Can a hen or a female chicken recognize her own chicks if they are mixed with other chicks? If so, how?

The normal behavior is that the hen will lay a clutch of eggs. She will not set on the nest until she lays the last egg, so that all the eggs hatch about the same time. Once she has laid enough eggs she settles down on the nest and hits her trance state. Every 15 minutes or so she will reach underneath herself and ruffle through the eggs turning a few of them at a time and adjusting their position in the nest so that all the eggs aren't in the same place all the time. She will come off the nest once a day for around 10-15 minutes to eat drink and eliminate waste. Around day 18 of incubation she stops turning the eggs and just sits there and usually will not get off the nest until her chicks have hatched. She will usually hold on the nest around 24 hours after the last chick hatches. If a hatch drags you can have problems with the first chicks hatching leaving the nest. For some reason the hen doesn't seem to recognize her own chicks and will kill these chicks if they try to come back into the nest. Some people put the chicks back under her at night, but I used to just raise them myself.

http://www.ithaca.edu/staff/jhenderson/chooks/chicks.html

Some sites indicate that recognition is related to sound: Since chickens are able to express over 30 different sounds, they also have a very good sense of hearing. This can be observed already with the communication between hen and chick, about 24 hours before hatching out. The chick chirps with long, high sounds and the hen answers with a deep, soft voice. Hen and chick can still understand each other at a distance of 20 meters, and the chicken chirps when it gets lost. At this distance chicks are able to recognize their mother’s voice out of a lot of other sounds.

chicken-yard.net/general/behavior.html webpage no longer exists