Champion filly Songbird has maintained her unbeaten record with a 6-1/2 length victory in the Grade Two Summertime Oaks at Santa Anita.

Songbird has won her eight career starts by a combined 42-1/2 lengths for Hall of Fame trainer Jerry Hollendorfer, who celebrated his 70th birthday on race day.

The filly missed the Kentucky Oaks with an elevated temperature but showed no ill effects in her comeback on Saturday (Sunday AEST).

"I was very happy the way she looked going down the back," Hollendorfer said.

"She was very comfortable, with her ears up, looking for something. The opportunity presented itself to be just a little off the pace and now we've shown everyone we can do that."

Songbird cruised to the lead leaving the three-furlong (600m) mark.

"She stayed in the spot that she wanted to be. It's just amazing, her cruising speed," Smith said.

"I knew she was going to fire. I just tried to stay out of her way. She has wings on her hooves. It scares me to think of how good she is."

The victory increased Songbird's career earnings to $US2,102,000 ($A2.84 million).