Great Blue Herons on Roberts Bay June 2, 2015

For the second day, Great Blue Herons have aggregated in Roberts Bay to feed on a “run” of small fish, that at long range, appear to be a species of Surfperch – perhaps Kelp Perch.

Maybe its a spawning aggregation. At noon there were 37 gathered, near maximum numbers recorded ( 46, I think it was).

It’s interesting that their aggregation is so intensely concentrated around a particular spot on the mudflats, directly off “Cockle Point” ( between 3rd and 5th Streets). This is not the usual location where they fish, nor does it involve the same prey species, or hunting technique. Typically in June or July, depending on lunar cycles, such aggregations occur when they are hunting spawning Gunnels in the “Gunnel Patch” off the end of Third Street. Gunnel hunting requires more stalking whereas the Sufperch technique involves standing still and upright.

The warm, estuarine waters of Roberts Bay provide productive and diversified habitat for a diversity of schooling fishes, that support the herons, kingfishers, ospreys and cormorants.

It takes a lot of fish to feed 37 Great Blue Herons and their growing families. It’s remarkable that they exchange knowledge of just where and when the conditions for optimal feeding occur.