Eubica americana 175 Jan 22 Jewel Lake, 510 ft., Tilden Park, Contra Costa Co. Cal. at 12:25 p.m. a momentary conflict occurred at D12. One bird challenged another, the second accepted the challenge and churned momentarily, quickly the another bird charged out of the nearby cat-tails and the second bird hastily moved off towards F12. Notes could not be heard because of the noisy waterfall behind me. 12:27-another short charge from C13 to D14 chased one of three intruders out away, Now Two birds are back to C14 while the defending birds are in the cat-tails: One of the defending birds crossed from D12 to E9, showing no interest in the birds at C14. Now those two have joined a board at H15.-At least 4 of the 6 birds on the lake have swollen frontal shields, and one definitely lacks it.- One bird apparently lacking the swollen shield, moved around the corners at M25.22, promptly gave the alarm signal with its tail upright, and turned to go to M27. No bird came out of that corner to pursue it, but one must have been threatening from in to cat-tails.- Later, a bird with a pin was seen at A8- had a swollen shield- as it moved out it gave a high pitched "peuk" moving out from B7 around to D12 where it joined a "pooonzing"