The shot of the Arkham Asylum plaque shown in the first episode is taken directly from Batman Forever.
The first episode features a reference to fellow WB series Smallville (2001): Helena Kyle mentions to Barbara Gordon and Dinah that meteors sometimes cause mutations. Inside reference: "Birds of Prey" and "Smallville" are both produced by Tollin/Robbins Productions. However, the two shows are not set within the same continuity.