Christine R. Dahlin

Stability and change in vocal dialects of the yellow-naped amazon

Cultural evolution is an important force in creating and maintaining behavioral variation in some species. Vocal dialects have provided a useful model for the study of cultural evolution and its interactions with genetic evolution. This study examined the acoustic and geographic changes in vocal dialects over an eleven-year span in the yellow-naped amazon, Amazona auropalliata, in Costa Rica. Contact calls were recorded at 16 communal night roosts in 1994 and 19 roosts in 2005, with 12 roosts sampled in both surveys. In both surveys three dialects were found, each characterized by a distinctive contact call type and each encompassing multiple roosts. The limits between two of these dialects, the North and South dialects, was found to be geographically stable, while at the boundary between the North and Nicaraguan dialect there was introgression of each call type into roosts in the bordering dialect. Acoustic measurements and cross-correlations of spectrograms detected no change in the acoustic structure of contact calls in the South dialect but did show significant differences in the calls of both the North and Nicaraguan dialect between 1994 and 2005. These results are consistent with the vocal convergence hypothesis that proposes that dialects are long-term features maintained through some combination of biased transmission of local call types and purifying selection against foreign call types. Migration, copying errors and cultural drift may also play a role in the more subtle changes seen in the acoustic form of dialect call types.

Pair duets in the yellow-naped amazon (Amazona auropalliata): Phonology and syntax

Summary Pair duets are acoustically complex communication signals formed jointly by members of a mated pair. Duets may serve multiple communication functions; quantitative studies of the acoustic structure and organization of notes (or ‘syntax’) within duets are an important step in identifying these functions. This study examined duets of the yellow-naped amazon (Amazona auropalliata) at two sites in Costa Rica to determine the syntactical rules underlying duet variation. Duets were composed of contact calls and three other note types found only in duets. These latter note types were sex-specific, with one type performed by females and the other two types by males. Sex-specific notes were delivered antiphonally and in distinct pairs, with the male note following and often overlapping that of the female. Note types appeared in a strict sequential order in which each note could be repeated a variable number of times or omitted entirely, a pattern previously termed ‘combinatorial syntax’. Additionally, there was considerable variation in acoustic parameters of notes within types. Many of these parameters varied significantly with note order within a duet. These syntactical features suggest a preliminary hypothesis that males and females encode different, and possibly multiple, messages in their respective contributions to duets.

A test of multiple hypotheses for the function of call sharing in female budgerigars, Melopsittacus undulatus

In many social species group, members share acoustically similar calls. Functional hypotheses have been proposed for call sharing, but previous studies have been limited by an inability to distinguish among these hypotheses. We examined the function of vocal sharing in female budgerigars with a two-part experimental design that allowed us to distinguish between two functional hypotheses. The social association hypothesis proposes that shared calls help animals mediate affiliative and aggressive interactions, while the password hypothesis proposes that shared calls allow animals to distinguish group identity and exclude nonmembers. We also tested the labeling hypothesis, a mechanistic explanation which proposes that shared calls are used to address specific individuals within the sender–receiver relationship. We tested the social association hypothesis by creating four–member flocks of unfamiliar female budgerigars (Melopsittacus undulatus) and then monitoring the birds’ calls, social behaviors, and stress levels via fecal glucocorticoid metabolites. We tested the password hypothesis by moving immigrants into established social groups. To test the labeling hypothesis, we conducted additional recording sessions in which individuals were paired with different group members. The social association hypothesis was supported by the development of multiple shared call types in each cage and a correlation between the number of shared call types and the number of aggressive interactions between pairs of birds. We also found support for calls serving as a labeling mechanism using discriminant function analysis with a permutation procedure. Our results did not support the password hypothesis, as there was no difference in stress or directed behaviors between immigrant and control birds.

Does syntax contribute to the function of duets in a parrot, Amazona auropalliata?

Complex acoustic signals in many animal species are characterized by a syntax that governs how different notes are combined, but the importance of syntax to the communicative function of signals is not well understood. Mated pairs of yellow-naped amazons, Amazona auropalliata, produce coordinated vocal duets that are used for territory maintenance and defense. These duets follow rules that specify the ordering of notes within duets, such as a strict alternation of sex-specific notes and a defined progression of note types through each duet. These syntactical rules may function to define sex-specific roles, improve coordination, and allow individuals to combine calls into meaningful sequences. As a first step toward understanding the functional significance of syntax, we conducted two separate audio playback experiments in which we presented nesting pairs with normal duets and duets with broken syntax (i.e., one of the syntactic rules was broken). In Experiment One, we reversed the order of female and male notes within note pairs while retaining the typical progression of note types through a duet. In Experiment Two we reversed the order of note types across a whole duet while retaining the typical female–male ordering within note pairs. We hypothesized that duets with broken syntax would be less-effective signals than duets with normal syntax and predicted that pairs would respond less to broken syntax than to normal duets. Contrary to predictions, we did not observe differences in response between treatments for any variables except latency to approach the speaker. After we combined data across experiments post hoc, we observed longer latencies to approach the speakers after playbacks of broken syntax duets, suggesting that pairs could differentiate between playbacks. These responses suggest that breaking one rule of duet syntax at a time does not result in detectable loss of signal efficacy in the context of territorial intrusions.

Vocal dialects in parrots: patterns and processes of cultural evolution

ABSTRACT Vocal dialects have fascinated biologists for over 50 years. This mosaic pattern of geographic variation in learned vocalisations was first described in a songbird, and since that time most studies investigating dialects have focused on songbird species. Here we examine patterns of geographic variation in the calls of a different group of vocal learning birds, the parrots (order Psittaciformes). We summarise the growing literature on vocal variation in parrots, and complement this review with a survey of variation in the genus Amazona using calls from sound libraries. We find strikingly similar patterns to those previously found in songbirds. Over 90% of parrots examined in the literature, and 69% of Amazona species surveyed, showed geographic variation consistent with a propensity to share local call types. This trait is evolutionarily labile and widespread; within Amazona most clades contained species with and without geographic variation, and most major lineages of parrots include representatives with dialects. We found little support for the long-standing hypothesis that dialects isolate populations and thus generate genetic differences among populations. Instead, most studies support the idea that dialects are maintained by social benefits of matching local call types, a finding that has implications for the management of captive and endangered populations. Considerable scope remains for studies that experimentally test hypotheses for the exact nature of these benefits, as well as studies that employ comparisons among species, to understand how the interplay between ecology, social dynamics and vocal learning capacities produces different patterns of variation across the parrots.

Implementation of a sampling strategy to detect West Nile virus in oral and cloacal samples in live song birds

In 1999, West Nile virus (WNV) first appeared in the United States and has subsequently infected more than a million people and untold numbers of wildlife. Though primarily an avian virus, WNV can also infect humans and horses. The current status of WNV and its effects on wildlife in Pennsylvania (PA) is sparsely monitored through sporadic testing of dead birds. In order to acquire a more comprehensive understanding of the status of WNV in wild birds, a study was designed and implemented to sample populations of migratory and local birds at Powdermill Nature Reserve near Rector, PA. Resident and migratory bird species totaling 276 individuals were sampled cloacally and orally to compare the effectiveness of sampling methods. The presence of WNV was tested for using RT-PCR. Two positive samples were found, one from a migrating Tennessee warbler and another from an American robin. The low infection rates indicate that WNV may not be a critical conservation concern in the Westmoreland County region of PA. There was also agreement between oral and cloacal swabs, which provides support for both methods. This study describes a surveillance method that is easily incorporated into any banding operation and which determines the risks of WNV to various bird populations.

Extreme vocal plasticity in adult budgerigars: Analytical challenges, social significance, and underlying neurogenetic mechanisms

Vocal learning is a complex trait that is expressed differently across different taxa. While many of the best-studied species exhibit close-ended learning, in which vocal signals are learned from adult tutors during juvenile critical learning periods, other species have open-ended learning in which new signals are learned throughout life. Budgerigars (Melopsittacus undulatus) are an extreme example of an open-ended learner, in which both sexes have a repertoire of multiple contact calls types that continually change through adulthood to match the call types of social associates. We discuss the analytical challenges posed by the rapid plasticity of the budgerigar vocal repertoire and compare results from several different approaches to characterizing call variation. We then consider the social implications and benefits of contact call matching in fission–fusion groups. Finally, we examine the mechanisms underlying this plasticity, with a special focus on the role of the gene FoxP2. We find downregulation of FoxP2 mRNA and protein in the primary parrot vocal learning center, MMSt, across a variety of social conditions in which birds also show vocal plasticity. The results support the hypothesis that FoxP2 is a key gene regulating the neural plasticity that underlies the persistent vocal plasticity exhibited by budgerigars.