I've found this to be a very lovely game

in the beginning when talking to Mama hen it is explained that;
" Chirpy could get lost looking for a place to sing"
"Chase could tire himself from running around"
"Cheri & Cherly might eat too many red apples"
and
"Choco might get stuck in some mud"
These are the clues given to help find the chicks

if you get lost at any point look at this Map to help you find them - the chicks are the yellow dots.

Cheryl is the very first bird you may find, this is done by heading straight to the left and following the hill to the very top, where you should see some scattered apples.
Once you are near the large tree click E to shake the tree, this should allow apples to drop down and Cheryl will appear.
After this simply go up to the bird and click E to carry them back to Mama Hen

Road Runner is found right after Cherri,
He is the only bird to be seen moving around a set race track "hence the name"
In order to get the achievement you must simply run after them (left shift) and catch them 3 times by getting close and clicking E.

Cheri is relatively easy to find simply head straight down from the path , you should have to jump across the mushrooms, and you can run by pressing left shift.

When you descend down the hill you should see two Lilly pads, after jumping across both knock the tree by pressing E and Cheri will appear.

Choco is very easy to find he is simply to the right of Mama hen and the fence, you should find him playing in the mud.

For song Bird - Also known as chirpy you need to head to the very far end of the map, once your near the hill (nearby road runner)
bounce up the mushrooms to the top. On the second set be sure to stick to the left - the path that looks higher as the other way leads to a dead end..



from here it should be a simple walk to retrieve Chirpy

To get this achievement simply head back to where you started and walk into the pen next to Mama hen, after the chicks have got off your back walk up to Mama hen and talk to her for the achievement and the end credits