The Institute for Bird Populations

Abstract Climate change is considered a major driver of recent avian population declines, particularly in the drought-stricken southwestern United States. Predicting how bird populations will respond requires understanding the climatic drivers influencing population density across the region’s diverse habitats. We modelled breeding-season densities of 50 bird species in relation to spring and summer drought and the timing of North American monsoon rainfall over a 12-year period (2007–2018) and across 4 habitats comprising an approximately 1,500 m elevational gradient. We estimated annual breeding-season population density in relation to climate in the previous year by fitting a Bayesian hierarchical N-mixture model to point-count data from each of 6 national parks on the Colorado Plateau. Specifically, we asked whether (1) population trends were stable, increasing, or decreasing in the focal parks; (2) breeding densities were affected by drought or the timing of monsoon rains; and (3) climatic effects differed across habitat types and among species that molt on the breeding grounds, the nonbreeding grounds, or stopover to molt in the monsoon region of northwestern Mexico (molt migrants). Population trends varied with habitat. Species of high-elevation mixed-conifer forest declined over the study period, matching regional Breeding Bird Survey trends, likely in response to climate-related habitat loss and disturbance. By contrast, lower-elevation pinyon-juniper and grassland-shrubland species density generally increased. Effects of drought varied by habitat with elevation: mixed-conifer species responded positively to drought in the previous year, likely due to earlier snowmelt and breeding phenology, whereas pinyon-juniper species were unaffected, and grassland-shrubland species responded negatively, perhaps due to reduced nest survival. Later arrival of monsoon rains, a common prediction of climate models, had a positive effect on grassland bird densities, but a negative effect on molt-migrant densities. Late monsoon rains may result in a phenological mismatch between migration timing and the pulse of resources required to molt.

thologist, and lifelong birder who devoted his professional life to understanding and addressing causes of bird

Abstract River regulation can alter the magnitude, frequency, duration, and timing of flows, which influences the function of downstream ecosystems. Bird communities can be useful indicators of ecosystem function as individual species respond to varied changes in habitat structure and food availability. We examined the relative importance of different aspects of a regulated flow regime (average daily flow, the number of days flows fell below the 25th percentile, the timing and magnitude of maximum flows, and the inter‐annual duration of flows below the historical median) on predicted bird abundance and diversity using 11 years of data collected within a floodplain meadow system located downstream of Hetch Hetchy Reservoir in Yosemite National Park, California. We found that prolonged periods of low flows were negatively associated with the number of breeding birds detected, as well as the species richness of the breeding bird community. Species richness was also negatively correlated with delays in spring runoff delivery. We opportunistically looked at the same hydrologic variables in a parallel unregulated system, the Merced River through Yosemite Valley, and did not find the same strong relationship with bird community data. This suggests that the dam may be exacerbating the effects of drought.

Cole, J. S., N. L. Michel, R. B. Siegel, and N. Somilleda, Jr. 2019. Effects of off-highway vehicles on avian abundance and diversity in a designated vehicular recreation area. Avian Conservation and Ecology 14(2):9. https://doi.org/10.5751/ACE-01422-140209

ABSTRACT We compared the primary molt of the 4 species of skuas and jaegers (Stercorariidae) that breed in the Northern Hemisphere: Long-tailed Jaeger (Stercorarius longicaudus), Parasitic Jaeger (S. parasiticus), Pomarine Jaeger (S. pomarinus), and Great Skua (S. skua). We analyzed primary molt data of 1,573 individuals of multiple age classes, mostly collected from photographs taken at sea but also from museum specimens and beached individuals. Whereas molt duration generally increased with species' size, molt duration in Parasitic and Pomarine jaegers was surprisingly similar given their size difference. Larger species started primary molt earlier and showed more overlap with postbreeding migration, such that there was complete overlap in Great Skua but no overlap in Long-tailed Jaeger. Within jaeger species, the first primary molt cycle took longer than later molt cycles. We suggest that, unlike birds in their first primary molt cycle, birds in their second or subsequent primary molt cycles are time-c...

Context Multi-use management of global forests has seen even-aged, high-stem density regrowth represent >50% of the world’s forest cover. Large areas of river red gum (Eucalyptus camaldulensis) forests have declined in ecological condition. Thinning has been promoted as a tool to reduce competition in dense, young stands of E. camaldulensis regrowth, yet responses of forest structure and fauna to large-scale thinning are largely unclear. Aims To establish a before-after-control-impact experiment to assess responses of forest structure and fauna to large-scale (compartment-level; ~440 ha) silvicultural thinning. Methods We measured immediate (<2 yrs) responses of forest structural components (living, dead and hollow-bearing stem densities, coarse woody debris (CWD) density and volumes and ground cover) and components of biodiversity (bats, birds, volant insects and non-volant mammals) before and after thinning within five control and three impact compartments. Key results Thinning reduced stem density by approximately two-thirds and was associated with a substantial increase in activity and richness of bats and a change in bat species composition. There was no change in richness for birds and non-volant mammals, nor insect biomass in relation to thinning. However, thinning affected composition of non-volant mammals, with the common brushtail possum (Trichosurus vulpecula) and red fox (Vulpes vulpes) less active post-thinning at impact plots relative to control plots. Thinning reduced the density of dead stems, though these were predominantly small (~13 cm diameter at breast height over bark, or dbhob) and mostly lacked hollows. Hollow-bearing tree density was not affected by thinning. Although thinning increased CWD densities, volume of CWD did not change, indicating that thinning contributed small-sized CWD. Thinning did not affect densities of hollow- and fissure-bearing CWD or ground cover, which was low (<7%) in control and impact plots. There were no other negative effects on biodiversity detected. Conclusions Short-term fauna responses to thinning were generally neutral or positive. Implications Ongoing monitoring is required to detect long-term changes that may result from colonisation or altered breeding success after thinning. We recommend that some unthinned stands should be retained throughout the landscape to provide a mosaic forest structure suitable for a diverse fauna.

The ratio of juvenile to adult birds in mist-net samples is used to monitor avian productivity, but whether it is a “true” estimate of per capita productivity or an index proportional to productivity depends on whether capture probability is not age-dependent (true estimate) or age difference in capture probability is consistent among years (index). Better understanding of the processes affecting age- and year-specific capture probabilities is needed to advance the application of constant-effort mist-netting for monitoring and conservation, particularly in many tropical settings where capture rates are often low. We ranked members of the avian community by capture frequencies, determined if temporary emigration influenced the availability of birds to be captured, and assessed the distribution of birds relative to mist-nets and the parity between capture-based productivity estimates and number of fledglings in nest plots in a tropical dry forest in Puerto Rico in 2009 and 2010. Few captures characterized the community of 25 resident species and, when estimable, capture probabilities were low, particularly for juveniles (typically < 0.1). Negative trends in capture probability, temporary emigration, and the distribution of birds suggest that avoidance of mist-nets influenced capture rates in our study. Increasing mist-net coverage or moving mist-nets between sampling periods could increase capture rates. The number of fledglings observed in nest plots (25 ha/plot) did not correlate well with capture-derived estimates (20 ha/net stations), suggesting the presence of immigrants or failure to find all nests. Our results suggest that indices of breeding productivity from mist-netting data may track temporal changes in productivity, but such data likely do not reflect “true” productivity in most cases unless age-specific differences in capture probability are incorporated into estimates. Pilot studies should be conducted to evaluate capture rates and the spatial extent sampled by mist-nets to improve sampling design and inferences before informing decisions. La proporcion de juveniles a adultos atrapados en redes de niebla son usados para monitorear la productividad de aves, pero si el estimado es “verdadero” o es un índice proporcional a la productividad depende de que la probabilidad de captura no sea dependiente de la edad (estimado verdadero) o que la diferencia en captura por edad sea consistentemente proporcional entre años (índice). Se necesita un mejor entendimiento de los procesos que afectan probabilidades de captura por edad y año para adelantar la aplicación de esfuerzo-constante de redes de niebla para monitorear y conservación, particularmente en ambientes tropicales donde la tasas de captura son bajas. Nosotros ordenamos miembros de la comunidad de aves por frecuencia de capturas, determinamos si emigración temporal influenció la disponibilidad de aves a ser capturadas, y evaluamos la distribución de las aves relativo a las redes de niebla y la paridad entre estimados de productividad a base de capturas y numero de volantones en parcelas con nidos en un bosque tropical seco en Puerto Rico en 2009 y 2010. Pocas capturas caracterizó la comunidad de 25 especies de aves, y cuando se estimaron, la probabilidades de captura fueron bajas, particularmente para juveniles (típicamente < 0.01). Tendencias negativas en probabilidad de captura, emigración temporal, y la distribución de aves sugirió que las mismas eluden las redes de niebla influenciando las tasas de captura. Ampliar la cobertura o mover las redes de niebla entre periodos de muestreo puede aumentar tasas de captura. Los volantones observados en parcelas de anidamiento (25 ha/parcela) no correlacionaron bien con los estimados derivados de captura (20 ha/estación de redes), apuntando a la presencia de inmigrantes o fallo de encontrar todos los nidos. Nuestros hallazgos sugieren que los índices de productividad reproductiva de redes de nieblas pueden rastrear cambios temporales en productividad, pero esos datos probablemente no reflejan “verdadera” productividad en la mayoría de los casos a menos que las diferencias en probabilidad de captura por edad se usen para ajustar los estimados. Estudios pilotos deben llevarse a cabo para evaluar tasas de captura y el ámbito espacial muestreado por redes de niebla para mejorar el diseño de muestreo e inferencias antes de informar decisiones. Table S1. Goodness-of-fit tests for robust design models for Puerto Rican Bullfinches (Loxigilla portoricensis), Bananaquits (Coereba flaveola), and Adelaide's Warblers (Setophaga adelaide) captured at Guánica State Forest in southwestern Puerto Rico, 2009–2010. Table S2. Model selection tables for Puerto Rican Bullfinches (Loxigilla portoricensis) captured at Guánica State Forest in southwestern Puerto Rico, 2009–2010. Table S3. Model selection tables for Bananquits (Coereba flaveola) captured at Guánica State Forest in southwestern Puerto Rico, 2009–2010. Table S4. Model selection tables for Adelaide's Warblers (Setophaga adelaide) captured at Guánica State Forest in southwestern Puerto Rico, 2009–2010. Fig. S1. Map showing estimated locations and the weighted bivariate ellipse for radio-tracked Bananaquits (Coereba flaveola) in the western tract of the Guanica Dry Forest in Puerto Rico. Fig. S2. Map showing estimated locations and the weighted bivariate ellipse for radio-tracked Adelaide's Warblers (Setophaga adelaides) in the western tract of the Guanica Dry Forest in Puerto Rico. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

ABSTRACT The appearance of wood substrates is likely relevant to bird species with life histories that require regular interactions with wood for food and shelter. Woodpeckers detect decayed wood for cavity placement or foraging, and some species may be capable of detecting trees decayed by specific fungi; however, a mechanism allowing for such specificity remains unidentified. We hypothesized that decay fungi associated with woodpecker cavity sites alter the substrate reflectance in a species-specific manner that is visually discriminable by woodpeckers. We grew 10 species of wood decay fungi from pure cultures on sterile wood substrates of 3 tree species. We then measured the relative reflectance spectra of decayed and control wood wafers and compared them using the receptor noise-limited (RNL) color discrimination model. The RNL model has been used in studies of feather coloration, egg shells, flowers, and fruit to model how the colors of objects appear to birds. Our analyses indicated 6 of 10 decayed ...

ABSTRACT Radiotransmitters can be tail‐mounted using cyanoacrylate glue and an accelerant rather than using a harness. Tail‐mounted transmitters are dropped or shed when the rectrices molt, which may reduce transmitter effects while providing retention times sufficient for most research objectives. However, retention times of tail‐mounted transmitters for birds are insufficiently described, and bias from not following all birds until transmitters are shed has been ignored. We studied transmitter retention of 106 birds of 6 species in the United States of America, 2010–2013, using direct observations and survival modeling based on radiotelemetry tracking. Cox proportional hazard survival models predicted median transmitter retention times from 4 to 53 days, depending on species. Our results suggest that researchers should anticipate premature (i.e., &lt;30 days) tag loss rates from 15% to 38% for adult birds, and adjust permit and funding applications accordingly. However, predicted premature tag loss approached 100% for independent juvenile birds, which frequently appeared to disperse long distances, leading to few or no failure events to inform models. Overall, our results provide guidance for the design of future telemetry studies while demonstrating that tail‐mounting transmitters can yield adequate data for a variety of research objectives. © 2018 The Wildlife Society.