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Function of the Common Loon foot waggle.

Article Excerpt
Common Loons (Gavia immer), diving ducks (Oxyura, Aythya), grebes (Aechmophorus, Podiceps), and mergansers (Mergus, Lophodytes) all foot waggle (McKinney 1965). A foot waggle consists of raising one foot in the air and either holding it there for a brief time, or shaking it, often several times in succession (McIntyre 1988). The foot may be dipped into the water again and the foot waggle repeated, or it may be placed under the wing, or "shipped" (McKinney 1965). Footshaking (or waggling) removes dirt and suspended particles, that accumulate while swimming, to avoid contamination or wetting of the flank feathers when the foot is shipped (McKinney 1965). Foot waggling occurs most frequently in birds that are about to sleep or rest and is primarily viewed as being a comfort movement (McKinney 1965). However, Lorenz (1953) showed that some comfort movements could serve as signals (e.g., head-shake, tail-shake) but others, that are associated with a disturbance or after copulation, are unlikely to have any signal function (e.g., head-up). McIntyre and Barr (1997) reported that no quantitative data exist on the Common Loon foot waggle.

McIntyre (1988) posited the loon foot, due to its large size and extensive vascularization, has a role in thermoregulation. Several studies have shown that birds regulate body temperatures using their feet and legs (Steen and Steen 1965, Johansen and Millard 1973, de Vries and van Eerden 1995, de Leeuw et al. 1998, Wilson et al. 1998). Loons have a venae comitantes system instead of a fete mirable network found in most similar waterbirds, e.g., grebes and mergansers (Midtgard 1981). The difference between the two systems is slight; the rete has more major veins that surround the artery going to the feet than the venae comitantes system. Both systems provide a marked reduction in heat loss via countercurrent exchange as well as allowing for heat dissipation. The foot is shipped in many instances after a foot-waggle, and it is likely a relationship exists between foot-waggling and a loon's thermal budget.

The objectives of this study were to examine the function of the Common Loon foot waggle by testing for an association between its frequency and (1) resting and preening behaviors, (2) changes in the environment, and (3) the behavioral and social context in which they are performed. These objectives relate to hypotheses about comfort movements, thermoregulation, and signaling.

METHODS

Study Sites.--Four pairs of loons were monitored in 1994 in the eastern Upper Peninsula of Michigan (45[degrees] N, 86[degrees] W) at Seney National Wildlife Refuge (SNWR) and one pair at Manistique Lake outside of SNWR. Five pairs of loons were monitored in 1995 and 1996 in northern Wisconsin (46[degrees] N, 90[degrees] W) at the Turtle Flambeau Flowage (TFF). Social behavior of loons was filmed in 1996 and 1997 at TFF and in 1998 at Azicohos Lake, Maine (45[degrees] N, 71[degrees] W). All lakes in the study areas are mesotrophic. Lakes at SNWR used by loons are shallow and <3 m deep throughout. Manistique Lake is natural, 285 ha in size and with an average depth of 3 m. TFF is a large impoundment covering 5,978 ha with an average depth of 3 m and maximum depth of 16 m. Azicohos Lake is also a large impoundment, 2,506 ha in size with an average depth of 9.9 m.

Data Collection.--Both members of all loon pairs (n = 10; 20 individuals) were captured and uniquely color-marked prior to observation (Evers 1993). Colored plastic bands were placed on the legs and were visible when...

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