JPMyers 1973 Calidris melanotos Grid 1 (Farmhouse Puddle) Estancia Medeland, 35 Km S of Juancho, Pcia de B.A., Argentina 26 December cottled the original chaser It then flew, as the bird it had been chasing had returned to the (4,3) site, where this series had begun. The chaser again supplanted the introducing bird in (4,3). After doing so, it landed in (4,0) and immediately was chased by the lapwing, 0650-0652 - lapwings dive bombed a pectoral in (4,3); in order to avoid being hit, the pectoral practically dove into the water, hitting the surface with a splash. This is the second time I have seen this response to lapwing attacks: the more frequent is a quick stoop. 0655 pectoral aggression in (1,2): they are feeding but displaying interest; unintently. Outstretched neck, raised back feathers. The intruder(s) ended without supplantation, the 2 feeding within 2 ft of one another for ~2 minutes, then they slowly worked out away from the territory boundary. 0656: a series of supplantations began with one bird being chased from (1,4) [aggression suit chart #2 page 16] to (2,4) to (3,4) to (4,3) to (0,1). Each supplan- tation was done by a different bird! When the supplanted bird would land, the resident put its neck out, chinned, and flew toward the intruder, which then left. I think that this strongly suggests that there are at least 5 territorial birds on the grid. The occupant at (0,1) has a huge territory controlling almost half the grid [this bird whom I've described several times earlier, whose territory goes over to (4,2) etc.] I have the impression that most of the obvious aggression that I am seeing on the grid is between resident birds and transient birds, rather than within members of the territorial population itself. Usually these encounters end with one of the birds leaving the grid area. However, taking following data I have begun to catch a more subtle interplay between the birds as they become closer to one another, feeding or territorial. The behavior in this case often involves much feeding, and a slow parallel (but separate) trend in movement along what may be boundaries. Neck stretching is common, as is: When the birds encircle into a WR-like closed pattern with back feathers raised. Birds flying in a chase off. Occasionally, neighboring territorial birds wander substantially into an adjacent territory. They are supplanted, and fly back to their territory. The number of acts of aggression taken this morning are interesting in that, the intruders are certainly not evenly distributed over the grid. There are several centers, centers, and most of the aggression occurs near what may be a perception of the boundaries between territories are. Units (0,3), (1,4), and (4,3) are particularly