It's hard to quantify what is "normal behaviour" for a reintroduced species or an introduced species. Pigeons were once canyon cliff dwellers and nesters from North Africa. Now they've become so accustomed to living in man's environment, their behaviour changed and they learned man is a better host than a cliff in North Africa. In turn, Peregrine Falcons and even Redtail Hawks have discovered they can adapt to cities to hunt these pigeons and taken advantage of man as a de facto host, not to mention the nesting opportunities on the ledges of skyscrapers. English Sparrows are the descendants of weaverbirds from Africa. They learned man is a much better host because food availability is better and nesting sites are easier in the eaves of buildings. Once an animal has man as a host, their behaviour changes, and what was once "normal" for them is no longer normal. And while wild animals can be introduced, man has unintentionally made himself the host of the animal and, thus, altered its normal behaviour. If man protects the wild animal, even more so has he become the host.
The English Sparrow was not native to North America; it was brought here by Europeans because they missed them. Because of its adaptable nature, the English Sparrow became highly successful, just as it did in Europe. It can outcompete the native sparrows here as well as other songbirds of its size. It can defeat Mountain Bluebirds in the fringe areas of towns and cities in certain regions for nesting sites. It can monopolize and aggressively defend birdfeeders and other food sources and thus propagate its species faster than other birds. Man became the host of this bird by introducing it to an area that had not seen this type of bird. Honestly, man is the host of introduced wolves in the same manner. Man captures them from one area, transports them to another area, and assumes this will be a natural thing. But this wasn't so with English Sparrows, nor is it so with wolves. It's like thinking that, ok, we wiped out the Passenger Pigeon, so the common pigeon in cities will restore that. And the effects of introduced species are not usually what was intended. As with the English Sparrow. And if tomorrow it was decided to get rid of English Sparrows, it couldn't be done. That bird has already adapted and is too intelligent to eradicate. It adapts too fast. Wolves, being transported and introduced, are unintentionally being taught rapid progress evolution and adaptation in the same way.
