Clean up the coop area. Clear away any and all:
- Brush and scrub
- Wood piles
- Garbage piles and clutter piles
- Decaying structures like sheds
- Overhanging tree limbs
Anyplace rats can hide, nest, or use as a runway to the coop. Keep the area VERY clean.
Search carefully for entry point holes. Rats can squeeze through openings of 1 inch. Mice: 1/4th inch. The size of a quarter and a dime, respectively. Repair any and ALL holes with hardwire cloth and/or concrete. Tightly seal around drain pipes, windows, and vents.
***Your best rodent control is going to be building them out and cleanliness.***
Keep all food tightly contained in chew-proof METAL containers and swept up.
Keep garbage and compost well away from the coop area.
Fill in burrows and keep an eye out for them.
Clean up any rat urine and feces immediately. Rats are practically blind, so they use their urine as a message system to the colony. Disrupt the scent, it slows them down.
Get snap traps and live traps and bait with peanut butter. I strongly urge against poison not just because of cross-toxicity to other animals, but also the fact that rats tend to crawl into places like your house and die. Then you have a huge bill to cut open your walls and ceiling to remove a decaying animal that stinks to high heaven.
First sign of rats, go through the steps again!
I'm terribly sorry you lost your babies. I really hope this helps you and your chicks.