The ornamental design for an incubator for chicks, as shown and described.
FIG. 1 is a perspective view of an incubator for chicks showing my new design;
FIG. 2 is a side elevational view thereof, the incubator for chicks being symmetrical with the front, rear, left side and right side elevational views all being the same;
FIG. 3 is a top plan view thereof; and,
FIG. 4 is a bottom plan view thereof.
The broken lines in FIG. 3 indicate that the area within the small circle is a portion of the incubator for chicks that forms no part of the claimed design.