While most bird studies on sexual signaling have focused on between-pair interactions, Conor Taff has instead looked outward.
Taff, whose research has just been published in Proceedings of the Royal Society B, deployed 5 song meters across multiple territories to study male calling behavior in relation to the fertility of female birds in neighboring territories. His findings suggest that birds' sexual signaling behavior is much more complex than we may have thought.
Taff’s paper, Fluctuations in Neighbourhood Fertility Generate Variable Signalling Effort, discusses how male common yellowthroats adjust song production in response to changes not only in within-pair social contexts, but also to changes in the fertility of neighboring females up to 400 meters away.
Taff used 5 Song Meter SM2+ devices, each with an SM-II mic. He downloaded the SD cards every 1-2 weeks and recorded on mono at a 32 kHz sample rate. The Song Meter also logged temperature via a thermal sensor to control for the effect of abiotic factors on calling behavior.
(Taff used the free configurator tool to determine how long batteries and SD cards would last using his custom schedule).
15 min before civil sunrise for 45 min bout, then alternated 10 min off, 10 min on for 3 hours. This was followed by 25 min off, 5 min on for 11.5 hours. This was to ensure that periods of most calling behavior were captured while maximizing card space and battery life.
After controlling for within breeding pair social context, there was strong support for the effect of fertile neighboring females, but the magnitude of this effect differed throughout the day. There was a moderate effect on singing during the dawn chorus and a larger effect on singing. Each fertile female led to a 15-20% increase in song production. Taff points out that in some neighborhoods, there were up to 6 fertile females at a time, which led a considerable change in calling behavior from the males.
On why he chose Song Meters:
“For my study, it was essential that I be able to record each of my birds on many days through the breeding season. The biggest advantage of the Song Meter was that I could easily move them around from territory to territory and set them up in just a few minutes. That allowed me to rotate the five units that I had among a large number of territories really easily.
The ability to have complete control over the recording schedule was also critical. All of my recordings were anchored to the time of sunrise with higher sampling during the dawn chorus and morning and lower sampling in the afternoon; that kind of dynamic sampling schedule was something that I could not do before using the Song Meters and it made my analyses much cleaner to have all the units synchronized this way.
My field sites also require some hiking to access, so it was great that the units were light and that I was able to deploy for weeks without having to swap out batteries and memory cards. That saved me (and my field assistants) a lot of hiking and gave me more time to focus on data collection for related projects during the field season.”
You can read the full paper here
Photo by Conor Taff