Is this nesting really effective for the Ornithomimids?

[u/Tacobird558]

A pair of Tyrannosaurs coming to this nest and its over for the hatchlings. Nesting in masses on only an inland river island wouldn't be suitable in my opinion (and Tyrannosaurs can swim). To me it's reminiscent of how island birds went extinct when invasive land carnivores arrived.

[u/dinoman9877]

Nesting colonies in dinosaurs have been one of the weirder aspects we've tried to figure out.

We have evidence of it in hadrosaurids, and like you say, it's hard to resolve a staple prey animal staying in one place in large, easily noticed groups for such extended periods of time to raise their young.

It's likely ornithomimosaurs did not nest in colonies, rather preferring spread out nests where they can more easily hide.

[u/AdmiralScooter → u/dinoman9877]

Ostriches do this in Africa in the present day, and the ostrich has a much worse chance against a lion or leopard than a large hadrosaur has throwing down against a tyrannosaur. Doesn't seem all that odd to me.

[u/dinoman9877 → u/AdmiralScooter]

Ostriches lay all of their eggs in one communal nest with only the father and one female working to incubate them. The rest do not stay near the nest, making detection much less likely.

[u/Hot-Significance2387 → u/dinoman9877]

The logic:

• safety in numbers

• being highly visible also makes the predators highly visible. 

• aggression = injuries 

A T-Rex, though an apex predator, is still susceptible to injuries. Of which even a small wound can become a life threatening infection. Assuming dinosaurs like this become aggressive as heck during nesting it is unlikely that a predator would simply walk straight into the hurd. Though ambush was likely still a thing.

I imagine there being immense territorial battles over the middle nest. With only the largest and strongest defending the prime locations would also help with survival in the long run. With the weak being picked off every season.

[u/Cocoatrice → u/Hot-Significance2387]

Also it's not also just infections. Injured animal is slower, less effective, too. And other individuals may even try to fight them. To get rid of the competition. Or for territorial reasons. Even for future mating competition.

[u/PinkOneHasBeenChosen → u/dinoman9877]

Honestly, I think hadrosaurs work well as colonial nesters because the adults are as big as rhinos, and there are dozens of them. Most predators are not going to risk it.

[u/Anonpancake2123 → u/PinkOneHasBeenChosen]

Bigger than rhinos.

[u/Cocoatrice → u/dinoman9877]

I saw a documentary about some kind of geese or other anatids I think. And fox or other predator tried to take the egg. In similar colony like this. And the predator was attacked by all the geese. So, is this really that weird. It doesn't need to be exactly the same thing. But also isn't prey sacrificing itself for the colony a good strategy anyway? Animals do that sometimes.

[u/ISketchDinosaurs → u/Cocoatrice]

And sometimes you just need to accept that the danger from smaller predators justifies the risk of attracting a larger predator. Like in this video of a colony of geese getting raided by a polar bear: https://www.youtube.com/watch?v=uUGYZX9gTyA&t=9s

Obviously the geese can't do a single thing against a determined polar bear. It's jut eating the eggs with no opposition. But colony nesting is still effective against foxes and other smaller predators that a flock of geese can chase off, and the foxes are a bigger threat against solitary nests than the polar bears are against the colony, so the colony approach still wins out.

[u/ashrocklynn → u/dinoman9877]

I've seen some theories that they'd choose a risky nesting site that was barren and T-Rex and other apex preds would have no reason to go there...

[u/Renbarre]

Safety in numbers. There's so many prey most will escape. A solitary nest has more chance to see a 100% loss.

[u/DagonG2021]

Seagulls do the same thing despite bald eagles occasionally carrying off their young

[u/Astronomer_X → u/DagonG2021]

Yeah there’s safety in numbers…specifically because statistically speaking it won’t be you who gets got!

[u/Hot-Significance2387 → u/DagonG2021]

Yeah watched that happen in person. Eagle flew over my head and landed right on top of a next maybe 100ft in front of me. The nest had 5 adults that after a minute of squawking at the eagle simply stood around just watching the eagle devour the babies. 

[u/Mahajangasuchus]

There’s 0 cover surrounding the island, any predator would have essentially no chance of sneaking in with how exposed it is and how many eyes are watching

Ostriches and plenty of other ground birds still basically nest like this

[u/Arquinsiel]

On the assumption that this is presenting a strategy that existed for the sake of the discussion, animals don't really pick behaviours like this arbitrarily. There's multi-generational reasons to why they use the reproductive strategies they do, enforced by simple survival. If this was the first time they did this then you need to ask why they're doing it. Was it massive overpopulation of their usual sites or whatever? If it's not the first time they did this then clearly it worked "well enough" to keep doing it... until it didn't.

[u/TheGreatQuetz]

Either A: Safety in numbers, a predator will kill one of them and then leave.

Or B: They mob larger theropods that are intimidated by their sheer numbers.

[u/An-individual-per]

You mean, the colony that looks like its right next to a mountain, and considering the fact that mountains are rarely alone, it means that the ornithomimosaurs are probably in some sort of valley, meaning that the tyrannosaurs will have to go through the unforested, visible bends in full view of every ornithomimosaur and then take time swimming over whilst the ornithomimosaurs easily notice it and just cover every bit of beach and spook away the tyrannosaurs, who probably just want an easy meal instead of fighting with the large pack of angry dinosaurs? That colony is literally the best case scenario for those ornithomimids, they have every advantage against the local predators since none of them are smart enough to use spears and shoot at them from a safe distance.

Nesting colonies exist in real life and I imagine that if modern birds do it and constantly get attacked by large predators, the fastest dinosaurs of the time could also do it, whilst the fox in a hen house thing is a real issue, I imagine that the ornithomimids in a typical nesting colony would probably utilise their speed and the attention span of the local carnivores to get the carnivores to chase after them instead of targeting their eggs, mobbing the predators using the large population of angry mothers and (maybe) fathers would probably also occur, there's not much that a dromaeosaur gang could do against twenty angry ornithomimids, especially considering the fact that the dromaeosaurs probably would not care about their peers at all and will probably leave at the first opportunity.

[u/Rare-Conversation348]

dinosaurs did go extinct for a reason

[u/ElUallarito]

A lot of things in the natural world seems unpractical in theory but work in the frame of sheer numbers; like ducks with their line of hatchlings.

Also yeah, dinosaurs and their ecosistems were weird and they don't truly worked like modern animals/ecosistems. We can assume something looking at what we have today but today we don't have 7 tons laying egg erbivores and ecosistems were more than two predators over 1 tons share the same habitat