MYERS, J. P. 1981. A test of three hypotheses for latitudinal segregation of the sexes in wintering birds. Can. J. Zool. 59: 1527-1534. Three hypotheses have been proposed to explain sexual differences in wintering latitude for different bird species: (1) intersexual behavioral dominance leads the subordinate sex to migrate farther to avoid competition; (2) intrasexual selection favors those individuals of one sex that arrive earlier and thus selects for wintering closer to the breeding ground; and (3) sexual differences in physiological tolerance allow the larger sex to survive harsher climates. Using sex, age, date, and location data from specimens collected south of the breeding range in the western hemisphere, I tested predictions of these hypotheses for two scolopacid shorebirds showing reverse sexual size dimorphism, the red phalarope, Phalaropus fulicarius, and the sanderling,
Calidris alba.Neither red phalaropes nor adult sanderlings showed any sexual difference in wintering latitude. First-winter male sanderlings tended to winter farther south than first-winter females. Combined with comparative data from other species of shorebirds and passerines, these results are consistent only with hypothesis 2.MYERS, J. P. 1981. A test of three hypotheses for latitudinal segregation of the sexes in wintering birds. Can. J. Zool. 59:1527-1534. Trois hypothkses ont Ct C proposkes dans le but d'expliquer pourquoi, chez diffkrentes espkces d'oiseaux, les mlles et les femelles passent l'hiver a des latitudes diffkrentes: (1) la dominance intersexuelle du comportement amkne le sexe domink a migrer plus au sud pour tviter la com@tition, (2) la selection intrasexuelle favorise les individus d'un sexe qui anivent plus t6t et leur donne l'avantage de passer l'hiver plus prks de l'aire de reproduction et (3) les diffCrences sexuelles de tolCrance physiologique permettent au sexe de plus grande taille de survivre A des climats plus rigoureux. L'examen de donnees sur le sexe, l'lge, la date et l'endroit de sCjour au sud de l'aire de reproduction, dans I'hCmisphkre occidental, a permis de mettre 1'Cpreuve ces hypothkses chez deux espkces de scolopacidCs 51 dimorphisme sexuel renvers6 quant a la taille, le phalarope
Phalaropus fulicarius et le sanderling Calidris alba.Ni les phalaropes adultes, ni les sanderlings adultes ne manifestent de diffkrences sexuelles quant a la latitude de leurs quartiers d'hiver. Le premier hiver, les sanderlings mlles tendent i se rendre plus au sud que les femelles de l'annte. Ces d o~C e s , combintes a des donnCes cornparables sur d'autres espkces d'oiseaux de rivage et d'oiseaux passereaux, ne verifient que l'hypothbse 2.[Traduit par le journal]
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