Dr. Eric Post, Professor of Biology, Penn State
Here is your thorough and detailed explanation of what is going on in the sonification:
Penn State researchers make observations at the Russell Glacier, located near Kangerlussuaq, Greenland, each year for approximately two months, from the end of April to the end of June (Julian Days 115-174). Musk ox inhabit the region year-round, and calve in early spring, while the area is still covered in snow. Caribou spend the winter in the coastal area of Sisimut, and migrate 250 km inland to the Russell Glacier in to calve in early June, when the landscape is green.
The caribou migrations are timed to the onset of grass, which has higher nutrition than lichens, which grow in winter. A caribou fetus can survive on the nutrition provided by lichens. But once they are born and dependent on their mother’s milk, grass is required for the mother to have adequate nutrition in the milk. Carrying a calf is less expensive for females, energy-wise, than is lactating. Thus, the survival of calves depends on the quality of the milk provided by a lactating female, which depends, in turn, on available supplies of grass.
There is concern among ecologists that the decline in caribou population over the last 15 years can be attributed to climate change, which moves the onset of plant growth to earlier times of the year, prior to the arrival of the caribou. Caribou are very conservative in their migration patterns, and it is unclear whether they have the ability to change their behaviors to leave their winter grounds earlier to adjust to changes in phenology.
The dataset includes observations taken in 1993, and in the years 2002-2015. Researchers stationed at Kangerlussuaq take daily counts of how many plant species have emerged. There are 9-14 plant species that are food sources for the musk ox and caribou, not all of which emerge each year. At the close of each year, the timing of available overall food supply is normalized as a mean proportion value, whereby each daily measurement of the number of species that has leafed out is divided by the maximum number of observed species that are observed on Julian Day 174 of that year. This mean proportion normalizes the availability of food supplies to a value between 0 and 1. The variability from year to year lies with the first day there is a measured value, and the slope of the progression from 0 to 1, which indicates the rate at which food supplies become available.
Daily counts are also taken of the number of musk ox and caribou observed. For each day, there is a value of either the total number of each animal observed or a zero if no animal was observed, or a skip in the date sequence if no observations were taken on a given day. To standardize the scaling between food availability and number of animals sighted, the daily counts of musk ox and caribou observed are also normalized as a mean proportion in the same way that the food supply is expressed as a value between 0 and 1.
The goal of sonifying the dataset described above is to find out whether patterns can be heard that indicate when the plants and animals first appear, both in terms of the absolute data and relative to each other, as well as changes in their rate of increase.
The date range is consistent for each year of data, spanning sixty Julian Days, from 115-174. The dataset consists of 900 total entries. The passage of time is represented by a percussive sound that plays a “tap” for each day, with an accented tap every five days. This is meant to allow listeners to easily hear a difference in arrival times of the plants and animals. At the end of each year there is a brief pause, followed by a longer, more pitched and ringing percussion sound, to indicate the onset of a new year of data.
The year and date are displayed on a GUI/mixer to add a visual reference to the current date. The dataset is also displayed with a slider moving horizontally across it. Moving the slider allows the date to be changed. A rate slider allows the time increment between dates to be adjusted, so that the time progression may be quickened or slowed.
The numbers that appear at each year’s increment on the caribou and muskox graphs indicate the maximum number of animals observed that year. One volume slider controls the level of a humming tone that indicates the relative population of caribou observed each year.
The rise in observed animals and plants are represented by three “instruments,” each of which plays a pitch based on the current day’s mean proportion value. Since each mean proportion value rises from 0 to 1 over the course of a year, each “instrument” rises an octave in pitch with this mapping.
The “phenology instrument” is a shimmery, percussive sound. Each data value pertaining to plant observations is mapped to its pitch as well as volume, tremolo rate, and attack time. This instrument is panned center.
The “musk ox instrument” is a flute-like sound, and is panned to the right. As is the case with the phenology instrument, each data value pertaining to musk ox observations is mapped to pitch, tremolo rate, volume, and attack time. The “caribou instrument” is a brass-like sound, panned to the left. As with the other two instruments, each data value pertaining to caribou observations is mapped to pitch, tremolo rate, volume, and attack time.