When my mom was working and breeding dogs, I was the one who would have to come home from school if someone went into labor, so we would take their temps in the morning for the last week and they would usually drop about a degree F the day of labor, so we had some warning. We got this info from one of the dog breeding books we had, written by a very old woman. My last pregnancy, someone on MDC tried to informally study this. So it was like getting pg again - wake up, take temp with basal body thermometer, etc. I forget how it turned out.
FWIW, the dogs would also not eat the day of labor, acted snappish, and tore up the newspaper in their whelping boxes. So when I hear the word nesting, I get an image of myself on all fours, furiously tearing up piles of newspaper with my nails. And when I hear of eating the placenta, I think of myself hungrily gobbling up the placenta and chewing the cord off my baby. Sometimes they were so eager to eat the afterbirth that they would chew it off too close to the puppy and they would bleed a little bit.