Ever seen an animal with a tag on it?
Farmers will tag animals to keep track of who’s who or what condition they’re in.
However scientists, specifically biologists and zoologists, will tag animals not only to keep track of who’s who but where they go, and how many other animals are “around.”
Tagging and recapturing animals is a method commonly used in ecology to track where animals go and estimate the population of the animal. The method is most useful when it is not practical to count all the individuals in the population, especially when they move around a lot.
Here’s how it works:
You enter a place and you’re trying to find out how many animals are in the area. Instead of counting every animal and potentially losing track of which ones you’ve counted, you capture a group of them temporarily to tag them and release them. Once you release them, these animals will “redistribute” themselves. Then after some time has passed, you capture another group of animals of the same kind and see how many of them are tagged. The expectation is that these sample percentages should vary "around" the true population percentage. Using this assumption, you can calculate the approximate population size.
Let’s say you capture and tag a group of animals and release them all at once in a large area with multiple habitats. After some time passes, you go through these multiple habitats and note that some of the animals you see have tags on them. This method is used to note whether animals stay in one place all the time or move around. If they do move around, it will give some further insight and significance on the places that they have moved to. Nowadays, there are high-tech tags that have a transmitter that sends GPS coordinates via satellite. This is especially useful when you're tracking movements or migration routes of animals.
Tagging animals is a very powerful tool for researching population dynamics and providing estimates. However it is also a very tricky tool because it relies on those tagged animals to come back (which doesn’t always happen…).
Once you release an animal with a tag on it, they are out and about in the world, doing their own thing. They may not necessarily come back to same place you tagged it or may not even come back at all. In fact the rate of recaptured animals is pretty low. This can be especially tricky for animals that migrate long distances like whales or birds.
For my “tool of the trade,” I have tagged horseshoe crabs with the goal of determining whether they move throughout their ecosystem and spawn at different beaches or return to the same beach each year. Understanding their movements with tag-recapture methods will help better understand their spawning behaviors, specifically within a localized population.
So you can imagine how happy I was when I saw a horseshoe crab on the beach the second year of my research… with a tag on it!
If you ever see a tagged animal on your nature walks, boating trips, swimming trips, excursions, or even in your own backyards, definitely report it! Often times on the tag, there is contact information either a phone number or an email address. Youd be helping scientists better understand and aid in the conservation with these amazing animals.