A major goal of this project is to map alarm call communication networks in red-winged blackbirds (Agelaius phoeniceus) by localizing alarm call sources using SM4TS units. We first conducted playback trials from known locations to ground-check acoustic localization results. We were able to devise an efficient, mostly-automated workflow to annotate, localize and map sounds from these trials (Figure 1).
We chose four breeding colonies of different sizes (1-19 nests) at Cedar Point Biological Station, Ogallala, Nebraska where we set up SM4TS microphone arrays in early June (Figure 2 shows the locations of microphones at one of the colonies). From mid-June to mid-July, we conducted experiments at 41 nests while recording the vocal responses using the microphone array. For each experiment, we recorded colonies during control (no stimuli), no-threat (tree swallow mount), and threat trials (brood parasite: brown-headed cowbird mount). Brown-headed cowbird presentations elicited alarm call cascades in colonies of varying intensities, and we were able to observe differences in responses by focal pairs and neighboring pairs. In addition, we were able to record a few natural alarm call cascade events within colonies and across colonies during the approximately 220 hours of continuous recordings of natural soundscape. We are excited to analyze these recordings over the off-season.
Over the next few years, we hope to conduct experiments at other colonies in both rural and urban habitats in order to understand how environmental pressures, particularly noise pollution, impact the alarm call communication networks in redwings.