Radio telemetry can be a valuable tool for studying the behavior, physiology, and demography of birds. We tested the assumption that radio transmitters have no adverse effects on body condition in an island population of Savannah Sparrows (Passerculus sandwichensis). To assess possible changes in condition, 20 radiotagged and 25 nontagged Savannah Sparrows were captured and recaptured throughout the postfledging period. We used four measures of condition: mass, an index of fat free dry mass (measured via heavy water dilution), pectoral muscle depth (measured via ultrasound imaging), and an index of fat mass (measured via heavy water dilution). Using both a generalized linear modeling framework and paired design, we found no significant differences in the body condition of radiotagged and nontagged adults and juveniles. Thus, our results provide evidence that radiotransmitters have no effect on the condition of Savannah Sparrows during the premigratory period.

Modification of the point count survey method to include playback of songbird mobbing calls in an attempt to increase detection probabilities has met with mixed success. We compared detection probabilities for boreal forest songbirds using traditional point count methods and counts using broadcasts of the mobbing calls of Black-capped Chickadees (Poecile atricapillus) in an attempt to increase detection probability. We conducted 594 point counts during the 2010 breeding season in Newfoundland, Canada. Each point count consisted of an 8-min silent observation period followed by an 8-min broadcast of Black-capped Chickadee mobbing calls. Occupancy model results showed that response to playback broadcast varied across species, with detection probabilities higher for seven of 17 species during the silent portions of point counts and three species more likely to be detected during playback intervals. For all species, the number of visual detections increased during periods of playback and, averaged across species, individuals were >6 times more likely to be seen during the playback period than during the silent period. Differences in detection probability among observers were apparent during both silent and playback periods. We suggest that using playback of chickadee mobbing calls during point count surveys of common boreal forest songbird species may be most beneficial when visual detection is important. However, playback may also be useful for species-specific surveys during periods when birds are less likely to be vocal or for studies of less common species with chronically low detection probabilities. A combined silent and playback approach could also be useful, although observer and species differences should be accounted for if comparing data across species or studies. RESUMEN. Efecto variable de las grabaciones de conducta de turbas en Poecile atricapillus, en la probabilidad de detectar aves en un bosque borealModificaciones en los conteos de puntos, para incluir grabaciones de llamadas de turbas, en el intento de incrementar las probabilidades de detección de aves han tenido resultados mixtos. Comparamos la probabilidad de detección para aves en bosques boreales, utilizando conteos de puntos tradicionales y llamadas de turbas del Carbonero Cabecinegro (Poecile atricapillus), en un intento de incrementar la probabilidad de detección de aves. Se condujeron 594 conteos de puntos durante el periodo reproductivo del 2010, en Newfoundland, Canadá. Cada punto consistió de 8 minutos de observación en silencio, seguido de 8 minutos de una grabación de la llamada de turba del Carbonero Cabecinegro. El modelo utilizado mostró que la respuesta a las grabaciones varía entre especies, con una alta probabilidad de detección de siete de 17 especies durante los periodos de silencio y de tres especies adicionales durante la exposición a grabaciones. Para todas las especies, el número de detecciones visuales incrementó durante los periodos de uso de grabaciones y el promedio entre todas estas, resultó con una probabilidad seis...

Aim Songbirds are sensitive to changes in forest structure and composition at various spatial scales, particularly during the breeding season. Habitat degradation associated with herbivore browsing may contribute to declines in songbird populations. Here, we evaluate songbird responses to herbivore-induced habitat change at multiple spatial scales.Location In Gros Morne National Park (GMNP), Newfoundland, Canada, browsing by hyperabundant moose (Alces alces) has changed forest structure by reducing understorey cover and converting regenerating stands to open areas dominated by grasses and shrubs.Methods We conducted point count surveys to measure bird occurrence throughout GMNP during the 2010 breeding season. Using vegetation information from ground plots and remote sensing, we characterized habitat at three scales: local, neighbourhood and landscape. Following a two-step procedure to model species occurrence with habitat, the most important habitat factors within each scale were retained for cross-scale modelling.Results Cross-scale models revealed patterns in the association of songbird habitat assemblages with moose-altered habitats. Early successional species such as mourning warbler (Geothlypis philadelphia) were positively associated with moose-browsed habitat at the landscape scale. Forest interior specialist (e.g. black-throated green warbler, Setophaga virens) and generalist species (e.g. boreal chickadee, Poecile hudsonicus) were negatively associated with moosebrowsed habitat at the neighbourhood scale. Local songbird species richness was independent of moose-browsed habitat at any scale.Main conclusions The influence of intense browsing on forest songbirds varies by species but has the potential to extend beyond the area of immediate impact. Continued intense browsing and resulting forest alteration could cause declines in forest specialists and generalists, but may increase populations of early successional species. To maintain bird assemblages characteristic of the region, we recommend management actions that lower moose density in areas with hyperabundant populations such as GMNP to maintain forest structure and regeneration comparable to that present prior to the introduction of moose.