[shkkmo]

The "change to the environment" that has the biggest effect is habitat destruction. There are places, especially remote islands, where cats have had significant effects on the environment, but in most places predation of songbirds by cats is dwarfed by predation from other animals.

[QuantumYeti]

That seems like a reasonable explanation to me, but to just give a reference for my train of thought... I was thinking of Macquarie Island, which has a weird history of animal/pest control. Rodents were introduced to the island, then cats to help with the rodents... and then the cats wiped out the native seabird population.

Edit: Just realized I'm mentioning a small island, like you said, hehe.

https://en.wikipedia.org/wiki/Macquarie_Island#Ecological_ba...