Red squirrels are a territorial species that actively defend exclusive, food-based territories from other conspecifics. One of the things the McAdam lab is interested in is how the composition of an individual red squirrel’s social environment (i.e. relatedness and familiarity of neighbours) affects how much time that individual expends on territory defense rather than devoting time and energy to foraging, feeding, and reproduction. One of the ways that we are measuring this is by deploying Zoom H2n audio recorders on red squirrel territories to look at rates of territorial vocalizations called “rattles”.
A red squirrel with red ear tags producing a territorial vocalization ('rattle') at a nearby neighbour. This is a squirrel's way of saying "stay off my territory!". Photo credit: Ryan Taylor
This past summer, I, along with two field assistants (Marta and Yuqing), deployed audio recorders on 112 red squirrel territories over the course of 4 ½ months. Audio recorders were put out first thing in the morning (ideally before squirrels woke up), which meant MANY early mornings for me and my assistants!
Here’s what an audio recorder set-up looks like in the field. Zoom recorders are kept under umbrellas to help protect them from the elements.
After returning from the field one of the things that we have to do with this data is determine a decibel threshold at which we can distinguish the territory owner’s rattle from neighbouring rattles (i.e. we want to know how loud owner rattles are compared to their neighbour's rattles). Nana, Cristina, and Adam are three work-study students at the University of Guelph that have been hard at work on this over the whole semester. They listen to the recordings of these red squirrel rattles and record the decibel level ("loudness") of known territory owner rattles versus rattles from neighbouring squirrels.
Above: Adam hard at work listening to red squirrel rattles. Below: Sonogram of a red squirrel rattle.
With this information and the help of Dr. Dave Wilson at Memorial University, who is currently working to develop an automated process to extract red squirrel rattles, we will soon be able to measure rattling rates for territory owners and assess whether these rattling rates are affected by the composition of the social neighbourhood. This will give us insight as to whether the phenotypic composition of the social environment might be an important selective pressure in a species typically considered to be “asocial”.
Erin Siracusa