Journal Linear grid, Arroyo Chico, Estancia Medaland, 35 km E of Tramelo by road, Pto de Madariaga, Pcia de Bs. As., Argentina 4 November (cast) I was surprised that the storm continued, especially as yesterday it began as a summer thunder- storm out of the NW. But the temperature dropped to 13° and the wind shifted to SW after south, in fact it blew all day.* This had a remarkable effect upon the distribution of H2O, -w-rump foraging habitat, and white-rumps in the Arroyo. The linear grid count contained 45 birds, over half of which were on subunit 1. There was another concentration of fusicolis between subunits 7 and 8. And, above the linear grid, in N(5,25), there was a third concentration. Although individuals and small groups could be found all along the linear grid, an overwhelming majority were to be found in these 3 areas. The locations were notable because in common they shared one characteristic: all 3 lie at the southeast of a lengthy S-N running strelch of the arroyo, and they because of local topography, all are structured such that a strong S wind, coming on top of (pre-existing) low water conditions, blows the water upstream, and because of natural 'dams' at these water levels, water to the soil these strelchus is pre- vented from filling the void & created. Therefore expanses of newly exposed bottom, and new areas of low water are made available for foraging. A servus, in effect, as a slow tide. (Bekman thus the storm introduced a fair degree of temporal instability to the arroyo, shifting (probably) areas of maximal foraging efficiency. Yet despite this 'instability' an incredible amount of space-specific aggression was occurring during our observation. Whatever interpretation is to be made, it is complicated by the fact that there was a large influx of birds into the area - at least 100 we mowed in, most in a different polymage than the mono-gray (that the local population had developed) (see our specimen + 1 August they are juveniles). Linear grid totals: Calidris fusicolis 45; Calidris baistii 10; Micropalama brisbanensis 1; Cinclus maculatus 2; Tringa flavipes 4; Charadrius fulvus 1; Himantopus 6-8. Returning to the question of stability: while I said that the storm had introduced a 'fair' degree of instability - that 'fair' is only in relation to the Arroyo, not to a good tidal mud flat (like