Did all dinosaurs Kill on Sight without reason or without need of doing?

[Newt]

Anyone who's kept a lot of fish has probably seen some apparently senseless killing. But who knows, maybe the gouramis got what was coming to them. And of course, animals act weird in captivity.

[stargatedalek]

According to Wikipedia: "Other than humans, surplus killing has been observed among zooplankton, damselfly naiads, predaceous mites, martens, weasels, honey badgers, wolves, orcas, red foxes, leopards, lions, spotted hyenas, spiders, brown and black and polar bears, coyotes, lynx, mink, raccoons, dogs, and house cats."

I think it's rather interesting to notice that all vertebrates listed there are mammals.

Probably largely by coincidence, as most large birds and reptiles are either herbivorous or comparatively docile.

[ITdactyl]

http://onlinelibrary.wiley.com/doi/10.1111/j.1469-7998.1972.tb04087.x/abstract

Observations were conducted on cases of surplus killing by mammalian predators.
Observed causes:
- apparently satiation inhibits "searching and hunting" behavior, but not "catching and killing" behavior
- ineffective (or total lack of) anti predator behavior by the prey species; prey cannot flee or fight due to enclosed space, limiting factors like deep snow, too young etc.

After killing all the prey species it can, the predator will only consume the amount of meat they normally take and then will treat the site as a cache for future easy meals.

natural cases observed:
wolf pack finding reindeer in deep snow
hyena chancing on impala birthing grounds

cases induced through human influence:
fox in hen house
caracal in sheep pen

...And I'm suddenly reminded of all those Europasaurs stuck in an island with some large carnosaurs.

[Neosodon]

According to Wikipedia: "Other than humans, surplus killing has been observed among zooplankton, damselfly naiads, predaceous mites, martens, weasels, honey badgers, wolves, orcas, red foxes, leopards, lions, spotted hyenas, spiders, brown and black and polar bears, coyotes, lynx, mink, raccoons, dogs, and house cats."

I think it's rather interesting to notice that all vertebrates listed there are mammals.

Probably largely by coincidence, as most large birds and reptiles are either herbivorous or comparatively docile.

I don't think there are any large birds or reptiles that are strictly herbivorous except for some turtles. Most reptiles are just to lazy to engage in surplus killing. But I have a hard time believing that there are no birds that do. Birds may seem docile to us in comparison to wolves and hyenas but they can actually be quite vicious hunters. I captured a mouse in the house once and when I let it go outside my rooster attacked and killed it without hesitation.

...And I'm suddenly reminded of all those Europasaurs stuck in an island with some large carnosaurs.

What's that about?

[CityRaptor]

So, your rooster did not eat the mouse? That would be odd.  Because chickens are normally very voracious.

[Neosodon]

So, your rooster did not eat the mouse? That would be odd.  Because chickens are normally very voracious.

I actually don't remember. I was pretty young when it happened.

[ITdactyl]

...And I'm suddenly reminded of all those Europasaurs stuck in an island with some large carnosaurs.

What's that about?

research article:  http://palaeo-electronica.org/content/2015/1166-langenberg-tracks
artwork:  https://hyrotrioskjan.deviantart.com/art/Mesozoic-Blitzkrieg-540261907

It seems there were large theropods in the same locale as the smallish Europasaurus.  While not really an example of "surplus killing", I just thought of the possibility since according to the observations in the surplus killing paper, predators may keep killing if the prey species has no means of fighting back or avoiding them.

[stargatedalek]

According to Wikipedia: "Other than humans, surplus killing has been observed among zooplankton, damselfly naiads, predaceous mites, martens, weasels, honey badgers, wolves, orcas, red foxes, leopards, lions, spotted hyenas, spiders, brown and black and polar bears, coyotes, lynx, mink, raccoons, dogs, and house cats."

I think it's rather interesting to notice that all vertebrates listed there are mammals.

Probably largely by coincidence, as most large birds and reptiles are either herbivorous or comparatively docile.

I don't think there are any large birds or reptiles that are strictly herbivorous except for some turtles. Most reptiles are just to lazy to engage in surplus killing. But I have a hard time believing that there are no birds that do. Birds may seem docile to us in comparison to wolves and hyenas but they can actually be quite vicious hunters. I captured a mouse in the house once and when I let it go outside my rooster attacked and killed it without hesitation.

Large as in comparable to the aforementioned mammals. Ostriches and rheas are herbivorous, and emus are primarily herbivorous.

I don't think you understand what surplus killing refers to. A mouse is a threat to chickens, they're going to attack it and kill it on sight because it will steal their food and predate their eggs and young. Whether they eat it or not is irrelevant, it wasn't "killing for no reason" or even surplus killing.

Yes birds are powerful predators but the ways in which they hunt generally keep them out of situations that would induce surplus killing. Birds are also a lot more used to complex interactions between species than most mammals are. For example falcons and snowy owls both will often nest alongside geese for mutual protection and even if the owls hunt the young of other geese they actively protect those of their neighbors, and of course there is morning birdsong. It could just be that birds are unlikely to partake in surplus killing because of underlying behavioral traits.

[Neosodon]

Ostriches and rheas are herbivorous

Well technically they are omnivores. Although they have a plant based diet they sometimes eat invertebrates, small mammals, lizards and frogs.

[stargatedalek]

Ostriches and rheas are herbivorous

Well technically they are omnivores. Although they have a plant based diet they sometimes eat invertebrates, small mammals, lizards and frogs.

As do deer, and no one is calling them omnivores.

It's generally accepted that an "herbivorous" animal will eat small animals or scavenge if presented a good opportunity, does not make them omnivores.

[tyrantqueen]

Another thing to think about is that active predation can be dangerous for the hunter as well as the hunted.

https://www.youtube.com/watch?v=LtE0N43_t3A

https://www.youtube.com/watch?v=ebb5MjHRUKs

And of course, all that running and biting uses up precious energy.

In response to the original question- no animal is dumb enough to constantly endanger itself like that. It would quickly find itself removed from the gene pool.

[HD-man]

or this:
https://www.ranker.com/list/animals-that-kill-for-no-reason/laura-allan

Laura Allan's list is full of contradictions: For 1, her list contradicts its own title ("14 Vicious Animals That Kill Just for Fun") by saying that "these animals kill for apparently no reason whatsoever" (Last I checked, fun IS a reason for doing something, whether or not it's a good reason); For another, every animal she lists contradicts her list (E.g. 1st it says that "by fun, we mean they don't do it over territorial disputes, in self-defense, to get food, or to move up in the pack hierarchy"; Then it says that "Chimps Eat Each Other as Part of Territorial Wars"); For yet another, the sources she cites contradict her list (E.g. "Mustela erminea [is] adapted to surviving periodic shortages by storage of surplus kills": http://www.iucngisd.org/gisd/species.php?sc=98 ).

Ostriches and rheas are herbivorous

Well technically they are omnivores. Although they have a plant based diet they sometimes eat invertebrates, small mammals, lizards and frogs.

As do deer, and no one is calling them omnivores.

It's generally accepted that an "herbivorous" animal will eat small animals or scavenge if presented a good opportunity, does not make them omnivores.

There's a difference btwn being an omnivore & being an otherwise strict herbivore who "will eat animal matter on occasion" ( http://scienceblogs.com/tetrapodzoology/2010/12/20/carnivory-in-cows-and-deer/ ). Ostriches are "largely omnivorous" ( https://books.google.com/books?id=gJVLXG-LOcMC&pg=PA145&dq=%22ostrich+it+is+largely%22&hl=en&sa=X&ved=0ahUKEwjbzMrk1fXWAhXNZiYKHaswBEoQ6AEIKDAA#v=onepage&q=%22ostrich%20it%20is%20largely%22&f=false ).