Those are not Fowler flaps, they are Slotted flaps.
The Fowler flaps combine very significant aft movement to increase wing area, with downward movement to increase camber.
Since such a mechanism is far more expensive to produce, with a questionable advantage for light aircraft, they are rather non cost effective which is probably the reason we usually see them only on heavy transport aircraft or very specialized STOL aircraft.
I think Robart used to sell a mechanism for making Fowler flaps on models.
The only requirement for a Fowler flap is to move rearward as it moves down. Fowlers increase the effective chord as they increase camber. They can simply pivot or they can slide. The ones on Cessnas pivot for simplicity and do create a slot and are called slotted fowler flaps. The slot allows airflow to pass through and over the flap's top surface to decrease turbulence and drag along the trailing edge, improving lift. In the case of the Bird Dog, they could lower a maximum of 60 degrees and significantly improve STOL performance on landing. If you note the picture above showing the full flap position, the forward edge of the corrugated surface is flush with the top of the wing when flaps are fully retracted, which shows how far back they have come as they drop. Up to 30 degrees can be used for takeoff. Note how little runway is behind this one as it takes off, which I have had the opportunity to ride in. It has no other specialized STOL devices that you see on a lot of bush planes.
