aves, y depende a menudo de ardillas arborícolas de los géneros Sciurus y Tamiasciurus. Estudiamos fuentes de presa alternativas de A. gentilis en las South Hills del centro sur de Idaho, un área donde las ardillas arborícolas están naturalmente ausentes y donde son poco comunes otras presas frecuentemente importantes en la dieta de A. gentilis, como córvidos más pequeños. Cuantificamos la dieta de A. gentilis colocando cámaras en los nidos y medimos la abundancia de presas usando transectas lineales. Encontramos que los individuos de A. gentilis consumieron aproximadamente 18.5% de aves y 78.7% de mamíferos en términos de biomasa, con una dieta dominada por la ardilla Urocitellus beldingi, también conocida como Spermophilus beldingi (74.8% de la biomasa total consumida). Sin embargo, los porcentajes de mamíferos y aves en la dieta variaron entre años. La dieta fue poco diversa, con un elevado solapamiento entre nidos, indicando una fuerte dependencia local en la presa dominante. Por último, la proporción de presas de mamíferos en la dieta fue mayor en las nidadas más grandes que en las pequeñas. Este estudio brinda una nueva perspectiva sobre la adaptabilidad de A. gentilis, particularmente en áreas con un ensamble de presa único.

Major stopover regions and migratory bottlenecks for Nearctic-Neotropical landbirds within the Neotropics: a review

Nearly 300 species of landbirds, whose populations total billions, migrate between the Neotropics and North America. Many migratory populations are in steep decline, and migration is often identified as the greatest source of annual mortality. Identifying birds’ needs on migration is therefore central to designing conservation actions for Nearctic-Neotropical migratory birds; yet migration through the Neotropics is a significant knowledge gap in our understanding of the full annual cycle. Here, we synthesise current knowledge of Neotropical stopover regions and migratory bottlenecks, focusing on long-distance, migratory landbirds that spend the boreal winter in South America. We make the important distinction between “true” stopover—involving multi-day refuelling stops—and rest-roost stops lasting

Effects of Regional Cold Fronts and Localized Weather Phenomena on Autumn Migration of Raptors and Landbirds in Southwest Idaho

Abstract. Weather has a significant effect on avian migration, but whether the influence is similar across diverse geographic regions and across all species remains to be determined. We evaluated the effect of regional cold fronts and localized weather phenomena on the timing of autumn migration of multiple species of landbirds and raptors in southwest Idaho. The focus of the analysis was on total landbirds and the ten most common landbird species, along with total raptors and the eight most common raptor species. Using 13 years of data from the Idaho Bird Observatory in southwest Idaho (1997–2009), including standardized mist-net captures of landbirds and counts of raptors during autumn migration, we determined significant patterns that advance our understanding of the variables influencing avian migration in the West. Our data show a depression of numbers of most migratory species on the days immediately before, during, and after the passage of a cold front, with peak flights of most species occurring several days prior to or after cold fronts. This pattern was further substantiated by a detailed analysis of many weather variables illustrating that the majority of species choose to migrate during calmer winds, high pressure, and between cold fronts when the opportunity presents itself. In the Intermountain West, cold fronts are fewer in fall than in much of the rest of North America, so migrants may have greater choice of conditions under which to migrate and this behavior may be more common.