[Tweeters] Pectoral Sandpiper hooting
dennispaulson at comcast.net
Fri Apr 2 11:39:34 PDT 2010
In a shorebird class I just taught, I told people about the hooting sound that male Pectoral Sandpipers make as they fly over the tundra in display flights on their arctic breeding grounds. I wasn't entirely sure how this sound was made, and I promised to look it up in Bird of North America. Here it is. I decided it was complex enough that I wouldn't try to paraphrase. Notice this has been the subject of quite a bit of speculation.
Most agonistic interactions of breeding males involve specialized secondary sexual characteristic of large, pendulous, and inflatable throat sac, accompanied by heavy fat deposits and vascularization of subcutaneous tissue of throat and neck (Nelson 1884,Sutton 1932, Pitelka 1959, Parmelee et al. 1967, Portenko 1968, MacLean 1969,Kistchinskii 1974, Flint and Tomkovich 1978, Myers 1982). Skin of throat and breast becomes flabby and loose, inner surface covered with thick fat deposits (Nelson 1884,Parmelee et al. 1967). Flaccid tissue around neck of 1 male weighed 30.0 g (Parmelee et al. 1967). When breeding male stands, neck skin hangs down in pendulous flap, likened to a dewlap (Nelson 1884; see Fig. 4B).
In Flight Display (see Spacing, below), throat sac expands rhythmically, and Hooting Call is given (see Sounds: vocalizations, above). Anatomical basis and mechanism for inflation not well understood. Proposals include (1) expansion of esophagus (Nelson 1884, Flint and Tomkovich 1978), (2) inflation of cervical air sacs (Kozlova 1962, Portenko 1968), or (3) blood or other fluid engorgement of highly vascularized subcutaneous neck tissue of male (Kistchinskii 1974). Best evidence supports esophageal expansion: Air blown into esophagus of dead male caused throat to inflate to normal “display” size while cervical air sacs remained “empty” (Flint and Tomkovich 1978, P. S. Tomkovich pers. comm.). Same experiment with female Pectoral Sandpipers and other calidridine species produced no such enlargement (P. S. Tomkovich pers. comm.). Similar but less pronounced throat sac also reported from Sharp-tailed Sandpiper, but vocalizations and underlying mechanism in that species appear different (Flint and Tomkovich 1978). Esophagus of male Pectoral reported to be soft and distensible (Nelson 1884, RTH) and elastic (Flint and Tomkovich 1978). One esophagus from a collected breeding male measured 137 mm in length and 15 mm in diameter, tapering to 7 mm at entrance to stomach, and was noted as “very elastic and thin” (RTH). Role of vascularization and fat deposits not clear; latter may (also) provide energy reserve useful in cool arctic environment (MacLean 1969; see Food habits: nutrition and energetics, above). More studies needed to determine morphological basis of this display characteristic, especially the possibility of air sac involvement, as well as function of fat deposits.
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dennispaulson at comcast.net
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