Summary
Victory displays are behaviours that occur after the conclusion of a signaling contest, performed solely by the contest winner. Victory displays may reinforce the dominance of the winner either to the loser or to other conspecifics within signaling range. Victory displays are poorly studied despite the significant consequences that post-conflict behaviour may have on the individuals involved. We examined the period immediately following 50 territorial countersinging contests between males in 10 neighbourhoods of black-capped chickadees (Poecile atricapillus) of known dominance rank. We characterized the post-contest singing behaviour of chickadees and evaluated whether post-contest behaviour is consistent with victory displays. Using a 16-microphone acoustic location system to simultaneously record entire neighbourhoods of breeding chickadees, we isolated 50 dyadic countersinging contests and measured the vocal behaviour of the contestants in the minutes following each interaction. Eighty-six percent of contests were followed by a period of solo singing by one of the contestants, while 14% were followed by silence. The post-contest singer was most often the contestant who held a subordinate dominance position in the previous winter’s dominance hierarchy; dominant males performed post-contest song bouts significantly less often. Asymmetry in overlapping between contestants did not predict which bird sang a post-contest bout. However, in a significant majority of cases, the post-contest singer was pitch-matched by his opponent during the contest more than he pitch-matched his opponent. Our results indicate that male chickadees do not perform acoustic victory displays after countersinging contests. In contrast, the post-contest behaviour of territorial chickadees is more consistent with a “loser display”.
Methodology
General field techniques
We studied a population of black-capped chickadees at the Queen’s University Biology Station (44°34′ N, 76°19′ W) in eastern Ontario, Canada, between January and July of 2005 and 2006. In January, adult chickadees were caught using treadle traps (149 birds in 2005 and 236 birds in 2006), and each bird was banded with an individually distinctive band combination. In February and March, we evaluated dominance hierarchies by observing pairwise aggressive interactions at feeders using the technique presented in Ratcliffe et al. (2007), sorting males into three rank categories: high-ranking males, mid-ranking males, and low-ranking males. In April, we observed birds as they split out of their winter flocks and began defending all-purpose territories against their former flockmates and birds from adjacent winter flocks.
We used a 16-channel microphone array to record chickadee song contests between 0600 and 1100 hours in ten black-capped chickadee neighbourhoods (on average, eight breeding pairs and 160,000 m2 per neighbourhood). We define a neighbourhood as a cluster of breeding territories with multiple males defending adjacent territories against one another (for details, see Fitzsimmons et al. 2008). Audio files were recorded as 16-channel sound files onto a notebook computer using chickadee multichannel recording software (J. Burt, Seattle, WA, USA) and analysed using Syrinx-PC sound analysis software (J. Burt). The microphone array technology is an extension of the eight-channel system described by Mennill et al. (2006). Recordings commenced April 27th and continued until May 15th. During this time of year, female black-capped chickadees are fertile, and male–male countersinging contests are common.
Contest definitions and analysis
We isolated 50 countersinging contests, each involving exactly two birds producing songs in an interactive, back-and-forth fashion within 200 m of one another. Contests were self-contained and isolated from other contests by at least 1 min. We measured the start time of each contest as the start of the first song produced by the second bird to start singing. We measured the end of each contest as the end of the last song of the final exchange before one or both birds dropped out of the contest. We considered a bird to have dropped out of a contest if he was silent for 60 s or more. We counted the number of songs sung 5 min prior to the start of all contests and 5 min after the end of all contests. We measured the pitch of each song using the frequency cursor in Syrinx-PC. We measured pitch as the frequency of greatest amplitude one quarter of the way into the bee note (Christie et al. 2004), which was repeatable to 2 Hz. One of the 64 males in this study sang an unusual “fee fee” song as opposed to the typical “fee bee”; we assessed the frequency of this aberrant song as the frequency of greatest amplitude one quarter of the way into the second “fee” note.