One of this year’s Student Presentation Awards goes to William Fetzner, who recently graduated from Texas Tech University with an M.S. in Biology. William presented his research in an oral presentation in a Vocalization & Communication session of the joint AFO-WOS meeting in Chattanooga, TN, USA. Below is a contributed post from William on his research:
The effect of whisper calls on the settlement decisions in female Veeries (Catharus fuscescens)
William Fetzner & Kenneth Schmidt – Texas Tech University, Lubbock, TX
Many bird species have incredible control over their vocalizations, and use this control to convey different messages to surrounding individuals. Specifically, vocalizations given at low (quiet) amplitudes (similar to a human’s whisper) have been found to be used in aggressive interactions between males. However, the function of these aggressive vocalizations in shaping where individuals settle within breeding populations remains unexplored. Individuals within a breeding population must account for a variety of different factors during nest site selection including resource quality & availability, location of con- and heterospecifics, and predation risk. However, these factors are not easily assessed; thus, individuals must rely on a combination of different cues to determine the optimal nest site. Upon arrival, females will assess male quality through the singing activity of males by eavesdropping upon male aggressive vocalizations. The highly-aggressive males that win these interactions are more likely to be favored by females (Kunc et al. 2006). Females may be able to utilize a reliable, aggressive signal to assess a male’s quality.
Low amplitude vocalizations have been shown to be one of the most reliable signals of impending attack in several species (Searcy et al. 2006; Ballentine et al. 2008; Hof and Hazlett 2010; Rek 2013; Xia et al. 2013; Belinsky et al. 2015). Females may use these signals as honest indicators of male quality and attempt to settle close to males that produced a higher amount of LAVs.
To determine a putative role of LAVs in the context of territory establishment, I experimentally tested the function of LAVs in the settlement decisions of a migratory songbird (the Veery; Catharus fuscescens) in a forest soundscape. The LAV of Veeries is known as a “whisper call” which is a short duration, unique call given by Veeries in agonistic interactions (Belinsky et al. 2015). To test the function of whisper calls in Veeries I manipulated twenty sites using randomized song samples taken from 3 previously recorded Veeries. Each site contained playback of song and whisper calls (depending on treatment) samples from a single male. At ten experimental sites, whisper calls were randomly interspersed approximately every 5 songs within the playback tracks, while the remaining ten control sites only received male Veery song.
Thirty nests were found during the 4-week experiment (20 near whisper call sites, 10 near control). Although nesting in proximity (within ~150m) to whisper call sites in comparison to control sites was marginally significant (p = 0.048), females nested at whisper call sites more often and earlier in the breeding season, and whisper call sites had higher numbers of breeding females in near proximity. These findings complement the increasing number of studies that have shown LAVs to be aggressive signals in songbirds by indicating that aggressive LAVs can have an impact upon the settlement decisions of females in a breeding population. Further, this is the first study to experimentally show how a low-amplitude, aggressive signal can affect female settlement decisions.