Geese are hyper aggressive animals, whereas ducks are relatively benign. The following are the best attempts at explaining why.
Sometimes a lot of behaviour is evolutionary. It’s a bit of a generalization to say that geese are hyper aggressive and ducks are meek (although anyone who’s been in Canada can tell you Canada geese have no fear). Realistically, there’s no exact answer (as far as I know), but I can talk a bit about conflict in birds.
Here’s the example I’ll bring up between two very closely related birds: the blue heron and the great egret. Blue herons and great egrets lay similarly sized nests. In herons, most of the chicks coexist alright. In egrets, however, the chicks will often (85%? of the time) kill one another (exemplifying siblicide). Parents typically won’t interfere with this behaviour – I suppose this could be defined as aggression. In fact, the parenting style was seen as an explanation for the siblicide. On the other hand, heron chicks do not really kill one another that often, since they had a different parenting style (loosely speaking). In the vein of great science, Mock & Parker decided to test out cross fostering (that is, having herons raise egrets and egrets raise herons).
They found that, in short, when a heron parents egret chicks, they still fight. I’m not going to mention the mechanism that encourages the siblicide in egrets, but the long and short is that egret chicks are vicious and will continue to kill one another, often leaving one chick to grow to adulthood. That is, the siblicide is obligate behaviour. When egrets parented herons, the mechanism for siblicide is there (parenting), and siblicide that wasn’t there previously developed in the chicks, with the largest chick killing the rest of the nest. So, the siblicide (aggression, I guess) was both “innate” behaviour (again, very loosely speaking) and “outside” behaviour encouraged (facilitated) by the parents.
tl;dr: even closely related species (birds, for example) can have wildly different behaviours. Aggression is not necessarily environmental. In the case of geese and ducks it’s probably many factors. There is, as far as I know, no short answer.
The important findings of the experiment were specific to the feeding methods. What you have to understand is that the method of feeding directly impacted the chicks getting larger and that
young animals are very selfish. If a chick can get larger (even or especially at the expense of its siblings), it will.
Egret parents fed their offspring selectively, but not deliberately selectively. What this means is that to receive food, a chick would engage in specific behaviour with the parent, and receive a disproportionate amount of food. The parent didn’t say “Oh, I’m only going to feed Chick #1”; more like, “Oh, Chick #1 asks for it so Chick #1 gets it.” This resulted in disproportionate growth and other chicks becoming disproportionately small, “easy victims” for the larger, fatter chick to kill them. When fostering heron chicks, the heron chicks engaged in this behaviour and this enabled them to engage in siblicide.
Heron parents fed their offspring en masse. A heron would bring a large piece of food and each chick would get a relatively equal share, equaling a relatively similar growth over time and a smaller proportion of siblicide events. When the herons fostered egrets, this mechanism of feeding did limit, but did not erase siblicide behaviour. This could be because of alternative methods that conferred disproportionate advantages to chicks regardless of disproportionate feeding.
So, those factors that affected the size a chick could be a combination of asynchronous hatching (chicks born earlier get bigger) or hormone investment (parents could choose to invest more GH or testosterone in their chicks – this is the really cool research). All in all a very complicated storm of behaviours, into which there is ongoing investigation.
This of course raises more questions; if most of their chicks are “doomed to die”, so to speak, why would egrets bother laying more eggs? Isn’t this a wasteful investment of the most important resource ever, energy? Good questions! Read the other papers I linked!!
Animals like geese, hyper-aggression is an intimidation tactic, which is basically all-or-nothing. Backing down will mean you get eaten, so you need to commit 100% to that kind of display. Ducks are simply too small to use that against common predators like foxes, raccoons, etc., but geese are big enough that, evolutionarily speaking, it’s generally an effective tactic.
Rottweilers and collies and poodles and wolves have very different behavior patterns. Some of it is inherited and some of it is learned.
As another poster pointed out, too, this behavior comes from being able to survive attacks. Ducks rely especially on camouflage while geese rely on more aggressive behavior. They have different adaptations for the same danger.
Depends on where they live and what they eat. Many animals have evolved to mooch off humans. Take wolves vs. dogs or tigers vs. cats.
Also, smaller animals have a stronger propensity toward flight (rather than fight). Wild ducks aren’t aggressive but they aren’t friendly… they’ll get the heck outta dodge if a strange animal approaches because they are easy prey.
Geese on the other hand are large enough that they have the clout to stand up to foxes, coyotes, raccoons, rodents, or anyone who tries to mess with them or their babies.
I work at a place with a collection of several different species of wildfowl, and it’s not really true that geese are aggressive whilst ducks are benign. There’s a lot of difference in levels of aggression between different geese and duck species, and it generally has to do with a couple of factors – the resources available in the environment they are usually found in, and their ability to blend in to that environment to avoid danger.
The Cereopsis, or Cape Barren Goose, lives on rocky beaches in Australia, and has to defend the scarce resources in its territory. They are highly aggressive at all times, and are built like tanks. Hawaiian geese, aka Nenes, on the other hand, only show aggression towards other Nenes or other species when defending a nest – the rest of the time they’re very chill and friendly. They are an island species with few natural predators and relatively good camouflage, so fighting for them is too much of a risk except when defending the next generation.
In ducks, it works the same way – larger, more conspicuous species originating from habitats where resources are scarcer tend towards aggression, and smaller, better camouflaged species from more abundant habitats are much more chill. Like any generalisation, there are exceptions – Buffleheads are tiny, but they are really feisty little ducks!