Yes, definitely Western Meadowlarks- they would be singing from fenceposts or scrub along the right of way in open country like the South Park, just as they do now on fencelines along roads. They want to sing from elevated perches, and fenceposts are all there are in rangeland. There can be a bird every 50 yd along a fence. Not too hard to approximate, if you have a small model bird, paint it light brownish on top and bright yellow underneath, with a black bib, and it will be recognizable. If you could have a recording of their songs to play in the background it would be perfect. One of my all-time favorite bird songs. Here's one example of many on Youtube.
https://www.youtube.com/watch?v=Sk4S2spFdcsCheers,
John
John Greenly
Lansing, NY