Good question, you might think...

The Principal Investigators (Chris and Christina) are recording vole populations over time to see the population growth and decrease over time. In the summer, after breeding season, vole population is at the highest. As more and more animals eat the voles, and breeding ends, the population decreases over time, until winter, where the population is at the lowest. Once spring hits, the population begins growing again.

Nova Scotia winters have been getting warmer over the past years, and the researchers are using vole populations to make a connection between increased populations in the winter and warmer temperatures.

Before we can make that connection, we first need to estimate the population in the area. To do this, we use a method called CAPTURE-MARK-RECAPTURE. This is the reason Dr. Bueshling was cutting fur on the back of the mice... to mark them so we know if they were caught before.

For an explanation of CAPTURE-MARK-RECAPTURE, see the video below. This is our second investigator, Dr. Newman. Forgive the shaky camerawork.

The equation we use to get the population of the area is:

**Population of the area= (N1 x N2)/R**

Where

N1= captured population of day 1

N2= captured population of day 2

R= number of recaptured population on day 2 (the ones that were marked)

So let's try this with the population that we captured for the past couple of days.

On day 1, we caught 6 total; 4 voles and 2 mice

On day 2, we caught 7 total, 2 mice and 5 voles.

On day 2, 4 of those caught were marked from the first day.

*Answer the questions below in the comments section of the blog.*

1. From the data, how many rodents (voles and mice) are in the total area? Show your work in your comment.

2. What assumptions do we make about the population? How could our numbers be off? (THINK ABOUT WHAT MIGHT HAPPEN TO THE POPULATION BETWEEN DAYS...)

3. How might this be helpful to estimating population?

4. What other ways do you think we can estimate population of larger animals that we cannot capture?