Acoustic monitoring of nocturnally migrating birds accurately assesses the timing and magnitude of migration through the Great Lakes

Tracking the movements of migratory songbirds poses many challenges because much of their journey takes place at night. One promising technique for studying migratory birds relies on microphones to record the nocturnal flight calls produced by birds on the wing. We compared recordings of night flight calls with bird-banding data in a southern Great Lakes ecosystem. We collected \u3e 6,200 hr of nocturnal recordings at 7 locations around Lake Erie. We detected \u3e 60,000 flight calls from migratory birds and classified 45,775 calls to species level or to a bioacoustic category comprising several species with similar calls. We compared these acoustic data with records of 5,624 birds captured in mist nets. We found that acoustic recordings accurately quantified the magnitude of migration; comparison with mist-net data revealed significant positive correlations between the number of acoustic detections and the number of mist-net detections across species. We also found that acoustic recordings accurately quantified the timing of migration; we found significant positive correlations between the date of passage of the 10th, 50th, and 90th percentiles of the populations of up to 25 groups of passage migrant species in the acoustic data and mist-net data. A careful examination of 6 species with distinctive flight calls revealed only subtle seasonal differences between peak detections via acoustic monitoring and mist netting, at both daily and weekly timescales. This research enhances our understanding of the role that acoustic sampling can play in monitoring migratory birds, providing important empirical support for the validity of night-flight-call monitoring. © 2014 Cooper Ornithological Society

Whip it good! Geographic consistency in male songs and variability in female songs of the duetting eastern whipbird Psophodes olivaceus

Geographic variation in male bird songs has been studied extensively, but there have been few investigations of geographic variation in female songs or sex differences in patterns of geographic variation. We compared patterns of variation in male and female songs of eastern whipbirds Psophodes olivaceus by analyzing recordings from 16 populations across the species’ geographic range in eastern Australia. We found remarkably different patterns of geographic variation between the sexes. Female eastern whipbird songs are easily categorized into discrete song types. Song types are shared between nearby females, but female songs show pronounced differences at a continental scale. In contrast, male eastern whipbird songs show high consistency throughout the species’ geographic range. All recorded males share the ability to transpose the frequency of the introductory whistle and most recorded males share the ability to vary the direction of the slope of the terminal whip crack. For eight of nine measured variables, female songs show significantly higher levels of variation than male songs. We discuss whether sex differences in dispersal, song learning strategies, and song function may explain these sex differences in patterns of song variation. We suggest that eastern whipbirds have experienced a decoupling of male and female song learning strategies and that the songs of each sex have responded to different selective pressures in the context of countersinging interactions. We speculate that consistency in male songs throughout the geographic range of eastern whipbirds may arise through female preference for males that perform large bandwidth whip cracks

Acoustic monitoring of migratory birds over western Lake Erie: avian responses to barriers and the importance of islands

Understanding the flight patterns of migrating birds is critical for informing conservation actions and management decisions. We studied the geographic and temporal distribution of birds migrating through the southern Great Lakes using nocturnal acoustic monitoring data and banding records from sites on Pelee Island in Lake Erie and on the mainland along the north shore of Lake Erie. Given that Lake Erie may represent an ecological barrier to migratory birds, we predicted that mainland and island sites would show different patterns in both the number of passage migrants and the timing of their migration. Analysis of over 60,000 flight calls from 6200 h of recordings revealed significantly more migrants over the island than the mainland in both spring and fall 2012. The acoustic data provide evidence that none of the species or species groups examined avoided crossing the lake. Birds were detected significantly earlier on Pelee Island than on the north shore of Lake Erie in spring, although they were not detected earlier on the mainland in fall. These results suggest that Lake Erie is not a major barrier to migration. The large number of birds detected over the island suggest that birds may concentrate their flight over islands in the middle of the lake, although recordings of migrants over open water will be required to support this suggestion. Our results show that Pelee Island is an important part of the migratory route of North American birds and provide valuable information on the movement of nocturnal migrants over the Great Lakes

A quantitative description of the vocalizations and vocal activity of the Barred Owl

Barred Owls (Strix varia) are highly vocal and perform a diverse array of vocalizations. They are often monitored by acoustic surveys, yet Barred Owl vocalizations and vocal behavior are poorly described. We present a detailed analysis of Barred Owl vocal behavior with four goals: (1) to provide a quantitative description of Barred Owl vocalizations, including those given within duets, (2) to examine diel variation in vocal output for multiple vocalizations, (3) to explore the use of vocalizations inside and outside of duets, and (4) to identify sex-specific vocal characteristics and discuss their utility in identifying an owl\u27s sex. Adult Barred Owls produced 13 distinct vocalizations that could be assigned to call type on the basis of fine-structural measurements. Barred Owls vocalized throughout the day but were more vocal at night with peaks in vocal activity from 18:00 to 20:00 and 02:00 to 05:00. Most calls were produced throughout the night, but some (e.g., alarm calls) were more common at particular times. Two types of vocalizations were produced only within duets, and one type of vocalization occurred primarily outside duets. Calls of females were higher in pitch with longer terminal notes and more vibrato than those of males. Using these differences, cluster analysis assigned owls to two groups corresponding to predicted sex with 91% accuracy. We discuss possible functions of certain vocalizations and how understanding the vocal repertoire and sex differences of this species\u27 acoustic signals will benefit behavioral studies and monitoring, including Spotted Owl (Strix occidentalis) conservation. © The Cooper Ornithological Society 2010

NEST DESCRIPTION AND NESTING BEHAVIOR OF THE RUFOUS-CAPPED WARBLER (BASILEUTERUS RUFIFRONS)

Abstract · The breeding biology of most tropical resident bird species is little-documented, particularly for sexually monomorphic species in which sex-specific contributions to nest-building and nestling provisioning are challenging to quantify. We describe nest structure and adult behavior throughout the nesting cycle for a color-banded population of Rufous-capped Warblers (Basileuterus rufifrons), a widespread sexually monomorphic tropical resident songbird. Using focal observations of 11 nests, combined with video monitoring during the incubation and nestling periods, we provide new information on this species’ nesting behavior, particularly sex-specific parental contributions to nest building, incubation, and nestling care. All nests were dome-shaped structures with a side entrance constructed of grasses, twigs, and leaves, as is typical for Basileuterus warblers. Females were the primary nest-builders, although we also observed male-assisted nest-building at one nest, which is a rare behavior in wood-warblers. Females were the sole incubators, and the incubation period in this population was 13–14 days. Video recordings confirmed that males and females made equivalent contributions to nestling feeding and nest sanitation. Our study provides detailed observations of both male and female Rufous-capped Warblers during all stages of the nesting cycle, and thus improves our understanding of nesting behavior in this common yet little-studied species.Resumen · Descripción del nido y comportamiento de anidación del Chipe gorrirrufo (Basileuterus rufifrons) La biología reproductiva de la mayoría de las aves residentes tropicales es poco conocida, particularmente para especies monocromáticas en que las contribuciones de cada sexo a la construcción de nido y la alimentación de los pichones son difíciles de observar. Describimos la estructura del nido y el comportamiento de los adultos durante todo el ciclo de anidación para una población anillada del Chipe gorrirrufo (Basileuterus rufifrons), una especie común de Paseriforme residente tropical monocromática. Con base en observaciones de 11 nidos y monitoreo de video durante los períodos de incubación y presencia de pichones, proveemos nueva información sobre el comportamiento de anidación de esta especie, particularmente sobre las contribuciones de cada sexo a la construcción de nido, la incubación, y el cuidado de los pichones. Todos los nidos presentaron estructura en forma de domo con entrada lateral, construidos con hierbas, palitos, y hojas, típicos de las especies de Basileuterus. Los nidos fueron construidos principalmente por las hembras, aunque en un nido observamos que la construcción fue asistida por el macho, un comportamiento raro en la familia Parulidae. Solo las hembras incubaron los huevos, y el período de incubación en esta población fue de 13–14 días. Los videos confirmaron que los machos y las hembras contribuyeron igualmente a la alimentación de los pichones y la limpieza del nido. Nuestro estudio provee observaciones detalladas de ambos sexos del Chipe gorrirrufo durante todo el ciclo de anidación, mejorando nuestro entendimiento sobre el comportamiento de anidación en esta especie común pero poco estudiada

Sex differences in singing and duetting behavior of neotropical Rufous-and-white Wrens (Thryothorus rufalbus)

In many tropical bird species, males and females sing together in coordinated vocal duets. Although studies of duetting present unique opportunities for understanding conflict and cooperation between the sexes, very few investigations describe the similarities and differences between male and female singing behaviors. Here, we present the first detailed account of the singing behavior of Rufous-and-white Wrens (Thryothorus rufalbus), a resident tropical duetting songbird. Male and female songs share a similar structure, yet show pronounced sex differences. Male songs have lower frequency characteristics and more repeated trill syllables, and often sound louder than female songs. Males sing more than females, and only males show elevated song output at dawn. Both males and females have song repertoires. Males have an average repertoire size of 10.8 song types, whereas females have a significantly smaller average repertoire size of 8.5 song types. Although males share proportionately more of their song types with neighbors than females do, both sexes share more song types with nearby individuals than with distant individuals. Breeding partners combine their solo songs to create duets. Duets assume a variety of different forms, ranging from simple, overlapping male and female songs to complex combinations of multiple male and female songs. Most duets (73%) are created by females responding to male song. Males respond to female-initiated duets with shorter latencies than when females respond to male-initiated duets. Each pair sings certain combinations of song types in duets more often than can be explained by random association, which demonstrates that Rufous-and-white Wrens have duet types. The most common duet type was different for each pair. Our results show that Rufous-and-white Wrens have pronounced sex differences in song structure, singing activity, repertoire size, repertoire sharing, and duetting behavior. © The American Ornithologists\u27 Union, 2005

The duetting behavior of pacific coast Plain Wrens

We provide the first detailed analysis of the vocal behavior of Pacific coast Plain Wrens (Thryothorus modestus modestus). Male Plain Wrens sing two categories of song phrase; one phrase is given as a solo song or duet introduction (I-phrases), while the other is sung primarily during duets (M-phrases). Females sing only one category of song phrase, usually during duets (F-phrases). Both sexes have repertoires of their respective song categories. Plain Wren duets show extreme temporal coordination: duets typically begin with male I-phrases, which are followed by the rapid alternation of female F-phrases and male M-phrases. These patterns are congruent with the solo and duet singing behavior of a sister taxon to the Plain Wren, the Canebrake Wren (Thryothorus modestus zeledoni). Our analyses of Plain Wren songs and duets reveal pronounced differences between males and females and contribute to our understanding of the complex duetting behavior of Thryothorus wrens. © The Cooper Ornithological Society 2007

Between-Year Survival and Rank Transitions in Male Black-Capped Chickadees (\u3cem\u3ePoecile Atricapillus\u3c/em\u3e): A Multistate Modeling Approach

In dominance-structured animal societies, variation in individual fitness is often related to social status. Like many passerine birds, Black-capped Chickadees (Poecile atricapillus) have a short average adult life-expectancy (Ø2 years); however, the maximum recorded life span is \u3e5× as long. Enhanced annual survival could contribute to greater lifetime reproductive success for male Black-capped Chickadees with high social rank. We used multistate capture–mark–recapture models to estimate annual survival of male Black-capped Chickadees in Ontario using resighting and recapture data collected from 1997 to 2002. Our goal was to evaluate support for an influence of rank on annual survival and estimate its effect size for a food-supplemented study site. We also statistically modeled the probability of between-year rank transitions. Model selection based on Akaike’s information criterion provided support for an effect of rank on survival. However, multimodel inference revealed that the size of the effect was rather small. Over the six study years, model-averaged estimates of the survival benefit of high versus low rank ranged from 5.0 to 7.3%. As expected, survival was strongly year-dependent, with model-averaged estimates of annual survival probability varying between 0.36 and 0.73. Age was an important predictor of the probability of rank transitions. Low-ranked second-year birds were less likely than older low-ranked birds to advance to high rank between years; likewise, high-ranked after-second-year birds were less likely to drop in rank. Other studies have found larger effects of rank on survival than we observed here. Future research should consider how interactions between social and environmental factors influence annual survival

Inconsistent geographic variation in the calls and duets of Barred Owls (Strix varia) across an area of genetic introgression

Much of our understanding of vocal geographic variation in birds is based on the dialects of oscine songbirds that learn their songs. Recent studies have revealed that nonoscine vocal behavior is more complex than previously thought, yet we still have a rudimentary understanding of how vocalizations of suboscine and nonpasserine birds are infuenced by genetic and geographic variation. We examined geographic variation in male calls, female calls, and duets of Barred Owls (Strix varia) among 10 locations across the southeastern United States. Recent molecular work revealed two genetically distinct clades of Barred Owl at either end of our transect, with substantial introgression in between. We predicted that calls would vary with genetic distance in a clinal pattern, but that duets and duetting behavior might exhibit dialects similar to that of learned bird song. Discriminant analysis did not reveal any components of vocalizations or vocal behavior that could be used to assign vocalizations to the correct recording location. There were no relationships between any aspect of vocal structure or behavior and geographic distance. Some characteristics of male and female calls and duets varied among locations, but there was no discernible geographic pattern. We suggest that such inconsistent geographic variation in vocalizations is not unexpected for non-song-learning species. The lack of geographic pattern in vocalizations may be due, in part, to high levels of individual variation, recent signal evolution, and local adaptations. We discuss the application of these results to the ontogeny and evolution of complex, coordinated vocal behavior in nonpasserines. © The American Ornithologists\u27 Union, 2012. Printed in USA

Continent-wide Patterns of Divergence in Acoustic and Morphological Traits in the House Wren Species Complex

Phenotypic traits are important for assessing differences between populations, especially in groups with poorly resolved taxonomy. One such group, the House Wren complex, presents extensive taxonomic controversy and is thought to comprise many independent evolutionary units. Although the songs and morphological features of House Wrens (Troglodytes aedon) show extensive variation, differences between populations have not been quantified. We assessed variation in acoustic and morphometric traits within this complex and compared patterns of variation with currently recognized subspecies boundaries. First, we compared songs and morphology among eight recognized subspecies (T. a. aedon, T. a. parkmanii, T. a. cahooni, T. a. brunneicollis, T. a. nitidus, T. a. musculus, T. a. beani, and T. a. rufescens), controlling for significant effects of latitude. Second, we used variation in male song, a trait with an important role in mate choice and male–male competition, to assess divergence among subspecies. We compared variation among subspecies to variation across seven currently recognized Troglodytes species (T. hiemalis, T. pacificus, T. tanneri, T. sissonii, T. cobbi, T. rufociliatus, and T. ochraceus). Our results, based on broad sampling of songs (n¼786) and morphological traits (n ¼ 401) from 609 locations throughout the Americas, show that most of the subspecies examined diverge in song, morphology, or both. In addition, the acoustic differences between subspecies are similar to, and in some instances greater than, the divergence between pairs of currently recognized species. Our results suggest that at least four allopatric subspecies—T. a. nitidus, T. a. musculus, T. a. beani, and T. a. rufescens—are likely different species, and we identify many other vocally and morphologically differentiated subspecies that may, upon further detailed genetic analysis, result in new species