So there was this researcher studying  fish who live in the coral reef.

They thought they had the perfect job. They get to swim with these  majestic fish every day, get up close and personal with a natural wonder of the world, and help animal conservation efforts by tracking how fish populations move.

And based on their counts, they calculated there were around 200 fish living in that reef. But it turned out that there was this  one fish that kind of ruined all of it. While the researcher was  trapping the fish in order to get a reliable estimate of how  many of them lived in the reef, a fish who we’ll call Phillip just  kept getting caught time and again, and totally biased the fish count.

There weren’t 200 fish in that reef. There were 100 and Phillip. Maybe Phillip loved this  researcher.

Or maybe they had beef. We’ll never know because this  particular story is made up. But it’s based on a real  problem in animal research!

Scientists have noticed that some  animals get caught again and again, while others in the same species never do. So in this video, we’re going  to try to get to the bottom of what makes some animals so dang trap happy. [♪ INTRO] So Phillip may be a red herring, but fish like him really are a big problem in  these population survey studies. In one study, there were 11 fish  that accounted for more than half of the catches, and one of  those was nabbed 9 times.

I guess that fish was hooked on the experience… But they really do cause  problems for the researchers, because they’re out there trying  to estimate population size so we know when a species needs protection. It’s no small issue.  Trap-happiness has been reported in all sorts of animals, from lamprey to badgers. And since they’ve been returning to the lab with reports of trap-happy animals for years, naturally, researchers have come  up with a lot of potential motives to explain why certain animals  are so into getting caught.

Specifically, they’ve suggested that being drawn to traps may be as simple as a personality type. They suggested that fish  like Phillip might be bold, risk-taking adrenaline junkies.  Or super active explorer types. But not everyone agrees.

The studies that suggest trap-happiness  is a personality type often only looked at a single species in a  limited location and period of time. When researchers compared  multiple species across different environments and on a longer  timescale, they found that trap-happiness wasn’t as universal  as some reports might suggest. A publication from the Department  of Wildlife, Fisheries and Conservation Biology at the University  of Maine detailed the behavior of a variety of different small  mammals, from shrews to squirrels.

They looked at stuff like if they  were more active than others, or explored new territory more  often than their neighbors. And when they saw certain behaviors being repeated reliably in the same individual over time, they considered that behavior a personality trait. Like, deer mice who jumped around  a lot and traveled through the middle of an empty space would  still do that stuff a month later.

And the ones that spent more time  in one place grooming themselves kept doing that in the follow up  observations too, meaning that activity and exploration counted as personality traits. So the researchers said these animals had “strong evidence of personality.” But just because animals can  have some personality traits doesn’t mean that being trap-happy is one of them. For instance, while they did  note that certain red squirrels were big explorers, those adventurous guys weren’t necessarily caught more often than the ones that spent less time investigating  stuff in their environment.

And animals that were trap  happy in one week weren’t consistently trap happy throughout the seasons. It could be that active  squirrels aren’t drawn to traps in early spring because  they’re more focused on mating and raising babies than in hanging out in traps, but then later in the year  they go all in on tasty bait. So they may like getting trapped at times, but not consistently enough for  it to be a personality trait.

This is a big shift in how researchers have historically thought of trap-happiness. But it comes from a more robust dataset than the studies that came before it. Now, since it sounds like the  reason that only some animals are trap-happy isn’t a personality trait, we still need to figure  out what’s going on to make some animals go for the same  trap over and over again.

When studying red-backed  voles, researchers have found that an individual’s size and sex are both factors that correlate to how likely they  are to be repeat trap customers. Size and sex matter for  snakes too, but so does age. That's also muddled up with  the fact that size can change through the seasons or even in an animal's life.

And then for some species like  badgers, their trappability doesn't correlate to any of these things, so it's really a big mess that researchers  are still trying to disentangle. This SciShow video is supported by Brilliant, the interactive online learning  platform with thousands of lessons in science, computer science, and math! And not just foundational concepts from the likes of Darwin and Lovelace.

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And you’ll get your first 30 days for free! Now back to the show! So if trap-happiness isn’t  about the animals themselves, it could have more to do with the trap being used.

An investigation of sea lamprey  compared two kinds of traps. One was a commonly used funnel  trap that consists of a cage with funnel-shaped entrances on each of its sides and metal curtains that keep  the lamprey from leaving. The other trap was a ramp with pegs on it, leading up to a collection basket.

Turns out that the funnel traps didn’t nab any super trap-happy animals, but the ramp traps had a high recapture rate. Meaning there was a consistently  higher rate of lamprey being return customers to the ramp traps than, and in some cases, they even  outnumbered first time visitors. So you can give the same animals  two different trap options and see totally different rates of behavior.

But that study didn’t compare  multiple species directly. So to get to the bottom of a  potential species explanation for trap-happiness, there  was a study that compared two snake species in the same area: the black swamp snake versus  the banded water snake. And instead of comparing them on  how often they entered the traps, they counted how many times  these snakes escaped from traps.

Their reasoning was that by only  counting the animals that are still in the traps when you  get there, you’re missing out on the animals that come and  go more or less as they please. They also claimed that the  patterns in escaped animals should be similar to the  patterns of overall capture. So if an animal is truly  trap-happy, it should escape less.

And they found that the escape rate was way higher for black swamp snakes than  for banded water snakes. Within 24 hours, 61% of the  black swamp snakes escaped compared to a measly 21%  of the banded water snakes. This may be because of an  interplay between trap type and how each species looks for food.

See, the trap used in this  experiment was submerged underwater. And while black swamp snakes  forage for their food underwater, banded water snakes generally look on the surface, meaning they may just have  found the traps less often. So whether any single finding  says anything about other species, like Phillip the fish, still needs to be tested.

Most of these studies describe specific  observations in certain animals. So instead of generalizing  that out to all animals, we need to reel it in, pun intended. Which brings us back to the  question that started this video: Why does any animal do this?!

Maybe they’re trap-happy  just because they’ve gotten used to being caught and think it’s no big deal. After all, they might have  an easier time finding food when it’s also trapped in there with them. Or maybe they’re just learning  that there’s really no downside to hanging out in a cage for a while,  since they’re probably not going to end up on the dinner  table for some other animal.

It’s hard to know for sure,  since these trap-loving animals can’t just tell us what’s going on in their heads. All we know is if you’re trap-happy for SciShow, we’ll catch you in the next video. [♪ OUTRO]