Giant Chilean Hummingbirds

I never got a picture of one of these, but they are HUGE for a picaflor. It was quite common to see them in large groups, flying around a  red-blooming succulent (aloe succotrina, native to South Africa),which I saw in many places around Viña.

 Well, I decided to look up "giant hummingbird" today, after I got home (I'm back in Peoria, as of about 6 hours ago-nice to be warm again!). And I found out that the common name for patagona gigas is indeed the giant hummingbird.
I saw them more frequently in the winter, perhaps because there were fewer flowers out, and thus the birds were more concentrated around the flowers in bloom. Like humming birds I've observed in North America, they are quite aggressive, darting around and chasing off others that come to feed in the same local. They made similar sounds to the hummers I know up here in the north, which is what first caught my attention. Then when I first saw them, I was really surprised at their size-as big as a sparrow, or bigger, but not as chunky. They are not very showy in terms of coloration, but are pretty stunning because of how big they are.
I'm just speculating here, because I haven't seen anything about this in my brief research...but I wonder if their size has something to do with the colder climates where they are found. Perhaps they need to be bigger to be able to come out of torpor each morning in this type of climate?