Abstract
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.
Highlights
Vocal displays coordinated in time and/or frequency between two individuals of the same or opposite sex are called duets and occur in diverse taxa [1]
Most duetting bird species are found in tropical regions rather than temperate zones because in tropical regions, female song occurs most commonly [1, 5 - 7], and this is a requirement for vocal duets in the majority of species [1, 4]; with the exception of Chiroxiphia manakins, another group of tropical species, duets are produced by two males [8, 9]
We found that territorial pairs of White-eared Ground-sparrows responded strongly to playbacks of complete duets as well as to playbacks of each sex’s duet contribution, approaching and producing vocalizations as responses
Summary
Vocal displays coordinated in time and/or frequency between two individuals of the same or opposite sex are called duets and occur in diverse taxa [1]. The Open Ornithology Journal, 2018, Volume 11 57 birds, and mammals) [1 - 3], birds are the group where this vocal behavior is most commonly reported and studied [1, 4]. This is because duets occur in several different related and non-related bird species in different geographical regions. The evidence from experimental studies has supported both groups of functions and all hypotheses proposed, it has shown that duets are sometimes multifunctional within species [1, 4]. Duet function hypotheses have been mostly studied in bird species that produce duets with male and female solo songs. 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
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