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Index of Subjects Natural selection will select for early male departure on both an individual (survival) basis and on a population-wide basis. The males contribute nothing to nestling survival. They may as well get going early while things are great all along the route south. This also frees up food resources for the later females & juveniles. The juveniles no doubt need to mature & build up maximum fat reserves before they undertake their first migration, for which they have no experience, aside from instinct, and on which they may make some errors. There are analogies in the way in which most shorebird species depart from the North. In many cases the adults leave first & in some species (aside from phalaropes) I believe the females leave before the males. They are burned out & need to start south for the richer staging areas like James Bay & Bay of Fundy. The males go next & juveniles last. The juveniles that don't have the skills to feed themselves & bulk up before leaving may not complete their first migration. So be it. Whatever works on a population-wide AND individual basis will be selected, over time. Top of the head comments; I don't teach this stuff, etc. Rick W. On Mon, Sep 10, 2012 at 11:41 AM, Christopher Majka <c.majka@ns.sympatico.ca> wrote: > Hi Andy, > > As I understand it, at least in terms of spring migration, the thought is > that males of some species (including Ruby-throated, Rufous, Allens, and > Calliope hummingbirds) migrate first to stake out territories. Females > follow some 2-3 weeks later to be able to take advantage of a nutritionally > richer supply of flowers along the migration route. On the southward > migration, juveniles tend to follow females. > > I know there has been a lot of investigation on survivorship of hummingbirds > related to the timing of migration, what plants are in bloom over what > portion of the migration route, and the ability to stake out territories in > optimal/suboptimal habitat. The situation with respect to hummingbirds is > also somewhat different from many other birds since male hummingbirds are > polygamous and because of the nutritional requirements and physiology of > hummingbirds. > > I don't have the time to investigate further but perhaps someone on the list > will know more. > > Cheers! > > Chris > > On 10-Sep-12, at 10:12 AM, andy dean wrote: > >> Our son-in-law is a budding birder and asked us an interesting question >> which we couldn't answer. >> Why do male hummingbirds migrate ahead of the females? Anybody know the >> answer? >> >> Andy and Lelia Dean >> 86 Baden Powell Drive >> Kentville, N.S. >> (902) 678-6243 >> >>
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Index of Subjects