I’m a teacher and am creating a presentation for my environmental science class about Mark-Recapture methods for estimating population sizes. I’m trying to create a comprehensive list of answers to these questions and would love your input!
What are different creative ways of marking animals that you’ve seen? For instance, I’ve seen nail polish on snails and even cutting off toes on rodents. If you have links to any pictures, I would love to include some in my presentation.
What are different reasons why someone would want to estimate the population size of animals? (E.g., to know if a lake needs to be restocked with fish, etc.)
There are many ways to mark animals for identification. What is chosen is largely dependent on your needs. Animals that are observed but not captured (birds, large/fast mammals) may have larger tags or collars. As you have mentioned, animals in hand vary from snails to rodents. Nail polish may work on a snail, but may rub off over time. On a reptile, it works until it sheds its skin. Coloured elastometer beads can be injected just below the skin for more permanent identification. Microchips do the same, but a read with a reading device. Cutting off digits, tail tips, scale clips, shell notching etc have all been done.
With whatever you do, you’ll want to run it through an Animal Care and Use Committee. Animals certainly feel pain, and we don’t want people cutting of fingers willy-nilly. Tagging methods can also have other drawbacks, including increased predation and reduced fecundity. Having a group of people (ACUC) review your protocol is great way to double check that you havn’t overlooked anything, and that your project is both ethical and worthwhile. It is also the law in most places (North America). Most provinces and states will also require some version of a “scientific collectors permit”. These can be easy to obtain, and are often combined with an ACUC review all in one step.
Lastly, see below for a review of animal identification techniques.
Just off the top of my head:
Visual implant elastomer (a kind of hardening gel that can be put under the skin in different locations/combos)
Ultraviolet fluorescing alpha numeric tags injected under the skin
PIT (passive integrated transponder) tags
Scale branding in snakes
Toe clipping in lizards and amphibians
Sharpies for short term marking
Sewing colored beads onto tails of reptiles
Spray painting livestock
Reasons are sometimes just knowing that an animal has been captured before (so not to capture again).
Detecting long-term population trends, assessing life span or reproductive output, tracking migration, are all reasons to do mark-recapture.
I also think it’s worth noting that not all mark-recapture involves physical recapture. It often can, but in many cases the “recapture” is just resighting the individual.
Penguins and leopards have individual spot patterns - so a good camera trap photo can ID an individual. Without capture or injury.
Same with whale tails! They’ve tracked whales across the world based on photos of the underside of their tails. https://nmsstellwagen.blob.core.windows.net/stellwagen-prod/media/archive/sister/pdfs/sbnms_fs_id_2011_1.pdf
We used these kind of methods for our studies in social spiders, that live with hundreds of conspecifics in a nest. They where marked with water-based colour on their backs for easy distinction during behavioural studies (in the field e.g. are always the same individuals attacking…)
I only found few of my pics online… am at the phone right now. I am sure I have some more somewhere on the drive… but on those pics one can see the differently coloured backs somewhat
I have heard of mark-recapture by proxy. The Adonis blue butterfly is a rare species in England, found on close-grazed chalk grassland. It was considered too vulnerable for mark-recapture. It shares its habitat with the chalkhill blue butterfly, a much less threatened species, so mark-recapture was done on the chalkhill blue and the Adonis blue population was estimated from the ratio of chalkhills to Adonises.
What about ethics as part of the presentation.
We had a story about a whale tracked from our shores across the Atlantic to Brazil.
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