Parrots (Order Psittaciformes) are secondary cavity-nesters that depend on existing cavities for nest sites, and consume plant resources of fruits, seeds, and flowers that are highly variable, but little is known of resource selectivity by parrots, or how they deal with variable environments. We reviewed published studies of nest-cavity use by parrots, and those evaluating parrot diet and their relationship with food resources. Most studies have been conducted within the last 20 years and these present data on resource use for only one-third of parrot species worldwide. However, basic information on resource requirements is lacking for the vast majority of Psittaciformes, particularly for species from the Asian region. Nesting studies have found that parrots use nest cavities in large trees, high above the ground, with large nest chambers, of 0.5-1 m deep, and entrance diameters related to body size of the parrot species. A few studies demonstrate that parrots select nest sites based on cavity characteristics, which may influence nest success, but a complete evaluation of adaptive nest site selection by Psittaciformes is lacking. Parrots have varied diets and may employ a combination of strategies of diet switching, habitat shifts, and movements to track food resources. This plasticity in diet and foraging strategy may influence the extent to which parrots can respond to anthropogenic pressures of global change. Parrots may also play an important functional role in forest ecosystems, yet little is currently known of plant-animal interactions of parrots, or the impact of parrot populations on forest dynamics. Based on our review of the literature, we suggest that to meet their resource requirements, parrots employ resource selection strategies of hierarchical nest site selection to increase the likelihood of nest success, and plasticity in diet and foraging strategy to track variable food resources. Future studies need to evaluate resource selection and the consequences of this for fitness in order to assess the potential impacts of global change on parrot populations, and to identify characteristics which make species vulnerable to human pressures.

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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.

Studies of avian vocal dialects commonly find evidence of geographic and acoustic stability in the face of substantial gene flow between dialects. The vocal imitation and reduced dispersal hypotheses are alternatives to explain this mismatch between vocal and genetic variation. We experimentally simulated dispersal in the yellow-naped amazon (Amazona auropalliata) by moving individuals within and across dialect boundaries in Costa Rica. One juvenile translocated across dialect boundaries altered its contact call to imitate the acoustic form of the local call six weeks post-release. In contrast, four adults translocated across dialect boundaries returned to their original capture site within 120 days, while five cross-dialect translocated adults who remained at the release site did not alter their contact calls. Translocated individuals were observed to show some segregation from resident flocks. The observation of vocal imitation by the juvenile bird supports the vocal imitation, whereas the behavior of adults is more consistent with the reduced dispersal hypotheses. Taken together, our results suggest that both post-dispersal learning by juveniles and high philopatry in adults could explain the stability of vocal dialects in the face of immigration and gene flow.

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