David E. Gammon

Song repertoire evolution and acoustic divergence in a population of black-capped chickadees, Poecile atricapillus

Socially learned vocalizations, such as the songs of many songbirds, commonly show repertoires and geographical variation or dialects, but we have only a limited understanding of the cultural evolutionary processes that produce these patterns. In this paper we describe the singing behaviour of populations of black-capped chickadees in Fort Collins, Colorado that represents the apparent evolution of a repertoire of song types. In contrast to most black-capped chickadee singing behaviour, which consists of a single song type that is remarkably invariant across North America, chickadees throughout Fort Collins sing three acoustically distinct song types. Individual males have an average repertoire of 2.8 song types and use all of them in dawn bouts and countersinging with neighbouring males. Two of the three song types contain novel introductory notes. These notes and the ratio between the pitches of the two whistled notes used in the song consistently define each song type. Individual birds slightly vary the pitches used during a bout of singing for a particular song type but always maintain a constant pitch ratio for that type. The song type repertoire appears to be restricted to the Fort Collins area and has persisted for several years. We outline some of the cultural evolutionary processes that may have produced this repertoire and conclude by discussing research opportunities that may yield insight into how and why socially learned traditions originate and evolve.

Persistence and change of vocal signals in natural populations of chickadees: annual sampling of the gargle call over eight seasons

A study of the gargle call, an agonistic call of the black-capped chickadee Poecile atricapillus, for eight successive fall/winter seasons in three resident populations in Colorado (USA) revealed the following:(1) Individuals had repertoires of calls averaging 8.1 distinct types per bird (range 2-18).(2) Among individuals in a local population many calls shared some of the component syllables constituting the whole gargle calls; often the shared syllables occurred in different locations in the sequences of syllables (syntax) making up the calls.(3) Individuals also shared many of the same calls (identical or near identical syllable sequences); thus in a local sample the ensemble of call types in the population (the population repertoire) could be found by recording less than 10 birds.(4) In each population, the ensemble of gargle call types found in a given season consisted of a core group of about 10 kinds of gargle calls that persisted over all or nearly all the eight seasons of the study, but also the ensemble included a number of call types that were present for only one or a few seasons, or that occurred intermittently across time.(5) The great majority of call types that were lost from a population were explained by the loss of individual birds (carriers) by emigration or death.(6) The great majority of call types new in a population in any given season were explained by the occurrence of a new bird in the sample (local recruitment or immigration).(7) Both qualitative classification of gargle syllables and whole gargle calls by the method of visual inspection of sound spectrograms and automated quantitative analysis of acoustic features of syllables and calls were carried out in some examples, and these comparisons gave highly concordant results.Long-term studies of cultural evolution of non-song calls are infrequent but important because the sources and strength of social selection on non-song vocalizations are often likely to differ from those social factors influencing cultural evolution in territorial songs, the more often studied kind of bird acoustic signals. As a primary finding of this study we showed, using fine-grained measurements of acoustic variables, that a population retains a set of core gargle groups, each group representing a cultural tradition (behavioral lineage) exhibiting virtually no drift in detailed structure across eight consecutive seasons. In a small set of samples of core groups going back to 1988, there also was no evidence of change within a vocal tradition. These results suggest the hypothesis of strong canalizing social selection on the acoustic structure of gargles.

BLACK-CAPPED CHICKADEE DAWN CHORUS AND SUBSEQUENT SEXUAL ACTIVITY

Abstract Male Black-capped Chickadees (Poecile atricapillus) sing for several minutes prior to dawn during the breeding season. In northeastern Colorado, dawn singing was associated with male-female interactions rather than male-male interactions; males did not approach one another during the chorus. Males sang until female arrival, at which point they attempted copulation. During copulation attempts, males always uttered strings of variable sees and nearly always attached gargles to these strings. All gargles terminated in an acoustically similar, low-pitched, buzzy syllable.

Vocal memes in natural populations of chickadees: why do some memes persist and others go extinct?

We obtained data on a cultural trait from an 8-year study of a bird species, the black-capped chickadee, Poecile atricapillus. The trait is a nonsong vocalization, the gargle call, which exhibits variant acoustic forms (memes) in local populations. Some forms persisted in the local population throughout the study period as traditions transmitted with high fidelity (core memes) and others (failed memes) appeared only briefly, destined for quick extinction. We used our data to test a number of hypotheses concerning the question of why some memes persist as traditions, whereas others are short lived. We found that the persisting core memes were more widely shared among individuals, more frequently expressed, and acoustically different from failed memes. Carriers of core memes were older on average than those expressing failed memes, and similar in body size, but greater in mass, a possible indication of condition. We hypothesize that social selection for conformity to core gargle memes occurs in the context of the agonistic encounters where these vocal signals are used.

Carrion-feeding by Barred Owls (Strix varia)

Abstract Few documented reports exist that describe carrion-feeding by owls. We produce a conclusive record of carrion-feeding by Barred Owls (Strix varia) from photographs taken with a passive-infrared wildlife camera trap baited with the whole or partial carcasses of road-killed mammals (eastern gray squirrel [Sciurus carolinensis] and white-tailed deer [Odocoileus virginianus]). We recorded multiple pictures in two documented occurrences (one in Oct 2010 and the other in Dec 2010) over multiple days of a Barred Owl visiting both fresh and mostly-decayed carcasses. Attempts to lure owls to camera traps through use of tainted chicken and turkey meat were unsuccessful, and no additional owl pictures were obtained from unbaited cameras throughout 2010.

A Geographical Perspective on the Biotic Homogenization Process: Implications from the Macroecology of North American Birds

The major concern regarding the current trend towards biotic simplicity is that it is occurring with unprecedented rapidity across the entire globe. Geographic ranges of many species are collapsing (Lomolino and Channel 1995, 1998; Channel and Lomolino 1999a), while species that are favored by ecological conditions associated with modern human-dominated ecosystems are expanding rapidly (see Bright 1996 and references therein). Invading species often establish viable populations in extremely disturbed conditions and persist by continual colonization of newly disturbed area (Bright 1996, Williams and Meffe 1999), and in some cases by altering ecosystem processes such as fire frequency to favor their persistence (e.g., Cronk and Fuller 1995). Often vigorous colonizers in early succession in their native ecosystems, invasive species put most of their energy into reproduction, are generally less well adapted to specific environments, and tend to be able to tolerate a wide variety of conditions (Williams and Meffe 1999).

How is model selection determined in a vocal mimic?: Tests of five hypotheses

Many animal species imitate the sounds of other species, but we know little about why vocal mimics copy some species while failing to copy other species, i.e., ‘model selection’. In this observational study of free-living northern mockingbirds (Mimus polyglottos), I tested five hypotheses of model selection: (1) Proximity hypothesis: preferential imitation of species found in close proximity to the vocal mimic, (2) Aggression hypothesis: preferential imitation of species with which the mimic interacts aggressively, (3) Passive sampling hypothesis: preferential imitation of species heard frequently by the mimic, (4) Acoustic similarity hypothesis: preferential imitation of species whose sounds are acoustically similar to the non-imitative songs of the vocal mimic and (5) Alarm hypothesis: preferential imitation of alarm-associated vocalisations. The data supported only the acoustic similarity hypothesis. Given that this hypothesis has been supported in two additional mimicking lineages, it suggests a potential non-adaptive explanation for the evolution of vocal mimicry. Species that learn vocalisations are already predisposed toward learning sounds with key acoustic characteristics. Whenever natural selection favours a widening of the auditory template that guides model selection, vocal imitation of heterospecifics becomes more likely because of ‘learning mistakes’.

NESTING BIOLOGY OF THE BLACK-BELLIED WREN (THRYOTHORUS FASCIATOVENTRIS) IN CENTRAL PANAMA

Abstract We describe the nest and nest site, and provide the first description of the eggs and nesting behavior of the Black-bellied Wren (Thryothorus fasciatoventris) in central Panama. Nine nests were found near tree-fall gaps, swamps, and roads in moist tropical forests. Nests were dome-shaped with a circular side entrance. They were composed chiefly of strips of dead palm fronds, and were generally built in places where leaf litter and other debris had accumulated at the convergence of several vines near the forest floor. Both males and females participated in building the nest. Clutch size was three, and eggs were laid on consecutive days. Egg color varied from creamy to beige with faint to dark brown speckles that were more concentrated at the blunt end. Females were the sole incubators, but males fed the incubating females. Only the female brooded the nestlings once they hatched, but both parents fed the nestlings.

Lack of discrimination of conspecific vocalizations by Black-capped Chickadees: Tests on hand-raised juveniles

Abstract We played conspecific and heterospecific vocalizations to juvenile, hand-raised Black-capped Chickadees (Poecile atricapilla) in the laboratory and monitored their behavior in tests of preferential response to conspecific vocalizations. The subjects did not respond differently to conspecific and heterospecific vocal stimuli in three playback tests. We conclude that there was no evidence of selective attention to conspecific vocalizations during early life in these individuals. We speculate that this may explain the general lack of success in obtaining evidence for imitation learning by laboratory-tutored individuals in this species. Falta de Diferenciación de las Vocalizaciones Coespecíficas por Parte de Poecile atricapilla: Pruebas con Juveniles Criados a Mano Resumen. Expusimos a juveniles Poecile atricapilla criados en el laboratorio a vocalizaciones coespecíficas y heteroespecíficas y seguimos su comportamiento mediante pruebas de respuesta preferente a vocalizaciones coespecíficas. Los sujetos no respondieron diferencialmente a los estímulos vocales coespecíficos ni heteroespecíficos durante tres pruebas con cantos pregrabados. Concluimos que no hay evidencia de atención selectiva a las vocalizaciones coespecíficas durante la vida joven de estos individuos. Especulamos que esto pueda explicar la falta de éxito en obtener evidencia de aprendizaje por imitación en individuos de esta especie.