Parallel run displays, Piping Plover, Mlf Pt 3 June 2010

This video shows two adult Piping Plovers on the Francis Street spit at Milford Point on 3 June 2010 engaged in "parallel run displays" (Birds of North America), whereby the birds draw a boundary between their territories. One bird is from a pair raising 3 chicks (from a clutch of 4); the other is from a pair with a nest newly established (with four eggs) to replace a lost nest. While most of the parallel running seems like an avian exercise in peaceful diplomacy, things get testy at the end of the video. We observed this behavior for about 1/2 hr; when we left they were still at it.

Here's the discussion of "parallel run displays" from Birds of North America:"Territorial to varying degrees throughout annual cycle. Territory boundaries defined and defended using a “parallel-run display”: two neighbors run in parallel along a common boundary with heads and necks stretched upward, breast feathers puffed smoothly, and dark sides of the neck band showing brightly against the white breast (Cairns 1982). After facing each other and head-bobbing, one turns at right angles and runs rapidly for a distance of 1–10 m along the disputed line. In the same manner, the second bird runs past the first and stops abruptly. This usually continues to the shoreline or grassline, upon which the birds abruptly turn around and come back. Both members of each pair may sometimes run parallel together. Encounters may last 30 minutes or more and continue sporadically for days. They usually subside once incubation has begun, but may resume at any time (SMH). Although most parallel runs occur with conspecifics, Piping Plovers have been observed running with Wilson’s Plovers (Bergstrom and Terwilliger 1987). Territories are also defended using “horizontal threat displays” (see Agonistic Behavior). Territorial behavior occurs during winter but is less vigorous (J. Stucker pers. comm.)."