Differential effects of moving versus stationary territorial intruders on territory defence in a songbird

Abstract

Summary1. In territorial contests, not only acoustic or other signals, but also the movements of a territorial intruder are likely to influence the response of a resident. 2. We tested this movement hypothesis by simulating moving vs. stationary intruders into the territories of winter wrens Troglodytes troglodytes, using the same non-interactive song playbacks in both treatments. 3. Male winter wrens showed a different long-term singing reaction in response to a moving than to a stationary intruder. 4. One day after experiencing an intruder that was switching between three locations, residents started to sing earlier before sunrise, and they sang more and longer songs at dawn than before the intrusion. 5. Residents receiving the same playback from one location only reacted by starting to sing later relative to sunrise, and by singing fewer and shorter songs than before the intrusion. 6. We could not discriminate between the treatments when examining the short-term singing reactions during and immediately after the playbacks. However, our results clearly demonstrate an effect of the spatial behaviour of territorial intruders on the long-term territory defence of residents at dawn, about 24 h after an intrusion. 7. We argue that spatial behaviour of territorial intruders should be an integral part of the study of animal territory defence behaviour. Investigating long-term changes in territory defence at dawn is a sensitive tool for discriminating between different types of intruders.

Great tits responding to territorial intrusions sing less but alarm more on colder days

“…Overall, our study thus indicates that, in response to temperature, birds shift their acoustic response behaviour to the shorter and simpler alarms, away from songs, the most frequent and supposedly more efficient signal. We assume such a difference in efficiency, because the majority of birds responded to an intruder with singing highlighting the importance of this behaviour in the context of territory defence (Amrhein & Lerch, 2010 Contrary to previous findings, night temperature did not affect the number of songs or calls (Garson & Hunter, 1979;Thomas, 1999). Furthermore, we also expected birds to replenish energetic shortages after colder nights by increasing early-morning foraging, as we have recently demonstrated for this population during winter (Moiron et al, 2018).…”

“…Overall, our study thus indicates that, in response to temperature, birds shift their acoustic response behaviour to the shorter and simpler alarms, away from songs, the most frequent and supposedly more efficient signal. We assume such a difference in efficiency, because the majority of birds responded to an intruder with singing highlighting the importance of this behaviour in the context of territory defence (Amrhein & Lerch, ). Furthermore, our previous work showed that relatively aggressive birds using alarming as a response to intrusions also gain relatively little extra‐pair paternity (Araya‐Ajoy et al, ), implying that alarming has a different signal value, potentially signalling a lack of reserves required for using song as a response.…”

Communication in the Third Dimension: Song Perch Height of Rivals Affects Singing Response in Nightingales

“…Earlier studies suggested that spatial movements within [8] as well as across territory boundaries can have strong implications on the behaviour of the resident [7], [34] as well as of neighbours [9]. Other studies showed that also the horizontal location of non-moving rivals within [5] and outside territory boundaries [4], [6] influence territory defence behaviour.…”

“…Also the location of non-moving rivals within [5] and outside [6] the territory boundaries has been shown to influence territory defence behaviour of residents. Moreover, spatial movements of rivals can affect territorial behaviour of resident males [7], [8] and of neighbours [9], thus highlighting the importance of spatial cues in communication.…”

The Return of the Intruder: Immediate and Later Effects of Different Approach Distances in a Territorial Songbird

“…), but the capability to adjust territorial defence behaviour to prior experience has only been shown recently in nightingales for particular singing strategies (song overlapping vs. song alternating, Schmidt et al. ) and in a few other songbird species (winter wren: Amrhein & Erne ; Erne & Amrhein ; Amrhein & Lerch ; banded wren: Hall et al. ).…”