Lauren P. Fitzsimmons

Individual Variation and Lek-Based Vocal Distinctiveness in Songs of the Screaming Piha (Lipaugus Vociferans), A Suboscine Songbird

Abstract One long-standing ornithological paradigm holds that song learning in oscine songbirds has a cultural component, whereas suboscine songbirds inherit songs genetically. Recent studies reveal that suboscine song may be more variable and complex than previously realized. Several suboscine species show marked individual variation in their songs—variation that may play a role in individual recognition and neighbor–stranger discrimination—and a few suboscine species show indications of song learning. We investigated individual variation in the vocalizations of a suboscine passerine, the Screaming Piha (Lipaugus vociferans), from recordings of 26 males at four lek sites along the Tambopata River in Peru. Male Screaming Piha songs consist of quiet introductory syllables followed by two explosively loud syllables that sound like an emphatic pee haw. We used three complementary methods to examine variation in song characteristics. Spectrogram cross-correlation revealed significant consistency within individual males and variability among males. Analysis of fine structural characteristics revealed that all measured song features were significantly less variable within individuals than among individuals. Canonical discriminant analysis based on these 13 song features correctly classified 93.2% of songs by individual and 76.4% of songs by lek site. Our results indicate that there is sufficient consistency in song features within males and sufficient variation among males for identification of individuals on the basis of songs and, to a lesser extent, that song features vary with the lek site of the singer. We conclude that Screaming Pihas sing songs that are individually distinctive and bear a lek signature.

Black-capped chickadee dawn choruses are interactive communication networks

Summary The dawn chorus of songbirds provides an ideal opportunity to study communication networks because multiple singers are within signalling range of each other, permitting eavesdropping by both males and females. Using an Acoustic Location System, we examined the dawn chorus singing behaviour of male black-capped chickadees (Poecile atricapillus )i n 15 neighbourhoods to determine whether singing behaviour is consistent with the communication network model. We calculated levels of frequency matching for 19 focal males and all of their neighbours. The observed level of frequency matching was greater than expected by chance. All males were involved in multi-way matching at dawn and often matched two or three neighbours simultaneously. The identity of individuals involved in three-way matches was related to both previous winter-flock membership and the relative dominance rank of the interacting males. We show that male black-capped chickadee dawn choruses are interactive communication networks where males are involved in high levels of matching with neighbours, and they match multiple individuals both simultaneously and sequentially. Additionally, the existence of multi-way matching and the identities of individuals involved suggest that individual males may eavesdrop at dawn. This is the first study to quantify network communication during the dawn chorus in multiple neighbourhoods.

Playing to an audience: the social environment influences aggression and victory displays

Animal behaviour studies have begun to incorporate the influence of the social environment, providing new opportunities for studying signal strategies and evolution. We examined how the presence and sex of an audience influenced aggression and victory display behaviour in field-captured and laboratory-reared field crickets (Gryllus veletis). Audience type, rearing environment and their interaction were important predictors in all model sets. Thus, audience type may impose different costs and benefits for competing males depending on whether they are socially experienced or not. Our results suggest that field-captured winners, in particular, dynamically adjust their contest behaviour to potentially gain a reproductive benefit via female eavesdropping and may deter future aggression from rivals by advertising their aggressiveness and victories.

Phenotypic covariance structure and its divergence for acoustic mate attraction signals among four cricket species

The phenotypic variance–covariance matrix (P) describes the multivariate distribution of a population in phenotypic space, providing direct insight into the appropriateness of measured traits within the context of multicollinearity (i.e., do they describe any significant variance that is independent of other traits), and whether trait covariances restrict the combinations of phenotypes available to selection. Given the importance of P, it is therefore surprising that phenotypic covariances are seldom jointly analyzed and that the dimensionality of P has rarely been investigated in a rigorous statistical framework. Here, we used a repeated measures approach to quantify P separately for populations of four cricket species using seven acoustic signaling traits thought to enhance mate attraction. P was of full or almost full dimensionality in all four species, indicating that all traits conveyed some information that was independent of the other traits, and that phenotypic trait covariances do not constrain the combinations of signaling traits available to selection. P also differed significantly among species, although the dominant axis of phenotypic variation (pmax) was largely shared among three of the species (Acheta domesticus, Gryllus assimilis, G. texensis), but different in the fourth (G. veletis). In G. veletis and A. domesticus, but not G. assimilis and G. texensis, pmax was correlated with body size, while pmax was not correlated with residual mass (a condition measure) in any of the species. This study reveals the importance of jointly analyzing phenotypic traits.

Tied to the nest: male black-capped chickadees decrease dawn chorus movement behaviour when their mate is fertile

Male songbirds typically mate-guard by closely following the female during her fertile period. At dawn, males may sing near the nest or roost to direct their chorus at mates. Recent evidence suggests males may also be involved in singing interactions with neighbours during the dawn chorus. We used a 16channel acoustic location system to examine the movement behaviour of 37 male black-capped chickadees, Poecile atricapillus, during the dawn chorus to determine if male proximity to the nest is a function of breeding stage. Males with fertile females covered a significantly smaller area within their territory, made fewer long-distance movements and sang at a lower song rate compared to males with nonfertile females. Males with fertile mates remained significantly closer to their nest cavity than males with incubating mates. Males with nonfertile mates spent more time near their neighbours with fertile mates than near their neighbours with nonfertile mates. Neither social rank nor age had a significant effect on movement behaviour or song rate. Our results clearly show that female fertility influences dawn chorusing behaviour in male black-capped chickadees. Males may remain near their nest to minimize the risk of cuckoldry, but when their partner is not fertile males may increase movement behaviour to interact with neighbours and/ or to advertise to potential extrapair mates.

Adaptive Plasticity in Wild Field Cricket’s Acoustic Signaling

Phenotypic plasticity can be adaptive when phenotypes are closely matched to changes in the environment. In crickets, rhythmic fluctuations in the biotic and abiotic environment regularly result in diel rhythms in density of sexually active individuals. Given that density strongly influences the intensity of sexual selection, we asked whether crickets exhibit plasticity in signaling behavior that aligns with these rhythmic fluctuations in the socio-sexual environment. We quantified the acoustic mate signaling behavior of wild-caught males of two cricket species, Gryllus veletis and G. pennsylvanicus. Crickets exhibited phenotypically plastic mate signaling behavior, with most males signaling more often and more attractively during the times of day when mating activity is highest in the wild. Most male G. pennsylvanicus chirped more often and louder, with shorter interpulse durations, pulse periods, chirp durations, and interchirp durations, and at slightly higher carrier frequencies during the time of the day that mating activity is highest in the wild. Similarly, most male G. veletis chirped more often, with more pulses per chirp, longer interpulse durations, pulse periods, and chirp durations, shorter interchirp durations, and at lower carrier frequencies during the time of peak mating activity in the wild. Among-male variation in signaling plasticity was high, with some males signaling in an apparently maladaptive manner. Body size explained some of the among-male variation in G. pennsylvanicus plasticity but not G. veletis plasticity. Overall, our findings suggest that crickets exhibit phenotypically plastic mate attraction signals that closely match the fluctuating socio-sexual context they experience.

The calling songs of male spring field crickets (Gryllus veletis) change as males age

Sexual traits are typically thought to convey information about a males quality or condition. Female preference for older males has been documented in many taxa, but the evidence that males signal their age is inconclusive. We investigated lifetime patterns of acoustic mate attraction signalling in a longitudinal study of the spring field cricket, Gryllus veletis. We recorded males continuously throughout their lives, such that every pulse of sound produced by every male was analyzed. Our study answers two main questions: (1) Do calls change as males age? Our results reveal that the calls of male spring field crickets change with age; the calls of older males were quieter, with more silent periods within and between chirps, and produced less often than those of younger males. As males aged most of the changes in call structure reflect decreased calling effort. (2) What is the relationship between calling effort and longevity? Lifetime calling effort was positively related to longevity, such that males that called the most over their life also lived longer than males that called less. Together, our findings provide the most thorough exploration of lifetime signalling patterns in crickets to date.

Strutting their stuff: victory displays in the spring field cricket, Gryllus veletis

Contest winners may perform victory displays at the conclusion of agonistic contests. Victory displays are hypothesized to function in browbeating or advertisement. To date, victory displays have received little attention. Following agonistic contests, several field cricket species produce aggressive songs and shake their body forwards and backwards (body jerks). We examined 20 agonistic contests between field-captured adult male spring field crickets, Gryllus veletis . We characterized the aggressive songs and body jerks that occurred both during and immediately following conflicts to evaluate whether these behaviours should be classified as victory displays. Aggressive songs and body jerks were observed throughout the contests, not just immediately following the conclusion of the fight. Winner aggressive song and body jerk rates were higher during the post-conflict period than during the fight period. Further, while both winners and losers performed aggressive songs and body jerks, winners performed them at five times the rate of the losers during the post-conflict period. We conclude that aggressive songs and body jerks should be considered victory displays, and that these victory displays may function as both browbeating and advertisement.

Post-contest behaviour in black-capped chickadees (Poecile atricapillus): loser displays, not victory displays, follow asymmetrical countersinging exchanges

Victory displays are behaviours that occur after the conclusion of a signaling contest, performed solely by the contest winner. Victory displays may reinforce the dominance of the winner either to the loser or to other conspecifics within signaling range. Victory displays are poorly studied despite the significant consequences that post-conflict behaviour may have on the individuals involved. We examined the period immediately following 50 territorial countersinging contests between males in 10 neighbourhoods of black-capped chickadees (Poecile atricapillus) of known dominance rank. We characterized the post-contest singing behaviour of chickadees and evaluated whether post-contest behaviour is consistent with victory displays. Using a 16-microphone acoustic location system to simultaneously record entire neighbourhoods of breeding chickadees, we isolated 50 dyadic countersinging contests and measured the vocal behaviour of the contestants in the minutes following each interaction. Eighty-six percent of contests were followed by a period of solo singing by one of the contestants, while 14% were followed by silence. The post-contest singer was most often the contestant who held a subordinate dominance position in the previous winter’s dominance hierarchy; dominant males performed post-contest song bouts significantly less often. Asymmetry in overlapping between contestants did not predict which bird sang a post-contest bout. However, in a significant majority of cases, the post-contest singer was pitch-matched by his opponent during the contest more than he pitch-matched his opponent. Our results indicate that male chickadees do not perform acoustic victory displays after countersinging contests. In contrast, the post-contest behaviour of territorial chickadees is more consistent with a “loser display”.

Signaling effort does not predict aggressiveness in male spring field crickets

The relationship between signaling and aggression is still unclear despite several decades of research. However, there is a growing interest in studying signals that predict aggressive behavior or fighting ability. The goals of our study were threefold: we investigated the relationship between signaling effort and aggression, the relationship between body condition and aggression, and the effect of fighting experience on subsequent signaling behavior in wild-caught and laboratory-reared male spring field crickets (Gryllus veletis). We found that aggressive behavior was not related to signaling effort, body size, or body condition. For contest winners, wild-captured males were more aggressive than laboratory-reared males. Signaling effort was highly repeatable within individuals, but aggressive behavior had low repeatability. We found no evidence for a winner or loser effect on signaling; there was no change in signaling effort when we compared contest winners and losers before and after they participated in aggressive contests. Long-distance acoustic signaling and aggressive behavior appear to be independent of one another in spring field crickets, perhaps serving different functions in female attraction and male–male competition, respectively.