The birdies in the pic are English house sparrows, and you
will get more if you put out more feeders. They hang around all year round.
They're an established invasive species, and actually on the decline in many parts of the eastern US (not sure about Canada), where another semi-exotic (the House finch from the west coast) has been introduced and seems to be outcompeting the house sparrows. That being said, they're still fun to watch.
But then, I'd rather watch
any birds than, say, turn on the TV or radio, so I may be biassed about what is and isn't fun to watch!
At any rate, if you put more feeders out, you'll likely get more birds. If you don't mind attracting sparrows, your bank account will be your limiter. Because birds will drain your bank accounts if you listen to how hungry they tell you they are!
Yes, I speak from experience!
When we get winter finches, our winter seed bill will literally go up $1,000!!!!
Good observation on the sentinels--a lot of birds (crows, jays, doves, cranes, geese, for sure and probably others) put out sentinels, especially if there are predators around. The years we get goshawks in winter, we also get huge bands (upwards of 100 individuals) of blue jays. The jays eat in shifts, and there's always a few of them on guard. And in winter, when a jay cries out a warning, the response can be astonishing! Every bird in the area scatters to cover. You can feel the air shudder with the sudden beat of bird wings. It's
awesome!