Ostriches are a recurring theme in Season Four. Most notably, Lindsay and Marky Bark move into Lucille's penthouse in Balboa Towers with Cindy the Ostrich. They are also mentioned in the Season One episode "Key Decisions".
Arrested Development showrunner Mitch Hurwitz has said that symbol of the ostrich works well for the Bluths as they share some of the same problems, they're unaware of how awkward they are and are essentially flightless (in the sense that flight equates to freedom.)
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Occurrences[]

Lindsay claims she's passionate for nature. Michael reminds her she's wearing ostrich-skin boots. She responds that she doesn't care about ostriches. ("Key Decisions")

Michael is run over by Cindy in Balboa Towers. ("Flight of the Phoenix")

Ostrich screeches can be heard while George is in Mexico. ("Borderline Personalities")

When George and Oscar see Divine Spirit while on maca, George thinks it was an ostrich. ("Borderline Personalities")

Lindsay travels to Shuturmurg, India. In Hindu, Shuturmurg translates to "ostrich". ("Indian Takers")

Lindsay's shaman tells her to "pull your head out of the sand." ("Indian Takers")

Lindsay sees an ostrich outside of her hotel where her shaman's tent once stood. ("Indian Takers")

Marky Bark and his mother Joan Bark own an ostrich farm in Mexico. ("Indian Takers")

The Google Street View car is nicknamed ostrich. ("The B. Team")

Lucille Austero is attacked by Cindy in her penthouse. ("A New Start")

G.O.B. tells his father he had to swerve to miss an ostrich while driving down to

Marky, Lindsay, and Cindy the Ostrich sneak into Balboa Towers. ("Red Hairing")

The last time Lucille cried was 60 years ago when she found the remains of her ostrich. ("Queen B.")

Lucille looks over at an ostrich pinata at Cinco de Cuatro. ("Queen B.")

An ostrich prop at Tony Wonder's show causes G.O.B. to have a flashback to his time in the storage locker (which contained a drinking bird toy.) ("A New Attitude")

The Fünkes watch a Thanksgiving cartoon featuring an ostrich. ("Señoritis")

The mascot of Balboa High School is an ostrich. ("Señoritis")

Buster sees a cartoon of an ostrich on his juice box. ("Off the Hook")

The painting that gets flipped over by the horde during Cinco is a painting of an ostrich.

While playing volleyball, Michael sticks his head in the sand.("Family Leave")

There's an ostrich pinata in the mexican artisan market visited by George Michael.("Self-Deportation")

Michael operates an unwieldy underwater mapping device called an "Ostrich. ("An Old Start")