Although they did not kill the animals particularly for studying their ecology, one of the most wellknown ecology studies on dead vertebrates must be the one conducted on lynx - snowshoe hare pelt-trading records of the Hudson's Bay Company which has ended up with the famous ecology textbook example for predator-prey models. But I am not sure if this justifies the death of animals! On the other hand, I do not know what would be the scale of benefit from a scientific study to justify death of animals!
I agree with you! I know that many invertebrates (especially insects) are killed for fundamental studies in ecology, and in my opinion it is just as sad ...