Chestnut-sided warblers use rare song types in extreme aggressive contexts

Long-distance dependencies in birdsong syntax

Songbird syntax is generally thought to be simple, in particular lacking long-distance dependencies in which one element affects choice of another occurring considerably later in the sequence. Here, we test for long-distance dependencies in the sequences of songs produced by song sparrows (Melospiza melodia). Song sparrows sing with eventual variety, repeating each song type in a consecutive series termed a 'bout'. We show that in switching between song types, song sparrows follow a 'cycling rule', cycling through their repertoires in close to the minimum possible number of bouts. Song sparrows do not cycle in a set order but rather vary the order of song types from cycle to cycle. Cycling in a variable order strongly implies long-distance dependencies, in which choice of the next type depends on the song types sung over the past cycle, in the range of 9-10 bouts. Song sparrows also follow a 'bout length rule', whereby the number of repetitions of a song type in a bout is positively associated with the length of the interval until that type recurs. This rule requires even longer distance dependencies that cross one another; such dependencies are characteristic of more complex levels of syntax than previously attributed to non-human animals.

Song type and song type matching are important for joint territorial defense in a duetting songbird

Birds have a diverse acoustic communication system, with species-specific repertoires facilitating more complex behaviors in terms of both within- and between-pair communications. Certain song types are produced for specific functions, such as aggressive encounters. In addition, song matching behaviors, whereby neighboring individuals match song types, can be used in aggressive interactions as a sophisticated acoustic behavior. In this study, we examined the functions of song types, in a duet context, of male yellow-breasted boubous (Laniarius atroflavus), an Afromontane bush-shrike with a vocal sexual dimorphism. We aimed at assessing whether, structurally, certain song types elicited a heightened reaction than others and also whether song matching affected response behavior. A dual speaker playback procedure was performed for 18 pairs of boubous, each pair being exposed to duets with three different male song types. We found differences in response toward the different duet types but these differences resulted from the amount at which males matched different song types. Pairs responded stronger when a focal male matched the playback type, and matching was significantly more often found in cases where the rarest type of male song was used. We found no sex differences in terms of response strength to playback type. Our results indicate a two-level way of coding aggression toward intruding pairs. The yellow-breasted boubous utilize their repertoires, linking matching with structure in order to show aggression in terms of territory defense and sexual conflict. This study also confirms joint territorial defense as a main function of duets in this species.

Territorial Responses of Nuthatches Sitta europaea—Evaluation of a Robot Model in a Simulated Territorial Intrusion

In birds, aggressive behavior can be elicited in the field with a simulated territory intrusion (STI). Here, we compared four different STI methods in nuthatches in the non-breeding season: playback only, playback combined with an inactive wooden model mounted on a robot device, playback and an active model mounted on a robot device, and playback with the robot device only. In the control treatment, birds were not exposed to STI. Experiments were carried out in 12 territories. Behavioral observations included latency to approach, latency to start calling, time spent in the same tree, number of flyovers, minimum distance, number of individuals, number of flights into the tree, and number of calls. There was no significant influence of stimulus presentation. Nuthatches responded equally to all four experimental manipulations, but order of presentation had a strong influence.

Song-type switching rate in the chaffinch carries a message during simulated intrusion

Abstract

Birds communicate their motivation and willingness to escalate a territorial conflict with a variety of agonistic signals. One of these, song-type switching, has been suggested to be a conventional signal in male–male interactions. However, this behavior does not show a consistent pattern across species. In this study, we asked whether variation in song-switching rate carries a message for song receivers among territorial chaffinches, Fringilla coelebs. Chaffinch song is well described, but only a few studies have focused on the communicative function of song-type switching or bout duration. Using data from playback experiments, we show here that variation in song-type switching rate affects the response of chaffinches. In response to the low switching rate treatment, territorial males began to sing later, produced fewer songs and more rain calls, decreased flight intensity, and spent more time close to the speaker than during playback of songs with a high switching rate. Our results provide strong evidence that the song-type switching rate is an agonistic signal in the chaffinch and that territorial males exhibit a stronger response toward rivals that sing with a lower song-type switching rate. A secondary purpose of our study was to determine the receivers’ response with respect to their own song rate and song repertoire. We found that the reaction of tested males was correlated with their own spontaneous song rate. This implies that a male’s response to stimuli may be predicted on the basis of his own song output.

Significance statement

Using playback experiments, we show that birds’ responses to simulated territorial intrusion vary not only with the type of stimulus but also with the tested males’ spontaneous song output. We found that, from the perspective of the song receiver, variation in switching rate carries a message for territorial chaffinches. Our findings add a new example of agonistic signaling in which territorial males exhibit a stronger response toward rivals singing with lower song-type switching rate, which up to now has only been demonstrated in a few species. Moreover, our results show that a male’s response to playback could be predicted using his song output. This may be associated with motivation and willingness to escalate a conflict and could possibly also indicate a male’s quality.