Background: Duet function hypotheses have been mostly studied in bird species that produce duets with male and female solo songs. However, in order to understand if patterns of duet function are similar across all duetting species, it is highly necessary to test the duet function hypotheses in species that produce duets with vocalizations other than solo songs. Objective: We studied the responses of territorial pairs to each sex’s individual duet contribution and complete duets in a species that produces duets with a vocalization other than male and female solo songs. Methods: We conducted a playback experiment where we presented duet contributions of each sex to three populations of White-eared Ground-sparrows (Melozone leucotis) in Costa Rica, during this species’ breeding season in 2016. Results: The responses to complete duets were stronger than those to each sex’s duet contribution, suggesting that complete duets and each sex’s duet contribution have different functions. Complete duets are used to protect resources from intruders (supporting the resource defense hypothesis), and to prevent the partner from being usurped by intruders (supporting the mate-guarding hypothesis). Males used solo songs in response to female duet contributions, and this may work to attract intruder females (increasing the probability of extra-pair copulation). Males also use solo songs in response to male duet contributions, which may work as a signal to repel intruder males and guard their female. In this case, where mate attraction occurs with a completely different type of vocalization than used for duetting, we found a clear pattern of a double agenda for males when a territorial intrusion occurs. Conclusions: This study provides strong support for the dual function hypothesis in duets and reveals conflicting selective pressures between pair members relative to each hypothesis.

Conceptual and statistical problems with the use of the Shannon-Weiner entropy index in bioacoustic analyses Information theory and its indices were developed for human communication to predict the amount of information transferred in a message. One such index, the Shannon-Weiner index (SWI), has often been used to analyze information from other fields in which its application may not be appropriate. In ecoacoustics, the SWI is used to compare acoustic diversity (i.e., a measure derived by integrating the richness and abundance of animal sounds) among locations. In animal communication, the SWI is used to quantify repertoire complexity (i.e., a measure derived by integrating the number and abundance of sound types produced by individuals or species) as an approach to understanding signal evolution. We discuss problems associated with using the SWI in ecoacoustics and animal communication. Specifically, we discuss conceptual and statistical problems associated with the SWI, and then illustrate these problems using hypothetical data. In ecoacoustics, the SWI's assumptions of random variables and independent samples are often violated. In animal communication, the SWI fails to distinguish among repertoires in which the number of sound types and the abundance of each sound type differ. We also show that other methods do capture these differences. We conclude that the SWI does not adequately represent acoustic diversity or repertoire complexity due to the multiple conceptual and statistical issues associated with its use. We recommend other analytical methods to more fully describe these biological systems, including goodness of fit, Morisita similarity index, and Markov chain analysis. These methods provide more information for future comparisons, and permit researchers to test hypotheses more directly.

In this study, we describe the nest size characteristics and the breeding attempt of Little Crake ( Zapornia parva) in the abandoned nest of Common Coot ( Fulica atra) at the small mid-field pond in the Masurian Lake District, northeast Poland. Based on the 6-year study during five breeding seasons, we found 123 nests of Little Crake, but such an instance was observed only once. To the best of our knowledge, this observation is the first record of the use of the same nest by two species of rallids. We discuss what could force crakes to make such a decision, why this breeding attempt failed and why such instances are so rare in marsh-nesting species. The nest size in mid-field ponds localized in northern Poland was slightly smaller than that recorded in fishponds in the Czech Republic, but larger than the records obtained in lakes in Germany and Russia.