So one of our readers asked us this question the other day: How do we know exactly that the bee population around the world is decreasing? How do we calculate the number of bees to begin with?
I know someone who works for USGS and calculates wild animal populations.
First, they map historically where the animal has been seen. Then they collect reports from the public, universities, and other government agencies that have seen the animal. Then they make a computer model of where they think the animal should be, based on environment, plant cover, etc. A simple one for butterflies I’ve seen her do is Butterfly X eats plant Y. Plant Y has this thermographic signature, pull up satellite data, I bet that butterfly is around areas where I think that plant is. Then you send people to look, and test your model to see how good it is.
If the animal is really endangered, they do a survey, go everywhere they think it is and survey. If there are too many to realistically survey they do a random sample. This is just like the polling used to predict elections. If there are 1,000 acres we think it could be at, we randomly select 20 and go. Now there is a ton of special statistics that goes into that, but that is the basic idea. Also, they might do “block” polling to make sure they go to different areas, or areas they think will help them model better in the future.
A team of biologists goes out to the survey sites, and looks for them. Ideally you send the same people to the same place at the same time every year, so you have an good idea what is happening with the population. Due to lack of funding (sequester ruined–put a huge hole in 100’s of years of scientific data collection), fires, changes in administrations, that doesn’t always happen. It is never perfect, some land is private, military, impossible to access, or too sensitive to send people into every year. But, especially with new drone technology and satellite data, they have gotten extremely accurate in their predictions in the last 10 years.