David M. Logue

Constrained performance in a communication network: implications for the function of song-type matching and for the evolution of multiple ornaments.

Many species of territorial songbirds exhibit a behavior known as song‐type matching, in which a male sings the same song type that his neighbor is singing. Song‐type matching is associated with increased aggression, but researchers have not come to a consensus on its adaptive function. Building on studies that identify singing performance as a variable relevant to sexual selection, we hypothesize that higher‐performance singers benefit from matching their opponent’s song type because matching improves eavesdroppers’ ability to compare the two males’ performances. We present a model of song‐type choice that predicts that males that can outperform their rivals benefit by matching. In contrast, lower‐performance males should avoid both matching and being matched. Our hypothesis is compatible with some existing hypotheses of song‐matching function, but it is not compatible with the hypothesis that song matching is a conventional signal of aggression. We offer unique predictions that could be used to test our idea. We speculate that lower‐performance individuals might have driven the evolution of repertoire complexity because they stand to benefit from novel, unmatchable songs. The phenomenon that dissimilar signals are less accurately compared than similar signals may favor the evolution of multiple ornaments and of plastic signal development (e.g., song learning) in general.

THE DUET CODE OF THE FEMALE BLACK-BELLIED WREN

Abstract In many duet-singing songbirds, paired birds combine their song types nonrandomly to form duet songs. Several different behavioral mechanisms could generate nonrandom song type associations in duets. I tested female Black-bellied Wrens (Thryothorus fasciatoventris) for one such mechanism: adherence to a set of rules linking female response songs to male stimulus songs. I call this set of rules a “duet code.” Duets of free-living Black-bellied Wrens were recorded in 2001 and 2002. In 2003 I returned to the same territories and played the male song types from the recorded duets. Females answered male song stimuli as if duetting with the playback speaker. Although the known repertoires of females averaged 8.4 song types, each female sang only a single song type in response to each male song type. Random answering could not account for this pattern, supporting the hypothesis that females abide by duet codes. Females that were still paired with their mates from 2001–2002 answered 100% of their mates songs with the same song types they had used previously, demonstrating that codes are stable over time. In contrast, females that were new to a territory answered an average of only 18% of their mates song types with the same song type as the previous female, indicating that duet codes are individually distinctive. Duet participation by female Black-bellied Wrens represents a special kind of animal communication, in which discrete vocal signals consistently elicit discrete vocal responses according to an individually distinctive set of rules.

A locally funded Puerto Rican parrot ( Amazona vittata ) genome sequencing project increases avian data and advances young researcher education

BackgroundAmazona vittata is a critically endangered Puerto Rican endemic bird, the only surviving native parrot species in the United States territory, and the first parrot in the large Neotropical genus Amazona, to be studied on a genomic scale.FindingsIn a unique community-based funded project, DNA from an A. vittata female was sequenced using a HiSeq Illumina platform, resulting in a total of ~42.5 billion nucleotide bases. This provided approximately 26.89x average coverage depth at the completion of this funding phase. Filtering followed by assembly resulted in 259,423 contigs (N50 = 6,983 bp, longest = 75,003 bp), which was further scaffolded into 148,255 fragments (N50 = 19,470, longest = 206,462 bp). This provided ~76% coverage of the genome based on an estimated size of 1.58 Gb. The assembled scaffolds allowed basic genomic annotation and comparative analyses with other available avian whole-genome sequences.ConclusionsThe current data represents the first genomic information from and work carried out with a unique source of funding. This analysis further provides a means for directed training of young researchers in genetic and bioinformatics analyses and will facilitate progress towards a full assembly and annotation of the Puerto Rican parrot genome. It also adds extensive genomic data to a new branch of the avian tree, making it useful for comparative analyses with other avian species. Ultimately, the knowledge acquired from these data will contribute to an improved understanding of the overall population health of this species and aid in ongoing and future conservation efforts.

Duetting in space: a radio-telemetry study of the black-bellied wren

In many birds, individuals ‘answer’ the songs of their pair-mates to produce vocal ‘duets’. One hypothesized function of song answering is that it prevents extra-pair birds from intruding into the duetting pairs territory to obtain copulations or usurp one of the pair-mates. In this capacity, answering may signal that the pair-mates are close together, and so are prepared to defend against such an intrusion. Another functional hypothesis states that answering helps pair-mates maintain contact, and so predicts that a bird is more likely to approach its mate after a duet than after a solo song. I used radio-telemetry to monitor the distance between mated black-bellied wrens (Pheugopedius fasciatoventris). I found that birds of both sexes were more likely to answer their mates song when the mate was close, and that maximum duet length was negatively related to the distance between pair-mates. Furthermore, song answering positively affected the likelihood of one pair-mate approaching the other after a song. In a significant majority of the approaches after duet songs, the answering bird approached the initiator. I conclude that in the black-bellied wren, (i) the occurrence and duration of vocal duets covary with physical closeness and (ii) contact maintenance is a secondary function of duet participation.

Migration and the evolution of duetting in songbirds

Many groups of animals defend shared resources with coordinated signals. The best-studied of these signals are the vocal duets produced by mated pairs of birds. Duets are believed to be more common among tropical-breeding species, but a comprehensive test of this hypothesis is lacking, and the mechanisms that generate latitudinal patterns in duetting are not known. We used a stratified sample of 372 songbird species to conduct the first broad-scale, phylogenetically explicit analysis of duet evolution. We found that duetting evolves in association with the absence of migration, but not with sexual monochromatism or tropical breeding. We conclude that the evolution of migration exerts a major influence on the evolution of duetting. The perceived association between tropical breeding and duetting may be a by-product of the migration–duetting relationship. Migration reduces the average duration of partnerships, potentially reducing the benefits of cooperative behaviour, including duetting. Ultimately, the evolution of coordinated resource-defence signals in songbirds may be driven by ecological conditions that favour sedentary lifestyles and social stability.

Developmental environment affects risk-acceptance in the hissing cockroach, Gromphadorhina portentosa.

Consistent individual differences in the tendency to accept risk have been demonstrated in invertebrates, fish, birds, and mammals, including humans. These individual differences have been associated with size, growth rate, survival, and reproductive success. Little research, however, has investigated the effect of developmental environment on individual differences in risk-acceptance. Competing hypotheses offer different explanations of how variation in the quality of the developmental environment affects risk-acceptance in adults. The first hypothesis states that individuals developing in poor quality environments take risks because such behavior is their only means of obtaining adequate fitness returns. The second hypothesis states that individuals developing in poor environments avoid risk because their poor physical condition makes them especially vulnerable to injury or death. We measured several forms of risk-accepting behavior (exploration, foraging, and recovery after disturbance) in male hissing cockroaches (Gromphadorhina portentosa) that had developed in nutritional and social environments of varying quality. Individuals raised on poor nutrition diets exhibited lower levels of risk-acceptance than those raised on high nutrition diets. Risk-acceptance among individuals that developed on poor nutrition diets was negatively correlated with body size. We conclude that quality of developmental environment affects risk-acceptance across behavioral contexts in male hissing cockroaches. Our findings are consistent with the hypothesis that condition-dependent vulnerability mediates the relationship between developmental environment and risk-acceptance.

Sexually antithetical song structure in a duet singing wren

Summary Black-bellied wrens (Thryothorus fasciatoventris) use loud songs to communicate sex over long distances. We compared male and female songs recorded from a central Panamanian population of black-bellied wrens. All nine measured features differed significantly between the sexes. Males sang lower fundamental frequencies than females, but this difference cannot be explained by simple body size-frequency scaling. A discriminant function analysis correctly discriminated the singer’s sex for all songs in the analysis. When viewed as sonograms, the terminal syllables of male and female songs exhibited opposite structure ‐ all male songs ended in V-shaped syllables, and all female songs ended in arc-shaped syllables. The degree and character of dimorphism lead us to describe song structure in this population as ‘sexually antithetical’. Variation in song dimorphism throughout this species’ range provides an excellent opportunity to test the hypothesis that signal degradation during transmission selects for divergent signal structure.

Duetting as a Collective Behavior

Mated birds of many species vocalize together, producing duets. Duetting behavior occurs at two levels of organization: the individual level and the pair level. Individuals initiate vocalizations, answer their mates’ vocalizations, and control the structure and timing of their own vocalizations. Pairs produce duets that vary with respect to duration, temporal coordination, and phrase-type combinations, among other properties. To make sense of this hierarchical structure, organize duetting research, and identify new avenues of investigation, we advocate a “collective behavior” approach to the study of duets. We critically review key terminology in the duetting literature in light of this approach, and elucidate six insights that emerge from the collective behavior approach: (1) Individual-level behaviors describe pair-level behaviors, but the opposite is not true; (2) The level of organization informs how we test for the rules that govern behavior; (3) Functional hypotheses about duetting must distinguish individual from group characters; (4) Stimulus-response, cybernetics, and entrainment offer alternative hypotheses for the cognitive control of duetting behavior; (5) Avian duetting has the potential to be a model system for the ontogeny of vocal interaction; and (6) The collective behavior approach suggests new avenues of research. Ultimately, we argue that nearly every aspect of duetting research stands to benefit from adopting a collective behavior approach. This approach also has applications to other forms of interactive vocal communication in birds and primates, including humans.

Aggressiveness and Size: A Model and Two Tests

Individual variation in aggressive behavior in animals might be caused by adaptive covariation with body size. We developed a model that predicts the benefits of aggressiveness as a function of body size. The model indicated that individuals of intermediate sizes would derive the greatest benefits from being aggressive. If we assume that the cost of aggression is approximately uniform with respect to body size, selection should favor higher aggression in intermediate-sized individuals than in large or small individuals. This prediction was tested by stimulating male Madagascar hissing cockroaches, Gromphadorhina portentosa, with disembodied antennae and recording the males’ aggressive responses. Antennae from larger males evoked weaker responses in subjects, suggesting that males obtained information about their opponents’ size from the opponents’ antennae alone. After accounting for this effect, we found support for the key prediction of our model: aggressiveness peaked at intermediate sizes. Data from actual male-male interactions validated that the antenna assay accurately measured aggressiveness. Analysis of an independent data set generated by staging male-male interactions also supported the prediction that intermediate-sized males were most aggressive. We conclude that adaptive covariation between body size and aggressiveness explains some interindividual variation in aggressiveness.

Typical Males and Unconventional Females: Songs and Singing Behaviors of a Tropical, Duetting Oriole in the Breeding and Non-Breeding Season

Recent research emphasizes that female song is evolutionarily important, yet there are still few species for which we have quantified the similarities and differences between male and female song. Comparing song rates and the structure of female and male song is an important first step to forming hypotheses about functional and evolutionary differences that may exist between females and males, especially in year-round territorial species that may use their songs for breeding and non-breeding activities. We compared female and male singing rates and song structure in a tropical New World oriole, the Venezuelan troupial (Icterus icterus) during both the breeding and non-breeding season and between the dawn and day. Males sang solos at particularly high rates during the breeding season before dawn. Females, however, sang at consistent rates year-round, primarily during the day. Females answered 75% of male day songs, producing duets, whereas males overlapped only 42% of female songs. Duets were common year-round, but occurred more often during the non-breeding season. Structurally, female songs were higher pitched and shorter than male songs. We detected no sex differences in the number or order of syllables, however, interestingly, answers were shorter than duet initiations and solos, and, during the breeding season, songs that initiated duets were characterized by higher syllable diversity than were answers or solos. The fact that males sing more during the breeding season supports the classical hypothesis that male song is a sexually selected trait. However, our findings that females sing solos and answer the majority of male songs to create duets year-round suggests that female song may have evolved to serve multiple functions not exclusively tied to breeding.