Chase the seagulls was a mission in The Precursor Legacy that Jak and Daxter completed to obtain a power cell. While exploring the beach, Daxter will eventually encourage Jak to scare the seagulls there "for kicks".
After scaring them away completely, the mission is temporarily renamed to Get the fallen power cell, up until it is collected.
On the far side of Sentinel Beach, three large stone sentinels rest on the sand. On the first of these is a flock of seagulls. Hop up onto the platform and approach them closely to scare them away. Repeat this two times, once for each sentinel, where after a cutscene will show the seagulls causing a small avalanche at the waterfall. The only enemies to be wary of is the hidden sand worm in between the second and third sentinels, as well as two babaks, roaming around in this area.
The power cell will pop out, landing atop a small platform, next to a large rock which has also fallen from the cliffside.