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10 hours ago, neilpa said:

Looking at the ripples, it seems like a number of them are swimming in circles. I recall from the Cornell shorebird course this is most common of Wilson's.

It is a behavior inherent in all phalaropes. In fact, the single lab study of which I am aware that has been focused on spinning as a foraging technique was conducted using Red-necked Phals (by Margaret Rubega and colleagues). From the Birds of the World account (subscription required):

Food Capture And Consumption

Forages  by swimming, wading and walking. Visual forager, pecking  prey from water. May up-end, but normally pecks at, or just below, surface; rarely, submerges head and neck. Mostly forages by rambling along a more or less linear track, but most conspicuous and well-known phalarope feeding behavior is a top-like spinning  on surface of water (Figure 2 and Figure 3). This behavior, shared by all phalaropes, has long been suspected of stirring up prey from bottom in shallow water (Tinbergen 1935, Michael 1938a, Johns 1969, Höhn 1971a) or stimulating prey immobilized in cold water (Tinbergen 1935). Individuals rarely spin in moving water (J. D. Reynolds unpubl.). Simultaneous spinning by pairs may also function as a courtship behavior (Höhn 1971a, Everett 1976). Salomonson (in Höhn 1971a: 341) reported that “they almost always spin anti-clockwise.” In a captive population, individuals spun in both directions, but any single individual always spun in only 1 direction; i.e., phalaropes may be “handed” (B. Obst unpubl., MAR). Spinning sets up a subsurface flow regimen that concentrates and lifts prey to within reach of individual (Obst et al. 1996). Rather than stirring up bottom (creating turbulence), phalaropes spin so fast (approximately 1 rotation/s, or as many as 54 rpm reported; Porter 2012, Chandler et al. 2015) that they kick water away from axis of their rotation on surface of water. This rapid displacement of water generates a deflection of free surface that drives an upward momentum jet; i.e., phalaropes create their own upwellings by moving surface water outward so fast that subsurface water must flow up to surface to replace it. Flow can be generated to depths of at least 0.5 m, explaining observations of individuals spinning in deep as well as shallow water (Sutton 1932b in Höhn 1971a, Johns 1969, MAR). Each turn of spin is slightly displaced so that phalarope moves slowly, inspecting and upwelling new water all the time (Obst et al. 1996).


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