Two methods commonly used to quantify ectoparasites on live birds are visual examination and dust-ruffling. Visual examination provides an estimate of ectoparasite abundance based on an observer's timed inspection of various body regions on a bird. Dust-ruffling involves application of insecticidal powder to feathers that are then ruffled to dislodge ectoparasites onto a collection surface where they can then be counted. Despite the common use of these methods in the field, the proportion of actual ectoparasites they account for has only been tested with Rock Pigeons (Columba livia), a relatively large-bodied species (238-302 g) with dense plumage. We tested the accuracy of the two methods using European Starlings (Sturnus vulgaris; ~75 g). We first quantified the number of lice (Brueelia nebulosa) on starlings using visual examination, followed immediately by dust-ruffling. Birds were then euthanized and the proportion of lice accounted for by each method was compared to the total number of lice on each bird as determined with a body-washing method. Visual examination and dust-ruffling each accounted for a relatively small proportion of total lice (14% and 16%, respectively), but both were still significant predictors of abundance. The number of lice observed by visual examination accounted for 68% of the variation in total abundance. Similarly, the number of lice recovered by dust-ruffling accounted for 72% of the variation in total abundance. Our results show that both methods can be used to reliably quantify the abundance of lice on European Starlings and other similar-sized passerines.
The nocturnal activity of burrow-nesting seabirds, such as storm-petrels and shearwaters, makes it difficult to study their incubation behavior. In particular, little is known about possible differences in the incubation behavior of adults at successful and unsuccessful nests. We combined the use of passive integrated transponder (PIT) technology and nest-temperature data loggers to monitor the incubation behavior of 10 pairs of Leach's Storm-Petrels (Oceanodroma leucorhoa). The mean incubation bout length was 3.31 +/- 0.59 (SD) days for individual adults at successful nests (N = 4) and 1.84 +/- 1.16 d for individuals at unsuccessful nests (N = 6). Mean bout length for pairs in successful burrows (3.51 +/- 0.56 d) did not differ significantly (P = 0.07) from that for pairs in unsuccessful burrows (1.80 +/- 1.20 d), perhaps due to one failed nest with a high mean bout length (4.15 d). The total number of incubation bouts per parent (4.3 +/- 1.9 bouts) did not differ with hatching success. Adults whose nests failed repeatedly exhibited truncated incubation bouts (< 12 h) prior to complete nest failure and were more likely than successful parents to make brief visits to nearby, occupied nesting burrows. Our results suggest that the decision by Leach's Storm-Petrels to abandon a nest is not an abrupt one. Rather, failed nesting attempts may be characterized by truncated incubation bouts where individuals pay the energetic cost of travel to and from the burrow, but do not remain long enough to successfully incubate the egg.
In at least 15 species of woodpeckers, the inner primaries of nestlings are reduced in size. This trait is polymorphic in Acorn Woodpeckers (Melanerpes formicivorus) at Hastings Reservation in central coastal California, where most nestlings (90.1%) had reduced first and second primaries, 9.8% had only a reduced first primary, and 0.1% had no reduced primaries. More males (11.1%) had large second primaries than did females (5.3%), and females with this trait were less likely to survive their first year of life. Smaller inner primaries may provide a temporary energetic savings for nestlings that facilitate faster growth, but, if so, why this trait is not more common among other cavity-nesting species remains unknown. This trait appears to be more ecologically interesting than previously suspected and warrants study in other species and populations of woodpeckers.
To investigate the possible effect of elevation on the prevalence of hematozoa infection, we collected blood smears from a population of Winter Wrens (Troglogytes troglodytes) in the Coast Mountains of southwestern British Columbia, Canada. We sampled 119 Winter Wrens, including 88 at low elevation (0–500 m) and 31 at high elevation (900–1100 m) sites. In addition, five other species, including Swainson's Thrush (Catharus ustulatus; N= 12), Dark-eyed Junco (Junco hyemalis; N= 11), Hermit Thrush (Catharus guttatus; N= 8), Varied Thrush (Ixoreus naevius; N= 4), and American Robin (Turdus migratorius; N= 4), were sampled. No Winter Wrens were infected by blood parasites. Among the other species, Haemoproteus infection was detected in one Varied Thrush (25%) and five Swainson's Thrushes (42%). Thus, despite the occurrence of infection in sympatrically breeding species, blood parasites are apparently absent or occur at extremely low prevalence in Winter Wrens in our study area. The presence of hematozoa in European populations of Winter Wrens, combined with an abundance of vector species in our study area, suggest population-level resistance to infection. Further study is needed to determine the specific mechanisms involved in the apparent lack of infection in our study population.
We tested the hypothesis that the abundance of Brown-headed Cowbirds (Molothrus ater) and their hosts, as well as parasitism rates, changed between 1992-1993 and 2001-2003 in riparian habitats in the Okanagan Valley, British Columbia, Canada, where riparian habitat has been reduced in area by more than 85% over the past 60 years. Cowbird abundance declined from a mean of 2.1 and 1.9 individuals per census plot in 1992 and 1993, respectively, to 0;66 individuals per plot in 2001-2002. The mean number of potential host individuals per census plot was also lower in 2001-2002 (5.5) than in 1992 (7.0) and 1993 (7.8). Although the percentage of Yellow Warbler (Dendroica petechia) nests parasitized declined (77% in 1992-1993 to 50% in 2002-2003), Yellow Warblers and Song Sparrows (Melospiza melodia) in the Okanagan Valley continue to be parasitized at high rates and have low nesting success. Host species and the distance of nests from the edge of nest patches were the strongest predictors of both nest success and parasitism, indicating the importance of large continuous patches of shrubs that allow nests to be located further from edges.
ABSTRACT Point counts are the most frequently used technique for sampling bird populations and communities, but have well-known limitations such as inter- and intraobserver errors and limited availability of expert field observers. The use of acoustic recordings to survey birds offers solutions to these limitations. We designed a Soundscape Recording System (SRS) that combines a four-channel, discrete microphone system with a quadraphonic playback system for surveying bird communities. We compared the effectiveness of SRS and point counts for estimating species abundance, richness, and composition of riparian breeding birds in California by comparing data collected simultaneously using both methods. We used the temporal-removal method to estimate individual bird detection probabilities and species abundances using the program MARK. Akaike's Information Criterion provided strong evidence that detection probabilities differed between the two survey methods and among the 10 most common species. The probability of detecting birds was higher when listening to SRS recordings in the laboratory than during the field survey. Additionally, SRS data demonstrated a better fit to the temporal-removal model assumptions and yielded more reliable estimates of detection probability and abundance than point-count data. Our results demonstrate how the perceptual constraints of observers can affect temporal detection patterns during point counts and thus influence abundance estimates derived from time-of-detection approaches. We used a closed-population capture–recapture approach to calculate jackknife estimates of species richness and average species detection probabilities for SRS and point counts using the program CAPTURE. SRS and point counts had similar species richness and detection probabilities. However, the methods differed in the composition of species detected based on Jaccard's similarity index. Most individuals (83%) detected during point counts vocalized at least once during the survey period and were available for detection using a purely acoustic technique, such as SRS. SRS provides an effective method for surveying bird communities, particularly when most species are detected by sound. SRS can eliminate or minimize observer biases, produce permanent records of surveys, and resolve problems associated with the limited availability of expert field observers.RESUMENLos conteos por punto son la técnica más utilizada para muestrear poblaciones y comunidades de aves, pero tienen limitaciones tales como los errores intra- e inter-observador y la escasa disponibilidad de observadores expertos. Una solución a estas limitaciones es el uso de grabaciones en el campo para censar aves. Diseñamos un sistema de grabación de paisajes sonoros, SRS (por sus siglas en inglés), que combina un sistema de grabación de cuatro canales discretos con un sistema de reproducción cuadrafónica para el censado de comunidades de aves. Comparamos la efectividad del SRS y la de los conteos por punto para estimar la abundancia, riqueza y composición de comunidades de aves en hábitats riparios en California, comparando los datos colectados simultáneamente con ambas técnicas. Utilizamos el método de remoción-temporal para estimar la probabilidad de detección de individuos y abundancia de especies utilizando el programa MARK. El Criterio de Información Akaike proveyó evidencia sustancial de que existen diferencias en la probabilidad de detección entre ambos métodos y entre las 10 especies más comunes de aves. La probabilidad de detección de aves resultó mayor cuando se escucharon las grabaciones del SRS en el laboratorio que durante los conteos por punto en el campo. Además, los datos tomados con la técnica SRS demostraron estar mejor adaptados a los supuestos del modelo de remoción-temporal y ofrecieron estimados más confiables de abundancia y de probabilidad de detección que los datos de conteos por puntos. Nuestros resultados demuestran cómo la percepción de los observadores puede afectar los patrones de detección temporal durante los conteos por punto, influyendo en las estimaciones de abundancia derivadas de procedimientos de tiempo de detección. Utilizamos el método de captura-recaptura de población cerrada para calcular las estimaciones de jackknife de riqueza de especies y la probabilidad de detección de especies para SRS y conteos por punto, utilizando el programa CAPTURE. Ambos tuvieron índices de riqueza de especies y probabilidades de detección similares. Sin embargo, los métodos difirieron en la composición de especies detectadas basados en el índice de similitud de Jaccard. La mayoría de los individuos detectados durante los conteos por punto (83%) vocalizaron al menos una vez durante el periodo de censado, y estuvieron disponibles para ser detectados utilizando una técnica acústica, como SRS. La técnica SRS provee un método efectivo para censar comunidades de aves, particularmente cuando la mayoría de las especies son detectadas por sus sonidos. El SRS puede eliminar o minimizar los sesgos del observador, producir registros permanentes de los censos, y resolver problemas asociados a la limitada disponibilidad de expertos en el campo.
Snowy Plovers (Charadrius alexandrinus) and Wilson's Plovers (C. wilsonia) are shorebird species of increasing conservation concern, with populations apparently declining in North America. However, estimates of current populations are needed before initiating long-term monitoring or planning. In 2004, we estimated abundance of breeding Snowy and Wilson's plovers in the lower Laguna Madre region of Texas using occupancy abundance estimation. We made repeated visits to survey plots from April to June, recording the number of adults of both species observed and the amount of suitable breeding habitat within each plot. We considered Bayesian occupancy abundance models with and without habitat covariates to explain the abundance of both species. For both Snowy and Wilson's plovers, the number of birds counted in each plot was influenced by the amount of suitable breeding habitat within the plot (Snowy Plover alpha(habitat) = 0.52, SD = 0.10, 95% CI = 0.33-0.71; Wilson's Plover alpha(habitat) = 0.48, SD = 0.12, 95% CI = 0.24-0.71). Using the habitat covariate models for each species, we estimated that 416 adult Snowy Plovers (95% CI = 394-438) and 279 adult Wilson's Plovers (95% CI = 262-296) were present in our study area. Our results illustrate the use of a relatively new method for abundance estimation, and indicate that the lower Laguna Madre region of Texas is an important breeding area for both Snowy and Wilson's plovers. Given the documented and suspected population declines for Snowy and Wilson's plovers, we recommend protection of their breeding habitats along the coast of Texas from development and degradation resulting from unregulated use.
To ensure adequate protection of nonbreeding habitats used by Neotropical migratory landbirds, we must first address questions about habitat use and quality. On the Yucatan peninsula, migrants use many habitats, several of which remain unstudied, and methodological differences preclude interhabitat comparisons based on studies to date. We used distance sampling along line transects in six habitats in northeast Belize to examine use of previously unstudied habitats (e.g., salt marsh) by Neotropical migrants and to permit comparison across habitats. We calculated unadjusted and adjusted (for detectability) density estimates for individual migrant species and for all species combined to generate hypotheses about habitat quality based on the assumption that density and quality are positively correlated. Adjusted density estimates for all migrants were highest in black mangrove habitat (1799 ± 110 ind/km²), intermediate in three forest types and milpa (range 598–802 ind/km²), and lowest in salt marsh (207 ± 32.3 ind/km²). By combining density estimates with habitat availability in our study region, we estimated that evergreen forest and black mangrove supported 70% and 9% of the region's migrant population, respectively. At the species level, five of the 10 most common species had habitat preferences (>50% detections in one habitat). Given the diversity of habitat preferences among species and apparent seasonal movements, our results indicate that Neotropical migrants in northeast Belize are dependent on a matrix of interconnected habitats.
Vinaceous Amazons (Amazona vinacea) are endemic to the Atlantic forest of southeastern Brazil, eastern Paraguay, and the province of Misiones in Argentina. We searched for Vinaceous Amazons throughout the western part of its range in Argentina and Paraguay during 1639 days of fieldwork from 1997 to 2006. These parrots have disappeared from most areas where they were historically recorded in these countries, and are now limited to a few sites in northeastern Paraguay and central Misiones (Argentina). We estimate the minimum remaining populations at 220 individuals in Paraguay and 203 individuals in Argentina. Important sites for the species are (1) the farming area from San Pedro to Tobuna (Misiones, Argentina) and (2) the Itaipú reserves complex and Reserva Natural Privada Itabó (Paraguay). In our surveys, Vinaceous Amazons were absent from the largest tracts of forest in Misiones, and were most often observed feeding, roosting, and nesting in small forest remnants and in agricultural areas that included forest fragments and isolated trees. Threats to amazons in these areas include nest poaching, forest clearing, and being shot as a crop pest. We confirmed 40 Vinaceous Amazons kept as pets in 35 homes between San Pedro and Tobuna. Environmental education and law enforcement are urgently needed to reduce threats in populated areas, and subsistence farmers need technical and logistical support to slow or stop the conversion of forest into cropland. Finally, additional study is needed to determine this amazon's habitat preferences, nest site requirements, and demography in different habitats.
Although breeding populations of Piping Plovers are well studied, their winter distribution is less clear. We studied the seasonal abundance of nonbreeding Piping Plovers (Charadrius melodus) during the winters of 2003–2004 and 2004–2005 on Little St. Simons Island (LSSI), Georgia. Our objectives were to determine the relative abundance of individuals from three breeding populations at LSSI, and identify possible differences among populations in arrival time, winter movements, or departure time. We observed up to 100 Piping Plovers during peak migration, and approximately 40 plovers wintered at LSSI. From July 2004 to May 2005, approximately 20% of the Great Lakes breeding population used LSSI. Plovers were not present at LSSI during June. All breeding populations of Piping Plovers had similar patterns of temporal occurrence on LSSI, suggesting no need for population-specific management plans at this site. Our results suggest that LSSI is among the most important wintering sites on the Atlantic coast for Piping Plovers, especially for individuals from the endangered Great Lakes population.
Distance sampling applied to point count surveys (point transects) has become a common method for estimating the absolute abundance of birds. When conducting point transects, detections of focal species are typically recorded during a fixed time interval. However, count duration has varied among studies and the effect of such variation on the resulting abundance estimates is unclear. My objective was to examine the effect of count duration on abundance estimates of male Black-capped Vireos (Vireo atricapilla). The abundance of these vireos in a 349-ha area in central Texas was estimated using 3-, 5-, and 6-min point transects and results were then compared to actual number present as determined by banding and territory mapping. The 3-min counts provided an estimate that was 26% greater than the actual number of male Vireos present (N = 201), but this number was within the corresponding 95% confidence interval (N = 157-413). Confidence intervals for the 5- and 6-min counts did not include the actual number of vireos present. The shortest count duration may have provided the most accurate abundance estimate because male Black-capped Vireos are typically active, sing intermittently, and sometimes move tens of meters between songs. Thus, shorter-duration counts may also yield the most accurate abundance estimates for other species that exhibit similar behavior. However, because behavior varies among species, I recommend that investigators collect preliminary data to establish an appropriate count duration when accurate estimates of absolute, rather than relative, abundance are important.
Forest fragmentation can create negative edge effects that reduce the reproductive success of birds nesting near the forest/nonforest interface, and threaten bird populations deeper in remnant forest habitats. Negative edge effects may be more pronounced in landscapes that are moderately fragmented, particularly where agriculture is the primary land-use fragmenting forests. Information about the extent and strength of edge effects at a site can help guide conservation actions, and determine their effectiveness. We examined edge effects for birds breeding in a nearly contiguous forest fragmented by relatively narrow agricultural corridors in Illinois (USA). We measured rates of nest predation and brood parasitism for Acadian Flycatchers (Empidonax virescens) over a continuum of distances from the edge of an agricultural inholding. Nest predation and brood parasitism were highest near the edge and decreased with increasing distance from the edge. Given the cumulative effects of nest predation and brood parasitism on reproductive success, we determined that forest within 600 m of the inholding was sink habitat. We found, however, that deeper forest interior areas currently serve as source habitat, and that conversion of the entire 205 ha agricultural corridor to forest would add 1350 ha of source habitat for Acadian Flycatchers. Such results provide support for a local conservation strategy of forest consolidation and establish baseline measures necessary to determine the relative effectiveness of any subsequent reforestation efforts.
The application of molecular tools to studies of avian mating systems has revealed that most songbird species engage in extra-pair matings. However, little is known about the possible effects of habitat fragmentation on extra-pair mating systems. During the breeding seasons of 2002 and 2003, we quantified the frequency of extra-pair matings in Acadian Flycatchers (Empidonax virescens) and Wood Thrushes (Hylocichla mustelina) nesting in forest fragments in southern Ontario. Acadian Flycatchers are at the limit of their northern range in southern Ontario and occurred at low densities (0.005-0.015 males/ha). Across forest fragments, 14% of young Acadian Flycatchers were the result of extra-pair fertilizations. In contrast, Wood Thrushes were common in forest fragments, with breeding densities ranging from 0.37 to 1 males/ha. Extra-pair mating was common among Wood Thrushes, with 40% of young the result of extra-pair matings. Compared to populations studied in less fragmented habitats in Pennsylvania, rates of extra-pair paternity in Ontario were lower for Acadian Flycatchers and higher for Wood Thrushes. Our results demonstrate that rates of extra-pair mating can vary across landscapes. However, the extra-pair mating systems of Acadian Flycatchers and Wood Thrushes appear to respond differently to fragmentation. We suggest that low breeding densities on fragments may be mediating the low rates of extra-pair mating observed in Acadian Flycatchers in southern Ontario, whereas changes to the behavioral tactics of male and female Wood Thrushes in southern Ontario may explain the high levels of extra-pair mating.
High rates of brood parasitism are generally associated with agricultural landscapes, but recent evidence suggests that urbanization may also increase the likelihood of brood parasitism. I evaluated the extent to which brood parasitism by Brown-headed Cowbirds (Molothrus ater) was explained by differences in (1) body size of adult hosts, presumably relating to the ability to defend nest from cowbirds, (2) nest placement in substrate and relative to habitat edges, (3) habitat structure surrounding nests, (4) host density, (5) cowbird abundance, both absolute and relative to host numbers, (6) landscape composition, and (7) Julian date. From 2001 to 2006, I monitored nest fate and measured vegetation characteristics surrounding nests of Acadian Flycatcher (Empidonax virescens) breeding in mature riparian forests in central Ohio, USA. The likelihood that a nest would be parasitized was best explained by the number of understory stems surrounding the nest and, to a lesser extent, by the amount of urbanization in the surrounding 1-km-radius landscape. Parasitized nests were surrounded by 1.6 times more stems and nearly twice the amount of urbanization than nonparasitized nests. Numbers of understory stems were positively associated with increasing urbanization, primarily due to invasion of urban forests by Amur honeysuckle (Lonicera maackii). Thus, urban-associated changes in habitat characteristics around nests may be important contributors to the greater vulnerability of urban nests to brood parasitism than nests in more rural landscapes. This pattern suggests that ecological restoration, such as removing exotic shrubs, may be an effective strategy to ameliorate certain negative consequences of urbanization near wooded reserves.
Measuring body movements using accelerometry data loggers is a relatively new technique, the full applicability of which has yet to be tested on volant birds. Our study illustrates the potential of accelerometry for research on large birds by using the technique to record the behavior of three species of raptors, mainly during flight. A tri-axial accelerometer was deployed on a trained Harris' Hawk (Parabuteo unicinctus), Tawny Eagle (Aquila rapax), and Griffon Vulture (Gyps fulvus). Comparison of flight-related variables calculated from video footage and that estimated from the acceleration data showed that the latter provided considerable and accurate information (usually <10% error) about the behavior of the birds, including wing-beat frequency and when they glided and flapped. Acceleration data permitted tentative comparisons of relative movement-specific rates of energy expenditure for the Griffon Vulture flying up versus flying down a small hill. The accelerometry data appeared to suggest, as expected, that the Griffon Vulture expended more energy flying uphill than flying back down. Our preliminary findings indicate that studies using accelerometers can likely provide information about the detailed time-energy budgets of large birds. Such information would aid in comparative analyses of behavior and energetics, and may also enhance efforts to conserve declining bird populations.
Various indices of reproductive activity (IRA) have been used to estimate the reproductive success of songbirds. However, the performance of IRAs varies among systems examined, and this approach still requires more effort than standard surveys. We tested the accuracy of an IRA in a survey of birds nesting in bogs in eastern New Brunswick, Canada. We compared an IRA obtained through point counts with playbacks ("extensive" IRA) to another IRA obtained through intensive searches for evidence of breeding ("intensive" IRA) by Palm Warblers (Dendroica palmarum). Both the extensive IRA and associated abundance index were correlated with the intensive IRA, the former correlation being stronger. However, the extensive IRA tended to underestimate the status of breeding birds and overestimate the status of nonreproducing individuals that behaved more conspicuously. Nonetheless, the extensive IRA obtained using song playbacks represents a time-efficient alternative to intensive nest monitoring when estimating habitat quality at the scale of small (0.78 ha) study plots.
The diet of Acorn Woodpeckers (Melanerpes formicivorus) in central coastal California consists of a mixture of high-quality (insects) and low-quality (stored acorns) food during the spring breeding season. We used stable isotope ratios obtained from blood samples to estimate possible differences in the proportion of these items being fed to nestlings and being consumed by breeding adults, as well as the extent to which the diet of nestlings shifts between insects and acorns during the nestling period. Based on both feeding observations and items recovered from nestlings, older nestlings were fed 28% acorns. Using this value as a baseline for the isotope analyses, the diet of breeding adults was estimated to consist of 90% acorns. Based on repeated samples from the same nestlings over time, the estimated proportion of acorns in their diet increased from 19% in 9- to 12-d-old nestlings to 42% in 23- to 26-d-old nestlings. There was a significant correlation between the isotope values of adults and the nestlings they fed, indicating that different groups of Acorn Woodpeckers have significantly different diets. Although important for successful reproduction in this species, stored acorns are not the primary food resource used to feed young. Instead, the availability of stored acorns allows adult Acorn Woodpeckers to provide nestlings with more protein-rich insects while maintaining themselves on relatively protein-poor, low-quality acorns. Differences in the diets of adults and their nestlings are likely widespread among species that feed, at least in part, on low-quality foods, such as fruit and seeds, during the breeding season.
ABSTRACT Playback experiments involve the broadcast of natural or synthetic sound stimuli and provide a powerful tool for studying acoustic communication in birds. Playback is a valuable technique for exploring vocal duetting behavior because it allows investigators to test predictions of the various hypotheses for duet function. Here, we adopt a methodological perspective by considering various challenges specific to studying duetting behavior, and highlighting the utility of different playback designs for testing duet function. Single-speaker playback experiments allow investigators to determine how duetting birds react to different stimuli, but do not simulate duets in a spatially realistic manner. Multi-speaker playback experiments are superior to single-speaker designs because duet stimuli are broadcast with spatial realism and unique and additional predictions can be generated for testing duet function. In particular, multi-speaker playback allows investigators to evaluate how birds respond to male versus female duet contributions separately, based on reactions to the different loudspeakers. Interactive playback allows investigators to ask questions about the time- and pattern-specific singing behavior of birds, and to understand how singing strategies correspond to physical behavior during vocal interactions. Although logistically challenging, interactive playback provides a powerful tool for examining specific elements of duets (such as the degree of coordination) and may permit greater insight into their functions from an operational perspective. Interactive playback designs where the investigator simulates half of a duet may be used to describe and investigate the function of pair-specific and population-wide duet codes. Regardless of experimental design, all playback experiments should be based on a sound understanding of the natural duetting behavior of the species of interest, and should aim to produce realistic and carefully controlled duet simulations. Future studies that couple playback techniques with other experimental procedures, such as Acoustic Location System recordings for monitoring the position of birds in dense vegetation or multimodal techniques that combine acoustic with visual stimuli, are expected to provide an even better understanding of these highly complex vocal displays.
Los experimentos de reproducción de sonidos grabados involucran el uso de sonido natural o sintético y proveen una herramienta poderosa para el estudio de la comunicación acústica de las aves. La reproducción de sonidos grabados es una técnica valiosa para explorar las duetas vocales porque permite probar las predicciones de varios hipótesis sobre la función de duetas. Aquí, adoptamos una perspectiva metodológica, considerando los varios retos específicos al estudio del comportamiento de duetas y resaltando la utilidad de diferentes diseños de reproducción de sonidos grabados para probar la función de las duetas. Experimentos de reproducción de sonidos grabados hechas con un parlante permiten una determinación de como las aves que realizan duetas reaccionan a diferentes estímulos, pero no simulan las duetas de una manera espacialmente realística. Experimentos de reproducción de sonidos grabados hechas con múltiples parlantes son superiores a diseños con un solo parlante porque transmiten el sonido de una manera espacialmente realística y generan predicciones únicas y adicionales para probar la función de la dueta. En particular, la reproducción de sonidos grabados con múltiples parlantes permite una evaluación de cómo las aves responden a las contribuciones del macho y de la hembra separadamente, basado en sus reacciones a los diferentes parlantes. La reproducción de sonidos grabados interactiva permite hacer preguntas temporalmente especificas y en relación a patrones especificas sobre el comportamiento de canto. También permite entender como las estrategias de canto corresponden al comportamiento físico durante las interacciones vocales. Aunque es un reto logístico, la reproducción de sonidos grabados interactiva provee una herramienta poderosa para examinar elementos específicos de las duetas (como el grado de coordinación) y podría permitir un mayor conocimiento sobre sus funciones de una perspectiva operacional. Los diseños de la reproducción de sonidos grabados interactivas, en la cual el investigador simula la mitad de una dueta, podrían ser usadas para describir e investigar la función de los códigos de dueta específicos a una pareja y a una población. Sin importar el tipo de diseño experimental, todos los experimentos de reproducción de sonidos grabados deberían ser basadas en una buena comprensión del comportamiento natural de las duetas en la especie de interés, y deberían tener la meta de producir simulaciones de duetas realísticas y cuidadosamente controladas. Se espera que los estudios futuros cuales combinan técnicas de la reproducción de sonidos grabados con otros procedimientos experimentales, como grabaciones del Sistema de Ubicación Acústica para monitorear la posición de aves en vegetación densa, o técnicas multimodales que combinan estímulos acústicos con estímulos visuales, provean un mejor entendimiento de estos despliegues vocales altamente complejos.
Populations of Warbling Vireos (Vireo gilvus) are declining in California, apparently due to low reproductive success. From 1989-2002, I studied the nest-site selection and reproductive success of Warbling Vireos across an elevational gradient in the southern Sierra Nevada. Warbling Vireos regularly nested in upland coniferous forests with few or no deciduous trees, and tree species used by nesting vireos included five species of conifers and four species of deciduous trees. Overall, hardwoods were used more than expected based on their availability, but 69% of all nests were in conifers. Hardwood trees were found only in low and mid-elevation ponderosa pine (Pinus ponderosa) and mixed-conifer sites. In low-elevation ponderosa pine habitat, 87% of nests were in hardwoods, with 67% in California black oaks (Quercus kelloggii), a species that typically occupies upland sites. In mixed-conifer sites where reproductive success was high, 65% of nests were in incense cedar (Calocedrus decurrens) and California black oak was the next most commonly used species. Because fire suppression has likely increased numbers of shade-tolerant tree species like incense cedar, shade-intolerant species like black oaks may have been more important as a nest substrate for vireos in the past. Only conifers were used as nesting substrates at higher elevations. Nest success was greater for Warbling Vireos that nested in tall trees in areas with high basal area. My results suggest that Warbling Vireos in the Sierra Nevada would benefit from management activities that encourage retention and recruitment of California black oaks at lower elevations, and development of stands with large trees, dense foliage, and semi-open canopy throughout their elevation range.
ABSTRACT For seabirds raising young under conditions of limited food availability, reducing chick provisioning and chick growth rates are the primary means available to avoid abandonment of a breeding effort. For most seabirds, however, baseline data characterizing chick growth and development under known feeding conditions are unavailable, so it is difficult to evaluate chick nutritional status as it relates to foraging conditions near breeding colonies. To address this need, we examined the growth and development of young Caspian Terns (Hydroprogne caspia), a cosmopolitan, generalist piscivore, reared in captivity and fed ad libitum and restricted (ca. one-third lower caloric intake) diets. Ad libitum-fed chicks grew at similar rates and achieved a similar size at fledging as previously documented for chicks in the wild and had energetic demands that closely matched allometric predictions. We identified three general characteristics of food-restricted Caspian Tern chicks compared to ad libitum chicks: (1) lower age-specific body mass, (2) lower age-specific skeletal and feather size, such as wing chord length, and (3) heightened levels of corticosterone in blood, both for baseline levels and in response to acute stress. Effects of diet restriction on feather growth (10–11% slower growth in diet-restricted chicks) were less pronounced than effects on structural growth (37–52% slower growth) and body mass (24% lower at fledging age), apparently due to preferential allocation of food resources to maintain plumage growth. Our results suggest that measurements of chick body mass and feather development (e.g., wing chord or primary length) or measurement of corticosterone levels in the blood would allow useful evaluation of the nutritional status of chicks reared in the wild and of food availability in the foraging range of adults. Such evaluations could also inform demography studies (e.g., predict future recruitment) and assist in evaluating designated piscivorous waterbird conservation (colony) sites.
Para aves marinas que crían pichones bajo condiciones de disponibilidad de comida limitada, reducir el aprovisionamiento a los pichones y las tasas de crecimiento de los pichones son la manera principal de evitar de abandonar un intento de reproducir. Sin embargo, para la mayoría de las aves marinas, los valores de referencia que caracterizan el crecimiento y desarrollo de pichones bajo condiciones conocidas de alimentación no están disponibles. Entonces, es difícil evaluar el estatus nutricional de los pichones en relación a las condiciones de forrajeo cerca de colonias de nidificacion. Para responder a esta necesidad, examinamos el crecimiento y desarrollo de pichones de Hydroprogne caspia, un piscívoro cosmopolita y generalista, cuales fueron criados en cautiverio y alimentados con dietas ad libitum y con dietas restringidas (con aproximadamente un tercio menos de las calorías). Los pichones dados a comer ad libitum tuvieron tasas de crecimiento similares y llegaron a un tamaño similar a pichones silvestres en la etapa de emplumamiento. También tenían una demanda energética que era muy similar a lo de predicciones alométricas. Identificamos tres características generales de pichones de H. caspia con dietas restringidas en comparación a pichones con dietas ad libitum: (1) un peso corporal más bajo específico a cada edad, (2) un tamaño del esqueleto y de plumaje más bajo por edad, como por ejemplo el largo del ala, y (3) niveles altos de corticosterona en la sangre, tanto para niveles de valores de referencia y en respuesta al estrés aguda. Los efectos de la restricción de la dieta al crecimiento de las plumas (crecimiento de 10–11% más lento en pichones con dieta restringida) fueron menos pronunciados que los efectos sobre el crecimiento estructural (crecimiento de 37–52% más lento) y peso corporal (24% más bajo a la edad de emplumamiento), aparentemente por alocar preferencialmente los recursos alimenticios para mantener el crecimiento del plumaje. Nuestros resultados sugieren que las medidas del peso corporal de pichones y el desarrollo del plumaje (ej., largo del ala o de las primarias) o las medidas de niveles de corticosterona en la sangre nos permitiría una evaluación útil del estatus nutricional de pichones silvestres y de la disponibilidad de comida en el área de forrajeo de los adultos. Estos tipos de evaluaciones también nos podrían proveer información para estudios demográficos (ej., el predecir la incorporacion futura de volantones) y asistir en la evaluación de áreas para la conservación de aves acuáticas piscívoras.
Avian embryos are incubated at temperatures only 2–6 °C below that at which hyperthermia begins to influence survival. In habitats where sunlight directly strikes the eggs, even for short periods, heat gain may be a substantial threat to survival, and reflective pigmentation may reduce the rate of heat gain. The results of previous studies suggest that light-colored eggs acquire heat slower than dark eggs, but artificial pigments were used to create differences in egg coloration. This approach is problematic because natural eggshell pigments have low absorbance in the near-infrared waveband that encompasses about half of incident solar radiation. We used naturally-pigmented eggs to measure the influence of egg coloration on heat gain. Triads (N= 18) of eggs from Brewer's (Euphagous cyanocephalus), Red-winged (Agelaius phoeniceus), and Yellow-headed (Xanthocephalus xanthocephalus) blackbirds were crossed with six nests of each species and either exposed to full sunlight or placed under a diffusing umbrella. Thermisters recorded internal egg temperature every minute until an asymptotic temperature was reached. Eggs in full sunlight acquired heat more rapidly than eggs in the shaded environment, but heat gain did not vary with egg color in either environment. Eggs placed in Yellow-headed Blackbird nests took longer to reach asymptotic temperature, but there was no significant egg-by-nest interaction. Thus, it appears that differences in reflectivity of eggshell pigments in the visible range (400–700 nm) do not result in different rates of heat acquisition. The thermoregulation hypothesis was not supported.
Infanticide and nonfatal aggression by adults toward unfamiliar chicks have been widely reported in colonial birds, and can be an important cause of chick mortality. We studied intraspecific aggression by adults toward chicks at a South American Tern (Sterna hirundinacea) colony in Patagonia, Argentina, during 2005 to characterize this behavior, evaluate its relationship with nesting density, chick age and microhabitat characteristics, and assess its effect on breeding success. Of 111 chicks in the study area, 45% were attacked at least once. Chicks older than 9 d posthatching were more likely to be attacked than younger chicks, and unattended chicks were more likely to be attacked than guarded chicks (88 vs. 12%). Chicks were also attacked more often when in their own territories (76% of cases), but were less likely to be attacked in territories with more vegetation cover and high-quality shelters (i.e., vegetation with characteristics that prevented adults from reaching chicks). The number of aggression events was not related to nest density. At least 8% of the chicks in our study area died as a result of adult intraspecific aggression. Our results indicate that intraspecific aggression by adult South American Terns toward chicks is relatively common in the Punta Loma colony and should not be underestimated as a factor affecting their breeding success.
For burrow-nesting seabirds, investigators have examined nestling diet by attaching harnesses to the bills of nestlings; to intercept food delivered by the parent. To determine whether this method provides an unbiased estimate of nestling diet, we evaluated its effect on the provisioning behavior of Tufted Puffins (Fratercula cirrhata) nesting on Triangle Island, British Columbia. Adults delivering food to nestlings with bill harnesses always hesitated before entering a burrow with food, increasing their susceptibility to kleptoparasitism by gulls, and did not always leave the food intended for the nestling. These responses by adult puffins could lead to underestimates of energy intake rates of nestlings and unreliable comparisons with other species if prey left by adults in nest burrows were the only source of data. We also compared estimates of the species, number, and size of prey delivered by adult puffins as determined by direct observation from blinds to samples of prey collected directly from nest burrows and found that the two sampling techniques produced similar results. However, identifying rare prey species and gathering precise information about prey length, mass, and condition require collection of prey, and we recommend using a combination of techniques to obtain the most reliable estimates of nestling diet.
Northern Shrikes (Lanius excubitor) are predatory songbirds found primarily in taiga regions throughout their Holarctic breeding range. The species is poorly known, especially in North America, and is generally thought to be sexually monomorphic. From 2004 to 2007, we captured 50 adults in northern Wisconsin during the nonbreeding season (December-March) and determined sex using DNA extracted from feather samples. Males had significantly longer wings, longer tails, and less black in the outer rectrix than females, but body mass did not differ between the sexes. A discriminant function equation using tail length and extent of black on the outer rectrix correctly assigned the sex of 97.4% of captured adults. Plumage dimorphism was also evident, with males having paler gray heads and backs without brown tones, whiter underparts with lighter barring, and a more distinct and horizontal border at the base of the sixth primary feather. The ability to accurately determine sex will provide opportunities to examine possible inter- and intrasexual differences in the behavior and ecology of adult Northern Shrikes.
Bands are a common marking method in bird studies and capture-mark-reencounter (CMR) models are often used to analyze banding data. Common to this family of models are two assumptions: marks do not fall off or become unreadable and individuals within groups remain equally detectable. When data fail to meet these assumptions, results of CMR analyses may be biased. In studies of long-lived seabirds exposed to coarse nesting substrates, band wear is especially problematic. We compared surface wear from abrasion against rocks on incoloy and darvic bands applied to a long-lived seabird, the Atlantic Puffin (Fratercula arctica). In 2003 and 2004, surface wear on bands applied to chicks and adults was scored at five colonies in the Gulf of Maine. We used logistic regression to analyze two subsets of these data by fitting the probability of being worn (one or more characters difficult to read or obliterated) to band age, bird age, and band type. In both analyses, an evidence ratio provided exclusive support for the model that included all factors. Immature puffins largely avoid colonies and remain at sea until their second or third summer after hatching. Consequently, probabilities of being worn were delayed on both band types by 4 yr on bands applied to chicks compared to adults. Based on our estimates, 25% and 87% of darvic bands applied to chicks and adults, respectively, were worn after 5 yr. Wear was reduced by 71% and 87% annually on incoloy compared to darvic bands applied to adults and chicks, respectively. To uphold assumptions of CMR models, we recommend incoloy bands over darvic in studies spanning more than about 5 yr of long-lived seabirds exposed to coarse substrates.
Estimating detection error, as well as the magnitude of other potential survey biases, is essential when sampling efforts play a role in the estimation of population size and management of wildlife populations. We quantified visual biases in aerial surveys of nesting wading birds (Ciconiiformes) in colonies in the Florida Everglades using a negative binomial count regression model to compare numbers of nests in quadrats counted on the ground with numbers estimated from aerial photographs of the same quadrats. The model also allowed the determination of degree of difference between monitoring results based upon such factors as nest density, vegetative cover, and nest turnover rates. Aerial surveys of White Ibis (Eudocimus albus) colonies underestimated the true number of nests found during ground counts by 11.1%, and underestimates were significantly greater (P = 0.047) in a colony with high nest turnover. Error rates did not differ for quadrats that varied in the density of White Ibis nests did not differ, and visual bias did not increase with vegetative complexity (P = 0.73). Estimates of nest density in colonies of Great Egrets (Ardea alba) based on aerial surveys were higher than ground counts for 38% of the quadrats sampled, and mean visual bias was 23.1%. Species misidentification likely contributed to visibility bias for Great Egrets in our study, with some Snowy Egrets almost certainly mistaken for Great Egrets in aerial photos. Biases of the magnitude we observed fro Great Egrets and White Ibises can mask true population trends in long-term monitoring and, therefore, we recommend that detection probability be explicitly evaluated when conducting aerial surveys of nesting birds.
Flipper bands are used to mark penguins because leg bands can injure their legs. However, concerns remain over the possible effects of flipper bands on penguins. We examined the effects of stainless-steel flipper bands on the duration of foraging trips by Magellanic Penguins (Spheniscus magellanicus) at Punta Tombo, Argentina, using an automated detection system. We predicted that, if bands were costly and increased drag, flipper-banded penguins would make longer foraging trips than those with small or no external markings. We tagged 121 penguins with radio-frequency identification (RFID) tags and an additional external mark. We placed either a stainless-steel band on the left flipper (N= 62) or a 2×10-mm small-animal ear tag in the outside web of the left foot (N= 59). We measured foraging-trip durations (N= 376 trips) for 68 adult penguins with chicks from 15 December 2007 to 28 February 2008. Contrary to predictions, trip duration was similar for banded and web-tagged penguins (P= 0.22) and for males and females (P= 0.52), with no interaction between tag type and sex (P= 0.52). No penguins marked in the 2007 breeding season and recaptured between 30 September and 30 November 2008 (N= 113) lost flipper bands or web tags, but three RFID tags failed between March and September 2008. Properly designed and applied flipper bands were a reliable marking method for Magellanic Penguins, had a lower failure rate than RFIDs, and did not affect foraging-trip duration.
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.
Food is generally considered to be the primary resource structuring winter territories in migrant songbirds, but there is little experimental evidence to support this. In southeastern Louisiana, ripe fruits, consumed opportunistically in the absence of preferred arthropod resources, are a primary food resource for wintering Hermit Thrushes (Catharus guttatus). To test the possible role of food in controlling space use during the winter, we reduced fruit availability in the territories of wintering Hermit Thrushes and compared responses of these thrushes to those in control territories where fruit availability was not altered. We found that thrushes did not adjust either territory size or location in response to midwinter reduction of fruit availability. One possible explanation for this lack of response is that sufficient food, including arthropods, was available in thrush territories even after removal of fruit. Another possibility is that the removal of fruit did reduce food levels below the level needed to meet energetic needs, but social constraints on territory structure, dictated by fall settlement spacing and maintained by agonistic interactions, prevented birds from adjusting territories to match food supply later in the season.
Territorial behavior of Broad-tailed ( Selasphorous platycercus ) and Rufous ( Selasphorous rufus ) hummingbirds in Colorado was measured at sites with feeders containing10%, 20%, and 30% sucrose solutions, respectively. The presence or absence of territory holders, number of intruders, and intensity of defense were measured at the three levels of energy availability. Migrating Rufous Hummingbirds displaced Broad-tailed Hummingbirds from territories they had defended during the breeding season; Broad-tailed Hummingbirds then defended only lower quality sites. Both Broad-tailed and Rufous hummingbirds employed more energetically expensive behaviors when defending high quality sites, with longer chases more often supplemented with chip calls and hovering. Other investigators have suggested that chip calls and hovering are precursors to a chase. However, I found that chasing was the default response to the presence of an intruder. Chip calls and hovering were added to intensify a chase. In the few cases where chip calls were uttered or hovering occurred without a chase, Rufous Hummingbirds were more likely to exhibit this behavior than Broad-tailed Hummingbirds.
Foraging behavior often reflects food availability, a resource that may increasingly limit breeding birds as intraspecific crowding increases. Measuring foraging behavior, therefore, provides a way to investigate effects of population density on food limitation, an important link in understanding how crowding functions to regulate populations. We quantified three components of foraging behavior (prey attack rate, foraging speed, and relative use of morphologically constrained attack maneuvers) for male Black-throated Blue Warblers (Dendroica caerulescens) breeding under experimentally manipulated density conditions. Building on the previous work showing the density of conspecific neighbors affects territory size, reproductive success, and the time budgets of males (Sillett et al. 2004, Ecology 85: 2467-2477), we further show that density affects male foraging strategies. Although not differing in attack rate or foraging speed, male Black-throated Blue Warblers on territories with reduced neighbor densities used energetically expensive aerial attack maneuvers significantly less frequently than males in control (high-density) territories during both the incubation period and when provisioning nestlings and fledglings. We conclude that males altered their foraging behavior to compensate for density-related reductions in time available for foraging and that population density may constrain the time available for foraging.
Anecdotal evidence suggests that Burrowing Owls have declined in the state of Washington. We examined the status of these owls in agricultural and urban habitats to better understand the underlying causes of these declines. Nest density was higher in the area dominated by agriculture (0.67 nests/km(2)) than in the urban area (0.28 nests/km(2)), and re-use of nest burrows was more common in the agricultural area. We found no difference in mean clutch size between the two areas, but nesting success was higher in the agricultural area. The mean number of fledglings per nesting attempt was higher in the agricultural area (2.02 vs. 1.47), but we found no difference between the two areas in the mean number of fledglings per successful nest (3.2 vs. 3.1). Both natal recruitment (4% vs. 8%) and annual return rate of adults (30% vs. 39%) were lower in the agricultural area than in the urban area, suggesting that the owl population in the agricultural area may not be stable and may be a "sink" population. Due to high burrow fidelity from year to year, and the tendency of some owls in Washington to overwinter, we recommend that legal protection of nest burrows be extended to the nonbreeding season.
ABSTRACT Over the past several decades, there have been numerous reports of hummingbirds wintering in the southeastern United States. However, little is known about the species present and their relative abundance. From November 1998 to March 2008, we examined the species diversity, sex and age ratios, and site fidelity of hummingbirds wintering in southern Alabama and northern Florida. We captured and banded 1598 individuals representing 10 species, and the most frequently captured species were Rufous Hummingbirds (Selasphorus rufus; 51.6%), Ruby-throated Hummingbirds (Archilochus colubris; 23.5%), and Black-chinned Hummingbirds (Archilochus alexandri; 16.9%). Other species captured included Buff-bellied Hummingbirds (Amazilia yucatanensis), Calliope Hummingbirds (Stellula calliope), Allen's Hummingbirds (Selasphorus sasin), Broad-tailed Hummingbirds (Selasphorus platycercus), Broad-billed Hummingbirds (Cynanthus latirostris), Anna's Hummingbirds (Calypte anna), and Costa's Hummingbirds (Calypte costae). Most hummingbirds (71.8%) were captured in December and January. For most species, sex ratios were male-biased for juveniles and female-biased for adults, indicating possible differential mortality. Of 1598 hummingbirds captured, 144 representing five species returned to the same wintering location at least once. Female Rufous Hummingbirds (20.4% of individuals captured) exhibited the greatest site fidelity. Recaptures of banded Rufous Hummingbirds in autumn and early winter revealed that some individuals moved south into Alabama or Florida from Tennessee, northern Georgia, and northern Louisiana. Same-season recaptures of banded Rufous Hummingbirds suggest that their spring migration route is west along the Gulf Coast. Our results suggest that Alabama and Florida are viable overwintering areas for several species of hummingbirds, with numbers of species and individuals higher than previously recognized. However, more study is needed to confirm migration routes and to determine if Ruby-throated Hummingbirds wintering in our study area are year-round residents or migrants.
A lo largo de las últimas décadas, han ocurrido numerosos reportes de Colibríes pasando el invierno en el sureste de los Estados Unidos. Sin embargo, poco se conoce sobre la presencia de las especies y su abundancia relativa. Desde Noviembre 1998 hasta Marzo 2008, nosotros examinamos la diversidad especies, el sexo y los rangos de edades y la fidelidad de lugares de Colibríes pasando el invierno en el sur de Alabama y el norte de la Florida. Nosotros capturamos y anillamos 1598 individuos pertenecientes a 10 especies, las especies capturadas con mayor frecuencia fueron Selasphorus rufus (51.6%), Archilochus colubris (23.5%) y Archilochus alexandri (16.9%). Entre las otras especies capturadas se incluyeron a Amazilia yucatanenses, Stellula calliope, Selasphorus sasin, Selasphorus platycercus, Cynanthus latirostris, Calypte anna, Calypte costae. La mayoría de los colibríes (71.8%) fueron anillados en Diciembre y Enero. Para la mayoría de las especies, los radios de los sexos estuvieron sesgados hacia los machos para los juveniles y hacia las hembras en individuos adultos, lo cual posiblemente indica una mortalidad diferencial. De los 1598 Colibríes capturados, 144 representaron cinco especies que retornaron por lo menos una vez a la misma localización invernal. Las hembras de Selasphorus rufus (20.4% de los individuos capturados) exhibieron la mas alta fidelidad espacial. Recapturas de individuos anillados de Selasphorus rufus en el otoño y temprano en el invierno revelaron que algunos individuos se movieron hacia el sur a Alabama o la Florida desde Tennessee, norte de Georgia y el norte de Louisiana. Recapturas durante una misma temporada de Selasphorus rufus sugieren que las rutas de migración durante la primavera se ubican al oeste d la costa del golfo. Nuestros resultados sugieren que Alabama y la Florida son áreas viables para pasar el invierno para varias especies de colibríes, con un número mayor de especies e individuos que los reportados previamente. Sin embargo, mas estudios son requeridos para confirmar las rutas de migración y para determinar si Archilochus colubris que pasa el invierno en nuestra área de estudio es un residente permanente durante todo el año o migra.
We studied the movements and foraging effort of radio-marked Steller's Eiders (Polysticta stelleri) and Harlequin Ducks (Histrionicus histrionicus) to evaluate habitat quality in an area impacted by industrial activity near Dutch Harbor, Alaska. Foraging effort was relatively low, with Steller's Eiders foraging only 2.7 +/- 0.6 (SE) hours per day and Harlequin Ducks 4.1 +/- 0.5 hours per day. Low-foraging effort during periods of high-energetic demand generally suggests high food availability, and high food availability frequently corresponds with reductions in home range size. However, the winter ranges of Harlequin Ducks did not appear to be smaller than usual, with the mean range size in our study (5.5 +/- 1.1 km(2)) similar to that reported by previous investigators. The mean size of the winter ranges of Steller's Eiders was similar (5.1 +/- 1.3 km(2)), but no comparable estimates are available. Eutrophication of the waters near Dutch Harbor caused by seafood processing and municipal sewage effluent may have increased populations of the invertebrate prey of these sea ducks and contributed to their low-foraging effort. The threat of predation by Bald Eagles (Haliaeetus leucocephalus) that winter near Dutch Harbor may cause Steller's Eiders and Harlequin Ducks to move further offshore when not foraging, contributing to an increase in range sizes. Thus, the movement patterns and foraging behavior of these ducks likely represent a balance between the cost and benefits of wintering in a human-influenced environment.
The nesting biology of the Eastern Yellow Wagtail (Motacilla tschutschensis) was studied at Cape Romanzof, Alaska, an arctic tundra site on the Bering Sea coast near the northeastern limit of the breeding distribution of the Yellow Wagtail (Motacilla flava/citreola/tschutschensis] species complex. Ninety-four nests were located and monitored from 1996 to 1999. Females built nests in 5-7 d, and nests were located on the ground. The mean clutch size was 5.6 eggs, and the mean incubation period was 11 d. Both adults incubated, and some males had a partial brood patch. The mean duration of the nestling period was 11.6 d, and both parents brooded and fed the young. Some adults began the complete prebasic molt (including primaries) while their young were still in the nest. Nestling development was similar to that reported for other Yellow Wagtails (sensu lato), but the breeding cycle and breeding season of Eastern Yellow Wagtails was compressed relative to Western Yellow Wagtails in Europe and to other passerine species breeding in western Alaska. Some breeding events overlapped, including initiation of egg laying before completion of nest building and initiation of adult molt while young were still in the nest. Clutch sizes were larger than reported for most European relatives. Clutch size generally fit with models predicting an increase of about one egg per 19 degrees of increased latitude. Rapid nest initiation, overlap of breeding cycle events, nest attendance (including incubation) by males, and slightly larger clutches appear to be adaptations to high-latitude breeding in this long-distance migrant.
Avian pox virus (Poxvirus avium) is a mosquito-borne disease that occurs worldwide in a variety of bird species, but little is known about its prevalence or effect on seabirds. We monitored prevalence of pox virus and its effect on fledging success of Laysan Albatross (Phoebastria immutabilis) on Oahu, Hawaii, from 2003 to 2007. Pox prevalence in albatross chicks averaged 88% in years with high rainfall and 3% in years with low rainfall. Diagnosis of pox virus was clinically confirmed in two birds by Muscovy Duck (Cairina moschata) fibrolast cultures. Severity of infection ranged from small wart-like nodules and lesions on the bill, face, eyes, tarsus, and feet, to large tumorous growths that completely covered both eyes and caused deformation of the bill and skull. Most chicks recovered from infection, and the fledging rate in pox epizootic years (82%) did not differ from that in years with low pox prevalence (80%) or the average fledging rate on Midway Atoll (86%). Three chicks with severe infections were resighted as healthy adults on Kauai and Oahu in 2007, confirming postfledging survival of at least some birds. The high recovery rate, fledging success, and postfledging survival indicate that Laysan Albatross have strong immunity to avian pox virus.
We examined the diet of White-throated Hawks (Buteo albigula) during the incubation and nestling periods in the southern temperate forest of Argentina. Pellets (N = 74) and prey remains (N = 59) were collected at 10 nests from 1998 to 2003, and preys delivered to two nests were monitored during the 2001-2002 breeding seasons. White-throated Hawks fed on small mammals, birds, lizards, and insects. The three methods of identifying prey (pellets, prey remains, and direct observation) produced different results. All types of prey except large birds were detected in pellets, and arthropods may have been over-represented in pellets due to secondary consumption. No remains of either arthropods or reptiles were identified among prey remains collected at nest sites and, during nest observations, we were unable to identify many of the prey items delivered by adults. Our results indicate that accurate determination of the diet of White-throated Hawks requires more than one method of identifying prey.
Birds in Neotropical forests frequently follow army ants to forage for insects. Here we report the first record of several species of Neotropical grassland birds following army ants (Labidus praedator) and yellow armadillos (Euphractus sexcinctus). We observed Strange-tailed Tyrants (Alectrurus risora) following army ants in El Bagual Ecological Reserve in Argentina. Other species also observed following army ants included Pampas Finches (Embernagra platensis), Wedge-tailed Grass-finches (Emberizoides herbicola), Long-tailed Reedfinches (Donacospiza albifrons), Great Kiskadees (Pitangus sulphuratus), Rufous Horneros (Furnarius rufus), Gray Monjitas (Xolmis cinerea), and Pale-breasted Spinetails (Synallaxis albescens). Strange-tailed Tyrants and Wedge-tailed Grass-finches were also observed following armadillos. Because birds were observed capturing insects flushed by the army ants and armadillos, our observations indicate that birds that opportunistically follow army ants and armadillos benefit from the association.
Although Savannah Sparrows (Passerculus sandwichensis) have been well studied across their North American range, few data are available for populations that breed in high-elevation habitats. We collected data over six years on the demography of a population of Savannah Sparrows (P. s. anthinus) breeding in alpine tundra and sub-alpine meadows in northern British Columbia, Canada. The mean duration of the breeding season at our site was 45.5 d, and pairs produced a maximum of one brood per season. Clutch sizes varied annually (mean = 4.37, range = 3.90 - 4.71 eggs). Nest fate also varied among years (range = 33 - 92%) due to variation in abiotic (weather) and biotic (predators) conditions. Uncorrected return rates of banded birds were 68% for adults and 17% for juveniles (N = 22 and 102, respectively). However, when resighting probability was taken into account, apparent annual survival was 75% for adults and 34% for juveniles. Compared to populations at lower elevations, Savannah Sparrows in our study had shorter breeding seasons, fewer broods per season, larger clutches, and higher adult and juvenile return rates. Our results suggest that Savannah Sparrows that breed in high-elevation habitats have adopted a low fecundity, high survival life history strategy that enables their persistence in these challenging environments.
Colder, unpredictable climates, and reduced food availability at high altitudes impose strong selective pressures that have driven the evolution of avian life histories. To fully understand this issue, data concerning the comparative demography of populations of the same species over sufficiently large altitudinal gradients are needed. However, few such studies have been conducted. We compared the breeding ecology of two populations of White-bellied Redstarts (Hodgsonius phaenicuroides), one in the subtropics of southwestern China at an altitude of 1300 m and another in the alpine zone of the Tibetan plateau at an altitude of 4300 m. Relative to their low-altitude counterparts, the high-altitude redstarts had a shorter breeding period (55 vs. 94 d), and had significantly smaller clutches (2.7 vs. 3.2 eggs) and larger eggs (5913 vs. 5033 mm(3)). Redstarts at our high-altitude site also had longer incubation (16 vs. 11 d) and nestling (16 vs. 12 d) periods than those at the low-altitude site. The observed patterns are consistent with an adaptive life history strategy, with birds whose reproductive output is constrained in stressful environments such as high altitudes tending to have reduced fecundity, but allocating more energy into each offspring as a buffer to the harsh conditions.
Little is known about the relationship between seasonal food availability and the foraging strategies of insectivorous Neotropical birds. We studied a population of Tropical Kingbirds (Tyrannus melancholicus), a primarily insectivorous species, in eastern Bolivia to examine relationships between rainfall, food availability, and foraging strategies throughout the year. Our study site in the southern Amazon Basin was characterized by strong seasonal variation in the abundance of the kingbird's main insect prey (coleopterans and hymenopterans), with reduced abundance during the nonbreeding season which largely overlaps the dry season. Overall, mean search times for insect prey by Tropical Kingbirds during the breeding (96.9 ± 85.6 [SD] sec) and nonbreeding (83.7 ± 91.2 sec) seasons did not differ (P= 0.23). However, during the nonbreeding season, kingbird search times were negatively, but nonsignificantly, correlated with coleopteran abundance (r²= 0.43, P= 0.16) and significantly and negatively correlated with hymenopteran abundance (r²= 0.72, P= 0.03). Although insect abundance differed seasonally, kingbird search times did not, perhaps because kingbirds forage on a greater variety of insects during the nonbreeding season or, during the breeding season, kingbird search times may be influenced by the need to monitor and defend nests as well as constraints on the types of prey that can be fed to nestlings. However, the reduced abundance of their primary insect prey and negative relationships between the abundance of those prey and search times during the dry, nonbreeding season suggest that Tropical Kingbirds in southern Amazonia may be food limited, potentially explaining why some migrate and spend that season elsewhere.
Data from roosts of Amazona parrots may be useful in creating demographic models, because these birds exhibit high roost fidelity and pairs are conspicuous in flight. However, few investigators have attempted to track changes in the number of pairs using such roosts. We studied Red-lored Amazons (Amazona autumnalis) at a communal roost in southwest Ecuador over a 1-yr period to understand better their population structure. Population size was estimated at 214 individuals. Counts revealed seasonal variation in numbers, but the occurrence of pairs and singles was seldom correlated. The number of paired individuals using the roost was lower during the breeding period. In contrast, the number of single birds at the roost nearly doubled during the breeding period. Overall, our data suggest that parental responsibilities during the nesting period explain fluctuations in the number of birds at the roost, and such fluctuations can be used to estimate the reproductive portion of the population. Protection of the small mangrove islands where the parrots roost would likely benefit a population that occupies a much larger area and would, at the same time, provide a useful tool for demographic studies of this poorly known neotropical parrot.