Do birds get ticks very often? This bird was clearly sick. It put a seed in its mouth and just left it there, without eating it. Just closed its eyes and seemed to fall asleep.
The size of the tick suggests that a lot of the bird's blood volume might be inside the tick.
I had a tick on the head of a Cardinal a few years ago while *cough* bird banding... I've heard that some birds can have a very difficult time (I think I remember a Rose-coloured Starling a few years ago in Britian that had some on its throat, and possibly died?).. But most are presumably ok, as the tick eventually falls off
Ticks are very common on birds. A single tick is usually not fatal to the individual. This bird may have other problems as well. The bloated tick here is likely a female who is having her last blood meal before falling off and laying eggs.
Be aware that some bird ticks- particularly those on seabirds- can carry Lyme Disease.
I've photographed various apparently healthy, active passerines hosting seriously engorged ticks. No doubt that tick-borne diseases can be serious, though.